5g network - iskd.in
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Cyber Security Technology
INNOVATIVE SKILLS AND KNOWLEDGE DEVELOPMENT 7
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InNOVATIVE SKILLS AND KNOWLEDGE DEVELOPMENT
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INDEX
Sr
No
Topic Page
No
1 What is 5G
2 4G to 5G Migration/Evolution
3 4G Vs 5G
4 Acronyms
5 Agreed items
6 Antenna Port
7 Beam Forming
8 Beam Management
9 BWP(Bandwidth Part)
10 Carrier Aggregation
11 Carrier Bandwidth Part(BWP)
12 Cell Search
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1. What is 5 G ?
From late 2016 many things started happening in 3GPP and now (Mar 2017)
we got several TRs (38.801, 38.802, 38.803, 38.804) that describes the details of
technical requirement to be specified in formal NR(5G) specification, meaning that now
we know what 5G (NR) will look like in pretty much detail.
Nothing about 5G is defined officially in any standard organization as of now. However
there are several organization that describes key technical component or key performance
indicator (KPI) that may envision on what 5G will be like. I would put the list of features
from several different organization.
Initial Definition
Formal (3GPP) Definition
Build Up Intuition on 5G
Definition by METIS
Definition by 5GNOW
Definition by SKT
Definition by 4G America
Definition by NTT DOCOMO
Initial Definition
When the first talk about 5G started and some of prototyping test result came out, the
focus was mainly around throughput. (This kind of focus hasn't been changed much until
mid 2013)
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At least, one thing for sure will be that the data rate will be at least several G bps. (The
final goal of 4G data rate is 1 Ghz and we still have a long way to go to achieve this 1Gb
rate).
By now (as of Nov 2015), you may see a couple of dozen whitepapers about the 5G. If
you read through all of these whitepapers, you would notice that the key concepts they
claim in the documents are almost same. Personally, I would recommend you to read
through the documents from METIS. I think METIS documents are by far the most
extensive and most in-depth. The only problem is that those documents are too thick :)
Followings are some of my personsl keywords about the 5G reading through most of
these papers.
Extremly High Data Rate
By far, we don't know yet (as of Nov 2015)
what would be the maximum throughput.
But I think it will be targeted to be at least
around 10 Gbps.
Extremly Low Data Rate
Just achieving the extermly low throughput
has no technical problem. But critical
technological
issue is that achieving the extremely low
data rate with extremly low cost and
extremely low energy (battery)
consumption. Refer to MTC criteria for the
details.
Extremly Low Latency
We don't know yet (as of Nov 2015) what
would be the target latency. But by far,
around 1 ms latency are the most
commonly mentioned number.
(In terms of subframe length, it would be
around 100us or 200 us)
Super High Frequency
The words 'High Frequency' or 'Low
Frequency' can be misleading because
it would be a relative concept, but I say
'Super High Frequency' comparing to
current cellular communication frequency
(mostly under 3 Ghz). By far (as of Nov
2015), the most frequently commented
frequenty blocks are 6 Ghz, 15 Ghz,
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20~30Ghz and the highest frequency being
tried is a little bit over 70 Ghz.
Super Wide Bandwidth
The words 'Wide Bandwidth' or 'Narrow
Bandwidth' can be misleading because it
would be a relative concept, but I say
'Super Wide Bandwidth' comparing to
current cellular communication bandwidth
(100 MHz, ideal max in 4G). The most
commonly mentioned bandwidths are 160
Mhz, 400 Mhz, 800 Mhz. Currently the
widest bandwidth being mentioned are 2
Ghz bandwidth.
Softwares as much as possible
Many components in core network would
be software based and with this it would
become very flexible and accomdate news
features in short time frame
Formal (3GPP) Definition
Recently (as of Jun 2016) there has been a couple of RAN meeting with major focus on
5G and several official technical terms has been defined.
The first thing to be defined would be 'what is the name that refers to the whole 5G
technology ?'. As we call 4G as LTE, there must be similar name for 5G. What is it ? At
least for now, the official name for 5G is NR that stands for New Radio. (I already see
many people saying NR is not a proper name because 5G does not refers only to Radio
Technology.. but anyway for now, NR is the official term.
Then what is official definition of NR. Since there is no single line official definition for
LTE, there is no single line official definition for NR. But in my personal definition, I
would say 'NR is a collection of technology from Physical layer to Core Network that
need to achieve the followiing three major feature (requirement) as illustrated below. The
term shown in this diagrams are also formal 3GPP terms and you will see these terms in
most of the 3GPP documents on NR. So it would be good for you to get familiar with
these terminologies.
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Build up Intuition on 5G
Before you read, just enjoy these video clips and let your brain build up its own
intuition(Insight).
World's first 5G mobile 'device'
Millimeter Wave Technology for 5G
Definition by METIS More organized and formal definition can be made from METIS which were proposed in
Aug, 2013. Even though METIS does not put forth explicit 'definition', it proposes
several KPI (Key Performance Indicator). I think we can say "A communication system
satisfying the METIS KPI can be categorized as 5G".
Following is the list of KIPs and test cases performing the measurement of KPIs
proposed by METIS. (Refer to D1.1 and D2.1 METIS document for details)
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Technical Requirement proposed by METIS to meet 5G goal are :
10-100 times higher typical user data rate, where in a dense urban environment the
typical user data rate will range from 1Gbit/s to 10Gbit/s;
1,000 times more mobile data per area (per user), where the volume per area (per
user) will be over 100 Gbps/km2;
Support for 10-100 times more connected devices;
10 times longer battery life for low-power massive machine communications
where machines such as sensors or pagers will have a battery life of a decade;
Support of ultra-fast application response times, where the end-to-end latency will
be less than 5ms with high reliability;
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Ability to fulfil these requirements under a similar cost and energy dissipation per
area as in today’s cellular systems.
Definition by 5GNOW 5GNOW does not decribe much about high level definition or use model of 5G. I guess
any 5G high level definition fall into the scope of METIS definition/use model. 5GNOW
discuss more on lower level impelmentation of 5G. Key implementation Item
discussed/proposed by 5GNOW is as follows.
After I've read most of 5GNOW Deliverable document, the key words that pop-up
consitantly in my mind are
Asynchronous
Bursty low data rate transmission
Enhanced PRACH
Think on your own why these would be issues and then refer to 5GNOW Deliverable
Documents.
Definition by SKT
Following came from the white paper issued by SKT (SK Telecom, South Korea)
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Following table also comes from SKT WhitePaper. To be honest, I am not sure how
much of these items will be eventually adopted by the industry standard, but I think this
can be a good list of starting points if you want to do some more detailed research on
specific technologies for future communication. I recommend you to read the original
WhitePaper a couple of times and search the related document (e.g, Related Paper and
Thesis for each items)
1. Realistic UX and 5G Contents Process
Object/space Recognition
Fast Recognition of surrounding objects
and
spaces by a camera or sensors
Real Time Rendering and Display
Display(Rendering) of an object in
realtime
recognized by glass or HMD
Real Time Hologram Processing
Reconstructing a real image of an object
with 360 degree field of
view in 3D space
2. Efficient Processing & Transmission of Tactile Multimedia
MMT(MPEG Media Transport)
a special MPEG technology to minimize
latency in media transmission in All-IP
network
High Efficiency Multimedia Coding
Multimedia Coding Technique for
efficient creation/transmission of realistic
3D multimeidia contents (e.g, MVC :
Multi-view Video Encoding)
Cloud-based Computing, Caching and
Orchastration Dynamic Allocation and Orchestration of
cloud resource and caching to process
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realistic high volume multimedia
3. Cloud-based All-IP Network and Service Platform
NFV-based Virtualied Core Network
Operation
Techniques to build the cloud by
virtualizing a standard hardware and
operate a range of networ/service
functions on the software-based network.
Virtualized RAN
Techniques to centralize and virtualize
DU(Digital Unit) of a base station into a
standard HW based cloud and process
RAN signals in real time.
SDN and integrated Orchestraion
Effective control and lifecycle
management of the software-based
network services from a centralized &
unified network service orchestrator
4. Analytics-based Network Intelligence & Optimization
Big Data Analysis
Techniques to process, analyze and infer
large volume of multi-
dimensional/unstructured data
Network Intelligence & Analysis
Techniques to optimize operation and
performance of networks from
information on performance, log, traffic
Analytics-based SON
Techniques to automatically detect
abnormality, to optimize and take
necessary measures
5. Fast, Flexible Transport Network
POTN (Packet Optical Transport Network)
All-IP/All-Optical transport technology
that converges multiple layers to increase
simplicity and efficiency of network
Transport SDN Integrated Networking technology to
efficiently use and automatically control
network resources in multi-layer, multi-
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vendor, multi-domain networking
environment
6. Beyond-Cellular Network Architecture
Direct D2D Communication Techniques to directly share information
and data between devices
Contents Centric Networking (CCN)
A network architecture that stores content
in a transport equipment on the network
path and provides it by a mapped name of
content
7. Enhanced Operation for Multi-cell/HetNet
Elastic Cell
Techniques to dynamically select and
communicate with a cell best for the
user's current channel environment in real
time
Aggregation of Heterogeneous Networks
Techniques to improve data rate by
combining cellular networ with different
networks such as WiFi or with unlicensed
LTE band
8. Ultra-Dense Small Cell
Dynamic interference control and
coordination
Techniques to improve signal Quality at
cell edges by enabling nearby cells to
cooperate in real time
HetNet SON
Techniques to automatically optimize
wireless network operation in diverse cell
environment to improve QoS
9. Wideband High Frequency RF & 3D BeamForming
3D BeamForming
Techniques that provies RF environment
for high-speed transmission by controlling
electromagnetic waves or forming
multiple beams in the vertical and
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horizontal directions
Beam Switching/Tracking
Techniques that provides an optimal link
by selecting an optimal beam out of many
or changing the direction of the antenna
beam according to the location of the
user.
10. Enhancement of Multiple Antenna Technology including Massive MIMO
UE-Specific Beamforming
Techniques that suppresses mutual
interference between multiple terminals
by utilizing independent and sharp beams
CSI/CQI Feedback
Techniques that enhances accuracy of CSI
and CQI while minimizing uplink
signaling overhead
11. Advanced IoT & New Waveform/Duplex
Cellular-based MTC (Machine Type
Comm)
High Capacity multiple access & machine
data processing technology to support IoT
service on mobile communication
network
New Waveform (NOMA, FBMC)
Transmit and receive technology that
increases efficiency of accommodating
multiple users and data through reciever
interference cancellation and filter-based
interference supporession
Hybrid duplex & Full Duplex
Communication
Flexible allocation scheme for DL/UL
resources and simultaneous transmit and
receive technology based on self -
interference cancellation
Definition by 4G America
The contents in this section is based on the WhitePaper : 4G Americas'
Recommendations on 5G Requirements and Solutions.
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Definition By NTT DoCoMo
The contents in this section is based on the WhitePaper : 5G Radio Access:
Requirements, Concept and Technologies - DOCOMO 5G White Paper
< Trends in Technology and Motivation for 5G >
This trend is mainly represented as M2M,
MTC, IoT these days. Actually each
component technology is already available
and has been adopted by various area, but
they hasn't been integrated across wide area.
We need a flexible cellular network that can
integrate all of these diverse component and
5G will be playing a crucial role for this.
These are emerging technolgies meaning relatively new
technology, but development/implementation for each
components has been adopted for a while. But this hasn't
been a target for cellular communication since the
required data rate is too high. To connect these
applications to cellular network, we need a new celluar
technology that support extermely high data rate. This
extremly high data rate will be one of the key feature of
5G.
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< Key Requirement >
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2.4G to 5G Migration/Evolution
If you just read all the 5G initial definition/requirement documents introduced in 5G
Definition page. You may think "It is too good to be realized. It would be easy to say but
almost impossible to implement." It would to true that we cannot realize all those
requirement overnight in a single step. But as you look back the history of wireless
communication (actually any technology), most of new technology start from what we
have now and gradually evolve piece by piece and eventually realize what we thought
would be impossible.
5G would be realized in the similar fashion even though many of 5G document say '5G
should take drastically different evolution path from the one we saw before'. We are
already seeing some of the features regarded as very advanced feature in current
technology (4G) but will become a kind of basic features in 5G. I think following
illustration gives us pretty good idea of the evolution path. If you are interested in 5G
technical details, but don't know what to do because there is no established
standard/specification, following current 3GPP specification along the eveolution path
can be a good starting point.
Following figure is from SK Telecom 5G WhitePaper
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Following is from the white paper : 4G Americas' recommendation on 5G Requirements
and Solution. Again, read the full document first and use this table to refresh your
memory as needed.
1. Enhancement of Network Flexibility
CDN(Content Distribution Network) : Inteligent content-reqest routing mechanism
New APN provisioning and associated signaling
2. Additional Support for Essential Functions as Fundamental Attributes of Network Layer
Automatic topology mapping and pathology-free routing
Research in the Future Internet Architecture
3. Providing More Flexible Mobility Solution
Reduce RAN and Core Network Signaling overhead (especially for Static devices)
Reduce overhead for the additional headers that are added for every packets (espeically
small packets)
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Improve tunneling algorithm to realize more efficient routing
4. Expanded Form of Multi-RAT Integration and Management
Continue to maintain/improve "trusted non-3GPP access" mechanism
5. Enhanced Efficiency for Short-Burst or Small-Data Communication
Support truly connectionless mode of operation
6. Expanding Context Information Known to the Network
Analyze and store more informations to provide better context-based services
< LTE in unlicensed spectrum >
Even without specification, this area has been discussed for pretty long time and some
chipset vendors are already at the stage of testing for several month now (Apr 2015).
This is a special kind of Carrier Aggregation and the basic idea is to use the licensed LTE
spectrum as a PCC and use unlicensed spectrum as SCC. The most common unlicensed
spectrum being used this purpose as of now is WLAN spectrum in 5 Ghz, but
theoretically we can extend it to any spectrum.
< Carrier Aggregation enhancements >
As of now (Rel 12), the maximum number of carrier we can aggregate is 5. The main
items for this activity is to extend the number of aggregated carrier up to 32. There has
already been a demo achieving 9 CC CA on Mar 31, 2015.
The network operator KT and mobile manufacturer SamSung did the demo for TDD 9
CC CA (Netmanias Interview with KT at MWC 2015: KT's demonstrations of LTE TDD
(9-carrier CA, LTE-UL/DL CA and triple mode femto)
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Refer to RP-142286 for details.
< LTE enhancements for Machine-Type Communications (MTC) >
Main objective for this activity is to implement a low throughput device at a very low
cost. See MTC page for my summary and see RP-141865 for further details.
I think it is highly likely that a lot of technology developed in this area would be adopted
by 5G as well.
< Enhancements for D2D >
D2D has been investigated since Rel 12 and basic concept is summarized in
my D2D/Prosec and D2D/Radio Protocol page. This objective of this activity is to make
some enhancement to the existing topics.
< Elevation Beamforming / Full-Dimension MIMO >
Main objective in this activity is to define the technology to increase the number of
downlink Antenna (max 64) and to arrange those antenna in 2 dimensional grid.
< Enhanced multi-user transmission techniques >
In this activie, it will be investigate to realize techniquest to achieve MU MIMO which is
tolerent to intra cell interference and can work even when the orthogonality is not
guaranteed.
I think this technique in combination with FD-MIMO will be very important technical
component in 5G. Refer to RP-142315 for details.
Main Study Topcis in Rel 14
No official 3GPP document about 5G in Release 14 is available for now, but following is
a list of maijor features of Rel 14 presented by Qualcomm in RAN 5 Meeting ( Sep
2015).
5G Requirement Study at RAN Level
5G Design Study Item : structure of air interface to cover multiple areas
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o mobile broadband
o internet of everything (IOE)
o mission critical
o high-freuquency range up to 100Ghz
Parallel study on high-frequency channel model ( > 6 Ghz)
LTE evolution to continue
Main Study Topics in Rel 15
From Jun 2017, early phase 3GPP Technical Specification (Release 15) has been
released (3GPP Specification 38 series)
NR Numerology (Subcarrier Spacing, OFDM Symbol Length)
NR Frame Structure
NR Resource Grid
SS/PBCH
RACH Process
Early phase of MAC / RLC / PDCP specification
Main Study Topics in Rel 16
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No official 3GPP document about 5G in Release 16 is available for now, but following is
a list of maijor features of Rel 16 presented by Qualcomm in RAN 5 Meeting ( Sep
2015).
Second Phase of 5G : all other 5G components
o 5G Mobile Broadband Standalone Operations
o Mission Critical
o mmWave & high frequency range
LTE evolution to continue
Final Submission to ITU for IMT-2020
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3.4G vs 5G
When I started writing the pages about 5G in around mid 2013, I thought we will have a
completely new (at least in Radio Access Protocol perspectivie) and I said to myself
"After spending a couple of years in LTE and with a lot of struggle, finally just started to
get used to this technology. Do I need to go through this kind of struggling again ?".
At the early discussion, most of the discussions were around new physical waveform,
implying that 5G is likely to be completely new technology from the bottom.
Fortunately to me (and probably to many people), with most of the initial implementation
target determined in 3GPP as of TR 38.801, 38.802, 38.803, 38.804, it seems to me that
most part (at least most part of Radio Access Procotol) overlaps with the current LTE and
only small portions of new items are to be implemented anew as illustrated below (Of
course this would sound over-simplified. You may say 'each of these new items are so
fundamental, it should be regarded as pretty new technology'. I agree with this to some
degree. It would be a huge changes in terms of low PHY. However, if you move forware
only a half step upward and getting into high PHY(e.g,physical layer processing) and
higher layer protocol, a lot of things would sound very similar (or almost same) to current
LTE.
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I would suggest you to keep this diagram in your mind and dig further into the details for
each items. If you have a certain level of knowledge on LTE, learning NR from these
differences will be more helpful rather than just looking into NR specification only.
Here I would write down short descriptions as a starting point of your study. Take this
just as an entry point and follow through the links under each of the items for further
details.
Multiple Numerology
mmWave
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Massive MIMO
Beam Management
LDPC/Polar Coding
SDAP Layer
Extremely complicated RRC
RRC / DCI Interplay
BWP
Flexible UL/DL Configuration
Multiple Numerology
Simply put, Numerology means 'Subcarrier Spacing'. In LTE, there is only one
numberology (subcarrier spacing) which is 15 Khz, but in NR various different types of
subcarrier spacing are supported.
See Numerology page to understand what kind of numerology are supported
Depending on Numberology, frame structure gets different.
See FrameStructure page for the details
Even more complex situation caused by this multiple numberology is the case
where different physical channels or signal use different subcarrier spacing, or
different numuerlogy is used for different BWP even in the same gNB. In this
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case, translation between each resource elements / resource block and physical
radio frequency gets complicated. To handle this kind of situation, we define a
specific reference sub carrier spacing depending on frequency range. See Resource
Block Indexing page for the details.
mmWave
Even though we will see NR deployment in Sub 6 Ghz (FR1) at early phase, the most
unique aspect of NR deployment will be the support of mmWave (FR2).
Massive MIMO
In order to operate NR in mmWave, we need a special technology that can transmit the
signal in a narrow beam. To do this, NR adopt a special technology called Massive
MIMO. See Massive MIMO page for the details.
Beam Management
Beam Management is a set of process that can select, maintain and change beams
between UE and gNB to maintain the stable connection. This process would be a critical
part of NR operation in mmWave range. See Beam Management page for the details.
LDPC/Polar Coding
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In LTE, Tail Bit Convolution Coding and Turbo Coding are the major technology for
channel coding, but in NR Polar Coding and LDPC are adopted as major technology of
channel coding. See Channel Coding page to see which channel uses which coding
method.
SDAP Layer
SDAP is a completely new layer added to NR on top of PDCP. Main role of SDAP is to
apply a sophisticated QoS for each of data stream.
Followings are not shown in the above diagram, but can be an important aspect worth
noticing. These are mostly based on my personal experience and some of you may not
agree with these.
Extremely complicated RRC
One of the best part of LTE that I found after struggling with WCDMA Release 99 for a
long time was that RRC parameter in LTE has become so simple and clear. However, in
NR I am afraid I start seeing the Rel 99-like complexity in NR RRC message. One of the
reason for this complexity would be that NR is designed to be very flexible to support
various use model (e.g, eMBB, eMTC, URLLC) and many parameters related to
transport channel process is configured by RRC. Just as an example of this complexity,
see NR RRC Reconfiguration page.
RRC / DCI Interplay
In LTE, the parameters in RRC and the parameters in DCI are pretty much independent
except the csi request filed in Aperiodic CSI report process, but in NR DCI and RRC
interplay become much more common practice as in the examples below.
Time domain resource assignment in DCI Format 0_0, DCI Format 0_1
Time domain resource assignment in DCI Format 1_0, DCI Format 1_1
BWP
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In NR, there is a mechanism to define a portions of frequency region within a given band
and let UE and gNB communicat within the portion. This fragment of band is called
BWP(Bandwidth Part). At high level view, BWP would be a similar concept
as Narrowband in LTE M1. But BWP can be defined in more flexible fashion than
Narrowband. Refer to BWP page for the details.
Flexible UL/DL Configuration
Even though some of FDD mode operation is defined in Sub 6 Ghz (FR1) in NR, it is
likely that the most of deployment would be done by TDD mode. Especially in
mmWAVE, only TDD operation is defined. Refer to FR/Bandwidth page to see the band
and frequency range and duplex mode.
In TDD operation, we need to define which time slot should be used for DL(Downlink)
and which time slot should be used for UL(Uplink). This kind of DL/UL transmission
pattern is called DL/UL Configuration. In LTE TDD, there are only 7 different pattern
are defined as shown here, but in NR the DL/UL pattern is configurable by RRC
parameter in much more flexible way as shown in TDD DL/UL Common Configuration.
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4. Acronyms
There are so many Acronyms in 3GPP (probably in all other technologies) and these
acronyms are defined in many different documents. In many cases I had to search
through many different documents just to find the meaning (full words) for those
acronyms. After repeating these open-look-close so many times, I decided to put all those
terms in a single page for quick search.
Acronym Meaning
5GC 5G Core Network
5QI 5G QoS Identifier
AAS BS Active Antenna System BS
ACK Acknowledgement
AM Acknowledged Mode
AMC Adaptive Modulation and Coding
AMF Access and Mobility Management Function
AP Application Protocol
ARP Address Resolution Protocol
ARQ Automatic Repeat request
AS Access Stratum
ASN.1 Abstract Syntax Notation One
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BA Bandwidth Adaptation
BCH Broadcast Channel
BLER Block Error Rate
BPSK Binary Phase Shift Keying
BSR Buffer Status Report
BWP Bandwidth part
CA Carrier Aggregation
CB Code block
CBG Code block group
CCCH Common Control Channel
CCE Control channel element
CE Control Element
CID Context Identifier
CM Connection Management
CMAS Commercial Mobile Alert Service
CP Cyclic prefix
CP Control Plane
CQI Channel quality indicator
CRC Cyclic redundancy check
CRI CSI-RS Resource Indicator
C-RNTI Cell RNTI
CS Configured Scheduling
CSI Channel state information
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CSI-RS Channel state information reference signal
CSI-RSRP CSI reference signal received power
CSI-RSRQ CSI reference signal received quality
CSI-SINR CSI signal-to-noise and interference ratio
CS-RNTI Configured Scheduling RNTI
CU Centeral Unit
CW Codeword
DC Dual Connectivity
DCCH Dedicated Control Channel
DCI Downlink control information
DFT-s-OFDM Discrete Fourier Transform-spread-Orthogonal Frequency Division
Multiplexing
DL Downlink
DL-SCH Downlink Shared Channel
DM-RS Dedicated demodulation reference signals
DRB Data Radio Bearer carrying user plane data
DRX Discontinuous Reception
DU Distributed Unit
EHPLMN Equivalent Home Public Land Mobile Network
EN-DC EUTRA-NR Dual Connectivity
EPC Evolved Packet Core
EPRE Energy per resource element
EPS Evolved Packet System
ETWS Earthquake and Tsunami Warning System
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E-UTRA Evolved Universal Terrestrial Radio Access
E-UTRAN Evolved Universal Terrestrial Radio Access Network
F1AP F1 Application Protocol
F1-C F1 Control plane interface
F1-U F1 User plane interface
FDD Frequency Division Duplex
FEC Forward Error Correction
FFS For Further Study
FMC First Missing Count
GERAN GSM/EDGE Radio Access Network
GF Grant Free
gNB NR Node B
gNB-CU gNB Central Unit
gNB-DU gNB Distributed Unit
GNSS Global Navigation Satellite System
GSCN Global Synchronization Raster Channel
GSM Global System for Mobile Communications
GTP-U GPRS Tunnelling Protocol
HARQ Hybrid Automatic Repeat Request
HARQ-ACK Hybrid automatic repeat request acknowledgement
HFN Hyper Frame Number
IE Information element
IETF Internet Engineering Task Force
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IMEI International Mobile Equipment Identity
IMSI International Mobile Subscriber Identity
IP Internet Protocol
kB Kilobyte (1000 bytes)
L1 Layer 1
L2 Layer 2 (data link layer)
L3 Layer 3 (network layer)
LCG Logical Channel Group
LDPC Low Density Parity Check
MAC Medium Access Control
MAC-I Message Authentication Code for Integrity
MCG Master Cell Group
MCS Modulation and coding scheme
MIB Master Information Block
MICO Mobile Initiated Connection Only
MIMO Multiple Input Multiple Output
MN Master Node
MR-DC Multi-RAT Dual Connectivity
N/A Not Applicable
NAS Non-Access Stratum
NCGI NR Cell Global Identifier
NCR Neighbour Cell Relation
NE-DC NR-E-UTRA Dual Connectivity
ng-eNB node providing E-UTRA user plane and control plane protocol terminations
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towards the UE, and connected via the NG interface to the 5GC
NGEN-DC NG-RAN E-UTRA-NR Dual Connectivity
NG-RAN NG Radio Access Network
NGAP NG Application Protocol
NR NR Radio Access
NSA Non StandAlone
O&M Operation and Maintenance
OFDM Orthogonal Frequency Division Multiplexing
OSI Other System Information
PBCH Physical Broadcast Channel
PCell Primary Cell
PCH Paging Channel
PDCCH Physical downlink control channel
PDCP Packet Data Convergence Protocol
PDSCH Physical downlink shared channel
PRACH Physical Random Access Channel
PSS Primary Synchronisation Signal
PUCCH Physical uplink control channel
PUSCH Physical uplink shared channel
PDU Protocol Data Unit
PHR Power Headroom Report
PLMN Public Land Mobile Network
PMI Precoding Matrix Indicator
PRACH Physical random access channel
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PRB Physical resource block
PRG Physical resource block group
PSS Primary synchronization signal
PTAG Primary Timing Advance Group
PT-RS Phase-tracking reference signal
PUCCH Physical uplink control channel
PUSCH Physical uplink shared channel
PWS Public Warning System
QAM Quadrature Amplitude Modulation
QCL Quasi-collocation
QFI QoS Flow ID
QoS Quality of Service
QPSK Quadrature Phase Shift Keying
RACH Random Access Channel
RAN Radio Access Network
RAT Radio Access Technology
RB Resource block
RB Radio Bearer
RBG Resource block group
RE Resource element
REG Resource element group
RF Radio Frequency
RI Rank indication
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RIV Resource indicator value
RLC Radio Link Control
RMSI Remaining Minimum SI(System Information)
RNA RAN-based Notification Area
RNAU RAN-based Notification Area Update
RNL Radio Network Layer
RNTI Radio Network Temporary Identifier
ROHC RObust Header Compression
RPLMN Registered Public Land Mobile Network
RQA Reflective QoS Attribute
RQoS Reflective Quality of Service
RRC Radio Resource Control
RS Reference signal
RSRP Reference signal received power
RTP Real Time Protocol
SA StandAlone
SAP Service Access Point
SCell Secondary Cell
SCG Secondary cell group
SCH Shared Channel
SCTP Stream Control Transmission Protocol
SDAP Service Data Adaptation Protocol
SDU Service Data Unit
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SFN System Frame Number
SI System Information
SIB System Information Block
SM Session Management
SMF Session Management Function
SMTC SS block based RRM measurement timing configuration
SN Sequence Number
SN Secondary Node
SpCell Special Cell
SPS Semi-Persistent Scheduling
SR Scheduling request
SRB Signalling Radio Bearer
SRB Signalling Radio Bearer carrying control plane data
SRS Sounding reference signal
SS Synchronisation signal
SSB Synchronization Signal Block
SS-RSRP SS reference signal received power
SS-RSRQ SS reference signal received quality
SSS Secondary synchronization signal
SS-SINR SS signal-to-noise and interference ratio
STAG Secondary Timing Advance Group
S-TMSI SAE Temporary Mobile Station Identifier
SUL Supplementary Uplink
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TA Timing advance
TAG Timing advance group
TB Transport Block
TCI Transmission Configuration Indicator
TCP Transmission Control Protocol
TPC Transmit Power Control
TDD Time Division Duplex
TDM Time division multiplexing
TM Transparent Mode
TNL Transport Network Layer
TPC-CS-RNTI Transmit Power Control-Configured Scheduling-RNTI
TPC-PUCCH-
RNTI Transmit Power Control-Physical Uplink Control Channel-RNTI
TPC-PUSCH-
RNTI Transmit Power Control-Physical Uplink Shared Channel-RNTI
TPC-SRS-RNTI Transmit Power Control-Sounding Reference Symbols-RNTI
TTI Transmission Time Interval
UCI Uplink control information
UDP User Datagram Protocol
UE User equipment
UICC Universal Integrated Circuit Card
UL Uplink
UL-SCH Uplink shared channel
UM Unacknowledged Mode
UP User Plane
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UPF User Plane Function
URLLC Ultra-Reliable and Low Latency Communications
UTC Coordinated Universal Time
UTRAN Universal Terrestrial Radio Access Network
X-MAC Computed MAC-I
Xn network interface between NG-RAN nodes
Xn-C Xn-Control plane (control plane interface between NG-RAN and 5GC)
Xn-U Xn-User plane (user plane interface between NG-RAN and 5GC)
XnAP Xn Application Protocol
5. Agreements
From RAN #84 meeting, a lot of detailed technical proposals start being documented and
some of the items reaches the agreement. Most of technical items are yet to be
determined, but I am trying to keep track of the agreed items in this page. There would be
many items that are not listed here since I haven't gone through all the TDocs from the
meeting. I am just putting those items that are closely related to my area.
New Terminology
Waveform/Modulation
Numerology / FrameStructure / TTI
Carrier Aggregation / Dual Connectivity
Multiple Access
MIMO Scheme (Codeword / Layer)
Massive MIMO
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Beam Management
Synchronization Signal/Process
Initial Access / RACH
Channel Coding
Physical Layer Procedure (Scheduling / HARQ)
Radio Interface Protocol Stack
New Terminology
Followings are from TR 38.804 section 3.
gNB : NR Node. Same component as eNB in LTE(4G)
TRxP (TRP) : Transmission Reception Point. Antenna Array (with one or more
antenna elements) available to the network located at a specific geographical
location. <= You would see this term a lot in many of NR TDocs
NextGen Core : Core Network for Next Generation System. Same component as
EPC in LTE(4G)
Nemerology : Subcarrier spacing (Frequency Domain Structure). <= This is one of
the term that confused me a lot when I was reading 5G/NR TDocs.
Waveform/Modulation
According to TR 38.804 (Ref [18]) section 5.3, it is agreed/determined as follows :
Support paired and unpaired spectrum
Support Multiple Numerology
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o Each of the numerology is derivided by scaling a basic subcarrier spacing
o The numerology can be selected independently of the frequency band
(however it is not assumed to select a very narrow subcarrier spacing in
very high frequency. <== this is physically difficult to implement)
Support flexible Network and UE channel bandwidth
Waveform
o Downlink : OFDM based waveform
o Uplink : Choice of two optioins
CP-OFDM : At least for eMBB up to 40 GHz, applicable for both
single stream and multi stream
DFT-S-OFDM : Limited to single stream transmission
Modulation
o Downlink : QPSK, 16 QAM, 64 QAM, 256 QAM with the same
constellation mapping as in LTE
o Uplink : QPSK, 16 QAM, 64 QAM, 256 QAM with the same constellation
mapping as in LTE
Followings are agreed at RAN1 #85
Largest component carrier bandwidth not smaller than 80 Mhz for at least one
numerology is supported ([1])
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Waveform is based on OFDM ([2])
o Multiple numeralogies are supported
o Additional functionality on top of OFDM such as DFT-S-OFDM, and/or
variants of DFT-S-OFDM. and/or filtering/windowing, and/or OTFS is
further considered
Complementary non-OFDM based waveform is not precluded for
some specific usecases (e.g, mMTC use case)
Followings are agreed at RAN1 #86
At least up to 40 GHz for eMBB and URLLC services, NR supports CP-OFDM
based waveform with Y greater than that of LTE (assuming Y=90% for LTE) for
DL and UL, possibly with additional low PAPR/CM technique(s) (e.g., DFT-S-
OFDM, etc.)
o Y is defined as Y = transmission bandwidth configuration / channel
bandwidth * 100% // This indicates how much guardband is required. Y =
90% implies it would require around 10% of guard band.
Numerology / FrameStructurre / TTI
According to TR 38.802 (Ref [17]) section 5.3 and TR 38.804 (Ref [18]) section 5.4.7, it
is agreed as follows :
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Maximum channel bandwidth per NR carrier is 400 Mhz in Rel 15.
All details for channel bandwidth up to 100 Mhz per NR Carrier are to be
specified in Rel 15
One Numerology corresponds to one subcarrier spacing in frequency domain
At least for single numerology case, candidates of the maximum numbers of
subcarrier is 3300 or 6600 in Rel 15
Subframe Duration is fixed to be 1 ms <== this is a little different from what many
people expected. It is likely that one TTI length is much shorter than this to meet
the latency requirement
One TTI duration corresponds to a number of consecutive symbols for one
transmission in time domain (TR 38.804 5.4.7)
The combination of one numerology and one TTI duration determines how
transmission is made on physical layer.
Frame Length is fixed to be 10 ms
Scalable numerology should allow the subcarrier spacing from 15 Khz to 480 Khz.
Number of subcarrier per PRM is 12
Number of OFDM symbols per slot may vary depending on subcarrier spacing
o For subcarrier spacing <= 60, the number of OFDM symbols / slot = 7 or
14
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o For subcarrier spacing > 60, the number of OFDM symbols / slot = 14
Slot Aggregation (data transmission scheduling to span one or multiple slots
No explicit DC subcarrier is reserved for both Downlink and Uplink
All numerologies align on symbol boundaries every 1 ms in NR carrier (regardless
of subcarrier spacing and CP-overhead)
Followings are agreed at RAN1 #85 <== Now that TR 38.802 is release, you may not
need to read following items.. but I will keep this to help you track down the history and
background of those decision in 38.802. Especially following through the TDocs
mentioned here would give you further details of the background.
It is necessary to support more than one values of subcarrier spacing ([2])
RAN1 will continue further study and conclude between following alternatives in
the next meeting ([2])
o Alt 1:
The subcarrier spacing for the NR scalable numerology should scale
as
f_sc = f0 x 2^m
where
f0 is FFS
m is an integer chosen from a set of possible values
o Alt 2:
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The subcarrier spacing for the NR scalable numerology should scale
as
f_sc = f0 x M
where
f0 is FFS
M is an integer chosen from a set of possible positive
values
At least the following should be supported for NR in a frequency portion([4])
o A time interval X which can contain one or more of the following
DL transmission part
Guard
UL transmission part
o FFS which combinations are supported and whether they are indicated
dynamically and/or semi-statically
o Furthermore, the following is supported
The DL transmission part of time interval X to contain downlink
control information and/or downlink data transmissions and/or
reference signals
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The UL transmission part of time interval X to contain uplink
control information and/or uplink data transmissions and/or
reference signals
Followings are agreed at RAN1 #86
Followings are considered as starting points of NR frame structure at least within
the CP overhead ([12])
o Subframe
Already agreed upon
Assume x=14 in the reference numerology for subframe definition
(for normal CP)
FFS: y=x and/or y=x/2 and/or y is signalled
o Slot
Slot of duration y OFDM symbols in the numerology used for
transmission
An integer number of slots fit within one subframe duration (at least
for subcarrier spacing is larger than or equal the reference
numerology)
The structure allows for ctrl at the beginning only
The structure allows for ctrl at the end only
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The structure allows for ctrl at the end and at the beginning
Other structure is not precluded
One possible scheduling unit
o Mini-slot
Should at least support transmission shorter than y OFDM symbols
in the numerology used for transmission
May contain ctrl at the beginning and/or ctrl at the end
The smallest mini-slot is the smallest possible scheduling unit (FFS:
smallest number of symbols)
o Note: the names are for the purpose of discussion. Whether some terms can
be merged or not is FFS
o FFS whether NR frame structure needs to support both slot and mini-slot or
these can be merged
Carrier Aggregation / Dual Connectivity
According to TR 38.802 (Ref [17]) section 5.5, it is agreed as follows :
Maximum number of Carrier Aggregation / Dual Carrier is 16
Maximun aggregated bandwidth in phase 1 is around 1 Ghz (contiguous or non-
contiguous)
Cross-carrier scheduling and joint UCI feedback is supported
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Per-carrier TB mapping is supported
Multiple Access
Followings are agreed at RAN1 #85
Non-orthogonal multiple access should be investigated for divsersified NR usage
scenarios and use case([3])
At least for UL mMTC, autonmous/grant-free/contention based non-orthogonal
multiple access should be studied ([3])
MIMO Scheme (Codeword / Layer)
According to TR 38.802 (Ref [17]) section 6.1.6.2, it is agreed as follows :
The number of codewords per PDSCH assignment per UE
o 1 codeword for 1 to 4-layer transmission
o 2 codewords for 5 to 8-layer transmission.
DL DMRS based spatial multiplexing (SU-MIMO/MU-MIMO) is supported
o At least, the 8 orthogonal DL DMRS ports are supported for SU-MIMO
o Maximum 12 orthogonal DL DMRS ports are supported for MU-MIMO
Massive MIMO
Followings are agreed at RAN1 #85
Max number of Antenna on eNB ([5])
o 256 for 30 Ghz
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o 1024 for 70 Ghz
Beam Management
In TR 38.802 and 38.804, Beam Management are described in terms of several different
aspects(Functions) and procedures. The summary here is based on TR 38.804 section
5.3.4.
Main functions of Beam Managements
o Beam Determination : for TRP(s) or UE to select of its own Tx/Rx beam
o Beam Measurement : for TRP(x) or UE to measure characteristics of
received beamformed signals
o Beam Reporting : for UE to report information a property / quality of
beamformed signal based on Beam Measurement
o Beam Sweeping : Operation of covering a spatial area, with beams
transmitted and/or received during a time interval in a predefined way
Main Procedure of Beam Managements
o P-1 : Beam Selection for TRP Tx/UE Rx, It is used to enable UE
measurement on different TRP Tx beams to support selection of TRP Tx
beams/UE Rx beam.
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o P-2 : Beam Reselection(Beam Change) for TRP Tx beam. It is used to
enable UE measurement on different TRP Tx beams to possibly change
inter/intra-TRP Tx beam.
o P-3 : Beam Reselection(Beam Change) for UE Rx beam. It is used to
enable UE measurement on the same TRO Tx beam to change UE Rx beam
in the case UE uses beamforming.
The following DL L1/L2 beam management procedures are supported within one or
multiple TRPs: ([15])
P-1: is used to enable UE measurement on different TRP Tx beams to support
selection of TRP Tx beams/UE Rx beam(s)
o For beamforming at TRP, it typically includes a intra/inter-TRP Tx beam
sweep from a set of different beams
o For beamforming at UE, it typically includes a UE Rx beam sweep from a
set of different beams
o FFS: TRP Tx beam and UE Rx beam can be determined jointly or
sequentially
P-2: is used to enable UE measurement on different TRP Tx beams to possibly
change inter/intra-TRP Tx beam(s)
o From a possibly smaller set of beams for beam refinement than in P-1
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o Note: P-2 can be a special case of P-1
P-3: is used to enable UE measurement on the same TRP Tx beam to change UE
Rx beam in the case UE uses beamforming
Strive for the same procedure design for Intra-TRP and inter-TRP beam
management
o Note: UE may not know whether it is intra-TRP or inter TRP beam
Note: Procedures P-2&P-3 can be performed jointly and/or multiple times to
achieve e.g. TRP Tx/UE Rx beam change simultaneously
Note: Procedures P-3 may or may not have physical layer procedure spec. impact
Support managing multiple Tx/Rx beam pairs for a UE
Note: Assistance information from another carrier can be studied in beam
management procedures
Note that above procedure can be applied to any frequency band
Note that above procedure can be used in single/multiple beam(s) per TRP
Related to different reciprocity assumptions in beam management procedures the
following agreements were reached ([15])
Consider different channel reciprocity assumptions in beam management
procedures
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o At a TRP or UE, with TX and RX channel reciprocity (full or partial) (e.g.,
beam reciprocity), TX beam (or RX beam) can be obtained from RX beam
(or TX beam) to reduce overhead and latency
o Without TX and RX channel reciprocity, beam management procedure may
require TX and RX beam sweeping in both DL and UL links
RAN1 study different methods of determining Tx and Rx beam(s) for
communication on one link direction (uplink or downlink), e.g.,
o Joint determination: Tx beam and Rx beam are determined jointly
o Separate determination: Tx beam or Rx beam are determined sequentially.
o Multi-stage determination: for instance, coarse Tx-Rx beam determination
followed by fine Tx-Rx beam determination
Study beam management procedure with and without explicit signaling of beam(s)
or beam group(s) used for transmission
Synchronization Signal/Process
RAN1 should strive for a common framework, including for example structure of
synchronization signals, for initial access ([14])
More specifically, especially within a group of frequency bands in the frequency range,
RAN1 should strive for an unified framework covering([14])
Single beam based and multi-beam based deployments
TDD and FDD operations
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Different/mixed numerologies
Standalone and non-standalone operations
Licensed band and unlicensed band operations
FFS: mMTC use case
RAN1 should take at least following requirements into account to design initial
access([14])
Providing at least following functionalities
Detection of NR cell and its ID
Note: In this context, NR cell corresponds one or multiple TRP(s)
Initial time/frequency synchronization to the cell
Providing necessary information for random access
Providing sufficient number of the identity values to allow deployment flexibility
FFS: supporting efficient mobility
FFS: supporting efficient inter-RAT measurement
Reducing the frequency hypothesis UE needs to search for compared to LTE
FFS: detecting beam ID(s)
For subcarrier spacing of each synchronization signal (e.g, NR PSS, SSS) in a NR
Carrier, the following alternatives should be studied : (Ref [7], [10])
Alt 1 : Subcarrier spacing is predefined in the specification for a given frequency
range
Ex: 15Khz for sub-6Ghz, 60 kHz for over-6Ghz
Alt 2 : Subcarrier spacing is selected by NR BS
FFS : Details on the set of possible numerologies
Note : Blind detection of multiple numerologies can be considered
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Alt 3 : Single Subcarrier spacing if predefined in the specification for all
frequency ranges
Oter alternatives are not precluded
NR synchronization signal is based on CP-OFDM
Note that DFT-spread-OFDM based design is not precluded
At least one transmission bandwidth within a carrier bandwidth can be specified for
transmission of each synchronization signal and at least some essential system
information. ([13])
The transmission bandwidth may be specified either differently according to the
frequency range or the same across the frequency ranges
FFS: transmission bandwidths for each synchronization signal and at least some
system information are same or not
FFS: the transmission bandwidth and the corresponding numerology
FFS: whether the used transmission bandwidth is blindly detected by UE from
specified bandwidths according to the frequency bands
Initial Access / RACH
General Design
RAN1 should strive for a common framework, including for example structure of
synchronization signals for initial access : (Ref [7], [10])
More specifically, especially within a group of frequency bands in the frequency
range, RAN1 should strive for a unified framework covering following items: (Ref
[7], [10])
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o Single beam based and multi-beam based deployments
o TDD and FDD operations
o Different/mixed numerologies
o Standalone and non-standalone operations
o Licensed band and unlicensed band operations
o FFS : mMTC use case
RAN1 should take at least following requirements into account to design initial
access
o Providing at least following functionalities
Detection of NR cell and its ID
Initial time/frequency synchronization to the cell
Providing necessary information for random access
o Providing suffcient number of the identity values to allow deployment
flexibility
o Reducing the frequency hopothesis UE needs to search for, compared to
LTE
o FFS : supporting efficient mobility
o FFS : supporting efficient inter-RAT measurement
o FFS : detecting beam ID(s)
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Random Access Procedure
RACH procedure including RACH preamble (Msg 1), Random Access Response
(Msg 2), Msg 3 and Msg4 is at least assumed for NR from RAN1 perspective:
(Ref [7], [10])
Simplified RACH procedure, e.g Msg 1(UL) and Msg 2(DL) should be further
studied: (Ref [7], [10])
o Details on Msg 1 and Msg2 are FFS
The design of the random access procedure should take into account the possible
use of single-beam and multiple bean operations including following items.: (Ref
[7], [10])
o Non Rx/Tx reciprocity at BS or UE
o Full or partial Rx/Tx reciprocity at BS or UE
In case that multiple team-forming is applied to DL broadcast channels/signals for
initial access: (Ref [7], [10])
o RACH resources is obtained by UE from detected DL broadcast
channels/signals
FFS : Details on association
o Other mechanism without association is also considered
Multiple occasions for RACH preamble transmission in a given time interval are
considered: (Ref [7], [10])
o Details are FFS
o Other mechanisms are not precluded.
Study further RACH Reception / RAR Transmission in TRPs/beams other than the
one transmitting synchronization signal: (Ref [7], [10])
Channel Coding
According to TR 38.802 (Ref [17]) section 6.1.5, it is agreed as follows :
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For eMBB Data channel, LDPC for all block size
For eMBB DCI, Polar Coding
Physical Layer Procedure (Scheduling / HARQ)
According to TR 38.802 (Ref [17]) section 6.2, it is agreed as follows :
< Scheduling >
supports both data and control with the same numerology.
supports at least same-slot and cross-slot scheduling for both DL and UL.
Timing between DL assignment and corresponding DL data transmission is
indicated by a field in the DCI from a set of values and the set of values is
configured by higher layer.
The timing(s) is (are) defined at least for the case where the timing(s) is (are)
unknown to the UE.
Both contiguous and non-contiguous resource allocation for data with CP-OFDM
is supported.
< HARQ >
HARQ-ACK feedback with one bit per TB is supported.
Operation of more than one DL HARQ processes is supported for a given UE
Operation of one DL HARQ process is supported for some UEs.
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UE supports a set of minimum HARQ processing time.
supports different minimum HARQ processing time at least for across UEs.
The HARQ processing time at least includes delay between DL data reception
timing to the corresponding HARQ-ACK transmission timing and delay between
UL grant reception timing to the corresponding UL data transmission timing.
UE is required to indicate its capability of minimum HARQ processing time to
gNB.
Asynchronous and adaptive DL HARQ is supported at least for eMBB and
URLLC.
From UE perspective, HARQ ACK/NACK feedback for multiple DL
transmissions in time can be transmitted in one UL data/control region.
Timing between DL data reception and corresponding acknowledgement is
indicated by a field in the DCI from a set of values and the set of values is
configured by higher layer.
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Radio Interface Protoocol Stack
Overall Radio Interface Protocol Stack of NR is almost identical to the radio protocol
stack of LTE except that in NR U-Plane a new layer (AS sublayer) is added.
Following diagram is based on TR 38.804 Figure 5.2.1.1-1 and Figure 5.2.2.1-1. (The
component in orange is the new component in NR)
Reference :
[1] 3GPP R1-163989. 3GPP TSG RAN WG1 Meeting #85 - Waveform for NR
[2] 3GPP R1-165242. 3GPP TSG RAN WG1 Meeting #85 - On FrameStructure for NR
[3] 3GPP R1-165242. 3GPP TSG RAN WG1 Meeting #85 - Contention based multiple
access for NR uplink
[4] 3GPP R1-166013. 3GPP TSG RAN WG1 Meeting #85 - WF on time interval X
[5] 3GPP R1-166013. 3GPP TSG RAN WG1 Meeting #85 - Multi-Antenna Technology
for NR Interface
[6] 3GPP R1-168258. 3GPP TSG-RAN1 Meeting #86 - LS on NR waveform
[7] 3GPP R1-168214. 3GPP TSG RAN1 Meeting #86 - LS on RAN1 agreements for NR
initial access and mobility
[8] 3GPP R4-167323. TSG-RAN WG4 Meeting #80bis Considerations on the
requirements for the initial access in NR
[9] 3GPP R4-167322. TSG-RAN WG4 Meeting #80bis Considerations on NR RRM
with the multiple numerologies
[10] 3GPP R4-167216. TSG-RAN WG4 Meeting #80bis LS on RAN1 agreements for
NR initial access and mobility
[11] 3GPP R1-1610203 3GPP TSG RAN WG1 Meeting #86bis Synchronization in NR
considering beam sweeping
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[12] 3GPP R1-1610307 3GPP TSG RAN WG1 Meeting #86bis Views on time domain
structure for NR
[13] 3GPP R1-1610351 3GPP TSG RAN WG1 Meeting #86bis A Framework for Initial
Access for NR
[14] 3GPP R1-1610400 3GPP TSG RAN WG1 Meeting #86bis On NR DL
synchronization
[15] 3GPP R1-1610239 3GPP TSG RAN WG1 Meeting #86bis On beam management in
NR – procedures
[16] 3GPP R1-1610287 3GPP TSG RAN WG1 Meeting #86bis On the synchronization
signal design principle in NR
[17] 3GPP TR 38.802 V2.0.0 (2017-03) - Study on New Radio (NR) Access Technology;
Physical Layer Aspects (Release 14)
[18] 3GPP TR 38.804 V1.0.0 (2017-03) - Study on New Radio Access Technology;
Radio Interface Protocol Aspects (Release 14)
[19] 3GPP TR 38.801 V2.0.0 (2017-3) - Study on New Radio Access Technology;Radio
Access Architecture and Interfaces (Release 14)
[20] 3GPP TR 38.803 V2.0.0 (2017-03) - Study on New Radio Access Technology; RF
and co-existence aspects (Release 14)
[21] 3GPP R2-1702534 TSG-RAN WG2 #97bis - RAN WG’s progress on NR
technology SI in the February meeting.
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6. Antenna Ports
The concept and definition of Antenna Ports are same as LTE Antenna Ports.
It is defined as follows (38.211-4.4.1).
An antenna port is defined such that the channel over which a symbol
on the antenna port is conveyed can be inferred from the channel over
which another symbol on the same antenna port is conveyed.
What does this mean ? I interpret this as follows :
Each Antenna ports carries its own resource grid and a specific set of reference
signal in the grid. The channel properties for RE(resource element) for the reference
signal is assumed to be same (or very close to same) as the resource elements
for other data(e.g, REs for PDSCH). Due to this facts, we can help demodulate
the data by using the channel information obtained by the anaysis of reference channel.
In NR, a certain range of antenna port number is assigned for each channel and signal as follows.
<38.211 - 6.2, 7.2>
Channel/Signal Antenna Ports
PDSCH Antenna ports starting
with 1000
PDCCH Antenna ports starting with 2000
CSI-RS Antenna ports starting with 3000
SS/PBCH Antenna ports starting with 4000
PUSCH/DMRS Antenna ports starting with 0
SRS Antenna ports starting with 1000
PUCCH Antenna ports starting with 2000
PRACH Antenna port 4000
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Reference
[1]
What is BeamForming ? It means just as it sounds. BeamForming is a techology to 'Form' a
'beam'.
Then what does it mean by 'beam' in this context ? I would say it means 'electromagnatic wave
radiation pattern(propagation pattern) for a set of antenna system'. Simply put, BeamForming is
a technic that constuct the antenna radation pattern as shown in < Case 2 > of the following
illustration.
High level meaning is simple like this.. but real implementation would be very complicated
and is out of my understanding. So I would just give you only a big picture of this technology.
Motivation (Why we need BeamForming ?)
How to 'Form' a beam ?
Technology for BeamForming
Basic Concept : Array Antenna
Charecterization of Array Antenna - Beam Pattern Plot
Basic Concept : Beam Forming - Phased Array
Modeling BeamForming
Beamforming in LTE
o Precoding for BeamForming
o Single-layer random beamforming (Antenna port 5, 7, or 8) : 36.101 B.4.1
o Dual-layer random beamforming (antenna ports 7 and 8) : 36.101 B.4.2
o Generic beamforming model (antenna ports 7-14) : 36.101 B.4.3
o Example 1 : 8 x 2 (8 Antenna, 2 Layers)
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o CSI RS Configuration
Beamforming in 5G/NR (Massive MIMO)
Motivation (Why we need BeamForming ?)
Why we need beamforming ?
It is simple. Let's look at the two illustrations as shown below. There are two antenna system
and let's assume that the two antenna is transmitting the exactly same amount of total energy.
In case 1, the antenna system is radiating the energy in almost same amount in all direction.
The three UEs around the antenna would receive almost same amount of the energy but a large
portions of energy not directed to those UEs is wasted.
In case 2, the signal strength of the radiation pattern ('beam') is specially 'formed' in such a
way that the radiated energy in direction to UEs are much stroger than the other parts which
is not directed to UEs.
How to 'Form' a beam ?
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By now, you would ask 'How can we form a beam ?'. If you want to understand this
mechanism in pricise and clear way, you need to turn to the dry and boring mathematics.
We will look into this mathematical way of explanation in following section
(Basic Concept : Array Antenna), but before falling asleep with math, let's build up
some intuitive understanding on the principles of the beam forming.
The simplest way of forming a beam is to put multiple antenna in an array.
There are many different ways of aligning those antenna antenna elements,
but one of the simplest way is to align the antenna along a line as shown in
the following example. The intuitive idea you should see here is that you will
get a sharper beam as you put more antenna elements in the array.
NOTE : This example plots were created by Matlab PhaseArrayAntenna toolbox and
the source code for this example and more examples are posted here.
Another way of arranging the elements in an array is align the elements in a two dimensional sqaure as shown in the following examples. The intuitive idea you
should see here is that you will get a sharper beam as you put more antenna elements in the array.
NOTE : This example plots were created by Matlab PhaseArrayAntenna toolbox and the source code for this example and more examples are posted here.
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Now let's think of another type of two dimensional array in which the shape of the array
is not square as shown below. The intuition you can get is that the beam compressed
more along the axis of more elements.
NOTE : This example plots were created by Matlab PhaseArrayAntenna toolbox and
the source code for this example and more examples are posted here.
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Technology for BeamForming
There are several different ways to implement the beamforming. Followings are couple of
techniques most commonly used (As I mentioned, the details of implementation is out of
my understanding).
For a little bit further details, see All Beamforming Solutions Are Not Equal. This is mainly for
WLAN, but can be a good introduction.
Switched Array Antenna : This is the technique that change the beam pattern (radiation form)
by switching on/off antenna selectively from the array of a antenna system.
DSP Based Phase Manipulation : This is the technique that change the beam pattern
(radiation form) by changing the phase of the signal going through each antenna.
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Using DSP, you can change the signal phase for each antenna port differently
to form a specific beam pattern that is best fit for one or multiple specific UEs.
Beamforming by Precoding : This is the technique that change the beam pattern
(radiation form) by applying a specific precoding matrix. This is the technique used in
LTE. In LTE, following transmission mode is implemeting 'BeamForming' implictely
or explicitely.
TM 6 - Closed loop spatial multiplexing using a single transmission layer.
TM 7 - Beamforming (Antenna port 5)
TM 8 - Dual Layer Beamforming (Antenna ports 7 and 8)
Basic Concept : Array Antenna
Since the BeamForming is mostly based on Array Antenna, let's take a look at the basic
principles of Array Antenna. Let's suppose we have a antenna array in which each of the
antenna is placed apart from each other with a certain distance (d). And then, suppose
multiple rays of beam transmitted from a single source is received by each of the antenna
in the array. If all the rays from the single source is coming directly (meaning theta in the
following illustration is 0) into the antenna, there would be no differences in terms of
distance along which each of the rays travelled from the source to each of the reciever antenna.
So if you sum up the energy recieved by each antenna, it will be same as each of the wave
sum up constructively. However, if the direction of the ray and the axis of antenna array is
not in right angle (meaning the theta is not 0), the travel distance of each ray (p1,p2,..,p8)
gets different and the difference can be expressed as d sin(theta) as shown in the following
illustration.
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Now let's describe what I explained above into mathematical expression.
If I take the received signal at the first antenna (the leftmost antenna) as the
reference antenna and the signal received at each of the antenna can be represented as follows. (This would the point where many people
gave up further reading/study because of the math. But in most of engineering and science, there are many cases where you can never
understand completely without a certain degree of math. So, don't give up just because of the math... and try to understand the meaning of
each mathematica terms. When I am explaining about this array antenna, I first talked about the travel path difference and angle between
antenna array axis and the beam ray hitting the antenna. In the mathematical expression, you still see the angle term 'theta', but you don't see
any direct term that look like 'travel path'. Actually we don't know the exact travel difference of each beam because we don't know the exact
location of the beam source. The only thing we know is the travel path difference between each beam hitting on each antenna. That travel
path difference can be expressed as e^(-j * n * d * theta) where n is the index of the antenna being numbered 0 from the leftmost antenna.
Keeping this in mind, take close loot at each mathematical expression and it would make sense to you. If you are not familiar with
interpreting the meaining of e^(-theta), you may refer to complex number page).
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Another way of visualizing this summation process would be as follows :
Now we formulated the signal coming into each antenna. Now let's formulate the signal
that combined all the signal coming into each antenna. It is simple, you only have sum
up all the signals comining into each antenna and it can be presented as follows.
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You can represent this equation into a vector notation as follows.(Many people even including me get intimidated when seeing this kind of
matrix/vector expression. Don't get scared. We have already learned basic operations from high school or freshmen university math course. We
just didn't have enough chance for enough practice. So if you get somehow uneasy feeling about this, just expand the following equation by
hand and you will get more familiar expression as above. Doing this kind of practice whenever you see this kind of vector/matrix notation,
gradually you will get more and more familiar and such an uneasy feeling would disappear. Nobody else can do this kind of practice for you)
Charecterization of Array Antenna - Beam Pattern Plot
When you characterize (represent the performance of an Antenna array), you might have seen the types of plots as shown below. In some
documents, you would see the plot like the one on the left and in some other document you would see the one on the right. Actually these two
represents the exact the same thing. They just plot the same thing in two different coordinate system. The one on the left is the representation
of (trancemitted or received power) vs angle in Cartesian coordinate and the right one is the representation of the same data in polar
coordinate.
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Power and Energy in the plot would be familiar to you. Then, what does the theta (angle) represents ? It is the angle between the direction of
ray and the axis of antenna array. If
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Reciever is the array antenna and the transmitter is a single transmitter far enough from the reciever antenna, the angle can be represented as
follows. In this illustration, I set the distance (r) to be infinite to assume that the all the rays reaches the reciever antenna in paralelle. It reality,
the distance cannot be infinite. it is just far enough to make the assumption meaningful. You can set the angle (theta) by placing the
transmitter antenna to different location on the circumference (as in the top track) or by rotating the antenna array (as in the bottom track). In
this case, you may think that the plots shown above reprents total power recieved by all the antenna on the array.
The same logic applies when the transmitter antenna is the array antenna and the reciever antenna is a point far away from the transmitter.
The angle is the angle between the direction of ray and the axis of antenna array. The angle can be represented as follows. In this illustration,
I set the distance (r) to be infinite to assume that the all the rays reaches the reciever antenna in paralelle. It reality, the distance cannot be
infinite. it is just far enough to make the assumption meaningful. You can set the angle (theta) by placing the recieving antenna to different
location on the circumference (as in the top track) or by rotating the antenna array (as in the bottom track). In this case, you may think that
the plots shown above represents total power recieved by the reciever antenna.
In above illustration, you have seen four different cases of representing the angle. Even though the function of the antenna array (being
reciever or transmitter) is different and the way making the angle (by moving reciever/transmitter antenna by rotating the antenna array), the
overall shape of the plot is same (at least in theory). The only difference would be the scale of Engergy/Power depending on whether it
represents the reciever power or transmitter power. So if we ignoare the scale of the engery/power axis, you can interpret the graph
(Power/energy vs theta) as shown below.
As you see here, the energy/power gets maximum when the angle (theta) is 0. To get the max energy when the angle is zero, the distance
between one antenna in the array and another antenna next to it should be a half of wave length.
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If you want to play with this graph, try running the follow matlab toy code.
theta = -0.5*pi:pi/100:0.5*pi;
d = 2.0;
a_theta = [exp(-j .* 0 .* d .* theta) ;
exp(-j .* 1 .* d .* theta);
exp(-j .* 2 .* d .* theta);
exp(-j .* 3 .* d .* theta);
exp(-j .* 4 .* d .* theta);
exp(-j .* 5 .* d .* theta);
exp(-j .* 6 .* d .* theta);
exp(-j .* 7 .* d .* theta)];
a_theta_sum = sum(a_theta);
a_theta_sum_abs = abs(a_theta_sum);
a_theta_sum_abs = a_theta_sum_abs ./ max(a_theta_sum_abs);
a_theta_sum_abs_dB = 10 .* log(a_theta_sum_abs);
for i = 1:length(a_theta_sum_abs_dB)
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if a_theta_sum_abs_dB(i) <= -30
a_theta_sum_abs_dB(i) = -30;
end;
end;
a_theta_sum_abs_dB = a_theta_sum_abs_dB - min(a_theta_sum_abs_dB);
a_theta_sum_abs_dB = a_theta_sum_abs_dB/max(a_theta_sum_abs_dB);
subplot(2,2,1);plot(theta,a_theta_sum_abs);
xlim([-pi/2 pi/2]);
set(gca,'xtick',[-pi/2 -pi/4 0 pi/4 pi/2]);
set(gca,'xticklabel',{'-pi/2' '-pi/4' '0' 'pi/4' 'pi/2'});
subplot(2,2,2);polar(theta + 0.5*pi,a_theta_sum_abs,'-r');
t = findall(gcf,'type','text');
delete(t);
subplot(2,2,3);plot(theta,10 .* log(a_theta_sum_abs));ylim([-30 1]);
xlim([-pi/2 pi/2]);
set(gca,'xtick',[-pi/2 -pi/4 0 pi/4 pi/2]);
set(gca,'xticklabel',{'-pi/2' '-pi/4' '0' 'pi/4' 'pi/2'});
subplot(2,2,4);polar(theta + 0.5*pi,a_theta_sum_abs_dB,'-r');
t = findall(gcf,'type','text');
delete(t);
By tweaking the phase of each antenna, you can create a beam pointing to multiple direction as shown the following example. (Upper track is
the power/energy in linear scale and Lower track is the power/energy in dB scale)
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Following is the matlab code for the plot shown above. Play with this by changing theta_shift
or any other values in a_theta array as you like until you get the intuitive understanding of
each parameters.
theta = -0.5*pi:pi/100:0.5*pi;
d = 2.0;
theta_shift = (0.25*pi);
a_theta = [exp(-j .* 0 .* d .* (theta-theta_shift));
exp(-j .* 1 .* d .* (theta-theta_shift));
exp(-j .* 2 .* d .* (theta-theta_shift));
exp(-j .* 3 .* d .* (theta-theta_shift));
exp(-j .* 0 .* d .* (theta+theta_shift));
exp(-j .* 1 .* d .* (theta+theta_shift));
exp(-j .* 2 .* d .* (theta+theta_shift));
exp(-j .* 3 .* d .* (theta+theta_shift))];
a_theta_sum = sum(a_theta);
a_theta_sum_abs = abs(a_theta_sum);
a_theta_sum_abs = a_theta_sum_abs ./ max(a_theta_sum_abs);
a_theta_sum_abs_dB = 10 .* log(a_theta_sum_abs);
for i = 1:length(a_theta_sum_abs_dB)
if a_theta_sum_abs_dB(i) <= -30
a_theta_sum_abs_dB(i) = -30;
end;
end;
a_theta_sum_abs_dB = a_theta_sum_abs_dB - min(a_theta_sum_abs_dB);
a_theta_sum_abs_dB = a_theta_sum_abs_dB/max(a_theta_sum_abs_dB);
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subplot(2,2,1);plot(theta,a_theta_sum_abs);
xlim([-pi/2 pi/2]);
set(gca,'xtick',[-pi/2 -pi/4 0 pi/4 pi/2]);
set(gca,'xticklabel',{'-pi/2' '-pi/4' '0' 'pi/4' 'pi/2'});
subplot(2,2,2);polar(theta + 0.5*pi,a_theta_sum_abs,'-r');
t = findall(gcf,'type','text');
delete(t);
subplot(2,2,3);plot(theta,10 .* log(a_theta_sum_abs));ylim([-30 1]);
xlim([-pi/2 pi/2]);
set(gca,'xtick',[-pi/2 -pi/4 0 pi/4 pi/2]);
set(gca,'xticklabel',{'-pi/2' '-pi/4' '0' 'pi/4' 'pi/2'});
subplot(2,2,4);polar(theta + 0.5*pi,a_theta_sum_abs_dB,'-r');
t = findall(gcf,'type','text');
delete(t);
Basic Concept : Beam Forming - Phased Array
In previous sections on basic Antenna array mode, we could see that just by arraning multiple antenna in an array we could create a beam with
the directivity to a certain direction and by physically rotating the antenna array we can change the direction of the beam. However, there will
be a lot of restrictions in terms of the shape of the beam and controlling the direction in simply placing multiple antenna in an array.
There are even smarter idea as invented as shown below. You can do everything explained above and do even more by placing the devices
that can control phase and amplitude of a wave to each antenna as illustrated below.
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The total energy pattern (beam pattern) created by summing up all the transmitted energy
coming out of each antenna can be described in mathematical form as shown below.
Again, you can simplify this long equation into a simple vector notation as shown below.
Theoretically, you can create a beam with any shape and any direction by changing the gain
and phase in the vector.
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Modeling of Beam Forming
As I mentioned above, theorectically you can create a beam with any shape and any angle
by chaning angle (phase) and gain connected to each antenna. Then the question is how to
find proper angle (phase) and gain value to each antenna to achieve the desired beam pattern.
Long story.. but the conclusion is not that complicated. Let's asume that we have the simplest
array antenna made up of just two antenna as shown below. The antenna array on the left is
transmitter antenna and the single antenna on the right is the reciever antenna. The blocks
labeled p1 and p2 is a complex number that representing phase and amplitude controller
(As you know, a complex number can represent both phase and amplitude). h1 and h2 is channel
coefficient between transmitter and reciever antenna.
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Now the question is how to represent the received signal y using these parameters.
It can be presented as shown below (If you are not familiar with this kind of channel
representation, refer to Channel Model page)
Now the question is how to find p1 and p2 value to make the beam properly point to the
reciever antenna. If you rewrite the question a little bit, it can be 'what is the p1 and p2
value that maximize the received energy at the reciever antenna ?'. In real situation, h1 and h2 act as some factors distorting/deteriorating the
signal between the transmitter and reciever antenna. So, if we can set p1 and p2 propery to compensate (undo) the effect of h1 and h2, that
would be the p value to make the received energy maximum. h1 and h2 are complex numbers, meaning h1 and h2 has gain component and
phase component. Therefore, the question becomes 'how to undo an effect caused by a complex number ?'.
Undoing a complex number is simple. Just multiplying a complex conjugate to the given complex number. (If you multiply a complex number
with its conjugate, the phase of the resulting complex number become always '0', meaning that imaginary part become always 0. So in this kind
of situation, we can say 'multiplying a complex number with its conjugate' is same as 'undoing the phase shift caused by the complex number'.
Therefore, if you put complex conjugate of h1 and h2 into p1 and p2 as shown below, this would undo the phase shifting effect of h1 and h2.
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This looks very handy and simple solution. However, there is a problem with this kind of undo. By multiplying the channel coefficient with
its conjudate, we can easily remove the phase part. However, the real value of the resulting number gets larger. To prevent this, you only have
to normalize those conjugate numbers with the norm of h vector (a vetor made of h1 and h2) as shown below.
Now with this, we found the p1 and p2 to make the beam in the best direction to the reciever antenna.
If you implement the p1 and p2 in DSP or FPGA, the illustration above is good enough. Because you can easily implement a complex number as it is. However, if
we implement p1 and p2 as analog component, probably following illustration would be a better representation.
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Beamforming in LTE
Overall procedure for LTE beamforming in the context of physical layer processing goes
as shown below.
< Precoding for BeamForming >
In case of BeamForming, Precoding is doing almost nothing and in stead something similar to Precoding happens at the stage labeled
as BF(Beam Forming) shown below. Theoretically we can implement Beamforming in roughly three different way as illustrated below. But
as far as I understand, in LTE < Case 1 > is most commonly used. (NOTE : in the system which use a lot of antenna as in 5G/NR, it is mostly
likely to use < Case 3 > )
< Case 1 : Pure Baseband >
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Basic Beamforming Model for this type is described in 36.101 (B.4.1, B.4.2, B.4.3) and it
propose three different categories as summarized below.
< Case 2 : Pure RF >
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< Case 3 : Hybrid >
< Single-layer random beamforming (Antenna port 5, 7, or 8) : 36.101 B.4.1>
This type has following two cases. TM8, DCI Format 2B single layer would fall into this type.
i) without a simultaneous transmission on the other antenna port
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ii) with a simultaneous transmission on the other antenna port
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< Dual-layer random beamforming (antenna ports 7 and 8) : 36.101 B.4.2>
TM8, DCI Format 2B dual layer would fall into this type.
< Generic beamforming model (antenna ports 7-14) : 36.101 B.4.3 >
TM9, DCI Format 2C dual layer would fall into this type.
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Unliked other model like B.4.1 and B.4.2, the definition of W(i) is not always obvious.
The 36.101 B.4.3 says "The precoder matrix W(i) is specific to a test case.", it means we
have to define a specific test case (situation) and then try to define the W(i).
Example 1 : 8 x 2 (8 Antenna, 2 Layers)
In this example, I will look into a case where two layered data is transmitted through 8
Tx antenna. Two UE
specific reference signal p7, p8 are subject to BeamForming and 8 CSI RS ports (p15~p22)
will be transmitted for CSI estimation on UE side. Overall mapping between antenna ports and
physical antenna is as shown below.
< Mapping between Antenna port and physical antenna >
First, it seems obvious that we need something to distribute the two layered data over 8 physical
antenna and it can be easily understood that we need following form of matrix.
< Beamforming Matrix converting two user ports to 8 physical antenna >
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Now we have to figure out (or define) values of each matrix element. For this, we have to define
our model more specifically.
36.213 7.2.4 Precoding Matrix Indicator (PMI) definition says as follows and this example is
the case described by the underlined parts.
For transmission modes 4, 5 and 6, precoding feedback is used for channel dependent codebook
based precoding and relies on UEs reporting precoding matrix indicator (PMI).
For transmission mode 8, the UE shall report PMI if configured with PMI/RI reporting.
For transmission mode 9, the UE shall report PMI if configured with PMI/RI reporting
and the number of CSI-RS ports is larger than 1. A UE shall report PMI based on the
feedback modes described in 7.2.1 and 7.2.2. For other transmission modes,
PMI reporting is not supported
The exact value of the matrix is determined by UE PMI report and network construct the
matrix W(i) based on following table.
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36.213 Table 7.2.4-2 Codebook for 2-layer CSI reporting using antenna ports 15 to 22
The first thing that confuses me was "Where is i_1 and i_2 is defined ?" and what do they mean (indicate) ? These are described in 36.213
section 7.2.1 "Wideband feedback -> Mode 1-2 description" as shown below. Of course it will take a long time to understand real meaning of
these variable. (First you have to understand everything on CQI/RI Feedback type page first just to understand these i_1 and i_2)
Following is more detailed information from 36.212 regarding the i1 and i2 report from UE.
< 36.212 - Table 5.2.3.3.1-3A: UCI fields for joint report of RI and i1
(transmission mode 9 configured with PMI/RI reporting with 2/4/8
antenna ports and transmission mode 10 configured with PMI/RI reporting with 2/4/8
antenna ports) >
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< 36.212 - Table 5.2.3.3.2-2B: UCI fields for channel quality feedback for UE-selected
sub-band reports (transmission mode 9 configured with PMI/RI reporting with 8 antenna
ports and transmission mode 10 configured with PMI/RI reporting with 8 antenna ports) >
< 36.212 - Table 5.2.3.3.2-2B: UCI fields for channel quality feedback for UE-selected
sub-band reports (transmission mode 9 configured with PMI/RI reporting with 8 antenna
ports and transmission mode 10 configured with PMI/RI reporting with 8 antenna ports) >
Now let's look into more details of W(i) matrix. Let's construct the generic form of W(i)
matrix for this case. The matrix is defined at the bottom of the table shown above.
You would notice that W(i) is made up of following two components.
With Reference to 36.213 7.2.4
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With the two components, you can contruct the generic form of W(i) matrix as shown below.
For each specific case, we have to figure out n,m',n to fill out the matrix with specific values.
and n,m',n is determined by the PMI report and Table 7.2.4-2.
With Reference to 36.213 Table 7.2.4-2
< CSI RS Configuration >
As described above, the key issue of Beamforming implementation is how to figure out proper
BeamForming matrix for each transmission. As in a common MIMO technology,
we can think of roughly a couple different approach as below.
i) Open Loop Method : This is based on the assumption that a
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ii) Network 'SOMEHOW'
iii) knows the proper beamforming matrix without any information from UE.
iv) Ideally we can think of two approaches as below. (Practically the method a)
v) would not be of much meaning)
a) Applying the same Beamforming matrix for all the transmission
b) Applying the dynamically chaning Beamforming matrix but not based on
specific UE Report
ii) Close Loop Method : This is the method where a Network generate the proper
beamforming matrix based on specific report from UE. For this purpose, network
transmit a specific pilot signal called (CSI-RS) and UE evaluate the it's receiving
signal quality based on the received CSI-RS and report the result to Network.
(For the CSI-RS configuration being used in LTE for this purpose, refer to
CSI-RS and Periodicitysection)
Beamforming in 5G/NR (Massive MIMO)
In NR specification, one of the most outstanding difference you may notice in terms of physical layer processing would be that there is no
Precoding stage in downlink process(See the PDSCH transport and physical layer processing page). However, you still see the precoding
process in Uplink process(See the PUSCH transport and physical layer processing page).
I think the main reason of excluding Precoding in downlink process would be that it is for certain that we need to use Massive MIMO
especially in mmWave spectrum. but there are some fundamental questions to be answered in NR MassiveMIMO/BeamForming. Would
3GPP specify any details on how to implement the MassiveMIMO/Beamforming ? or just leave everything to gNB manufacturer ? Are they
going to apply Massive MIMO/Beamforming
in sub 6 Ghz range as well ? If they decided not to use it, how to handle the possible problems
caused by missing Precoding step ? These are some of the questions in my mind for now.
You may noticed that I used the term MassiveMIMO and BeamForming as almost the same meaning,
but technically MassiveMIMO is not necessarily same as BeamForming. The term 'Beam Forming'
is pretty clearn concept as described above, but the term MIMO(Multiple Input Multiple Output)
is getting more and more blurry concept. It seems that people tend to call a system a MIMO
almost automatically if they see any system using multiple Tx antenna and multiple Rx antenna.
This kind of simple interpretation would not be a big problem until LTE (at least in TM3, TM4),
but in 5G 'Multiple Tx/Rx antenna = MIMO' rule may not always be true.
When we say 'MIMO', it usually mean it as a mean to transfer multiple streams of data
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simultaneously to increase data throughput. More accurately this should be called
as 'Spatial Multiplexing'. To do this, we use multiple Tx antenna and multiple Rx antenna.
However, when we say 'Massive MIMO' in 5G, it does not necessarily imply the way of
increasing
throughput, the major purpose of what we call 'Massive MIMO' is to implement Beam Forming
(I personally think the term 'Massive MIMO' is a little misleading term). I would suggest
you to refer to following notes for Massive MIMO
What is it ?
Why we need it ?
Channel Model
FD-MIMO
MU-MIMO
Regarding the implementation of NR/5G Beamforming/MassiveMIMO, I haven't seen any
explicit specification yet. It would remain open to each network equipment vendor for the
method of implmentation, but roughly a few different methods as follows are suggested in
various technical discussions. Each one has its own Pros and Cons, but practically it is likely
that Hybrid mode would be the dominent way of implementation.
< Case 1 : Pure RF >
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< Case 2 : Pure Baseband >
< Case 3 : Hybrid >
YouTube :
BeamForming
802.11ac: Why Beamforming?
Demystifying Beamforming - Steven Glapa, Ruckus Wireless
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Antenna array part-I
Antenna parameters
Various forms of Antenna array
References :
These are not my posting, but I would like to recommend these for further understanding
and giving you different perspective.
[1] Digital BeamForming
[2] TD-LTE 8-antenna dual-stream beamforming technology
5G/NR - Beam Management
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Even though 3GPP would not preclude the use of Sub 6 Ghz deployment of 5G(NR), at least based on the current status it
seems that most of the deployment would be in very high
frequency (millimeter wave) and this high frequency deployment would be one of the most important
characteristics of 5G (NR).
Why we need Beam ?
Why Beam Management / Beam Control ?
Beam Management/Control when a transmitter has no information
on the location of the reciever
Beam Management/Control when the connection is already
established
NR Beam Management in a Nutshell
Where to point my beam ?
P1, P2, P3 - What is It ?
Why we need Beam ?
Mostly by Nature of the wave (by Physics), when we use low and mid range of frequency, we can transmit a signal in
all direction (as in (A)) or relatively wide angles (as in (B)).
However, when we use very high frequency, we would not have much choice except using a huge antenna array. As a
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result of using this kind of huge antenna array, the resulting radiation would be a beam as in (C). Refer to Why Massive
MIMO page for the details of this background.
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Why Beam Management / Beam Control ? I don't think trasmitting signal in Beam in high frequency
deployment would be the matter of choice. It is a kind of 'MUST' implementation. In case of low / mid frequency
region without using massive antenna array (as in (A) / (B)),
a single transmission would cover a lot of UEs simultaneously. However, when the radiation become beam-
shaped as (C), it is very difficult to cover multiple UEs in
single transmission unless those multiple UEs are located in very close proximity. To handle this problem, we need a
very sophisticated idea of managing/controlling the beam to
cover the multiple devices scattered in all directions and the management/control mechanism should be
different depending on the situtations. All of these collection
of idea would fall into the title of "Beam Management" in the specification.
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Beam Management/Control for each specific situation will
be described in separate pages with relavent situation (like Beam Management during Synchronization, Beam
Management during Initial Attach, Beam Management in
connected status etc). In thise page, I would describe on general idea.
Beam Management/Control when a transmitter has no
information on the location of the reciever
Now let's look into a more specific cases where the Beam
Management/Control become crucial. As an example, let's think of following case. There is a Base Station with
Massive MIMO operating at the very high frequency. There
is a UE around the Base Station and you are just about to turning on the UE. Once the UE is turned on, it would
start Synchronization process. For this step, the Base Station
would transmit the special signal called Synchronization Signal and the signal should be able to reach to every UEs
around the base station. However, here comes a serious
problem with the base station sending signal in Beam. It is the fact that the signal beam can point to a very narrow area
and it cannot cover a very wide area at the same time.
Simply put, now you have the following question.
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What would be the answer for this ? If everything works as you draw in power point, you may draw a solution as
follows. You may want to transmit a lot of beams in all
direction simultaneously. Looks good ? Looks like a flower :).
Would the solution above be feasible, reasonable and
effective ? The simple answer is NO (I would not explain
why. You may easily guess why).
Then what can be another idea (possible soultion) for the
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problem ? There can be multiple ideas and proposals, but the most popular proposal as of now seems to be that the base
station transmit the beam to a specific direction at a specific
time and then change the direction a little bit in a next time frame and so on until it can scan all the area it should cover.
Then, the next question would be "how to reflect /
implement this concept in the radio frame design ?". I would not go too much detail on this until this is explicitely
determined in 3GPP TS (Technical Specification) document,
but you can get the general ideas on various options /proposals from TDocs listed in Reference Section.
// Now that 3GPP Technical Specification on Beam
Management has been released and I could write on this mechanism based on the formal specification. You may
jump to NR Beam Management in a Nutshell section and
read from there if you are interested in the formal specification.
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Beam Management/Control when the connection is already
established
Now let's talk about more serious case of Beam Management. In terms of 3GPP TDocs, Beam Management
handles mostly with this topic (Beam Management during
the connected states) and the one mentioned in previous section are described as a part of the topic Cell Search /
Initial Access.
Once UE gets into a connection states with a Network, at
least one beam (or multiple beam) is properly in connection between UE and the network. Theretically there can be so
many different ways in which UE and Network beam is
connected, but we can reduce it down to roughly four differences case as shown below.
In case 1, UE and Network is connected through a single
TRP (Tx/Rx Point) and a single beam.
In case 2, UE and Network is connected through multiple TRP (Tx/Rx Point) and a single beam for each
TRP.
In case 3, UE and Network is connected through a single TRP (Tx/Rx Point) and multiple beams
In case 4, UE and Network is connected through
multipe TRP (Tx/Rx Point) and multiple beams for each TRP
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You may think of many other cases and ask "How about this
case ? How about that case ?". Whatever you think of and
whatever you are asking, I think all of those would be valid thinking and valid question until 3GPP reach a explicit
conclusion. So keep asking and try to find your own answers until you see the explicit 3GPP specification.
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Now the important and tough task is to maintain the
connection. For this, I would not write much details until 3GPP specifies it in detail. Sorry for skipping too much with
the execuse of 3GPP specification unavailability :). But I
don't want to write many things now and rewrite too much after 3GPP Technical Specification come out. For now, my
purpose is to give you very broad and general idea, and let you know what you may need to study in further details if
you are really interested in technical details. For this
purpose, I will list up most of TDocs about each topics in Reference section, so that you can get more detailed idea
proposed by many companies / organizations in the industry.
The general idea of the beam management during the
connected states would be i) Network transmit a specific reference signal for
beam management
ii) UE detect the signal and perform some measurement and send feedback to Network
As you may notice, the general idea would be very similar
to CSI report mechanism that are currently used in current LTE. However, a lot of details are yet to be determined. For
example,
i) Baseband Signal (Symbol) generation formula ii) Resource Allocation mapping (How to allocate
these reference symbols to which specific resource
element) iii) How often UE need to perform these measurement
iv) How UE report the measurement result ? (via RRC
messages ? or via MAC / PHY layer transactions ?) NOTE : Now that the technical specification on all of the
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questions listed above has been released and I wrote a few separate pages regarding this topic. Refer to CSI RS signal
page and CSI Reportpage for further details based on 3GPP
technical specification.
NR Beam Management in a Nutshell
If you ask me to explain about NR Beam Management in a
few seconds, I would summarize the whole process in an illustration as shown below. As you see here, Beam
Management plays important role in two period - During
RACH procedure and After the call connection.
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Where to point my beam ?
We can think of this question in terms of two different cases : transmitting case and receiving case.
When transmitting,
Now let's think of which direction a gNB or UE has to point its beam when they try to transmit the signal ?
The answer is simple. They (gNB or UE) has to transmit the signal in the
direction that can reach the reciever with the best signal quality'.
Then you would have another question. How can they(gNB or UE) figure out which direction is the one that can reach the reciever with the best
signal quality ?
Now the answer would be a little bit trickier, but the big picture is as follows.
When gNB is transmitting, gNB figure out this direction by
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evaluating the quality of a specific reference signal of multiple
beam from UE. gNB evaluate the quality of the reference signal
from each of the multiple beam and chose the best one. The
reference signal from UE is called SRS.
When UE is transmitting, UE figure out this direction by evaluating
the quality of a specific reference signal of multiple beam from gNB.
UE evaluate the quality of the reference signal from each of the
multiple beam and chose the best one. The reference signal from
gNB in this case can vary depending on situation. Sometimes it can
be SSB and sometimes it can be CSI-RS. (NOTE : CSI-RS play
many different roles in addition to beam management and very
complex topic. Refer to CSI-RS signal generation and CSI report
page for further details).
NOTE : This kind of estimation of reference signal quality should be
done sometime before they transmit signal.
3GPP TR 38.802 (V14.2.0)-6.1.6.1 describes on this situation as follows :
TRP is able to determine a TRP Tx beam for the downlink
transmission based on TRP’s uplink measurement on TRP’s one or
more Rx beams
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UE is able to determine a UE Tx beam for the uplink transmission
based on UE’s downlink measurement on UE’s one or more Rx
beams
NOTE : TRP is a transmission point of a gNB.
When recieving, Now let's think of which direction a gNB or UE has to point its beam
when they try to recieve signal ? (In this case, the word 'beam' may be a little misleading because the reciever does not form any real beam. So it
would be better to change the phrase 'to point its beam' to 'to tune its
reciever to a certain direction'). The answer is simple. They (gNB or UE) has to tune their reciever in the
direction in which they can receive the signal from the transmitter with
best quality.
Then you would have another question. How can they(gNB or UE) figure out which direction is the one in which they can receive the signal from
the transmitter with best quality ?
Overall logic is as follows :
When gNB receiving signal from UE, (before doing this) gNB is
supposed to get the information of the best direction from UE in the
form of CSI report.
When UE receiving signal from gNB, (before doing this) UE is
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supposed to get the information of the best direction from gNB (gNB
has detected the best direction based on the measurement of SRS
signal quality of multiple beams from UE and indicates the UE of
the best direction).
3GPP TR 38.802 (V14.2.0)-6.1.6.1 describes on this situation as follows :
TRP is able to determine a TRP Rx beam for the uplink reception
based on UE’s downlink measurement on TRP’s one or more Tx
beams.
UE is able to determine a UE Rx beam for the downlink reception
based on TRP’s indication based on uplink measurement on UE’s
one or more Tx beams.
P1, P2, P3 - What is It ?
As illustrated in Beam Management in a Nutshell, P1/P2/P3 are a set of processes that are designed for beam management while in connected
state.
I will talk about a high level view on these processes in this section. For
further details, you would need to understand the very details on CSI
report for Beam Management which is another huge topic and will be
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described in a separate page here.
According to 38.802-6.1.6.1, P1/P2/P3 are stated as follows.
P-1: is used to enable UE measurement on different TRP Tx beams to support selection of TRP Tx beams/UE Rx beam(s). For beamforming at
TRP, it typically includes a intra/inter-TRP Tx beam sweep from a set of
different beams. For beamforming at UE, it typically includes a UE Rx beam sweep from a set of different beams.
Does this make sense to you ? It may take time to get clear understanding on this. Following illustration is my understanding/interpretation of this
statement.
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P-2: is used to enable UE measurement on different TRP Tx beams to possibly change inter/intra-TRP Tx beam(s). From a possibly smaller set
of beams for beam refinement than in P-1. Note that P-2 can be a special
case of P-1.
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Following is my understanding on this process in illustration.
P-3: is used to enable UE measurement on the same TRP Tx beam to
change UE Rx beam in the case UE uses beamforming
Following is my understanding on this process in illustration.
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Reference
[1]3GPP R1-166089. 3GPP TSG RAN WG1 Meeting #86 - Beam
Management Procedure for NR MIMO
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[2] 3GPP R1-166214. 3GPP TSG RAN WG1 Meeting #86 - Discussion on the beam management for the NR
[3] 3GPP R1-166389. 3GPP TSG RAN WG1 Meeting #86 - Beam
Management in Millimeter Wave Systems [4] 3GPP R1-166565. 3GPP TSG RAN WG1 Meeting #86 - Beam
management without prior beam information [5] 3GPP R1-166657. 3GPP TSG RAN WG1 Meeting #86 - Views on
beam management for NR
[6]3GPP R1-166785. 3GPP TSG RAN WG1 Meeting #86 - Discussion on TRP beamforming and beam management
[7]3GPP R1-167466. 3GPP TSG RAN WG1 Meeting #86 - Key
principles for beam management [8] 3GPP R1-167467. 3GPP TSG RAN WG1 Meeting #86 - Reference
signals and reports to support beam management
[9] 3GPP R1-167543. 3GPP TSG RAN WG1 Meeting #86 - Beam Management Considerations for above 6 GHz NR
[10] 3GPP R1-1712221. 3GPP TSG RAN WG1 Meeting #90 - DL Beam
Management Framework [11] 3GPP R1-1610243. 3GPP TSG-RAN WG1 #86-BIS : On procedures
for beam selection and feedback signaling
[12] 3GPP 38.300 NR;Overall description;Stage-2 - 9.2.4 Measurements [13] 5G NR Beam Management and Beam Scheduling (everything about
the beams)
[14] 5G NR Beam Managament SA, NSA | Beam Management in 5G NR
[15] 3GPP TR 38.802 - 6.1.6.1 Beam Management
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5G/NR - Carrier Aggregation
Carrier Aggregation
The detailed mechanism of Carrier Aggregation in 5G/NR is not specified yet (as of Sep
2017), but I think overall mechanism will be similar to LTE Carrier Aggregation.
However at least followings has been determined :
Carrier Aggregation is specified from the first specification of NR (i.e, Release 15)
Maximum number of Secondary Componnent Carrier in addition to Primary
Carrier is 15 (38.211 - 4.5)
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5G/NR - Carrier Bandwith Part
Carrier Bandwidth Part
This page is about another new concept in NR called BWP(BandWidth Part). I think the purpose
and concept of BWP is very similar to NarrowBand in LTE M1.
Definition of BWP
Carrier Bandwidth Part allocation for DL and UL
Mapping between nCRB and nPRB
RRC Parameters for BandwidthPart Configuration
How BWP are defined ?
How a specific BWP is selected (BWP switching) ?
Why BWP ?
Definition of BWP
According to 38.211 4.4.5, A carrier bandwidth part is defined as follows :
Carrier Bandwidth Part is a contiguous set of physical resource blocks,selected from a
contiguous subset of the common resource blocks for a given numerology(u) on a given
carrier. It can be illustrated as below.
NOTE : Maximum 4 BWP can be specified in DL and UL. Following illustration is only
an example showing the case of 3 BWP. (NOTE : CRB in this illustration stands for
Carrier Resource Block which is numbered from the one end through the other end of
Carrier Band (this is a kind of global resource block), the PRB stands for Physical
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Resource Block is the resource blocks numbered within each BWP).
Point A indicates a common reference point for resource block grids and is obtained from
the following higher-layer parameters as described in 38.211 - 4.4.4.2:
PRB-index-DL-common for a PCell downlink represents the frequency offset
between point A and the lowest subcarrier of the lowest resource block of the
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SS/PBCH block used by the UE for initial cell selection;
PRB-index-UL-common for a PCell uplink in paired spectrum represents the
frequency offset between point A and the frequency location based on ARFCN of
the uplink indicated in SIB1;
PRB-index-UL-common for a PCell uplink in unpaired spectrum represents the
frequency offset between point A and the lowest subcarrier of the lowest resrouce
block of the SS/PBCH block used by the UE for initial cell selection;
PRB-index-DL-Dedicated for an SCell downlink represents the frequency offset
between point A and the frequency location based on ARFCN in the higher-layer
SCell configuration;
PRB-index-UL-Dedicated for an SCell uplink represents the frequency offset
between point A and the frequency location based on ARFCN in the higher-layer
SCell configuration;
PRB-index-SUL-common for a supplementary uplink represents the frequency
offset between point A and the frequency location based on ARFCN in the higher-
layer SUL configuration.
Carrier Bandwidth Part allocation for DL and UL
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< Downlink >
A UE can be configured with up to four carrier bandwidth parts
The bandwidth of each BW should be equal or greater than SS Block BW, but it
may or may not contain SS Block.
Only one carrier bandwidth part can be active at a given time
The UE is not expected to receive PDSCH, PDCCH, CSI-RS, or TRS outside an
active bandwidth part.
Each DL BWP include at least one CORESET with UE Specific Search Space
(USS).
In primary carrier, at least one of the configured DL BWPs includes one
CORESET with common search space (CSS)
< Uplink >
A UE can be configured with up to four carrier bandwidth parts
Only one carrier bandwidth part can be active at a given time
If a UE is configured with a supplementary uplink
o The UE can in addition be configured with up to four carrier bandwidth parts
in the supplementary uplink
o Only one carrier bandwidth part can be active at a given time
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The UE shall not transmit PUSCH or PUCCH outside an active bandwidth part.
Mapping between nCRB and nPRB
nCRB indicates a resource block location in common resource block, nPRB indicates a
resource block within a specific carrier bandwidth part. In other words, you can think of
nCRB is a position in an absolute (reference) coordinate system and nPRB is a position in
a relative coordinate system. The relationship between nCRB and nPRB is defined as
follows (38.211 v2.0.0 - 4.4.4.4).
This can be illustrated as an example shown below.
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RRC Parameters for BandwidthPart Configuration
Following is based on 38.331 v15.1.0
ServingCellConfig ::= SEQUENCE {
tdd-UL-DL-ConfigurationDedicated TDD-UL-DL-ConfigDedicated OPTIONAL,--
Cond TDD
initialDownlinkBWP BWP-DownlinkDedicated OPTIONAL, -- Cond
ServCellAdd
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downlinkBWP-ToReleaseList SEQUENCE (SIZE (1..maxNrofBWPs)) OF
BWP-Id OPTIONAL,
downlinkBWP-ToAddModList SEQUENCE (SIZE (1..maxNrofBWPs)) OF
BWP-Downlink OPTIONAL
firstActiveDownlinkBWP-Id BWP-Id OPTIONAL, -- Need R
bwp-InactivityTimer ENUMERATED {ms2, ms3, ms4, ms5, ms6, ms8, ms10,
ms20,
ms30, ms40,ms50, ms60, ms80, ms100, ms200,
ms300, ms500, ms750, ms1280, ms1920, ms2560,
spare10, spare9, spare8, spare7, spare6,
spare5, spare4, spare3, spare2, spare1 } OPTIONAL,
defaultDownlinkBWP-Id BWP-Id OPTIONAL, -- Need M
uplinkConfig UplinkConfig OPTIONAL, -- Cond ServCellAdd-UL
supplementaryUplink UplinkConfig OPTIONAL, -- Cond ServCellAdd-SUL
pdsch-ServingCellConfig SetupRelease { PDSCH-ServingCellConfig }
OPTIONAL, -- Need M
csi-MeasConfig SetupRelease { CSI-MeasConfig } OPTIONAL, -- Need
M
carrierSwitching SetupRelease { SRS-CarrierSwitching} OPTIONAL, --
Need M
sCellDeactivationTimer ENUMERATED {ms20, ms40, ms80, ms160, ms200,
ms240, ms320,
ms400, ms480, ms520, ms640, ms720, ms840,
ms1280, spare2,spare1} OPTIONAL,-- Cond
UplinkConfig ::= SEQUENCE {
initialUplinkBWP BWP-UplinkDedicated OPTIONAL, -- Cond
ServCellAdd.
uplinkBWP-ToReleaseList SEQUENCE (SIZE (1..maxNrofBWPs)) OF BWP-Id
OPTIONAL,-- Need N
uplinkBWP-ToAddModList SEQUENCE (SIZE (1..maxNrofBWPs)) OF BWP-
Uplink OPTIONAL,
firstActiveUplinkBWP-Id BWP-Id OPTIONAL, -- Need R
pusch-ServingCellConfig SetupRelease { PUSCH-ServingCellConfig }
OPTIONAL,
...
}
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BWP-Downlink ::= SEQUENCE {
bwp-Id BWP-Id,
bwp-Common BWP-DownlinkCommon
bwp-Dedicated BWP-DownlinkDedicated
...
}
BWP-DownlinkCommon ::= SEQUENCE {
genericParameters BWP,
pdcch-ConfigCommon SetupRelease { PDCCH-ConfigCommon }
pdsch-ConfigCommon SetupRelease { PDSCH-ConfigCommon }
...
}
BWP-DownlinkDedicated ::= SEQUENCE {
pdcch-Config SetupRelease { PDCCH-Config}
pdsch-Config SetupRelease { PDSCH-Config }
sps-Config SetupRelease { SPS-Config }
radioLinkMonitoringConfig SetupRelease { RadioLinkMonitoringConfig }
...
}
BWP-Uplink ::= SEQUENCE {
bwp-Id BWP-Id,
bwp-Common BWP-UplinkCommon
bwp-Dedicated BWP-UplinkDedicated
...
}
BWP-UplinkCommon ::= SEQUENCE {
genericParameters BWP,
rach-ConfigCommon SetupRelease { RACH-ConfigCommon }
pusch-ConfigCommon SetupRelease { PUSCH-ConfigCommon }
pucch-ConfigCommon SetupRelease { PUCCH-ConfigCommon }
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...
}
BWP-UplinkDedicated ::= SEQUENCE {
pucch-Config SetupRelease { PUCCH-Config } OPTIONAL,--
Need M
pusch-Config SetupRelease { PUSCH-Config } OPTIONAL,--
Need M
configuredGrantConfig SetupRelease { ConfiguredGrantConfig
} OPTIONAL,--Need M
srs-Config SetupRelease { SRS-Config } OPTIONAL,--Need
M
beamFailureRecoveryConfig SetupRelease { BeamFailureRecoveryConfig
} OPTIONAL,--Need M
...
}
BWP ::= SEQUENCE {
locationAndBandwidth INTEGER (0..37949),
subcarrierSpacing SubcarrierSpacing,
cyclicPrefix ENUMERATED { extended }
}
initialDownlinkBWP : The dedicated (UE-specific) configuration for the initial
downlink bandwidth-part.
firstActiveDownlinkBWP-Id : If configured for an SpCell, this field contains the ID of
the DL BWP to be activated upon performing the reconfiguration in which it is received.
If the field is absent, the RRC reconfiguration does not impose a BWP switch
(corresponds to L1 parameter 'active-BWP-DL-Pcell'). If configured for an SCell, this
field contains the ID of the downlink bandwidth part to be used upon MAC-activation of
an SCell. The initial bandwidth part is referred to by BWP-Id = 0
bwp-InactivityTimer : The duration in ms after which the UE falls back to the default
Bandwidth Part. The value 0.5 ms is only applicable for carriers >6 GHz. When the
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network releases the timer configuration, the UE stops the timer without swithching to
the default BWP
initialUplinkBWP : If configured for an SpCell, this field contains the ID of the DL
BWP to be activated upon performing the reconfiguration in which it is received. If the
field is absent, the RRC reconfiguration does not impose a BWP switch (corresponds to
L1 parameter 'active-BWP-UL-Pcell'). If configured for an SCell, this field contains the
ID of the uplink bandwidth part to be used upon MAC-activation of an SCell. The initial
bandwidth part is referred to by BandiwdthPartId = 0
firstActiveUplinkBWP-Id : The dedicated (UE-specific) configuration for the initial
uplink bandwidth-part.
BWP-Id : An identifier for this bandwidth part. Other parts of the RRC configuration
use the BWP-Id to associate themselves with a particular bandwidth part. The BWP ID=0
is always associated with the initial BWP and may hence not be used here (in other
bandwidth parts).
The NW may trigger the UE to swtich UL or DL BWP using a DCI field. The four code
points in that DCI field map to the RRC-configured
BWP-ID as follows: For up to 3 configured BWPs (in addition to the initial BWP)
the DCI code point is equivalent to the BWP ID
o (initial = 0, first dedicated = 1, ...). If the NW configures 4 dedicated
bandwidth parts, they are identified by DCI code
o points 0 to 3. In this case it is not possible to switch to the initial BWP using
the DCI field.
o Corresponds to L1 parameter 'UL-BWP-index'.
locationAndBandwidth : Frequency domain location and bandwidth of this bandwidth
part defined commonly in a table. The location is given as distance (in number of PRBs)
to point A (absoluteFrequencyPointA in FrequencyInfoDL). It Corresponds to L1
parameter 'DL-BWP-loc'. In case of TDD, a BWP-pair (UL BWP and DL BWP with the
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same bwp-Id) must have the same location
subcarrierSpacing : Subcarrier spacing to be used in this BWP for all channels and
reference signals unless explicitly configured elsewhere. It corresponds to subcarrier
spacing according to 38.211-Table 4.2-1. The value kHz15 corresponds to µ=0, kHz30 to
µ=1, and so on. Only the values 15 or 30 kHz (<6GHz), 60 or 120 kHz (>6GHz) are
applicable.
How BWP are defined ?
As mentioned in Carrier Bandwidth Part allocation for DL and UL, maximum 4 BWPs
can be defined in DL and UL. Each of BWP are configured by RRC messages as
described in RRC Parameters for BandwidthPart Configuration.
How a specific BWP is selected (BWP switching) ?
Even though multiple (max 4) BWPs can be defined in DL and UL, only one BWP can
be active at each specific moment. It implies there is some mechainism to select a
specific BWP as the active one. According to 38.321-5.15 Bandwidth Part (BWP)
operation, BWP selection (or BWP switching) can be done by several different ways as
listed below.
By PDCCH (i.e, DCI) : A specific BWP can be activated by Bandwidth part
indicator in DCI Format 0_1 (a UL Grant) and DCI Format 0_1 (a DL Schedule)
By the bwp-InactivityTimer : ServingCellConfig.bwp-InactivityTimer
By RRC signalling
By the MAC entity itself upon initiation of Random Access procedure
With using the mechanisums listed above, a specific BWP become active depending on
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various situations in the call processing. Followings are some of the examples of BWP
switching for specific cases.
Case 1 : Reconfiguration with sync (based on 38.331 - 5.3.5.5.2)
"Reconfiguration with sync" is a common mechanism of activing NR cell in NSA
(i.e, Adding NR Cell to LTE cell). In this case, Active BWP for DL and UL is set
to be as follows .
o Active BWP for DL = firstActiveDownlinkBWP-Id
o Active BWP for UL = firstActiveUplinkBWP-Id
Case 2 : Upon initiation of the Random Access procedure on a Serving Cell
(based on 38.321 - 5.15)
if PRACH occasions are not configured for the active UL BWP:
For UL,set the active UL BWP = initialUplinkBWP;
For DL,
if the Serving Cell is a SpCell:
set the active DL BWP = initialDownlinkBWP.
if PRACH occasions are configured for the active UL BWP
For UL,set the active UL BWP = the configured UL BWP
For DL,
if the Serving Cell is a SpCell:
set the active DL BWP = DL BWP with the same bwp-Id as the active UL
BWP.
Perform RACH procedure with the active BWP selected as above.
Case 3 : DCI with Bandwidth part indicator is recieved
Check if there is any on-going RACH procedure. If there is no on-going RACH
procedure or RACH procedure is just completed by the received DCI (masked with
C-RNTI).
set the active BWP = the BWP specified by the DCI
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Why BWP ?
When I first saw the descriptions on BWP, I asked myself 'why we need this ? We
already has pretty flexible mechanism of changing Bandwidth dynamically. Just by
changing the number of RBs and starting RB, we can change the operation bandwidth.
Then, why we still need another mechanism of restricting bandwidth ?'.
The purpose of BWP is more for UE rather than for Network, especially for low end UEs
which cannot afford to such a wideband operation.
In most case, NR would operate in very wideband and there wouldn't be any issues for
the network (gNB) and high end UEs to handle the full operating band, but we cannot
expect every types of UE to be able to work with this kind of wideband. So we need
another special mechanism to tell some UEs 'Hey... we are operating in this wide band,
but you don't need to worry about covering the full band. this is a fraction of spectrum
you only need to care'. This is how (and why) we came out with the new concept called
BWP. It would remind you of NarrowBand in LTE M1. (Refer to Ref[1] if you want to
know more detailed stories on various alternatives on NR Wideband operation).
Reference
[1] NR Wide Bandwidth Operations by Jeongho Jeon, Intel Corporation