02 Ra41202en20gla0 Lte Air Interface v03

RA41202EN20GLA0

LTE Air Interface

1

1 Nokia Siemens Networks RA41202EN20GLA0

LTE RPESSLTE Air Interface

RA41202EN20GLA0

LTE Air Interface

2


Nokia Siemens Networks Academy

Legal notice

Intellectual Property RightsAll copyrights and intellectual property rights for Nokia Siemens Networks training documentation, product documentation and slide presentation material, all of which are forthwith known as Nokia Siemens Networks training material, are the exclusive property of Nokia Siemens Networks. Nokia Siemens Networks owns the rights to copying, modification, translation, adaptation or derivatives including any improvements or developments. Nokia Siemens Networks has the sole right to copy, distribute, amend, modify, develop, license, sublicense, sell, transfer and assign the Nokia Siemens Networks training material. Individuals can use the Nokia Siemens Networks training material for their own personal self-development only, those same individuals cannot subsequently pass on that same Intellectual Property to others without the prior written agreement of Nokia Siemens Networks. The Nokia Siemens Networks training material cannot be used outside of an agreed Nokia Siemens Networks training session for development of groups without the prior written agreement of Nokia Siemens Networks.

RA41202EN20GLA0

LTE Air Interface

3


Module Objectives

After completing this module, the participant should be able to:

Understand the basics of the OFDM transmission technology Explain how the OFDM technology avoids the Inter Symbol Interference Recognise the different between OFDM & OFDMA Identify the OFDM weaknesses Review the key OFDM parameters Analyze the reasons for SC-FDMA selection in UL Describe the LTE Air Interface Physical Layer Calculate the Physical Layer overhead Identify LTE Measurements List the frequency allocation alternatives for LTE Review the main LTE RRM features Identify the main voice solutions for LTE

RA41202EN20GLA0

LTE Air Interface

4


Module Contents

OFDM Basics OFDM & Multipath Propagation: The Cyclic Prefix OFDM versus OFDMA OFDM Weaknesses OFDM Key Parameters SC-FDMA LTE Air Interface Physical Layer Physical Layer Overhead LTE Measurements Frequency Variants RRM Overview VoIP in LTE

RA41202EN20GLA0

LTE Air Interface

5


Module Contents


RA41202EN20GLA0

LTE Air Interface

6


The Rectangular Pulse

Advantages:+ Simple to implement: there is no complex filter system required to detect such pulses and to generate them.+ The pulse has a clearly defined duration. This is a major advantage in case of multi-path propagation environments as it simplifies handling of inter-symbol interference.

Disadvantage: - it allocates a quite huge spectrum. However the spectral power density has null points exactly at multiples of the frequency fs = 1/Ts. This will be important in OFDM.

time

ampl

itude

Ts f s =1Ts

Time Domain

frequency f/fs

spec

tral

pow

er d

ensi

ty Frequency Domain

fs

FourierTransform

Inverse FourierTransform

RA41202EN20GLA0

LTE Air Interface

7


TDMA

f

t

f

Time Division

FDMA

f

f

t

Frequency Division

CDMA

f

tcode

s

f

Code Division

OFDMA

f

f

t

Frequency Division Orthogonal subcarriers

Multiple Access Methods User 1 User 2 User 3 User ..

OFDM is the state-of-the-art and most efficient and robust air interface

RA41202EN20GLA0

LTE Air Interface

8


OFDM Basics

Transmits hundreds or even thousands of separately modulated radio signals using orthogonal subcarriers spread across a wideband channel

Orthogonality:

The peak ( centre frequency) of one subcarrier

intercepts the nulls of the neighbouring subcarriers

15 kHz in LTE: fixed

Total transmission bandwidth

RA41202EN20GLA0

LTE Air Interface

9


OFDM Basics

Data is sent in parallel across the set of subcarriers, each subcarrier only transports a part of the whole transmission

The throughput is the sum of the data rates of each individual (or used) subcarriers while the power is distributed to all used subcarriers

FFT ( Fast Fourier Transform) is used to create the orthogonal subcarriers. The number of subcarriers is determined by the FFT size ( by the bandwidth)

Power

frequency

bandwidth

RA41202EN20GLA0

LTE Air Interface

10


Module Contents


RA41202EN20GLA0

LTE Air Interface

11


Tg: Guard period durationISI: Inter-Symbol Interference

Propagation delay exceeding the Guard Period

12

34

time

TSYMBOLTime Domain

time

time

Tg

1

2

3

time

4

Delay spread > Tg ISI

The Guard Period should be designed such that it is always longer than the multipath delay spread, in order to avoid inter-symbol interference between successive OFDM symbols.Note that in the example of this slide, the Guard Period is too short, so there will be inter-symbol interference!

RA41202EN20GLA0

LTE Air Interface

12


The Cyclic Prefix OFDM symbol

OFDM symbol

OFDM symbol

OFDM symbol

Cyclic prefix

Part of symbol used for FFT processing in the receiver

In all major implementations of the OFDMA technology (LTE, WiMAX) the Guard Periodis equivalent to the Cyclic Prefix CP.

This technique consists in copying the last part of a symbol shape for a duration of guard-time and attaching it in front of the symbol (refer to picture sequence on the right).

CP needs to be longer than the channel multipath delay spread (refer to previous slide).

A receiver typically uses the high correlation between the CP and the last part of the following symbol to locate the start of the symbol and begin then with decoding.

RA41202EN20GLA0

LTE Air Interface

13


The OFDM Signal

The OFDM signal is made of multiple subcarriers.The distance between the center frequencies of the subcarriers is exactly the inverse of the Symbol period (Ts). Bigger Ts means subcarriers will allocated closer and more subcarriers could be allocated on a given spectrum bandwidth.An OFDM symbol is the combination of n subcarrier Symbol being produced in parallel at the same time.

RA41202EN20GLA0

LTE Air Interface

14


Module Contents


RA41202EN20GLA0

LTE Air Interface

15


OFDM

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

Plain OFDM

time

subc

arrie

r

...

...

...

...

...

...

...

...

...

1 2 3 common info(may be addressed viaHigher Layers)

UE 1 UE 2 UE 3

OFDM stands for Orthogonal Frequency Division Multicarrier

OFDM: Plain or Normal OFDM has no built-in multiple-access mechanism.

This is suitable for broadcast systems like DVB-T/H which transmit only broadcast and multicast signals and do not really need an uplink feedback channel (although such systems exist too).

Now we have to analyze how to handle access of multiple users simultaneously to the system, each one using OFDM.

RA41202EN20GLA0

LTE Air Interface

16


OFDMA

11

1

.

.

.

2

.

.

.

3

.

.

.

.

.

.

.

.

.

Orthogonal FrequencyMultiple Access

OFDMAtime

...

...

...

...

...

...

...

...

...

11

1 1

222

2 2

3 33 3 3

1

subc

arrie

r

11 1 1

111

3 3 333 3 3 33

Resource Block (RB)

1 2 3 common info(may be addressed viaHigher Layers)

UE 1 UE 2 UE 3

OFDMA stands for Orthogonal Frequency Division Multiple Access

registered trademark by Runcom Ltd. The basic idea is to assign subcarriers to users based on their

bit rate services. With this approach it is quite easy to handlehigh and low bit rate users simultaneously in a single system.

But still it is difficult to run highly variable traffic efficiently. The solution to this problem is to assign to a single users so

called resource blocks or scheduling blocks. such block is simply a set of some subcarriers over some

time. A single user can then use 1 or more Resource Blocks.

RA41202EN20GLA0

LTE Air Interface

17


Module Contents


RA41202EN20GLA0

LTE Air Interface

18


Inter-Carrier Interference (ICI) in OFDM

The price for the optimum subcarrier spacing is the sensitivity of OFDM to frequency errors. If the receivers frequency slips some fractions from the subcarriers center frequencies,

then we encounter not only interference between adjacent carriers, but in principle between all carriers.

This is known as Inter-Carrier Interference (ICI) and sometimes also referred to as Leakage Effect in the theory of discrete Fourier transform.

One possible cause that introduces frequency errors is a fast moving Transmitter or Receiver (Doppler effect).

RA41202EN20GLA0

LTE Air Interface

19


f0 f1 f2 f3 f4

P

I3I1I4I0

ICI =

Inte

r-C

arrie

r Int

erfe

renc

e

Leakage effect due to Frequency Drift: ICI

Two effects begin to work:1. -Subcarrier 2 has no longer its

power density maximum here -so we loose some signal energy.

2.-The rest of subcarriers (0, 1, 3 and 4) have no longer a null point here. So we get some noise from the other subcarrier.

RA41202EN20GLA0

LTE Air Interface

20


Module Contents


RA41202EN20GLA0

LTE Air Interface

21


OFDMA Parameters in LTE

Channel bandwidth: DL bandwidths ranging from 1.4 MHz to 20 MHz Data subcarriers: the number of data subcarriers varies with the

bandwidth 72 for 1.4 MHz to 1200 for 20 MHz

RA41202EN20GLA0

LTE Air Interface

22


OFDMA Parameters in LTE Frame duration: 10ms created from slots and subframes. Subframe duration (TTI): 1 ms ( composed of two 0.5ms slots) Subcarrier spacing: Fixed to 15kHz ( 7.5 kHz defined for MBMS) Sampling Rate: Varies with the bandwidth but always factor or

multiple of 3.84 to ensure compatibility with WCDMA by using common clocking

Frame Duration

Subcarrier Spacing

Sampling Rate ( MHz)

Data Subcarriers

Symbols/slot

CP length

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

10 ms

15 kHz

Normal CP=7, extended CP=6

Normal CP=4.69/5.12 s, extended CP= 16.67s.

1.92 3.84 7.68 15.36 23.04 30.72

72 180 300 600 900 1200

10ms

Fixed 15kHz: reduces the complexity of a system supporting multiple channel bandwidthsMBMS: Multimedia Broadcast Multicast system

To ensure that all signals are received correctly, the receiver sampling rate must be slightly higher than the bandwidth of the signal used to carry it (i.e. for a channel bandwidth of 1.75MHz the sampling rate should be 2 MHz)

RA41202EN20GLA0

LTE Air Interface

23


Module Contents


RA41202EN20GLA0

LTE Air Interface

24


Peak-to-Average Power Ratio in OFDMA

The transmitted power is the sum of the powers of all the subcarriers

Due to large number of subcarriers, the peak to average power ratio (PAPR) tends to have a large range

The higher the peaks, the greater the range of power levels over which the transmitter is required to work.

Not best suited for use with mobile (battery-powered) devices

RA41202EN20GLA0

LTE Air Interface

25


SC-FDMA in UL

Single Carrier Frequency Division Multiple Access: Transmission technique used for Uplink

Variant of OFDM that reduces the PAPR: Combines the PAR of single-carrier system with the

multipath resistance and flexible subcarrier frequency allocation offered by OFDM.

It can reduce the PAPR between 69dB compared to OFDMA

TS36.201 and TS36.211 provide the mathematical description of the time domain representation of an SC-FDMA symbol.

Reduced PAPR means lower RF hardware requirements (power amplifier)

SC-FD

MA

OFD

MA

RA41202EN20GLA0

LTE Air Interface

26


SC-FDMA and OFDMA Comparison (2/2)

RA41202EN20GLA0

LTE Air Interface

27


Module Contents


RA41202EN20GLA0

LTE Air Interface

28


LTE Physical Layer - Introduction

FDD..

..

..

..

Downlink Uplink

Frequency band 1

Frequency band 2

.. ..Single frequency bandTDD

It provides the basic bit transmission functionality over air LTE physical layer based on OFDMA DL & SC-FDMA in UL

This is the same for both FDD & TDD mode of operation There is no macro-diversity in use System is reuse 1, single frequency network operation is feasible

no frequency planning required There are no dedicated physical channels anymore, as all resource

mapping is dynamically driven by the scheduler

RA41202EN20GLA0

LTE Air Interface

29


LTE Physical Layer Structure Frame Structure (FDD)

10 ms frame

0.5 ms slot

s0 s1 s2 s3 s4 s5 s6 s7 s18 s19..

1 ms sub-frame

SF0 SF1 SF2 SF9..

sy4sy0 sy1 sy2 sy3 sy5 sy6

0.5 ms slot

SF3

SF: SubFrame

s: slot

Sy: symbol

FDD Frame structure ( also called Type 1 Frame) is common to both UL & DL Divided into 20 x 0.5ms slots

Structure has been designed to facilitate short round trip time

- Frame length = 10 ms- FDD: 10 sub-frames of 1 ms for UL & DL- 1 Frame = 20 slots of 0.5ms each- 1 slot = 7 (normal CP) or 6 OFDM

symbols (extended CP)

In FDD, there is a time offset between uplink and downlink transmission.

RA41202EN20GLA0

LTE Air Interface

30


LTE Physical Layer Structure Frame Structure (TDD)

SF#0SF#0

. . .f

time

UL/DL carrier

radio frame 10 ms

subframe

Dw

PTS

Dw

PTS

GPGP

UpP

TSU

pPTS SF

#2SF#2

SF#4SF#4

. . .

half frame

DwPTS: Downlink Pilot time Slot

UpPSS: Uplink Pilot Time Slot

GP: Guard Period to separate between UL/DL

Downlink Subframe

Uplink Subframe

Frame Type 2 (TS 36.211-900; 4.2) each radio frame consists of 2 half frames Half-frame = 5 ms = 5 Sub-frames of 1 ms UL-DL configurations with both 5 ms & 10 ms DL-to-UL switch-point periodicity are supported Special subframe with the 3 fields DwPTS, GP & UpPTS; length of DwPTS + UpPTS +GP = 1

subframe DL / UL ratio can vary from 1/3 to 8/1 according to service requirements of the carrier

SF#0SF#0 Dw

PTS

Dw

PTS

GPGP

UpP

TSU

pPTS SF

#2SF#2

SF#4SF#4

subframe

RA41202EN20GLA0

LTE Air Interface

31


Subframe structure & CP length

Short cyclic prefix:

Long cyclic prefix:

Copy= Cyclic prefix

= Data

5.21 s

16.67 s

Subframe length: 1 ms for all bandwidths Slot length is 0.5 ms

1 Subframe= 2 slots Slot carries 7 symbols with normal CP or 6 symbols with long CP

CP length depends on the symbol position within the slot: Normal CP: symbol 0 in each slot has CP = 160 x Ts = 5.21s;

remaining symbols CP= 144 x Ts = 4.7s Extended CP: CP length for all symbols in the slot is 512 x Ts = 16.67s

Ts: sampling time of the overall channel basic Time Unit = 32.5 nsec

Ts =1 sec

Subcarrier spacing X max FFT size

RA41202EN20GLA0

LTE Air Interface

32


Resource Block and 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 60 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 60 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

Subcarrier 1

Subcarrier 12

180

KH

z

1 slot 1 slot

1 ms subframe

RB

Resource Element

Physical Resource Block PBR or Resource Block RB: 12 subcarriers in frequency domain x 1 slot period in time domain Capacity allocation based on Resource Blocks

Resource Element RE: 1 subcarrier x 1 symbol period theoretical min. capacity allocation unit 1 RE is the equivalent of 1 modulation

symbol on a subcarrier, i.e. 2 bits (QPSK), 4 bits (16QAM), 6 bits (64QAM).

RA41202EN20GLA0

LTE Air Interface

33


Physical Resource Blocks

....

12 subcarriers

Time

Frequency

0.5 ms slot

1 ms subframeor TTI

Resource block

During each TTI, resource blocks for different UEs are scheduled in the eNodeB

During each TTI, resource blocks for different UEs are scheduled in the eNodeB

In both the DL & UL direction, data is allocated to users in terms of resource blocks (RBs).

a RB consists of 12 consecutive subcarriers in the frequency domain, reserved for the duration of 0.5 ms slot.

The smallest resource unit a scheduler can assign to a user is a scheduling block which consists of two consecutive resource blocks

RA41202EN20GLA0

LTE Air Interface

34


LTE Channel Options

Bandwidth options: 1.4, 1.6, 3, 3.2, 5, 10, 15 and 20 MHzBandwidth options: 1.4, 1.6, 3, 3.2, 5, 10, 15 and 20 MHz

Subcarriers in frequency domain (15 kHz or 7.5 kHz subcarrier spacing)

Channel bandwidth (MHz)

Number of subcarriers

Number of resource blocks

1.4

72

6

3

180

15

5

300

25

10

600

50

15

900

75

20

1200

100

Each channel bandwidth offers a certain number of subcarriers, or - expressed in another way - a certain number of resource blocks. From the table you can easily see that a resource block always occupies 12 subcarriers.

RA41202EN20GLA0

LTE Air Interface

35


DL Physical Resource Block

....

12 subcarriers

Time

0.5 ms slot

1 ms subframe

or TTI

DL reference signal

Reference signals position in time domain is fixed (symbol 0 & 4 / slot for Type 1 Frame) whereas in frequency domain it depends on the Cell ID

Reference signals are modulated to identify the cell to which they belong.

This signal, consisting of a known pseudorandom sequence, is required for channel estimation in the UEs. (like CPICH in WCDMA).

Note that in the case of MIMO transmission, additional reference signals must be embedded into the resource blocks.

RA41202EN20GLA0

LTE Air Interface

36


DL Physical Channels

PDSCH: Physical Downlink Shared Channel carries user data, L3 Signalling, System Information Blocks & Paging

PBCH: Physical Broadcast Channel for Master Information Block only

PMCH: Physical Multicast Channel for multicast traffic as MBMS services

PCFICH: Physical Control Format Indicator Channel indicates number of OFDM symbols for Control Channels = 1..4

PDCCH: Physical Downlink Control Channel carries resource assignment messages for DL capacity allocations & scheduling

grants for UL allocations

PHICH: Physical Hybrid ARQ Indicator Channel carries ARQ Ack/Nack messages from eNB to UE in respond to UL transmission

There are no dedicated channels in LTE, neither UL nor DL.

RA41202EN20GLA0

LTE Air Interface

37


UL Physical Channels

PUSCH: Physical Uplink Shared Channel Transmission of user data, L3 & L1 signalling (L1 signalling: CQI, ACK/NACKs, etc.)

PUCCH: Physical Uplink Control Channel Carries L1 control information in case that no user data are scheduled in this subframe

(e.g. H-ARQ ACK/NACK indications, UL scheduling request, CQIs & MIMO feedback). These control data are multiplexed together with user data on PUSCH, if user data are

scheduled in the subframe

PRACH: Physical Random Access Channel For Random Access attempts; SIBs indicates the PRACH configuration (duration;

frequency; repetition; number of preambles - max. 64)

RA41202EN20GLA0

LTE Air Interface

38


UL Physical Resource Block: DRS & SRS

....

12 subcarriers

Time

0.5 ms slot

1 ms subframeor TTI

Frequency

Sounding Reference Signal on last OFDM symbol of 1 subframe;Periodic or aperiodic

transmission

Sounding Reference Signal on last OFDM symbol of 1 subframe;Periodic or aperiodic

transmission

Demodulation Reference Signal in subframes that carry

PUSCH

Demodulation Reference Signal in subframes that carry

PUSCH

Note: when the subframe contains the PUCCH, the Demodulation

Reference Signal is embedded in a different way

Note: when the subframe contains the PUCCH, the Demodulation

Reference Signal is embedded in a different way

The Demodulation Reference Signal is transmitted in the thirdSC-FDMA symbol (counting from zero) in all resource blocks allocated to the PUSCH carrying the user data.

This signal is needed for channel estimation, which in turn is essential for coherentdemodulation of the UL signalin the eNodeB.

The Sounding Reference Signal SRS provides UL channel quality information as a basis for scheduling decisions in the base station. This signal is distributed in the last SC-FDMA symbol of subframesthat carry neither PUSCH nor PUCCH data. [SRS is always disabled in FDD RL20 and before.]

PUCCH: Physical UL Control Channel

SRS can be used to implement beamforming in TDD.

RA41202EN20GLA0

LTE Air Interface

39


b0 b1

QPSK

Im

Re10

11

00

01

b0 b1b2b3

16QAM

Im

Re

0000

1111

Im

Re

64QAM

b0 b1b2b3 b4 b5

3GPP standard defines the following options: QPSK, 16QAM, 64QAM in both directions (UL & DL)

UL 64QAM not supported in RL10 Not every physical channel is allowed to use any

modulation scheme: Scheduler decides which form to use depending on carrier

quality feedback information from the UE

Modulation Schemes

QPSK: 2 bits/symbol

16QAM: 4 bits/symbol

64QAM: 6 bits/symbol

QPSKPDCCH, PCFICH

Physical channel

Modulation

PDSCH QPSK, 16QAM, 64QAM

PMCH QPSK, 16QAM, 64QAM

PBCH QPSK

PHICH BPSKPUSCH QPSK,

16QAM, 64QAM

PUCCH BPSK and/or QPSK

RA41202EN20GLA0

LTE Air Interface

40


Module Contents


RA41202EN20GLA0

LTE Air Interface

41


DL Reference Signal Overhead

Reference Signal (RS)- If 1 Tx antenna*: 4 RSs per PRB- If 2 Tx antenna*: there are 8 RSs per PRB- If 4 Tx antenna*: there are 12 RSs per PRB

Example below: Normal CP (84 RE) & 2 Tx antenna*, DL RS overhead = 8 / 84 = 9.52 %

* with 1/2/4 Antenna PortsPRB: Physical Resource Block

RA41202EN20GLA0

LTE Air Interface

42


Synchronization Signals Overhead

Primary Synchronization Signal (PSS) - occupies 144 Resource Elements per frame (20 timeslots); i.e. (62 subcarriers + 10

empty Resource Elements) x 2 times/frameExample: Normal CP, 10 MHz bandwidth; PSS overhead = 144 / (84 20 50) = 0.17 %

Secondary Synchronization Signal (SSS) Identical calculation to PSS; same overhead as for PSS

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 Subframe SSSPSS

0.5ms = 1 slot

Normal CP

Extended CP

PSS & SSS frame + slotstructure in time domain

(FDD case)

checking for SSSat 2 possible positions CP length

checking for SSSat 2 possible positions CP length

RA41202EN20GLA0

LTE Air Interface

43


The combination of PDCCH, PCFICH & PHICH occupies the first 1, 2 or 3 symbols per TTI*

Resource Elements reserved for

Reference Symbols(2 antenna port case)

Control ChannelRegion (1-3 OFDM symbols*)

12 s

ubca

rrie

rs

Freq

uenc

y

TimeData Region

One subframe (1ms)

PDCCH, PCFICH & PHICH overhead (1/2)

* up to 4 OFDM symbols in case of 1.4 MHz bandwidth

12 x7x2 = 12 x7 reflects the number of RE per RB and x2 reflects there are 2 RBsper TTI

RA41202EN20GLA0

LTE Air Interface

44


PDCCH, PCFICH & PHICH overhead (2/2)

The number of RE occupied per 1 ms TTI is given by (12 y x), where: y depends upon the number of OFDM symbols per TTI (1, 2 or 3*) occupied by

Control Channels x depends upon the number of RE already occupied by the Reference Signal

x = 2 for 1 Tx antenna (Antenna Port) x = 4 for 2 Tx antennas (Antenna Ports) x = 4 for 4 Tx antennas (Antenna Ports) when y = 1 x = 8 for 4 Tx antennas (Antenna Ports) when y = 2 or 3

Example: in the case of normal CP, 2 Antenna Ports & 3 OFDM symbols occupied by Control Channels:

Control Channel Overhead = (12 3 - 4) / (12 7 2) = 19.05%

* up to 4 OFDM symbols in case of 1.4 MHz bandwidth

RA41202EN20GLA0

LTE Air Interface

45


PBCH Overhead

Occupies (288* x) Resource Elements (REs) per 20 timeslots per transmit antennaThe value of x depends upon the number of REs already occupied by the Reference Signal:x = 12 for 1 Tx antenna, x = 24 for 2 Tx antennas & x = 48 for 4 Tx antenna- Example: normal CP, 2 Tx antennas, 10 MHz bandwidth;

PBCH Overhead = (288 24) / (84 20 50) = 0.31%

72 s

ubca

rrie

rs

Repetition Pattern of PBCH = 40 ms

one radio frame = 10 ms

PBCH* PBCH uses central 72 Subcarrier over 4 OFDM symbols in Slot 1

RA41202EN20GLA0

LTE Air Interface

46


UL Demodulation Reference Signal Overhead (1/2)

Demodulation Reference Signal (DRS)

The DRS is sent on the 4thOFDM symbol of each RB occupied by the PUSCH.

PUCCH

PUCCH

PUSCH

UL DRS occupies the whole allocated band except 2 RB bandwidth in the both end.Reference signal: 12 RE (per RB) x (50-2) RBs not dedicated to PUCCH /(84 x50) =13.14%

RA41202EN20GLA0

LTE Air Interface

47


Example:For 1.4 MHz Channel Bandwidth, the PUCCH occupies 1 RB per Slot.The number of RE per RB is 84 when using the normal CP. This means the DRS overhead* is: ((6-1) 12)/(6 84) = 11.9 %

Channel BW PUCCH RB/slot DRS Overhead*1.4 MHz 1 ((6-1) 12) / (6 84) = 11.9 %3 MHz 2 ((15-2) 12) / (15 84) = 12.38 %5 MHz 2 ((25-2) 12) / (25 84) = 13.14 %10 MHz 4 ((50-4) 12) / (50 84) = 13.14 %15 MHz 6 ((75-6) 12) / (75 84) = 13.14 %20 MHz 8 ((100-8) 12) / (100 84) = 13.14 %

UL DRS Overhead (2/2)

* for normal CP

RA41202EN20GLA0

LTE Air Interface

48


PRACH Overhead

PRACH PRACH uses 6 Resource Blocks in the frequency domain. The location of those resource blocks is dynamic. Two parameters from RRC layer define it:

PRACH Configuration Index: for Timing, selecting between 1 of 4 PRACH durations and defining if PRACH preambles can be send in any radio frame or only in even numbered ones

PRACH Frequency offset: Defines the location in frequency domain PRACH Overhead calculation: 6 RBs * RACH Density / (#RB per TTI) x 10 TTIs per frame

RACH density: how often are RACH resources reserved per 10 ms frame i.e. for RACH density: 1 (RACH resource reserved once per frame)

Channel BW PRACH Overhead1.4 MHz (6 1) / (6 10) = 10 %3 MHz (6 1) / (15 10) = 4 %5 MHz (6 1) / (25 10) = 2.40 %10 MHz (6 1) / (50 10) = 1.20 %15 MHz (6 1) / (75 10) = 0.8 %20 MHz (6 1) / (100 10) = 0.6 %

RA41202EN20GLA0

LTE Air Interface

49


PUCCH Overhead PUCCH Ratio between the number of RBs used for PUCCH and the total number of RBs in frequency

domain per TTIChannel BW PUCCH RB/slot PUCCH Overhead

1.4 MHz 1 1 / 6 = 16.67 %3 MHz 2 2 / 15 = 13.33 %5 MHz 2 2 / 25 = 8 %10 MHz 4 4 / 50 = 8 %15 MHz 6 6 / 75 = 8 %20 MHz 8 8 / 100 = 8%

Time

Tota

l UL

Ban

dwith

PUCCH

PUCCH

PUSCH

1 subframe = 1ms

Freq

uenc

y

12 s

ubca

rrie

rs

PUCCH carries UCI(Uplink Control Information), ie, Aperiodic CQI reports and ACK/NACK

RA41202EN20GLA0

LTE Air Interface

50


Physical Layer Overhead Example

Example of overhead: DL 2Tx 2RX UL 1TX - 2RX PRACH in every frame 3 OFDM symbols for PDCCH

RA41202EN20GLA0

LTE Air Interface

51


Module Contents


RA41202EN20GLA0

LTE Air Interface

52


LTE Measurements

Physical layer measurements have not been extensively discussed in the LTE standardization. They could change. Intra LTE measurements ( from LTE to LTE) UE measurements

CQI measurements Reference Signal Received Power (RSRP) Reference Signal Received Quality ( RSRQ)

eNB measurements Non standardized (vendor specific): TA, Average RSSI, Average SINR, UL CSI,

detected PRACH preambles, transport channel BLER Standardized: DL RS Tx Power, Received Interference Power, Thermal Noise Power

Measurements from LTE to other systems UE measurements are mainly intended for Handover.

UTRA FDD: CPICH RSCP, CPICH Ec/No and carrier RSSI GSM: GSM carrier RSSI UTRA TDD: carrier RSSI, RSCP, P-CCPCH CDMA2000: 1xRTT Pilot Strength, HRPD Pilot Strength

CSI: Channel State Information (received power per PRB)TA: Timing Advance

List of detected preambles: The eNB shall report a list of detected PRACH preambles to higher layers. Higher layer utilize this info for the RACH procedure Transport BLER: The ACK/ NACKs for each transmission of the HARQ process are reported to the MAC. Based on these ACK/NACKs the higher layers compute the BLER for RRM issues.TA: The eNB needs to measure the initial timing advance (TA) of the uplink channels based on the RACH preamble Average RSSI: Measured in UL by eNB. It can be used as a level indicator for the UL power control. The RSSI measurements are all UE related and shall be separately performed for ( TTI intervals) UL data allocation (PUSCH) UL control channel (PUCCH) Sounding reference signal (SRS)Average SINR: In UL the eNB measures SINR per UE. The average SINR can be used as a quality indicator for the UL power control UL CSI: channel state information per PRB for each UE. The CSI shall be the received signal power averaged per PRB.

RA41202EN20GLA0

LTE Air Interface

53


UE Measurements: RSRP & RSRQ

RSRP (Reference Signal Received Power) Average of power levels (in [W]) received across all Reference Signal symbols

within the considered measurement frequency bandwidth. UE only takes measurements from the cell-specific Reference Signal elements of

the serving cell If receiver diversity is in use by the UE, the reported value shall be equivalent to

the linear average of the power values of all diversity branches Reporting range -44-133 dBm

RSRQ ( Reference Signal Received Quality) Defined as the ratio NRSRP/(E-UTRA carrier RSSI), where N is the number of

RBs of the E-UTRA carrier RSSI measurement bandwidth. The measurements in the numerator and denominator shall be made over the same set of resource blocks

Reporting range -3-19.5dB

Seems that it has been removed: E-UTRA Carrier Received Signal Strength Indicator, comprises the total received wideband power observed by the UE from all RS symbols for antenna port 0, including co-channel serving and non-serving cells, adjacent channel interference, thermal noise etc.

RA41202EN20GLA0

LTE Air Interface

54


eNodeB Measurements

DL Reference Signal Transmitted Power Average of power levels (in [W]) transmitted across all Reference Signal symbols

within the considered measurement frequency bandwidth Reference point for the DL RS TX power measurement: TX antenna connector The DL RS TX power signaled to the UE is not measured, it is just an eNB internal

settingReceived Interference Power: Received interference power, including thermal noise, within one PRBs bandwidthThermal noise power: No x W Thermal noise power within the UL system bandwidth (consisting of variable # of

resource blocks) No: white noise power spectral density on the uplink carrier frequency and W: denotes

the UL system bandwidth. Optionally reported with the Received Interference Power Reference point: RX antenna connector In case of receiver diversity, the reported value is the average of the power in the

diversity branches

Thermal noise power and Received Interference Power are measured for the same period of time.

RA41202EN20GLA0

LTE Air Interface

55


Module Contents


RA41202EN20GLA0

LTE Air Interface

56


LTE Frequency Variants in 3GPP FDD

123

45

789

62x25

2x752x602x60

2x70

2x45

2x352x35

2x10824-849

1710-17851850-19101920-1980

2500-2570

1710-1755

880-9151749.9-1784.9

830-840

BW[MHz] Uplink [MHz]

869-894

1805-18801930-19902110-2170

2620-2690

2110-2155

925-9601844.9-1879.9

875-885

Downlink [MHz]

10 2x60 1710-1770 2110-217011 2x25 1427.9-1452.9 1475.9-1500.9

1800

2600

900

US AWS

UMTS coreUS PCS

US 850Japan 800

Japan 1700

Japan 1500Extended AWS

Europe Japan Americas

788-798 758-768777-787 746-756

Japan 800

US7002x102x1013

12 2x18 698-716 728-746

14 US700

US700

815 830 860 875 704 716 734 746

2x152x1217

18US700

Band

UHF (TV)832 862 791 821 830 845 875 890

2x302x1519

20Japan 800

1626.5 1660.5 1525 15592x34241447.9 1462.9 1495.9 1510.92x1521

RA41202EN20GLA0

LTE Air Interface

57


LTE Frequency Variants - TDD

333435

3637

3940

381x20

1x601x151x20

1x40

1x60

1x100

1x501910 - 1930

1850 - 19102010 - 20151900 - 1920

1880 - 1920

1930 - 1990

2300 - 2400

2570 - 2620

BW[MHz] Frequency[MHz]

UMTS TDD 1

UMTS TDD 2US PCS

US PCSUS PCS

Euro midle gap 2600China TDDChina TDD

Band

RA41202EN20GLA0

LTE Air Interface

58


Module Contents

OFDM Basics OFDM & Multipath Propagation: The Cyclic Prefix OFDM versus OFDMA OFDM Key Parameters OFDM Weaknesses SC-FDMA LTE Air Interface Physical Layer Physical Layer Overhead LTE Measurements Frequency Variants RRM Overview VoIP in LTE

RA41202EN20GLA0

LTE Air Interface

59


RRM building blocks & functionsOverview

Scope of RRM:Management & optimized utilization of the radio resources:

Increasing the overall radio network capacity & optimizing quality

Provision for each service/bearer/user an adequate QoS (if applicable)

RRM located in eNodeBMIMO Ctrl., LA & schedulers act on TTI basis.

NSN LTE RRM Framework consists of RRM building blocks, RRM functions and RRM algorithms.L3 RRM: ICIC: Selects certain parts of the Frequency Spectrum of the LTE Carrier. Exclusively for PDSCH and PUSCH on Cell Basis. Remaining channels not affected.DRX/DTX algorithm: To support provisioning of measurement gaps for Inter-RAT-HO and DRX/DTX mode in later product releases. Not supported in RL09.Differences with RRM WCDMA: Softer and Soft handovers are not supported by the LTE system LTE requirements on power control are much less stringent due to the different nature of LTE radio interface i.e. OFDMA (WCDMA requires fast power control to address the Near-Farproblem and intra-frequency interferences)On the other hand LTE system requires much more stringent timing synchronization for OFDMA signals.

RA41202EN20GLA0

LTE Air Interface

60


LTE RRM: Scheduling (1/4)

Motivation Bad channel condition avoidance

OFDMA

The part of total available channel experiencing bad channel condition (fading)

can be avoided during allocation procedure.

CDMA

Single Carrier transmission does not allow to allocate only particular frequency parts. Every fading gap

effects the data.

RA41202EN20GLA0

LTE Air Interface

61


Scheduler (UL/DL) (2/4)

Cell-based scheduling (separate UL/DL scheduler per cell) Scheduling air interface resource on a 1ms 12sub-carrier (PRB pair) basis Scheduler controls UEs & assigns appropriate grants per TTI Proportional Fair (PF) resource assignment among UEs Uplink:

Channel unaware UL scheduling based on random frequency allocation Descending resource handling priority in UL for

1. Hybrid ARQ retransmission2. Random access procedure3. Signaling radio bearer with or without data radio bearer4. Scheduling request5. Conversational voice data6. Data radio bearer

Downlink: Channel aware DL scheduling - Frequency Domain Packet Scheduling (FDPS) -

based on CQI with resources assigned in a fair manner

RA41202EN20GLA0

LTE Air Interface

62


Downlink Scheduler (3/4)Algorithm

Determine which PRBs are available (free) and can be allocated to UEs

Allocate PRBs needed for common channels like SIB, paging, and random access procedure (RAP)

Final allocation of UEs (bearers) onto PRB. Considering only the PRBs available after the previous steps

Pre-Scheduling: All UEs with data available for transmission based on the buffer fill levels

Time Domain Scheduling: Parameter MAX_#_UE_DL decides how many UEs are allocated in the TTI being scheduled

Frequency Domain Scheduling for Candidate Set 2 UEs: Resource allocation in Frequency Domain including number & location of allocated PRBs

Evaluation of available resources (PRBs/RBGs ) for dynamic allocation on PDSCH

Resource allocation and schedulingfor common channels

DL scheduling of UEs :Scheduling of UEs /bearers to PRBs /RBGs

Start

End

Pre -Scheduling :Select UEs eligible for scheduling

-> Determination of Candidate Set 1

Time domain schedulingof UEs according to simple criteria

-> Determination of Candidate Set 2

Start

End

Frequency domain schedulingof UEs /bearers

-> PRB /RBG allocation to UEs /bearers

SIB: System Information BroadcastMAX_#_UE_DL depends on the bandwidth: 7UEs (5 MHz), 10UEs (10MHz) and 20 UEs (20MHz)

RA41202EN20GLA0

LTE Air Interface

63


Uplink Scheduler (4/4)Algorithm

Evaluation of the #PRBs that will be assigned to UEs Available number of PRBs per user: resources are assigned via PRB groups (group of

consecutive PRBs)Time domain: Max_#_UE_UL which can be scheduled per TTI time frame is restricted by an O&M

parameter and depends on the bandwidth: 7 UEs (5 MHz), 10 UEs (10MHz) and 20 UEs(20MHz)

Frequency Domain: Uses a random function to assure equal distribution of PRBs over the available frequency

range (random frequency hopping)

a) b)

Feature ID(s): LTE45

Example of allocation in frequency domain:

Full Allocation: All available PRBs are assigned to the scheduled UEs per TTI

Fractional Allocation: Not all PRBs are assigned. Hopping function handles unassigned PRBs as if they were allocated to keep the equal distribution per TTI

PRBs allocated for PRACH, PUCCH are excluded for PUSCH scheduling

RA41202EN20GLA0

LTE Air Interface

64


LTE RRM: Link Adaptation by AMC (UL/DL) (1/6)

Motivation of link adaptation: Modify the signal transmitted to and by a particular user according to the signal quality variation to improve the system capacity & coverage reliability.

It modifies the MCS (Modulation & Coding Scheme) & the transport block size (DL) and ATB (UL)

If SINR is good then higher MCS can be used more payload per symbol more throughput.

If SINR is bad then lower MCS should be used (more robust) Flexi Multiradio BTS performs the link adaptation for DL on a TTI basis The selection of the modulation & the channel coding rate is based:

DL data channel: CQI report from UE UL: BLER measurements in Flexi LTE BTS

LTE31: Link Adaptation by AMC

Optimizing air interface efficiency

Adaptive Transmission Bandwidth (ATB): Calculates maximum number of PRBsthat UL SCH can assigned to a particular UE taking into account UE QoS profile and available UE power headroom

RA41202EN20GLA0

LTE Air Interface

65


Link Adaptation / AMC for PDSCH (2/6)

Procedure: Initial MCS is provided by O&M

(parameter INI_MCS_DL) & is set as default MCS

If DL AMC is not activated (O&M parameter ENABLE_AMC_DL) the algorithm always uses this default MCS

If DL AMC is activated HARQ retransmissions are handled differently from initial transmissions (For HARQ retransmission the same MCS has to be used as for the initial transmission)

A MCS based on CQI reportingfrom UE , shall be determined for the PRBs assigned to UE as indicated by the DL scheduler

yes

no

no

RA41202EN20GLA0

LTE Air Interface

66


Link Adaptation / AMC for PUSCH (3/6)

Functionality UL LA is active by default but can be deactivated by O&M parameters. If not active,

the initial MCS is used all the time UE scope Two parallel algorithms adjust the MCS to the radio channel conditions:

Inner Loop Link Adaptation (ILLA): Slow Periodic Link adaptation (20-500ms) based on BLER measurements

from eNodeB (based on SINR in future releases) Outer Loop Link Adaptation (OLLA): event based

In case of long Link Adaptation updates and to avoid low and high BLER situations, the link adaptation can act based on adjustable target BLER:

- Emergency Downgrade if BLER goes above a MAX BLER threshold (poor radio conditions)

- Fast Upgrade if BLER goes below of a MIN BLER threshold (excellent radio conditions)

RA41202EN20GLA0

LTE Air Interface

67


Downlink fast

1 TTI channel aware

CQI based MCS selection

1 out of 0-28 output

MCS TBS

up to 64QAM support

Uplink slow periodical

~30ms channel partly aware

average BLER based MCS adaptation

+/- 1 MCS correction output

MCS ATB

up to 16 QAM support

Comparison: DL & UL Link adaptation for PSCH (4/6)

MCS: Modulation & Coding SchemeTBS: Transport Block SizeATB: Automatic Transmission Bandwidth

Adaptive Transmission Bandwidth (ATB): Responsible for defining maximum number of PRBs that can be assigned to a particular UE by UL SCH

RA41202EN20GLA0

LTE Air Interface

68


Outer Link Quality Control (OLQC) (5/6)

Feature: CQI Adaptation (DL) CQI information is used by the scheduler & link adaptation in such a way that a certain

BLER of the 1st HARQ transmission is achieved CQI adaptation is the basic mean to control Link Adaptation behaviour and to remedy UE

measurement errors Only used in DL Used for CQI measurement error compensation

CQI estimation error of the UE CQI quantization error or CQI reporting error

It adds a CQI offset to the CQI reports provided by UE. The corrected CQI report is provided to the DL Link adaptation for further processing

CQI offset derived from ACK/NACK feedback

Optimize the DL performance


RA41202EN20GLA0

LTE Air Interface

69


Support of aperiodic CQI reports (6/6)

Functionality Aperiodic CQI reports scheduled in addition to periodic reports

Periodic CQI reports on PUCCH Aperiodic CQI reports on PUSCH

Description Controlled by the UL scheduler

Triggered by UL grant indication (PDCCH) Basic feature


Benefits Not so many periodic CQIs on PUCCH

needed Allow frequent submission of more detailed

reports (e.g. MIMO, frequency selective parts)

RA41202EN20GLA0

LTE Air Interface

70


LTE RRM: Power Control (1/4)

Downlink: There is no adaptive or dynamic power control in DL but semi-static power

setting

eNodeB gives flat power spectral density (dBm/PRB) for the scheduled resources:

The power for all the PRBs is the same If there are PRBs not scheduled that power is not used but the power of the

remaining scheduled PRBs doesnt change: Total Tx power is max. when all PRBs are scheduled. If only 1/2 of the PRBs are

scheduled the Tx power is 1/2 of the Tx power max ( i.e. Tx power max -3dB)

Semi-static: PDSCH power can be adjusted via O&M parameters Cell Power Reduction level CELL_PWR_RED [0...10] dB attenuation in 0.1 dB steps

Improve cell edge behaviour, reduce inter-cell interference & power consumption


RA41202EN20GLA0

LTE Air Interface

71


Power Control (2/4)

Uplink: UL PC is a mix of Open Loop Power Control & Closed Loop Power Control:

Closed Loop PC component f(i): Makes use of feedback from the eNB. Feedback are TCP commands send via PDCCH to instruct the UE to increase or decrease its Tx power

Improve cell edge behaviour, reduce inter-cell interference and power consumption

Feature ID(s): LTE27&LTE28

])}[()()()())((log10,min{)( _010 dBmifiPLjjPiMPiP TFPUSCHPUSCHCMAXPUSCH ++++=

UL Power control is Slow power control: No need for fast power control as in 3G:

if UE Tx power was high it incremented the co-channel for other UEs.

In LTE all UEs resources are orthogonal in frequency & time

TPC: Transmit Power Control

WCDMA: If UE Tx power was high it increased the co-channel interference for other UEsOpen loop suffers from errors in UE path loss measurement and tx power setting whereas closed loop PC is less sensitive to errorsControl over power spectral density, not absolute power. The power is changed by the UL scheduler by varying the bandwidth granted. The power per Hz remains constant.

RA41202EN20GLA0

LTE Air Interface

72


Power Control (3/4)

Uplink (cont.): UL PC is a mix of Open Loop Power Control & Closed Loop Power Control:

PCMAX: max. UE Tx power according to UE power class; e.g. 23dBm for class 3 MPUSCH: # allocated PRBs. The UE Tx Power is increased proportionally to the # of allocated

RBs. Remaining terms of the formula are per RB

P0_PUSCH: eNB received power per RB when assuming path loss 0 dB. Depends on : Path loss compensation factor. Three values:

= 0, no compensation of path loss = 1, full compensation of path loss (conventional compensation) { 0 ,1 } , fractional compensation

PL: DL Path loss calculated by the UE Delta_TF: increases the UE Tx power to achieve the required SINR when transmitting a

large number of bits per RE. It links the UE Tx power to the MCS.

Feature ID(s): LTE27&LTE28

])}[()()()())((log10,min{)( _010 dBmifiPLjjPiMPiP TFPUSCHPUSCHCMAXPUSCH ++++=

PL calculated by UE using a combination of RSRP measurements and knowledge of the RS transmit power (broadcasted in SIB2)Power control does not control the absolute UE Tx. power but the Power Spectral Density (PSD), power per Hz, for a device The PSDs at the eNodeB from different users have to be close to each other so the receiver doesnt work over a large range of powers.Different data rates mean different tx bandwidths so the absolute Tx power of the UE will also change. PC makes that the PSD is constant independently of the txbandwidth

RA41202EN20GLA0

LTE Air Interface

73


Conventional & Fractional Power Control (4/4)

Conventional PC schemes: Attempt to maintain a constant SINR at the receiver UE increases the Tx power to fully compensate for increases in the path loss

Fractional PC schemes: Allow the received SINR to decrease as the path loss increases. UE Tx power increases at a reduced rate as the path loss increases. Increases in

path loss are only partially compensated. [+]: Improve air interface efficiency & increase average cell throughputs by reducing

Intercell interference 3GPP specifies fractional power control for the PUSCH with the option to disable it &

revert to conventional based on

Conventional Power Control: =1If Path Loss increases by 10 dB the UE Tx power increases by 10 dB

Fractional Power Control: { 0 ,1}If Path Loss increases by 10 dB the UE Txpower increases by < 10 dB

UE TxPower UE Tx

Power

UL SINR UL SINR

RA41202EN20GLA0

LTE Air Interface

74


LTE RRM: Radio Admission Control (RAC)

Objective: To admit or reject requests for establishment of Radio Bearers (RB) on a cell basis

Based on number of RRC connections and number of active users per cell Non QoS aware Both can be configured via parameters

RRC connection is established when the SRBs have been admitted & successfully configured

UE is considered as active when a Data Radio bearer (DRB) is established Upper bound for maximum number of supported connections depends on the

BB configuration of eNB : RL10: support for 200, 400 & 800 active users respectively in 5, 10 & 20 MHz RL20: up to 840 active users in 20MHz

Handover RAC cases have higher priority than normal access to the cell

At reception of the HO request message the RAC decides in an all-or-nothingmanner on the admission / rejection of the resources used by the UE in the source cell (prior to HO). 'All-or-nothing' manner means that either both SRB AND (logical) DRB are admitted or the UE is rejected. RL09 all SRB are admitted.SRB: between UE and eNB.This is introduced in RL10. In RL09, All RRC connection setup request are admitted by default to avoid RAC complexity

RA41202EN20GLA0

LTE Air Interface

75


LTE RRM: MIMO / Antenna Control (1/5)Transmit diversity for 2 antennas

Benefit: Diversity gain, enhanced cell coverage Each Tx antenna transmits the same stream of data with Receiver gets

replicas of the same signal which increases the SINR. Synchronization signals are transmitted only via the 1st antenna eNode B sends different cell-specific Reference Signals (RS) per antenna It can be enabled on cell basis by O&M configuration Processing is completed in 2 phases:

Layer Mapping: distributing a stream of data into two streams Pre-coding: generation of signals for each antenna port

Additional antenna specific coding is applied to the signals before transmission to increase the diversity effect. Transmit diversity is open loop (it doesnt take any advantage of any feedback from the UE as weights are fixed). It is simpler to implement and doesnt have the overhead generated by the feedback information. Tx diversity is the solution for open loop spatial multiplexing when transferring a single code word.

RA41202EN20GLA0

LTE Air Interface

76


S1

S2

Spatial multiplexing (MIMO) for 2 antennas (2/5)

Benefit: Doubles peak rate compared to 1Tx antenna

Spatial multiplexing with 2 code words Supported physical channel: PDSCH

Two code words (S1+S2) are

transmitted in parallel to 1 UE double peak rate

Layer Mapping

L1

L2

PrecodingMap onto Resource Elements

Map onto Resource Elements

OFDMA

OFDMA

Modulation

Modulation

Code word 1

Code word 2

Scale

W2

W1

2 code words transferred when channel conditions are good

Signal generation is similar to Transmit Diversity: i.e. Layer Mapping & Precoding

Can be open loop or closed loop depending if the UE provides feedback

RL20: LTE703: DL adaptive closed loop MIMO

The cyclic delay operation for the second antenna causes a linear phase shift along the frequency dimension. Thus, summing the cyclically delayed signal in the receiver and the un-delayed signal from the first antenna causes a frequency selective fading pattern UE provides feedback in terms of:

CQIRank Indication (RI) number of layers to usePrecoding Matrix Indicator (PMI) set of weights to apply during precoding

RA41202EN20GLA0

LTE Air Interface

77


Precoding (3/5)

Precoding generates the signals for each antenna port Precoding is done multiplying the signal with a precoding matrix selected from a

predefined codebook known at the eNB and at the UE side Closed loop: UE estimates the radio channel, selects the best precoding matrix

(the one that offers maximum capacity) & sends it to the eNB Open loop: no need for UEs feedback as it uses predefined settings for Spatial

Multiplexing & precoding

Pre-coding codebook for 2 Tx antenna case

RA41202EN20GLA0

LTE Air Interface

78


DL adaptive MIMO for 2 antennas (4/5)

Benefit: High peak rates (2 code words) & good cell edge performance (single code word)

2 TX antennas Dynamic selection between

Transmit diversity Spatial Multiplexing

Supported physical channel: PDSCH Dynamic switch considers the UE specific

link quality, UE capability, etc. Enabled/disabled on cell level (O&M)

If disabled case either static spatial multiplexing or static Tx diversity can be selected for the whole cell (all UEs)

2 code words (A+B) are transmitted in parallel to 1 UE which doubles the peak rate

1 code word A is transmitted via 2

antennas to 1 UE; improves the LiBu*

AB

A

(RL10) LTE70: DL Adaptive Open Loop MIMO

(RL20) LTE703: DL Adaptive Closed Loop MIMO, utilising PMI report for precoding

* LiBu: Link Budget

Note: CQI adaptation needs to be supported/enabled ;Tx diversity needs to be supported/enabled. MIMOThis feature was introduced in RL10. In LTE70, UE radio capabilities, andUECQI, andUE rank information, are considered.Performance counter for transmission mode usage is supported per cell

RA41202EN20GLA0

LTE Air Interface

79


MIMO, DL channels & RRM Functionality (5/5)

Available MIMO options vs. channel type Options for Transmit Diversity (2 Tx):

Control Channels PDSCH

Options for spatial Multiplexing: Only DL PDSCH

MIMO is SW feature

Channel can be configured to use MIMO modeChannel cannot be configured to use MIMO mode

In UL, Flexi eNodeB has 2Rx Div. : Maximum Ratio Combining

Benefit: increase coverage by increasing the received signal strength and quality

RRM MIMO Mode Control Functionality Refers to switch between: Tx Diversity (single stream) MIMO Spatial Multiplexing (single / dual stream) 1x1 SISO / 1x2 SIMO

Provided by eNB only for DL direction

RA41202EN20GLA0

LTE Air Interface

80


LTE RRM: Connection Mobility Control Handover Types

Intra-RAT handover Intra eNodeB (Intra or Inter Frequency / Band) Inter eNodeB (Intra or Inter Frequency / Band)

If X2 available Data forwarding High performance for 15120 km/h Optimized performance for 015 km/h

If no X2 HO via S1 interface (LTE54, RL20)

Inter-RAT Handover Support Plan PS domain only RL20: LTE CDMA2000 (Idle) RL30: LTE WCDMA (PS InterRAT HO & SRVCC) RL30: LTE GSM (SRVCC & NACC)

RU20: W(PS domain)InterRAT HOL is nominally supported, but NED has no relevant parameters.RU30 plan: WHOL.SRVCC(single radio voice call continuity): function that is responsible for the handover from a packet-switched access to a circuitswitched access

RA41202EN20GLA0

LTE Air Interface

81


Intra frequency handover via X2

Basic Mobility Feature Event triggered handover based

on DL measurements (ref. signals)

Network evaluated HO decision Operator configurable

thresholds for coverage based & best cell based handover

Data forwarding via X2 Radio Admission Control (RAC)

gives priority to HO related access over other scenarios S1

S1 X2

MMES-GWP-GW


A reliable and lossless mobility

RA41202EN20GLA0

LTE Air Interface

82


Intra LTE Handover via S1

Extended mobility option to X2 handover

Handover in case of no X2 interface between eNodeBs, e.g. multi-vendor scenarios eNodeBs connected to different CN elements Operator configurable thresholds for coverage based (A5) and best cell based (A3) handover

DL Data forwarding via S1


RL20

Admission Control gives priority to HO related access over other scenarios

Blacklists

this feature allows to hand over a UE in RRC_Connected mode between two LTE cells operating on different carriers (frequencies/bands).

the trigger for this procedure is: better neighbor cell (frequency) coverage;better neighbor cell (frequency) quality; limited serving

cell (frequency) and sufficient neighbor cell (frequency) coverageintra LTE inter-frequency handover is classified as a:

hard handover: connection to one cell only at the same time gap assisted measurements are usually requirednetwork controlled and UE assisted handover: network takes decision based on measurements delivered by UEbackward handover: The resources at target cell (frequency) are reserved in advance

handover performed via X2 or S1 interface: data forwarding between serving and target eNB may be applied

RA41202EN20GLA0

LTE Air Interface

83


Inter Frequency Handover

Multi-band mobility

Network controlled Event triggered based on DL

measurement RSRP and RSRQ Inter frequency measurements

triggered by events A1/A2 Operator configurable thresholds for

coverage based (A5),best cell based (A3) handover

Service continuity for LTE deployment in different frequency bands as well as for LTE deployments within one frequency band but with different center frequencies

Blacklists


RL20

Requires feature Redirect LTE to other technologies (LTE _423) i.e. RRC Connection Release with Redirect (RL10 feature): message is triggered based on source cell downlink RSRP measurements (even A2)A1: start A2:stop inter frequency measurements

RA41202EN20GLA0

LTE Air Interface

84


Inter RAT Handover to WCDMA

Coverage based inter-RAT PS handover Only for multimode devices supporting

LTE and WCDMA Event triggered handover based on DL

measurement RSRP (reference signal received power)

Operator configurable RSRP threshold Network evaluated HO decision Target cells are operator configurable An ANR functionality may be applied

optionally


Blacklisting eNB initiates handover via EPC

In RL30 Plan

source cell thresholds (RSRP), target cell thresholds (RSCP, EcN0), hysteresis, time to trigger and speed dependent scaling are operator configurable. Handover preparationThe Flexi Multiradio BTS initiates a handover after receiving a measurement report form the UE by sending a S1AP:HANDOVER REQUIRED message to the MME.The Flexi Multimode BTS takes the first target cell indicated by the UE measurements for the handover.The MME responds to this with a S1AP:HANDOVER COMMAND message indicating that the resources at the target have been reserved.Handover executionThe Flexi Multiradio BTS sends after this a RRC:MobilityfromEUTRAcommandmessage to the UE, which forces to the to a WCDMA cell.The Flexi Multimode BTS performs handover retries to other target cells provided by the UE measurements in case of unsuccessful handovers.

RA41202EN20GLA0

LTE Air Interface

85


eNACC to GSM Network Assisted Cell Change to GSM

Service continuity to GSM

Network change from LTE to GSM in RRC Connected Mode when LTE coverage (RSRP) is ending

Prior to actual reselection process the measurements of 2G network are triggered

Only applicable for NACC capable devices

Inter RAT measurements triggered by events A1/A2

Operator configurable handover threshold (event B2)

Target cells for IRAT measurements can be configured by the operator

Blacklisting of target cells is supportedFeature ID(s): LTE442

In RL30 Plan

A1: activate interRAT measurementsA2: deactivate inter RAT measurementsB2:Inter RAT measurementsData forwarding is not supported for NACCMeasurements are triggered early enough to take to take the necessary actions on the UE side (in contrast to triggering the RL10 redirection procedure performed in critical conditions related to LTE coverage end without prior measurements of 2G/3G)

RA41202EN20GLA0

LTE Air Interface

86


Module Contents

OFDM Basics OFDM & Multipath Propagation: The Cyclic Prefix OFDM versus OFDMA OFDM Key Parameters OFDM Weaknesses SC-FDMA LTE Air Interface Physical Layer Physical Layer Overhead LTE Measurements Frequency Variants RRM Overview VoIP in LTE

RA41202EN20GLA0

LTE Air Interface

87


VoIP in LTE

Voice is still important in LTE CS voice call will not be possible in LTE since there is no CS core interface Voice with LTE terminals has a few different solutions The first voice solution in LTE can rely on Call Setup FallBack redirection

where LTE terminal will be moved to 2G/3G to make CS call The ultimate LTE voice solution will be VoIP + IMS

RL20

(RL20) LTE10: EPS Bearers for Conversational Voice(RL20) LTE562: Call Setup FallBack (CSFB)

IP Multimedia Subsystem, a set of specifications from 3GPP for delivering IP multimedia to mobile users VoIP: supported in RL20

RA41202EN20GLA0

LTE Air Interface

88


Single Radio Voice Call Continuity (SR-VCC)

LTE VoIP

3G CS voice

LTE VoIP

3G CS voice 3G CS voice 3G CS voice

Single Radio Voice Call Continuity (SR-VCC)

Options for voice call continuity when running out of LTE coverage 1) Handover from LTE VoIP to 3G CS voice

Voice Handover from LTE VoIP to WCDMA CS voice is called SR-VCC No VoIP needed in 3G

2) Handover from LTE VoIP to 3G VoIP VoIP support implemented in 3G

In RL40 Plan

RA41202EN20GLA0

LTE Air Interface

89


LTE Voice Evolution

VoIPLTEHSPAI-HSPA2G/3G

EPC

MSS

LTE broadband for high speed data Fast-Track VoLTE

IMS for enriched IP multimedia services

LTEHSPAI-HSPA

Simple upgrade of MSS with NVS (VoIP) function

Fully IMS compatible reuse of CS infra-structure for LTE VoIP capable handsets

SRVCC (HO LTE VoIP to 3G CS)

IMS-centric service architecture

Rich Communication Services with full multimedia telephony

Support for any access SRVCC (HO LTE VoIP

to 3G VoIP)

NVS

LTEHSPAI-HSPA2G/3G

EPCMSS

EPC

VoIP

NVSIMS

Main focus on LTE data CS Fallback to 2G/3G

CS access for voice Re-use existing MSC

Server system for voice

Evolution to IMSVoIP solution

Introduce NVSVoIP solution

MSS: Mobile Softwitching solutionNVS: Nokia Siemens Networks Voice ServerIMS: IP Multimedia Subsystem

CSPs can use their existing mobile softswitching and Nokia Siemens NetworksMobile VoIP Server (NVS) infrastructure to manage voice traffic over the LTE network, a function that will eventually be handled by IP Multimedia Subsystem (IMS). This gives CSPs an important time-to-market advantage.Fast Track VoLTE provides a transitional step between traditional networks and the all-IP world of LTE. The solution allows CSPs to exploit their existing circuit-switched mobile core network investments, while providing next-generation service. Investments in Fast Track VoLTE are fully re-usable when upgrading network architecture to IMS, thus reducing capital expenditure (CAPEX) in the long term.NVS: if MSC, NVS is provided by a SW upgrade and a minor HW addition.

Documents

02 Ra41202en20gla0 Lte Air Interface v03