session 1 lte air interface

LTE Air Interface

Schedule for 3GPP Releases

year

UMTS Rel 99/4 UMTS Rel 5 UMTS Rel 6 UMTS Rel 7 UMTS Rel 8

2007200520032000 2008

IMS

HSDPA

MBMS

HSUPA

IMS Evolution

LTE Studies

iHSPA

LTE

Specification

2009

Summary of Capabilities & Benefits of LTE/EPC

Fully packet-oriented mobile

broadband network providing:

Peak data rates of 150 Mbps (DL)

Peak data rates of 50 Mbps (UL)

Very low latency

Seamless and lossless handover

Sophisticated QoS to support

important real time applications

such as voice, video and

interactive gaming

Support for terminal speeds of

150-500 Km/h

Cell ranges of up to 100 Km.

Reduced cost per bit Simplified Architecture

All IP

Maximised exploitation of frequency

Resources Supports flexible frequency

bandwidths

by means of OFDM, MIMO, HARQ etc.

an outstanding spectrum efficiency

can be achieved

Extended Interworking Functionality seamless mobility with other 3GPP

access systems (UMTS, GPRS),

with 3GPP2/cdma2000

Reduced Terminal Complexity Specific transmission schemes

Minimize power consumption

Ericsson Internal | 2015-11-06 |

LTE FDD and TDD Modes

Uplink Downlink

Bandwidth

up to 20MHz

Duplex Frequency

f

t Bandwidth

up to 20MHz

Guard

Period

f

t

Uplink

Downlink

Bandwidth

up to 20MHz


Requirement: Latency and Signal Performance

User Plane Latency

cell

Gateway

IP Network

< 5 ms (unloaded condition)

Control Plane Latency

IDLE

(no resources)

ACTIVE

< 100 ms

No resourceResource

Allocated

< 50 ms


LTE/SAE Network ElementsMain references to architecture in 3GPP specs.: TS23.401,TS23.402,TS36.300

NOTE: Interface names are from draft specification and may not be the final interface names.

LTE-UE

Evolved UTRAN (E-UTRAN)

MME S10

S6a

Serving

Gateway

S1-U

S11

PDN

Gateway

PDN

Evolved Packet Core (EPC)

PCRF

S7 Rx+

SGiS5/S8

Evolved Node B

(eNB)

X2

LTE-Uu

HSS

Mobility

Management

EntityPolicy & Charging

Rule Function

SAE

Gateway

eNB


Functions of main LTE elements eNodeB Function :

o Radio Admission Control

o Inter Cell RRM : HO, Load balancing between cells

o Radio Bearer Control : Setup, modification and release of Radio Resources.

o MME selection at Attach of the UE

o User Data Routing to the S-GW

HSS (Home Subscriber Server ):

o concatenation of the HLR (Home Location Register) and the AuC (Authentication Center)

o User identification and addressing – this corresponds to the IMSI (International Mobile Subscriber Identity) and MSISDN (Mobile Subscriber ISDN Number) or mobile telephone number.

o User profile information – this includes service subscription states and user-subscribed Quality of Service information (such as maximum allowed bit rate or allowed traffic class).

o The AuC part of the HSS is in charge of generating security information from user identity keys


Functions of main LTE elements MME - Mobility Management Entity :

o Control plane and pure Signaling entity inside EPC

o Idle state mobility handling

o Tracking Area update

o NAS signaling and its security

o Authentication; Authorization

SGW - Serving Gateway :

o Manage user data path within EPC

o Mobility anchoring for inter-3GPP mobility, serve as anchor point during inter e-NodeBhandover

o Packet routing and forwarding

PDN GW - Packet Data Network Gateway

o UE IP address allocation

o Per-user based packet filtering (by deep packet inspection)

o Serve as mobility anchor point during inter system mobility


Resource Block and Resource Element

– Physical Resource Block or Resource Block ( PRB or RB):

› 12 subcarriers in frequency domain x 1 slot period in time domain.

0 1 2 3 4 5 6 0 1 2 3 4 5 6Subcarrier 1

Subcarrier 12

18

0 K

Hz

1 slot 1 slot

1 ms subframe

• Capacity allocation is based on Resource Blocks

• Resource Element ( RE):

– 1 subcarrier x 1 symbol period

– Theoretical minimum capacity allocation unit.

– 1 RE is the equivalent of 1 modulation symbol on a subcarrier, i.e. 2 bits for QPSK, 4 bits for 16QAM and 6 bits for 64QAM.

Resource Element

0 1 2 3 4 5 6 0 1 2 3 4 5 6

0 1 2 3 4 5 6 0 1 2 3 4 5 6

0 1 2 3 4 5 6 0 1 2 3 4 5 6

0 1 2 3 4 5 6 0 1 2 3 4 5 6

0 1 2 3 4 5 6 0 1 2 3 4 5 6

0 1 2 3 4 5 6 0 1 2 3 4 5 6

0 1 2 3 4 5 6 0 1 2 3 4 5 6

0 1 2 3 4 5 6 0 1 2 3 4 5 6

0 1 2 3 4 5 6 0 1 2 3 4 5 6

0 1 2 3 4 5 6 0 1 2 3 4 5 6

0 1 2 3 4 5 6 0 1 2 3 4 5 6


Physical Resource Blocks

•In both the downlink and uplink

direction, data is allocated to users

in terms of resource blocks (RBs).

•A resource block consists of 12

consecutive subcarriers in the

frequency domain, that are

reserved for the duration of one

0.5 millisecond time slot.

•The smallest resource unit a

scheduler can assign to a user is a

scheduling block which consists of

two consecutive resource blocks

....

12 subcarriers

Time

Frequency

0.5 ms slot

1 ms subframe

or TTI

Resource

block

During each TTI,

resource blocks

for different UEs

are scheduled in

the eNodeB


OFDM Key Parameters for FDD and TDD Modes

Bandwidth

(NC×Δf)

1.4 MH 3 MHz 5 MHz 10 MHz 15 MHz 20 MHz

Subcarrier Fixed to 15 kHz (7.5kHz defined for MBMS)

Spacing (Δf)

Symbol Tsymbol = 1/Δf = 1/15kHz = 66.67μs

Duration

Data

Subcarriers (NC)

72 180 300 600 900 1200

Number of

Resource Blocks

6 15 25 50 75 100

Symbols/slot Normal CP=7; extended CP=6

CP length Normal CP=4.69/5.12μsec., Extended CP= 16.67μsec


Upper Layers

RLC

MAC

PHY

Logical channels

Transport channels

BC

CH

CC

CH

PC

CH

MT

CH

MC

CH

BC

H

PC

H

DL

-SC

H

RA

CH

UL

-SC

H

PB

CH

PD

SC

H

PH

ICH

PD

CC

H

PC

FIC

H

PM

CH

PU

CC

H

PR

AC

H

PU

SC

H

MC

H

CC

CH

DC

CH

DT

CH

ULDL

Air interface

DC

CH

DT

CH

Ericsson Internal | 2015-11-06 | Page 14

The end user is switching on his/her LTE mobile

› and would like to download something

› from the Internet

UE

eNodeB

What are all the steps and

the physical channels

involved ??

Scenario:


› What do I need on the first place?

Find one cell

Get synchronisation → time & frequency

Finally I read system info to find out:

› Global cell id

› Cell bandwidth

› …

Cell Search


Cell Search (1/2) 1. PSS Primary Synchronisation Signal

(Time-slot & Frequency synchronisation

+ Physical cell id (0,1,2) )

2. SSS Secondary Synchronisation Signal

(Frame synchronisation

+ Physical Cell id group (1..168) )

4. PBCH – Physical Broadcast Channel

(MIB* – DL system bandwidth, PHICH

configuration)

3. DL Reference Signals

(Channel estimation & measurements –

like CPICH* in UMTS)

eNodeB

UE

*CPICH = Common Pilot Channel

MIB = Master Information Block

PHICH = Physical HARQ

Indicator Channel


› Challenge:

The PBCH contains only the MIB (Master Information Block) → the

SIBs(System Information Blocks) are on the PDSCH (Physical Downlink

Shared Channel)!!

need to read SIBs on PDSCH

The UE should read PDSCH but it doesn't know which resource blocks

are reserved for it and where are they placed (in time and frequency)

› Solution:

PCFICH (Physical Control Format Indicator Channel) indicates the size

of PDCCH (Physical Downlink Control Channel)

the PDCCH is indicating which resource blocks are scheduled and

where are located

Cell Search


Cell Search (2/2) 5. PCFICH Physical Control Format Indicator Channel

(How many symbols (1,2,3) in the beginning

of the sub-frame are for PDCCH)

6. PDCCH Physical Downlink Control Channel

(Resource allocation for PDSCH )

7. PDSCH Physical Downlink Shared Channel

(*SIBs: Cell global ID, parameters for cell

selection reselection, … )eNodeB

UE

→ CELL SELECTION &

RESELECTION *SIB = System Information Block


Cell Search

1. PSS Primary Synchronisation Signal







(MIB – DL system bandwidth, PHICH

configuration)



like CPICH in UMTS) eNodeB

UE


› Challenge 1: find the cell

› UE receives synchronisation signals from several cells

› Challenge: How to distinguish between several cells??

› Solution:??

› → Physical cell identity

Synchronisation

eNodeB

UEeNodeBPSS = Primary Synchronisation Signal

SSS = Secondary Synchronisation Signal


› Challenge 2: time synchronisation

› Get time synchronisation (symbol, time-slot, frame)

› The system may use long/ short cyclic prefix

› How can the UE know the position in time of the synchronization

signals??

› Solution:??

› →Fixed time position for the synchronisation signals

Synchronisation

eNodeB

UE

PSS = Primary Synchronisation Signal

SSS = Secondary Synchronisation Signal


› Challenge 3: frequency synchronisation

› Get the frequency synchronisation

› The UE does not know the system bandwidth:

› → 5, 10 .. 20 MHZ ?

› How big is the Bandwidth? Where are the synchronisation signals placed

in frequency domain??

› Solution:??

› →Fixed frequency position for the synchronisation signals

› →Fixed bandwidth for the synchronisation signals

Synchronisation

eNodeB

UE


› Each cell has a physical layer ID (number)

› 1..504 physical layer IDs

› Physical layer ID: 3 → 0,1,2

› → From PSS = Primary Synchronisation Signal

› Physical layer cell id group: 168

› → From SSS = Secondary Synchronisation Signal

› Total 168 x 3 = 504 cell IDs

› → Subject to network planning

› See next slide

1. Find the Cell


Physical layer

cell identity

(1 out of 504)

1. Find the Cell - Hierarchical Cell Identities

0 1 … 167

0 1 20 1 2 0 1 2…

Possible planning of the 504 sequences:

3 (orthogonal) X 168 (pseudo-random) = 504

Cells belonging to the same Node-B get the 3

different cell IDs from the same group

Cells belonging to different Node-Bs get the

different cell IDs from different groups

Cell groups

Cell IDs


2 3 4 5 7 8 9 10

1 2 3 4 5 6 7

1 2 3 4 5 6

10ms Radio frame

1ms SubframeSSS

PSS0.5ms (One slot)

Normal CP

Extended CP

PSS and SSS frame and slot structure in time domain in the FDD

case

2. Time Synchronization FDD Mode


› At this stage the cyclic prefix length is not known:

• Normal

• Extended

› It is important for PBCH decoding

› How can I learn about the CP length?

› Solution:??

› The position of SSS is changed in time (symbol 5 or 6 inside the time slot)

› The UE is using blind detection to find the position so to find the CP length

› The mobile may also learn whether the system is operated on FDD or on TDD

mode

› → different placement for PSS and SSS in time

Cyclic Prefix Length and FDD/TDD Mode


PSS and SSS Frame in Frequency and Time Domain for FDD Case

10 ms Radio frame

5 ms repetition

period

One subframe (1 ms)

6 R

Bs

–7

2 s

ub

ca

rrie

rs =

1.4

MH

z

(min

imu

m L

TE

Ba

nd

wid

th)

Fre

qu

en

cy

Time

SSS

PSS

Reference signals

Unused RE


Cell Search 1. PSS Primary Synchronisation Signal








configuration)



like CPICH in UMTS)

eNodeB

UE


› Used for:

› DL channel quality measurements

› DL channel estimation for coherent demodulation at the UE

› Like CPICH (Common Pilot Channel) in UMTS

› → Principle: insert known reference signals

DL Reference Signals

eNodeB

UE

RS = Reference Signals


› Challenges:

› How many reference signals?

– Too many signals reduce the DL capacity

– Too less signals may be not be enough for channel estimation

› What should be their position in time-frequency ?

– Easy to be found by UEs

› How to distinguish between different cells?

– Reduce the possible inter-cell interference

DL Reference Signals

eNodeB

UE


How Many Reference Signals? (1)F

req

ue

ncy

Time

First slot Second slot

Reference signal

*Normal CP (cyclic prefix) assumed

In Frequency: 1 reference symbol to

every 6th subcarrier

In one RB (resource block = 12

subcarriers): every 3rd subcarrier

Exact position dependent on cell ID

In Time is fixed: 2 reference symbols per

Time slot (TS 0 & TS 4)3GPP TS 36.211 V8.6.0 (2009-03)

1 2 3 4 5 6 7 1 2 3 4 5 6 7


› Reference Signals (RS) frequency hopping

› Frequency domain positions of the RS may be changed between consecutive

subframes (1 ms)

› Adding a frequency offset to the basic RS pattern:

› → 6 different hopping shifts possible (the distance in frequency

domain between the RSs is 6 subcarriers)

› → What shift to use is in a cell is dependent on the physical layer

cell ID (504 possibilities)

› Reduce collision risk between neighbour cells

› (see next slide)

How to Distinguish Between Different Cells? (2)

eNodeB

UEeNodeB


Reference signal

Fre

qu

en

cy

Time

Shift = 0 Shift = 1 Shift = 5

Different Reference Signals Frequency Shift


Antenna port 0 Antenna port 1

Reference signal Unused symbol

Cell-specific Reference Signals in Case of Multi-Antenna Transmission


Cell-specific Reference Signals in Case of Multi-Antenna Transmission


Cell Search

1. PSS Primary Synchronisation Signal








configuration)



like CPICH in UMTS)

eNodeB

UE


› Detectable without the knowledge of system Bandwidth

› → mapped to the central 72 subcarriers

› → over 4 symbols

› → during second slot of each frame

› Low system overhead & good coverage

– Send minimum information → only the MIB (Master Information Block)

– SIBs (System Information Blocks) are sent on PDSCH

› MIB (Master Information Block) content:

› DL system Bandwidth

› PHICH configuration (PHICH group number)

› System frame number SFN

PBCH Design Criteria

eNodeB

UE


PBCH Mapping

6 R

Bs

–7

2 s

ub

ca

rrie

rs =

1.4

MH

z

(min

imu

m L

TE

Ba

nd

wid

th)

First subframe (1 ms)

Slot 0 Slot 1

SSS

PSS

Reference signals

Unused RE

PBCH

Fre

qu

en

cy

Time


PBCH Repetition Pattern 7

2 s

ub

ca

rrie

rs

Repetition Pattern of PBCH = 40 ms

one radio frame = 10 ms


• CFI = control format indicators

• Indicates how many OFDM symbols per subframe are for PDCCH: 1, 2 or 3

symbols

• The CFI is carried by 32 bits of information

• 16 RE Resource Elements distributed in frequency

• Cell specific offset applied to distinguish from neighbour cells (based

on the Physical cell ID)

• Sent in the first 3 symbols of the subframe

PCFICH Physical Control Format Indicator Channel

eNodeB

UE


PDCCH Resource Adjustment from PCFICH

First subframe (1ms) Second subframe (1ms)

12 s

ub

carr

iers

Fre

qu

en

cy

Time

Control region -

1 OFDM symbol

Control region –

3 OFDM symbols

Indicated by PCFICH


72 s

ubcarr

iers

Time

PCFICH resource elements

Resource elements reserved

for reference symbols

Rate 1/16

block codeScrambling

QPSK

modulation

2 bits 32 bits 32 bits 16

symbols

4

4

4

4

One Resource

Element Group (REG) = 4 RE

D.C.

2 input bits are enough

to signal the PDCCH

size: 1, 2 or 3 symbols

PCFICH Structure


1 CCE (Control Channel Element) = 9 REGs (Resource Elements Groups)

The number of bits for one particular PDCCH may change based on channel

conditions:

1.UE with good DL channel quality (closed to Node-B) one CCE may be

enough

2.UE at the cell edge – several CCEs – up to 8 CCEs could be allocated

Size of one PDCCHPDCCH format id Number of CCE's Number of RE

groups

Number of PDCCH

bits

0 1 9 72

1 2 18 144

2 4 36 288

3 8 72 576


Size of one PDCCH Example

1 CCE = 9 REGs = 36 RE

CCE = Control Channel Elements

REG = Resource Elements Groups

RE = Resource Elements

UE 1

UE 2

Allocation for UE 1

Allocation for UE 2

Fre

qu

en

cy

Time

PCFICH

PHICH

PDCCH


Fre

qu

en

cy

Time

Slot No. 0 1 2 3 4 5 6 7 8 9 ….

Subframe 0 Subframe 1 Subframe 2 Subframe 3 Subframe 4 …..

SSS

PSS

PBCH

PCFICH

PHICH

PDCCH

Reference signals

PDSCH UE1

PDSCH UE2

PDSCH – Physical Downlink Shared Channel


System Information ( )

SIB 2 SIB 3 SIB 4 SIB 11

•Fixed repetion 80 ms

•First transmission in subframe #5 for

which SFN mod 8 = 0

•Indicates the allocation of the other

SIBs 2...11

SIB 1

System Information

MIB: Master Information Block

SIB: System Information Block

SFN: System Frame Number

UE

eNodeB

MIB

Sent on PBCH!

40 ms repetition


Special Use of PDSCH – System Information Blocks

SIB 1

- Cell access related information (PLMN, cell identity, Tracking Area code etc.)

- Information for cell selection

- Information about time-domain scheduling of the remaining SIBs

SIB 2

- Access barring information

- Parameter related to Cell Selection

- It contains information of common control and shared channels (e.g. PCCH)

SIB 3 - Cell-reselection information mainly related to the serving cell.

SIB 4

Contains information about the serving frequency

and intra-frequency neighboring cells relevant for cell re-selection (including cell

re-selection parameters common for a frequency as well as cell specific reselection

parameters

SIB 5 contains information about other E-UTRA

frequencies and inter-frequency neighboring cells relevant for cell re-selection


Special Use of PDSCH – System Information Blocks

SIB 6

contains information about UTRA frequencies

and UTRA neighboring cells relevant for cell re-selection (including cell reselection

parameters common for a frequency as well as cell specific re-selection

parameters);

SIB 7 - Information relevant only for cell re-selection to the GERAN

SIB 8 - Information relevant only for cell re-selection to the cdma2000® system.

SIB 9 - Home eNodeB identifier

SIB 10 - Earthquake and Tsunami Warning System (ETWS) primary notification

SIB 11- Earthquake and Tsunami Warning System (ETWS) secondary notification


PUCCH and PUSCH Multiplexing

Time

To

tal

UL

Ban

dw

ith

PUCCH

PUCCH

PUSCH

1 subframe = 1ms

Fre

qu

en

cy

12 s

ub

carr

iers


› Questions:

› What are the main differences

› from the DL transmission ??

› Why?

› Answers (1/2):

• No UL signalling indicating the transport format (like on PDCCH)

• This is because the UE always follows the Node-B scheduling

• eNode-B has exact knowledge of the UL transport format

Differences from DL Transmission (1/2)

eNodeB

UE


› Answers (2/2):

› UL L1/L2 signalling is divided:

• Control signalling in the absence of the UL user data -> sent on PUCCH (Physical

UL Control Channel)

• Control signalling in the presence of UL user data -> sent on PUSCH (Physical

UL Shared Channel)

› → Not possible to send PUCCH and PUSCH at the same time

›

This is because UL SC-FDMA is using single carrier

To separate PUCCH and PUSCH in frequency -> destroy the single carrier feature

To separate PUCCH and PUSCH in time -> impact on coverage (low coverage for

both PUCCH and PUSCH)

Differences from DL Transmission (2/2)


› Challenge 1: Where should be PUCCH placed? Why?

› Achieve frequency diversity by using frequency hopping from one edge of the

bandwidth to the other edge

› PUCCH as a kind of guard band for the UL transmission (defining the maximum

UL Transmission Bandwidth)

› Maximize the available PUSCH region for user data

› Solution:??

› → Placed at edge of the UL Bandwidth


PUCCH Design (1)

eNodeB

UE


PUCCH Design (1)To

tal

UL

Ban

dw

ith

PUCCH

PUCCH

PUSCH

1 subframe = 1ms

Fre

qu

en

cy

12 s

ub

carr

iers


Mapping of PUCCH Formats to the Physical Resources

Time

To

tal

UL

Ban

dw

ith

PUCCH

PUCCH

PUSCH

1 subframe = 1ms

Fre

qu

en

cy

12 s

ub

carr

iers

Format 2/2a/2b Format 2/2a/2b

Format 1/1a/1b Format 1/1a/1b

Format 2/2a/2b

Format 1/1a/1b

Format 2/2a/2b

Format 1/1a/1b

Format 2/2a/2b


› Challenge 2: Distinguish between different information on PUCCH

› PUCCH contains UCI = UL Control Information

› UCI could indicate:

• Scheduling requests

• HARQ ACK/NACK for DL transmission

• CQI = Channel Quality Indicator

› How to distinguish between the different information on PUCCH?

› Solution:??

› →Use several formats

› (See next slide)

PUCCH Design (2)

eNodeB

UE


PUCCH Formats

PUCCH

format

Modulation scheme Number of bits per

subframe

Type of information

1 N/A N/A Scheduling Request (SR)

1a BPSK 1 ACK/ NACK

1b QPSK 2 ACK/ NACK

2 QPSK 20 CQI

2a QPSK+BPSK 21 CQI + 1 bit ACK/ NACK

2b QPSK+QPSK 22 CQI + 2 bits ACK/ NACK

eNodeB

UE


› Associated with PUCCH and PUSCH data transmission

– Basically the same structure for both PUCCH DRS and PUSCH DRS

– The main differences are the allocated bandwidth and the timing

› Used for channel estimation:

– For coherent detection and demodulation

– Power control in UL

– Timing estimation

› Like DPCCH (Dedicated Physical Control Channel) in UL in UMTS

Demodulation Reference Signals DRS

eNodeB

UE


› Challenge 1: Is it possible to use the same structure for the reference signals like

in DL?

› Remember the “grid-like” structure of the reference signals in the DL

› But in UL there are some other issues to consider:

– The variations in UL transmission power should be kept as low as possible

– Maximise the power available for data transmission (for coverage reasons)

› Therefore:

– It is not suitable to multiplex in time and frequency the user data and the

reference signals

– Some SC-FDMA symbols will be reserved for the transmission of the UL

reference signals

› Solution:??

› → In UL the reference signals are time multiplexed with the data

transmission of the same terminal

Design of Demodulation Reference Signals DRS (1)


› Challenge 2: What should be the position of the DRS?

› Time domain:

› For PUCCH: the number and the exact position of the DRS is dependent on the

format (1/1a/1b or 2/2a/2b) used

› For PUSCH: every 4th symbol in every time

› slot (the 3rd symbol for the extended cyclic

prefix)

› Frequency domain:

› DRS has the same bandwidth like

› the UL transmission of the terminal




› Challenge 3: What should be the length of the DRS?

› Since the DRS is sent on the UL transmission bandwidth then the length should

be variable

› The minimum length should be 12 (minimum number of subcarriers in one

resource block)

› The length should be variable and support all the allowed number of resource

blocks in UL

› There are sequences of different length:

– For BW = 12, 24, … 60 subcarriers

– For BW > 60 subcarriers

› Solution:??

› → variable, multiple of 12


eNodeB

UE


Intra RAT HO events

› A1 -> Serving cell becomes better than threshold

› A2 -> Serving cells becomes worse than threshold

› A3 -> Neighbour becomes offset better than serving

› A4 -> Neighbour becomes better than threshold

› A5 -> Serving becomes worse than threshold 1 & neighbour

becomes better than threshold 2


Inter RAT HO events

› Event B1 -> Inter RAT neighbour becomes better than threshold

› Event B2 -> serving becomes worse than threshold 1 and

neighbour becomes better than threshold 2

session 1 lte air interface

Technology