4g long term evolution introduction_18-jan-2014
DESCRIPTION
4G Long Term Evolution Introduction_18-Jan-2014TRANSCRIPT
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where LTE will lead, we know not; but we can be sure that it will not be the last development in wireless telegraphy Guglielmo Marconi
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[1] LTE/SAE INTRODUCTION
EVOLUTION OF MOBILE COMMUNICATION NETWORKS
3GPP RELEASES & LTE TERMINOLOGY
LTE DRIVERS
FREQUENCY BANDS
LTE-ADVANCED (LTE-A)
[2] EVOLVED PACKET SYSTEM (EPS) ARCHITECTURE & PROTOCOLS
OVERVIEW EPS ARCHITECTURE
EPS FUNCTIONALITY
LTE PROTOCOL STACK
LTE UE STATES AND AREA CONCEPTS
[3] LTE AIR INTERFACE
OFDMA/SC-FDMA BASICS
LTE FRAME & CHANNEL STRUCTURE
LTE DOWNLINK & UPLINK PHYSICAL CHANNEL
[4] LTE KEY TECHNOLOGY INTRODUCTION
MULTIPLE INPUT MULTIPLE OUTPUT (MIMO)
CSFB (CIRCUIT SWITCHED FALLBACK )
SON (SELF ORGANIZING NETWORKS)
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Contents
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[1] LTE/SAE INTRODUCTION
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1st Generation or 1G 2nd Generation or 2G , 2nd Generation Transitional or 2.5G,2.75G 3rd Generation or 3G , 3rd Generation Transitional or 3.5G,3.75G,3.9G 4th Generation or 4G
Evolution of Mobile Communication Networks
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LTE Parallel Evolution Path to HSPA+
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3GPP RELEASES & LTE TERMINOLOGY
Long Term Evolution (LTE) and System Architecture
Evolution (SAE) are specified by the Third Generation
Partnership Project (3GPP) in Release 8 specifications.
The standard development in 3GPP is grouped into two
work items, where LTE targets the radio network evolution
and System Architecture Evolution (SAE) targets the
evolution of the packet core network.
Long Term Evolution (LTE) : Evolution of 3GPP UMTS Terrestrail Radion Access (E-UTRA) Technology.
Evolved Packet System (EPS) : Evolution of the complete 3GPP UMTS Radio Access, Packet Core and its integration
into legacy 3GPP/non-3GPP network.
EPS includes:
Evolved UTRAN (eUTRAN) Radio Access Network Evolved Packet Core (EPC) System Architecture.
A detailed description of SAE/LTE Specifications are available at
the 3GPP website: http://www.3gpp.org/ftp/Specs/archive/
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E-UTRA Design Performance Targets
Scalable transmission bandwidth(up to 20 MHz) Improved Spectrum Efficiency
Downlink (DL) spectrum efficiency should be 2-4 times Release 6 HSDPA. Downlink target assumes 2x2 MIMO for E-UTRA and single Txantenna with Type 1 receiver HSDPA. Uplink (UL) spectrum efficiency should be 2-3 times Release 6 HSUPA. Uplink target assumes 1 Tx antenna and 2 Rx antennas for both E-UTRA and Release 6 HSUPA.
Coverage Good performance up to 5 km Slight degradation from 5 km to 30 km (up to 100 km not precluded)
Mobility Optimized for low mobile speed (< 15 km/h) Maintained mobility support up to 350 km/h (possibly up to 500 km/h)
Advanced transmission schemes, multiple-antenna technologies Inter-working with existing 3G and non-3GPP systems
Interruption time of real-time or non-real-time service handover between E-UTRAN and UTRAN/GERAN shall be less than 300 or 500 ms.
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E-UTRA Air Interface Capabilities
Bandwidth support Flexible from 1.4 MHz to 20 MHz
Waveform OFDM in Downlink SC-FDM in Uplink
Duplexingmode FDD: full-duplex (FD) and half-duplex (HD) TDD
Modulation orders for data channels Downlink: QPSK, 16-QAM, 64-QAM Uplink: QPSK, 16-QAM, 64-QAM
MIMO support Downlink: SU-MIMO and MU-MIMO (SDMA) Uplink: SDMA
Single & same link of communication for DL & UL
DL serving cell = UL serving cell No UL or DL macro-diversity
UEs Active Set size = 1
Hard-HO based mobility UE assisted (based on measurement reports) and network controlled (handover decision at specific
time) by default.
During a handover, UE uses a RACH based mobility procedure to access the target cell
Handover is UE initiated if it detects a RL failure condition.
Load indicator for inter-cell load control (interference management)
Transmitted over X2 interface
UE e-NB Communication Link E-UTRA Air Interface Capabilities
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LTE DRIVERS
Branding
Marketing
Technical
For branding image
For competition
For better data service
For SME & Industry user
For frequency issue
For network quality
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LTE DRIVERS
Ericsson Mobility Report November 2013
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LTE DRIVERS
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LTE DRIVERS
LTE operation benefits
Enhanced
experience for
E2E quality
Spectrum
flexibility
Lower cost
Higher speed (x10)
Lower latency (1/4 )
Lager capacity (x3)
New or re-farmed spectrum
Varity channel bandwidth
IP based flat network architecture
Low OPEX: SON
High re-use of asset
Flat Overall Architecture
2-nodes architechture IP routable transport architechture Lower cost.
Improved Radio Aspects
Peak data rates [Mbps] DL=300,UL=75 Scalable Bandwidth:1.4,3,5,10,15,20 MHz Short latency:
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Achievable & Supported Peak Data Rates
Achievable LTE Peak Data Rate
Peak Data rate scale with the bandwidth
2x2 MIMO supported for the initial LTE deployment.
UE Supported Peak Data Rate (Mbps)
Similar peak data rates defined for FDD & TDD. All categories support 20 MHz, 64QAM downlink and receive antenna diversity.
Category 2,3 ,4 expected in the first phase with bit rates up to 150 Mbps.
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Frequency Band of LTE
TDD Frequency Band
FDD Frequency Band From LTE Protocol:
Duplex mode: FDD and TDD
Support frequency band form 700MHz to 2.6GHz
Support various bandwidth: 1.4MHz, 3MHz,
5MHz, 10MHz, 15MHz, 20MHz.
E-UTRA
Band
Uplink (UL) Downlink (DL) Duplex
ModeFUL_low FUL_high FDL_low FDL_high
1 1920 MHz 1980 MHz 2110 MHz 2170 MHz FDD
2 1850 MHz 1910 MHz 1930 MHz 1990 MHz FDD
3 1710 MHz 1785 MHz 1805 MHz 1880 MHz FDD
4 1710 MHz 1755 MHz 2110 MHz 2155 MHz FDD
5 824 MHz 849 MHz 869 MHz 894MHz FDD
6 830 MHz 840 MHz 875 MHz 885 MHz FDD
7 2500 MHz 2570 MHz 2620 MHz 2690 MHz FDD
8 880 MHz 915 MHz 925 MHz 960 MHz FDD
9 1749.9 MHz
1784.9 MHz 1844.9 MHz
1879.9 MHzFDD
10 1710 MHz 1770 MHz 2110 MHz 2170 MHz FDD
111427.9 MHz 1452.9 MHz 1475.9 MHz 1500.9 MHz FDD
12 698 MHz 716 MHz 728 MHz 746 MHz FDD
13 777 MHz 787 MHz 746 MHz 756 MHz FDD
14 788 MHz 798 MHz 758 MHz 768 MHz FDD
17 704 MHz 716 MHz 734 MHz 746 MHz FDD
...
E-UTRA
Band
Uplink (UL) Downlink (DL) Duplex
ModeFUL_low FUL_high FDL_low FDL_high
33 1900 MHz 1920 MHz 1900 MHz 1920 MHz TDD
34 2010 MHz 2025 MHz 2010 MHz 2025 MHz TDD
35 1850 MHz 1910 MHz 1850 MHz 1910 MHz TDD
36 1930 MHz 1990 MHz 1930 MHz 1990 MHz TDD
37 1910 MHz 1930 MHz 1910 MHz 1930 MHz TDD
38 2570 MHz 2620 MHz 2570 MHz 2620 MHz TDD
39 1880 MHz 1920 MHz 1880 MHz 1920 MHz TDD
40 2300 MHz 2400 MHz 2300 MHz 2400 MHz TDD
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Frequency Band of LTE Release 8
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FREQUENCY BANDS
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EARFCN (E-Absolute Radio Frequency Channel Numnber)
eNB
UE
FDL = FDL_low + 0.1(NDL - NOffs-DL)
FUL = FUL_low + 0.1(NUL - NOffs-UL)
Frequency
Uplink Downlink
100kHz Raster
2127.4MHz1937.4MHz
FDL = FDL_low + 0.1(NDL - NOffs-DL)
(FDL - FDL_low)
0.1+ NOffs-DL
(2127.4 - 2110)
0.1+ 0
NDL =
NDL = = 174
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LTE EVOLUTION (LTE-Advanced)
LTE-Advanced (LTE-A) is introduced in 3GPP release10 and its the Global 4G solution. Improves spectrum efficiency, delivers increases in capacity and coverage, and the ability to support more customers /devices more efficiently, to maintain and improve the user experience of mobile broadband.
Increased data rates and lower latencies for all users in the cell. Data rates scale with bandwidthUp to 1 Gbps peak data rate.
Aggregating 40 MHz to 100 MHz provide peak data rates of 300 Mbps to 750 Mbps1(2x2 MIMO) and over 1 Gbps(4x4 MIMO)
Multicarrier Enables Flexible Spectrum Deployments [Key features] Carrier Aggregation Higher order MIMO SON/Hetnets Interference management Relays
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LTE EVOLUTION (LTE-A)
LTE-A introduces higher order MIMO 8x8 DL MIMO, 4x4 UL MIMO and UL Beamforming
More Antennas to
Leverage Diversity
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[2] EVOLVED PACKET SYSTEM (EPS)
ARCHITECTURE & PROTOCOLS
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System Architecture Evolution (SAE)
EPS is all PS (IP based no CS domain )
[Main drivers] All-IP based Reduce network cost Reduce data latency & signalling load
Better network topology scalability & reliability
Inter-working & seamless mobility among heterogeneous
access networks(3GPP & non-
3GPP).
Better always-on user experience
Simpler and more flexible Qos Suppport
Higher level of security
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PS Domain Architecture Evolution
EPS flat architecture, with User Plane direct tunneling between SAE-GW and eNode B is similar to the super flat architecture option for HSPA+, where GGSN connects directly to a collapsed RNC+Node B entity or to an evolved Node B. As the color legend
shows, the location of the migrated network functions in EPS are as follows:
RNC functions are in eNB & MME
SGSN functions are in the MME
GGSN functions are in SGW & PGW
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Overall EPS Architecture
Main Network Element of EPS (Evolved Packet System)
E-UTRAN (Evolved UTRAN ) consists of e-NodeBs, providing the user plane and control plane.
EPC (Evolved Packet Core ) consists of MME, S-GW and P-GW.
Network Interface of EPC (Evolved Packet System)
e-NodeBs are interconnected with each other by means of the X2 interface, enabling direct transmission of data and signaling.
S1 is the interface between e-NodeBs and the EPC, to the MME via the S1-MME and to S-GW via the S1-U.
EPC includes; MME (Mobility Management Entity) handling Control Plane.
S-GW (Serving Gateway) & P-GW (PDN Gateway) handling User Plane
Note:
HSS (Home Subscriber Server) is formally out of the EPC, and will need to be updated with new EPS
subscription data and functions.
PCRF and Gx/Rx provide QoS Policy and Charging control (PCC),
similarly to the UMTS PS domain.
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E-UTRAN Entities/Interfaces Evolved Node B (eNB) provides the E-UTRA User Plane (PDCP/RLC/MAC/PHY) and Control Plane (RRC) protocol terminations toward
the UE. An eNB can support FDD mode, TDD mode, or dual mode operation. eNBs can optionally be interconnected with each
other by means of the X2 interface or connected by means of the S1 interface to the Evolved Packet Core (EPC).
e-Node hosts the following functions:
Radio Resource Management: Radio Bearer Control,
Radio Admission Control, Connection Mobility Control,
Dynamic allocation of resources to UEs in both uplink and
downlink (scheduling)
IP header compression
Encryption /Integrity protection of user data
MME selection (among MME pool)
Routing of User Plane data towards S-GW
Scheduling and transmission of paging and broadcast
messages (originated from the MME)
Measurement and measurement reporting configuration
for mobility and scheduling
S1 interface
Can be split S1-U (S-GW) & S1-C(MME).
X2 interface
Used for inter-eNB handover, load balacing and
interference cancellation.
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EPC Entities/Interfaces
S-GW (Serving Gateway) main functions:
Packet routing and forwarding
E-UTRAN and inter-3GPP mobility anchoring
E-UTRAN Idle mode DL packet buffering
UL and DL charging per UE, PDN, and QCI
Transport level QoS mapping
P-GW (PDN Gateway) main functions:
Per-user based packet filtering UE IP address allocation UL and DL service level charging User Plane anchoring for 3GPP and non-3GPP mobility
MME (Mobility Management Entity) main functions:
NAS signaling and security
AS Security control
Idle state mobility handling
P-GW and S-GW selection
EPS (Evolved Packet System) bearer control;
Support paging, handover, roaming and authentication
S10 interface
Support mobility between MMEs
S11 interface
Support EPS Bearer management between MME & S-GW
S6a interface
Used for subscription & security control between MME&HSS
S5 interface
Between S-GW and P-GW
Called S8 for Inter-PLMN connection (roaming)
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LTE Radio Protocol Stack
Two Planes in LTE Radio Protocol: (1) User-plane: For user data transfer (2) Control-plane: For system signaling transfer
Over LTE-Uu radio interface, protocols are split in: (AS) Access Stratum: RRC/PDCP/RLC/MAC/PHY. (NAS) Non Access Stratum: EMM (Mobility Management) and ESM (Session Management)
Control plane
Over S1 and X2 interfaces, two RNL application protocols (S1-AP and X2-
AP), using a new transport protocol called SCTP (Stream Control
Transmission Protocol).
S1-AP: Supports all necessary EMM-eNB signaling and procedures, including RAB management, mobility, paging, NAS transport, and many
other S1 related functions.
X2-AP: Supports Intra LTE-Access-System Mobility, Uplink Load Management, and X2 error handling functions.
Main Functions of Control-plane:
RLC and MAC layers perform the same functions as for the user plane
PDCP layer performs ciphering and integrity protection
RRC layer performs broadcast, paging, connection management, RB control, mobility functions, UE measurement reporting and control
NAS layer performs EPS bearer management, authentication, security control
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LTE Radio Protocol Stack
User plane on the S1-U uses GTP-U for
tunneling. The same protocol stack
would apply to the X2 interface, for
data packet forwarding during handover
between eNBs.
The concatenation of LTE RB + S1 Bearer
+ S5 Bearer makes the EPS Bearer,
which can be shared by multiple Service
Flows with the same level of QoS.
EPS Bearer (similar to a PDP context of
previous 3GPP releases) is defined between
the User Equipment (UE) and the P-GW
node in the EPC (which provide the end
users IP point of presence towards
external networks).
User-plane
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LTE Radio Interface structure
The radio interface is structured in a layered
model, similar to WCDMA, with a layer 2
bearer (here called EPS Bearer Service),
which corresponds to a PDP-context in Rel. 6,
carrying layer 3 data and the end-to-end
service.
The EPS bearer is carried by the E-UTRA
Radio Bearer Service in the radio interface. The
E-UTRA radio bearer is carried by the radio
channels.
The radio channel structure is divided into
logical, transport and physical channels.
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LTE UE STATES AND AREA CONCEPTS
LTE is developed to have a simpler
architecture (fewer nodes) and
less signaling (fewer messages) than
the UTRAN. The number of states
which the UE can be in (corresponding
to RRC states) are reduced from five in
the UTRAN (DETACHED, IDLE,
URA_PCH, CELL_FACH, CELL_DCH)
to only three in the eUTRAN
(DETACHED, IDLE and CONNECTED)
In LTE only one area for idle mode
mobility is defined; the Tracking Area
(TA). In UTRAN, Routing Area (RA) and
UTRAN Registration Area (URA) is
defined for PS traffic and
Location Area (LA) for CS traffic.
In ECM-IDLE (EPS Connection
Management IDLE) the UE position is
only known by the network on TA level,
whereas in ECM-CONNECTED, the UE
location is known on cell level by the
eNodeB.
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[3] LTE AIR INTERFACE
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Duplex Techology
Frequency Division Duplex (FDD):
Distinguish uplink and downlink according to frequencies.
Time division duplex (TDD):
Distinguish uplink and downlink according to timeslots.
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Multiple Access Technology
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OFDM Basics
LTE radio interface is based on OFDM (Orthogonal Frequency Division Multiplex) and OFDMA (Orthogonal Frequency Division
Multiple Access) in DL and SC-FDMA (Single Carrier Frequency Division Multiple Access) in UL.
OFDM uses a large number of closely spaced narrowband carriers.In a conventional FDM system, the frequency spacing between
carriers is chosen with a sufficient guard band to ensure that interference is minimized and can be cost effectively filtered. In OFDM,
however, the carriers are packed much closer together.
OFDM Orthogonality
Each of the 15 kHz LTE air interface subcarriers are Orthogonal to each other , there is zero inter-carrier interference at the center frequency of each
subcarrier. Orthogonality allows simultaneous transmission on many
subcarriers in a tight frequency space without interference from each other.
The spectrums of the subcarriers are not separated, but overlap.
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OFDM Basics
The transmitter combines all the subcarriers using an Inverse Fast Furrier Transform (IFFT) function where the outcome is single
signal which is basically a sum of sinusoids having an amplitude that varies depending on the number of subcarriers. The receiver
uses a Fast Fourier Transform (FFT) function to recover each subcarrier.
OFDM also shows very good performance in highly
time dispersive radio environments (i.e. many
delayed and strong multipath reflections).
That is because the data stream is distributed over
many subcarriers. Each subcarrier will thus have a
slow symbol rate and correspondingly, a long
symbol time. This means that the Inter Symbol
Interference (ISI) is reduced.
Sub-carriersFFT
Time
Symbols
System Bandwidth
Guard
Intervals
Frequency
Sub-carriersFFT
Time
Symbols
System Bandwidth
Guard
Intervals
Frequency
FFT = Fast Fourier Transform, IFFT = Inverse FFT FFT/IFFT allows to move between time and frequency domain representation
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OFDM & SC-FDMA
OFDM & OFDMA
OFDM (Orthogonal Frequency Division Multiplexing) is a modulation multiplexing technology, divides the system
bandwidth into orthogonal subcarriers.
OFDMA is the multi-access technology related with OFDM, is used in the LTE downlink. OFDMA is the
combination of TDMA and FDMA essentially.
Advantage: High spectrum utilization efficiency due to orthogonal subcarriers need no protect bandwidth.
Support frequency link auto adaptation and scheduling.
Easy to combine with MIMO.
Disadvantage: Strict requirement of time-frequency domain synchronization. High Peak-to-Average Power
Ratio (PAPR).
DFT-S-OFDM & SC-FDMA
DFT-S-OFDM (Discrete Fourier Transform Spread OFDM) is the modulation multiplexing technology
used in the LTE uplink, Each user is assigned part of
the system bandwidth.
SC-FDMASingle Carrier Frequency Division Multiple Accessingis the multi-access technology related with DFT-S-OFDM.
Advantage: High spectrum utilization efficiency due to orthogonal user bandwidth need no protect
bandwidth.
Low Peak-to-Average Power Ratio (PAPR)
User 1
User 2
User 3
Sub-carriers
TTI: 1ms
Frequency
System Bandwidth
Sub-band12Sub-carriersTime
User 1
User 2
User 3
User 1
User 2
User 3
Sub-carriers
TTI: 1ms
Frequency
System Bandwidth
Sub-band12Sub-carriersTime
Sub-carriers
TTI: 1ms
Frequency
Time
System Bandwidth
Sub-band12Sub-carriers
User 1
User 2
User 3
Sub-carriers
TTI: 1ms
Frequency
Time
System Bandwidth
Sub-band12Sub-carriers
User 1
User 2
User 3
User 1
User 2
User 3
SC-FDMA : PRBs are grouped to bring down PAPR , better power efficiency at the UE
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Time & Frequency Domain Organization
LTE Time Domain is organized as
Frame (10 ms) Sub-frame (1ms) Slot (0.5ms) Symbol (duration depends on configuration)
Radio Frame Structures Supported by LTE:
Type 1, applicable to FDD
Type 2, applicable to TDD
LTE Frequency Domain LTE DL/UL air interface waveforms use a number of Orthogonal subcarriers to send users & control data.
Pre-defined spacing between these subcarriers (15 KHz for regular operation and 7.5 KHZ for MBSFN operation)
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DC subcarrier which has no energy and is located at the center of the frequency band.
Two guard bands at the edges of the OFDM/OFDMA-signal (no RF transmission in this subcarriers). This is a
guard band to avoid interference with adjacent bands.
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Frequency Domain Configurations
Various channel bandwidths that may be considered for LTE deployment are shown in the table. One of the typical LTE deployment options (10 MHz) is highlighted.
Assuming 15 KHz Carrier Spacing
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UL/DL Resource Grid Definitions
Resource Element (RE) One element in the time/frequency resource grid.
One subcarrier in one OFDM/LFDM symbol for DL/UL. Often used for Control channel resource assignment.
Resource Block (RB) Minimum scheduling size for DL/UL data channels Physical Resource Block (PRB) [180 kHz x 0.5 ms] Virtual Resource Block (VRB) [180 kHz x 0.5 ms in virtual frequency domain]
Localized VRB Distributed VRB
Resource Block Group (RBG) Group of Resource Blocks
Size of RBG depends
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UL/DL Resource Grid Definitions
Resource Element Group (REG) Groups of Resource Elements to carry control information. 4 or 6 REs per REG depending on number of reference signals per symbol, cyclic prefix configuration.
REs used for DL Reference Signals (RS) are not considered for the REG.
Only 4 usable REs per REG.
Control Channel Element (CCE) Group of 9 REGs form a single CCE.
1 CCE = 36 REs usable for control information. Both REG and CCE are used to specify resources for LTE DL control channels.
Antenna Port One designated reference signal per antenna port. Set of antenna ports supported depends on reference signal configuration within cell.
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TDD Radio Frame Structure Applies OFDM, same subcarriers spacing and time unit with FDD.
Similar frame structure with FDD. radio frame is 10ms shown as
below, divided into 20 slots which are 0.5ms.
The uplink-downlink configuration of 10ms frame are shown in
the right table.
Uplink-downlink Configurations
Special Subrame Structure
Special Subframe consists of DwPTS, GP and UpPTS .
9 types of Special subframe configuration.
Guard Period size determines the maximal cell radius. (100km)
DwPTS consists of at least 3 OFDM symbols, carrying RS, control message and data.
UpPTS consists of at least 1 OFDM symbol, carrying sounding RS or short RACH.
DL to UL switch point in special subframe #1 and #6 only Other subframes allocated to UL or DL Sum of DwPTS, GP and UpPTS always 1 ms Subframe #0 and #5 always DL - Used for cell search signals (S-SCH)
Uplink-
downlink
configuration
Downlink-to-Uplink
Switch-point
periodicity
Subframe number
0 1 2 3 4 5 6 7 8 9
0 5 ms D S U U U D S U U U
1 5 ms D S U U D D S U U D
2 5 ms D S U D D D S U D D
3 10 ms D S U U U D D D D D
4 10 ms D S U U D D D D D D
5 10 ms D S U D D D D D D D
6 5 ms D S U U U D S U U D
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Cyclic Prefix (CP) Transmission
CP Length Configuration:
Cyclic Prefix is applied to eliminate ISI (Inter-symbol Interference) of OFDM.
CP length is related with coverage radius. Normal CP can fulfill the requirement of common
scenarios. Extended CP is for wide coverage scenario.
Longer CP, higher overheading.
Configuration DL OFDM CP Length UL SC-FDMA CP
Length
Sub-carrier of
each RB
Symbol of
each slot
Normal CP f=15kHz 160 for slot #0
144 for slot #1~#6
160 for slot #0
144 for slot #1~#6 12 7
Extended CP f=15kHz 512 for slot #0~#5 512 for slot #0~#5 6
f=7.5kHz 1024 for slot #0~#2 NULL 24 (DL only) 3 (DL only)
Slot structure under Normal
CP configuration
(f=15kHz)
Slot structure under Extended
CP configuration
(f=15kHz)
Slot structure under Extended
CP configuration
(f=7.5kHz)
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Cyclic Prefix (CP) Transmission
Cyclic Prefix (CP) insertion helps maintain
orthogonality Reduces efficiency (or Usable
Symbol time, Tu) .
Mitigates Inter-Symbol Interference (ISI) Reduces efficiency
Useable time per symbol is Tu/(Tu+TCP) Selection of Cyclic Prefix governed by delay spread
In OFDM, multipath causes loss of orthogonality Delayed paths cause overlap between symbols
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LTE Channel Structure
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LTE Channel Structure
Logical Channel
Control Channel Broadcast Control Channel (BCCH) DL broadcast of system control information. Paging Control Channel (PCCH) DL paging information. UE position not known on cell level Common Control Channel (CCCH) UL/DL. When no RRC connection exists. Multicast Control Channel (MCCH) DL point-to-multipoint for MBMS scheduling and control, for one or several MTCHs.
Dedicated Control Channel (DCCH) UL/DL dedicated control information. Used by UEs having an RRC connection.
Traffic Channel
Dedicated Traffic Channel (DTCH) UL/DL Dedicated Traffic to one UE, user information. Multicast Traffic Channel (MTCH) DL point-to-multipoint. MBMS user data.
Transport Channel
DL Channel Broadcast Channel (BCH) System Information broadcasted in the entire coverage area of the cell.Beamforming is not applied. Downlink Shared Channel (DL-SCH) User data, control signaling and System Info. HARQ and link adaptation.Broadcast in the entire cell or beamforming. DRX and MBMS supported. Paging Channel (PCH) Paging Info broadcasted in the entire cell. DRX Multicast Channel (MCH) MBMS traffic broadcasted in entire cell. MBSFN is supported.
UL Channel Uplink Shared channel (UL-SCH) User data and control signaling. HARQ and link adaptation. Beamforming may be applied. Random Access Channel (RACH) Random Access transmissions (asynchronous and synchronous). The transmission is typically contention based. For UEs having an RRC connection there is some limited support for contention free access.
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LTE Channel Structure
Physical channels Physical Downlink Shared Channel (PDSCH) transmission of the DL-SCH transport channel
Physical Uplink Shared Channel (PUSCH) transmission of the UL-SCH transport channel
Physical Control Format Indicator Channel (PCFICH) indicates the PDCCH format in DL
Physical Downlink Control Channel (PDCCH) DL L1/L2 control signaling
Physical Uplink Control Channel (PUCCH) UL L1/L2 control signaling
Physical Hybrid ARQ Indicator Channel (PHICH) DL HARQ info
Physical Broadcast Channel (PBCH) DL transmission of the BCH transport channel.
Physical Multicast Channel (PMCH) DL transmission of the MCH transport channel.
Physical Random Access Channel (PRACH) UL transmission of the random access preamble as given by the RACH transport channel.
Physical signals Reference Signals (RS) support measurements and coherent demodulation in uplink and downlink. Primary and Secondary Synchronization signals (P-SCH and S-SCH)
DL only and used in the cell search procedure. Sounding Reference Signal (SRS) supports UL scheduling measurements
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Synchronization Signals (PSS & SSS)
PSS and SSS Functions Frequency and Time synchronization
Carrier frequency determination OFDM symbol/subframe/frame timing determination
Physical Layer Cell ID (PCI) determination Determine 1 out of 504 possibilities
PSS and SSS resource allocation Time: subframe0 and 5 of everyFrame Frequency: middle of bandwidth (6 RBs = 1.08 MHz)
Primary Synchronization Signals (PSS) Assists subframe timing determination Provides a unique Cell ID index (0, 1, or 2) withina Cell ID group
Secondary Synchronization Signals (SSS) Assists frame timing determination Provides a unique Cell ID group number among 168 possible Cell ID groups
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Cell Identity Determination from PSS and SSS
Physical Cell Identity (PCI) is uniquely defined by: A number in the range of 0 to 167, representing the Physical Cell Identity (PCI) group
A number in the range of 0 to 2, representing the physical identity within the Physical Cell Identity (PCI) group
S-SCH Provides 168 sequences, each associated to a cell ID group information
These sequences are interleaved concatenations of two length-31 binary sequences
P-SCH Three (NID=0,1,2) frequency domain Zadoff-Chu sequences of length 62
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Physical Broadcast Channel (PBCH)
PBCH Function Carries the primary Broadcast Transport Channel Carries the Master Information Block (MIB), which includes:
Overall DL transmission bandwidth PHICH configuration in the cell System Frame Number Number of transmit antennas (implicit)
Transmitted in Time: subframe 0 in every frame 4 OFDM symbols in the second slot of corresponding subframe Frequency: middle 1.08 MHz (6 RBs)
TTI = 40 ms Transmitted in 4 bursts at a very low data rate Same information is repeated in 4 subframes Every 10 ms burst is self-decodable CRC check uniquely determines the 40 ms PBCH TTI boundary
Last 2 bits of SFN is not transmitted
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System Information in PBCH & PDSCH
The System Information (SI) that is broadcasted in the whole cell area, is carried by the logical channel BCCH, which in turn is
carried by either of the transport channels BCH or DL-SCH. A static part of SI is called MIB (Master Information Block) is
transmitted on the BCH, which in turn is carried by the PBCH. A dynamic part of SI, called SIBs (System Information Blocks) is
mapped onto RRC System Information messages (SI-1,2,3) on DL-SCH, which in turn is carried by PDSCH.
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System Information (MIB & SIB)
MIB (Master Information Block) Repeats every 4 frames (40 ms) and includes DL Tx bandwidth, PHICH configuration, and SFN. This
information is necessary to acquire (read) other channels in the cell. ***( LTERelease 8 has 11 different SIB types)
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Physical Control Format Indicator Channel (PCFICH)
Carries the Control Format Indicator (CFI) Signals the number of OFDM symbols of PDCCH:
1, 2, or 3 OFDM symbols for system bandwidth > 10 RBs 2, 3, or 4 OFDM symbols for system bandwidth > 6-10 RBs Control and data do not occur in same OFDM symbol
Transmitted in: Time: 1st OFDM symbol of all subframes Frequency: spanning the entire system band
4 REGs -> 16 REs Mapping depends on Cell ID
PCFICH in Multiple Antenna configuration 1 Tx: PCFICH is transmitted as is 2Tx, 4Tx: PCFICH transmission uses Alamouti Code
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Physical Downlink Control Channel (PDCCH)
Used for: DL/UL resource assignments Multi-user Transmit Power Control (TPC) commands Paging indicators
CCEs are the building blocks for transmitting PDCCH 1 CCE = 9 REGs (36 REs) = 72 bits The control region consists of a set of CCEs, numbered from 0 to N_CCE for each subframe
The control region is confined to 3 or 4 (maximum) OFDM symbols per subframe (depending on system bandwidth)
A PDCCH is an aggregation of contiguous CCEs (1,2,4,8) Necessary for different PDCCH formats and coding rate protections
Effective supported PDCCH aggregation levels need to result in code rate < 0.75
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Physical Downlink Shared Channel (PDSCH)
Transmits DL packet data One Transport Block transmission per UEs code word per subframe A common MCS per code word per UE across all allocated RBs Independent MCS for two code words per UE 7 PDSCH Tx modes
Mapping to Resource Blocks (RBs) Mapping for a particular transmit antenna port shall be in increasing order of:
First the frequency index, Then the time index, starting with the first slot ina subframe.
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Physical Downlink Shared Channel (PDSCH)
Code Words (maximum of 2) A code word represents an output from the channel coder 1 code word for rank 1 Transmission 2 code words for rank 2/3/4 Transmissions
Layer Mapping Number of layers depends on the number of Tx antennas and Wireless Channel Rank Fixed mapping schemes of code words to layers
Tx Antennas (maximum of 4) Maximum of 4 antennas (potentially upto 4 layers)
Pre-coding used to support spatial multiplexing Code book based precoding
PDSCH Generalized Transmission Scheme
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Physical HARQ Indicator Channel (PHICH)
Used for ACK/NAK of UL-SCH transmissions Transmitted in:
Time Normal duration: 1st OFDM symbol Extended duration: Over 2 or 3 OFDM symbols Frequency Spanning all system bandwidth Mapping depending on Cell ID
FDM multiplexed with other DL control channels
Support of CDM multiplexing of multiple PHICHs
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DL Reference Signals (RS)
The downlink reference signals consist of so-called reference symbols which are known symbols inserted within in the OFDM
time/frequency grid.
Similar with Pilot signal of CDMA. Used for downlink physical channel demodulation and channel quality measurement (CQI)
Three types of RS in protocol. Cell-Specific Reference Signal is essential and the other two types RS (MBSFN Specific RS & UE-Specific RS)
are optional.
Characteristics:
Cell-Specific Reference Signals are generated from cell-specific RS sequence and frequency shift mapping. RS sequence also carriers one
of the 504 different Physical Cell ID.
The two-dimensional reference signal sequences are generated as the symbol-by-symbol product of a two-dimensional orthogonal sequence and a two-dimensional pseudo-random sequence:
There are 3 different two-dimensional orthogonal sequences There are 168 different two-dimensional pseudo-random sequences
The frequency interval of RS is 6 subcarriers.
RS distributes discretely in the time-frequency domain, sampling the channel situation which is the reference of DL demodulation.
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DL Reference Signals (RS)
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Resource element (k,l)
Not used for transmission on this antenna port
Reference symbols on this antenna port
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even-numbered slots odd-numbered slots
Antenna port 0
even-numbered slots odd-numbered slots
Antenna port 1
even-numbered slots odd-numbered slots
Antenna port 2
even-numbered slots odd-numbered slots
Antenna port 3
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Antenna Port 0 Antenna Port 1 Antenna Port 2 Antenna Port 3
R1: RS transmitted in 1st ant port
R2: RS transmitted in 2nd ant port
R3: RS transmitted in 3rd ant port
R4: RS transmitted in 4th ant port
Downlink RS consist of know reference symbol locations Antenna ports 0 and 1
Inserted in two OFDM symbols (1st and 3rd last OFDM symbol) of each slot. 6 subcarriers spacing and 2x staggering (45kHz frequency sampling)
Antenna ports 2 and 3 Inserted in one OFDM symbol (2nd OFDM symbol) of each slot. 6 subcarriers spacing and 2x staggering across slots.
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DL Reference Signals (RS) Measurement Reference
3GPP is defining following measurements:
RSRP (Reference Signal Received Power) RSRQ (Reference Signal Received Quality)
RSRP, 3GPP definition RSRP is the average received power of a single RS resource element. UE measures the power of multiple resource elements used to transfer the reference signal but then takes an average of them rather than summing them.
Reporting range -44-140 dBm
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DL Reference Signals (RS) Measurement Reference
RSSI (Received Signal Strength Indicator)
RSSI not reported to eNodeB by UE Can be computed from RSRQ and RSRP that are reported by UE RSSI measures all power within the measurement bandwidth
Measured over those OFDM symbols that contain RS Measurement bandwidth RRC-signalled to UE
RSSI = wideband power= noise + serving cell power + interference power
Without noise and interference, 100% DL PRB activity: RSSI=12*N*RSRP
RSRP is the received power of 1 RE (3GPP definition) average of power levels received across all Reference Signal symbols within the considered measurement frequency bandwidth
RSSI is measured over the entire bandwidth N: number of RBs across the RSSI is measured and depends on the BW
Based on the above, under full load and high SNR:
RSRP (dBm)= RSSI (dBm) -10*log (12*N)
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DL Reference Signals (RS) Measurement Reference
RSRQ ,3GPP definition
RSRQ = N x RSRP / RSSI N is the number of resource blocks over which the RSSI is measured, typically equal to system bandwidth
RSSI is pure wide band power measurement, including intracell power, interference and noise
RSRQ reporting range -3-19.5dB
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Uplink RS (Reference Signal)
Uplink RS (Reference Signal):
The uplink pilot signal, used for synchronization between E-
UTRAN and UE, as well as uplink channel estimation.
Two types of UL reference signals:
[1] DM RS (Demodulation Reference Signal),
-Associated with transmission of PUSCH or PUCCH
-Purpose: Channel estimation for Uplink coherent
demodulation/detection of the Uplink control and data
channels
-Transmitted in time/frequency depending on the channel
type (PUSCH/PUCCH), format, and cyclic prefix type
[2] SRS (Sounding Reference Signal), -Not associated with transmission of PUSCH or PUCCH
-Purpose: Uplink channel quality estimation feedback to the
Uplink scheduler (for Channel Dependent Scheduling) at the
eNodeB
-Transmitted in time/frequency depending on the SRS
bandwidth and the SRS bandwidth configuration (some rules
apply if there is overlap with PUSCH and PUCCH)
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Physical Random Access Channel (PRACH)
Basic Principle of Random Access :
Random access is the procedure of uplink synchronization between UE and E-UTRAN.
Prior to random access, physical layer shall receive the following information from the higher layers:
Random access channel parameters: PRACH configuration, frequency position and preamble format, etc.
Parameters for determining the preamble root sequences and their cyclic shifts in the sequence set for the cell, in order to demodulate the random access preamble.
1.Either network indicates specific PRACH resource or UE selects from
common PRACH resources.
2.UE sends random access preambles at increasing power.
3.UE receives random access response on the PDCCH which includes
assigned resources for PUSCH transmission.
Physical Resource Blocks (PRB) and Modulation and Coding Scheme (MCS)
4.UE sends signaling and user data on PUSCH.
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Physical Uplink Shared & Control Channel (PUSCH & PUCCH)
Physical Uplink Control Channel (PUCCH)
Carries Hybrid ACK/NACK reponse DL transmission Always transmitted using QPSK Is punctured into UL-SCH to avoid errors due to missed DL assignments and thus different
interpretations of ACK/NACK symbols
Carries Sceduling Request (SR) Carries CQI (Channel Quality Indicator)
Physical Uplink Shared Channel (PUSCH)
Carries data from the Uplink Shared Channel (UL-SCH) transport Channel.
If data and control are transmitted simultaneously -> PUSCH control located in the same region as data (time multiplexed) required to preserve single-carrier properties
If only control is transmitted -> PUCCH control located at reserved region at band edges one RB is shared by multiple UEs through orthogonal spreading sequences
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Initial Acquisition Procedure ( Cell Search) Cell search is the process of identifying and obtaining downlink synchronization to cells, so that the broadcast information from
the cell can be detected. This procedure is used both at initial access and at handover.
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[4] LTE KEY TECHNOLOGY INTRODUCTION
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LTE MIMO (Multiple Input Multiple Output)
LTE specifications support the use of multiple antennas at both transmitter (tx) and receiver (rx). MIMO (Multiple Input Multiple Output) uses this antenna configuration.
LTE specifications support up to 4 antennas at the tx side and up to 4 antennas at the rx side (here referred to as 4x4 MIMO configuration).
In the first release of LTE it is likely that the UE only has 1 tx antenna, even if it uses 2 rx antennas. This leads to that so called Single User MIMO (SU-MIMO) will be supported only in DL (and maximum 2x2 configuration).
OFDM works particularly well with MIMO MIMO becomes difficult when there is time dispersion OFDM sub-carriers are flat fading (no time dispersion)
3GPP supports one, two, or four transmit Antenna Ports Multiple antenna ports Multiple time-frequency grids Each antenna port defined by an associated Reference Signal
LTE DL transmission modes
Multiple layers means that the time- and frequency resources (Resource Blocks) can be reused in the different layers up to a number of times
corresponding to the channel rank. This means that the same resource allocation is made on all transmitted layers.
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LTE MIMO (Multiple Input Multiple Output)
DL Single User MIMO with 2 antennas
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LTE MIMO (Multiple Input Multiple Output)
DL Multi User MIMO (MU-MIMO)
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LTE MIMO (Multiple Input Multiple Output)
UL Multi user MIMO (virtual MIMO)
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LTE MIMO Evolution
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CSFB (CIRCUIT SWITCHED FALLBACK )
LTE Voice Solution Options
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CSFB (CIRCUIT SWITCHED FALLBACK )
LTE Voice Solution in 3GPP & GSMA
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CSFB (CIRCUIT SWITCHED FALLBACK )
Voice Options Comparison in LTE Environment
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CSFB (CIRCUIT SWITCHED FALLBACK )
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CSFB (CIRCUIT SWITCHED FALLBACK )
Flash CSFB (R9 Redirection with SIB)
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SON (SELF ORGANIZING NETWORKS)
SON (Self Organization Network) is introduced in 3GPP release 8. This function of LTE is required by
the NGMN (Next Generation Mobile Network) operators.
From the point of view of the operators benefit and experiences, the early communication systems
had bad O&M compatibility and high cost.
New requirements of LTE are brought forward, mainly focus on FCAPSI (Fault, Configuration, Alarm,
Performance, Security, Inventory) management:
Self-planning and Self-configuration, support plug and play
Self-Optimization and Self-healing
Self-Maintenance
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SON (SELF ORGANIZING NETWORKS)
Three SON RRM functionalities have been standardized in Rel 8.
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SON_ANR (Automatic Neighbor Relation)
The ANR function relies on cells broadcasting their identity on a global level
E-UTRAN Cell Global Identifier (ECGI) The eNB instructs UE to perform measurements on neighbor cells The eNB can decide to add this neighbor relation and can use the Physical Cell ID and ECGI to: Look up transport layer address to the new eNB Update Neighbor Relation List If needed, set up a new X2 interface toward the new eNB
Main ANR management functions:
Automatic detection of missing neighboring cells
Automatic evaluation of neighbor relations
Automatic detection of Physical Cell Identifier (PCI) collisions
Automatic detection of abnormal neighboring cell coverage
Automatic Neighbor Relation (ANR) can automatically add and
maintain neighbor relations. The initial network construction,
however, should not fully depend on ANR for the following
considerations:
ANR is closely related to traffic in the entire network
ANR is based on UE measurements but the delay is
introduced in the measurements.
After initial neighbor relations configured and the number of UEs
increasing, some neighboring relations may be missing. In this case,
ANR can be used to detect missing neighboring cells and add
neighbor relations.
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SON_MLB( Mobility Load Balancing)
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END OF DOCUMENT
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