03 Ra41203en30gla0 Lte Air Interface Gc

8/11/2019 03 Ra41203en30gla0 Lte Air Interface Gc

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LTE RPESSLTE Air Interface




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




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




Module Contents

• OFDM Basics



• OFDM Weaknesses






• RRM Overview

• VoIP in LTE




The Rectangular Pulse

Advantages:

+ Simple to implement: there is no complexfilter 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 simplifieshandling of inter-symbol interference.

Disadvantage:

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

time

a m p l i t u d e

Ts f s 1

T s

Time Domain

frequency f/f s

s p e c t r a l p o w e r d e n s

i t yFrequency Domain

f s

Fourier

Transform

InverseFourier

Transform




TDMA

f

t

f

• Time Division

FDMA

f

f

t

• Frequency Division

CDMA

f

t

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


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OFDM Basics

• Transmits hundreds or even thousands of separately modulated radiosignals 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



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. Thenumber of subcarriers is determined by the FFT size ( by the bandwidth)

Power

frequency

bandwidth



Module Contents

• OFDM Basics



• OFDM Weaknesses






• RRM Overview

• VoIP in LTE



Tg: Guard period duration

ISI: Inter-Symbol Interference

Propagation delay exceeding the Guard Period

1

2

3

4

time

TSYMBO

L

Time Domain

time

time

Tg

1

2

3

time

4

Delay spread > Tg ISI



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 Period is 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 thefollowing symbol to locate the start of the

symbol and begin then with decoding.




The OFDM Signal




Module Contents

• OFDM Basics



• OFDM Weaknesses






• RRM Overview

• VoIP in LTE




OFDM

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

Plain OFDM

time

s u b c a r r i e r

...

...

...

...

...

...

...

...

...

1 2 3 common info

(may be addressed via

Higher 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.




OFDMA®

1

1

1

.

.

.

2

.

.

.

3

.

.

.

.

.

.

.

.

.

Orthogonal Frequency

Multiple Access

OFDMA®

time

...

...

...

...

...

...

...

...

...

1

1

1 1

2

22

2 2

3 33 3 3

1

s u b c a r r i e r

1

1 1 1

111

3 3 3

33 3 3 3

3

Resource Block (RB)

1 2 3 common info

(may be addressed via

Higher Layers)

UE 1 UE 2 UE 3

OFDMA® stands for Orthogonal Frequency DivisionMultiple 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 handle

high 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.




Module Contents

• OFDM Basics



• OFDM Weaknesses


• SC-FDMA • LTE Air Interface Physical Layer




• RRM Overview

• VoIP in LTE




Inter-Carrier Interference (ICI) in OFDM

• The price for the optimum subcarrier spacing is the sensitivity of OFDM to frequency errors.

• If the receiver’s 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).






Module Contents

• OFDM Basics



• OFDM Weaknesses






• RRM Overview

• VoIP in LTE




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 thebandwidth

– 72 for 1.4 MHz to 1200 for 20 MHz






Module Contents

• OFDM Basics



• OFDM Weaknesses






• RRM Overview

• VoIP in LTE




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 therange of power levels over which the

transmitter is required to work.

• Not best suited for use with mobile

(battery-powered) devices




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 themultipath resistance and flexible subcarrier

frequency allocation offered by OFDM. – It can reduce the PAPR between 6…9dB compared

to OFDMA

– TS36.201 and TS36.211 provide the mathematicaldescription of the time domain representation of anSC-FDMA symbol.

• Reduced PAPR means lower RF hardwarerequirements (power amplifier)

S C -F DMA

O

F DMA




SC-FDMA and OFDMA Comparison (2/2)




Module Contents

• OFDM Basics



• OFDM Weaknesses






• RRM Overview

• VoIP in LTE




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 resourcemapping is dynamically driven by the scheduler




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)




LTE Physical Layer Structure – Frame Structure (TDD)

SF

#0

. . .

f

time

UL/DL

carrier

radio frame 10 ms

subframe

D w P T S

G P

U p P T S SF

#2

SF

#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

#0 D w P T S

G P

U p P T S

SF

#2

SF

#4

subframe






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 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

Subcarrier 1

Subcarrier 12

1 8 0 K H z

1 slot 1 slot

1 ms subframe

ResourceElement

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




Physical 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 arescheduled in the

eNodeB

• In both the DL & UL direction, data isallocated 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




LTE Channel Options

Bandwidth 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




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 frequencydomain 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. (likeCPICH in WCDMA).

• Note that in the case of MIMO

transmission, additional reference

signals must be embedded into the

resource blocks.

DL Ph i l Ch l




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.

UL Ph i l Ch l




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)

UL Ph i l R Bl k DRS & SRS




UL Physical Resource Block: DRS & SRS

....

12 subcarriers

Time

0.5 ms slot

1 ms subframe

or TTI

Frequency

Sounding Reference

Signal on last OFDM

symbol of 1 subframe;Periodic or aperiodic

transmission

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

• The Demodulation Reference

Signal is transmitted in the third

SC-FDMA symbol (counting

from zero) in all resource blocksallocated to the PUSCH

carrying the user data.

• This signal is needed for

channel estimation, which in

turn is essential for coherent

demodulation of the UL signal in

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 subframes that

carry neither PUSCH nor

PUCCH data. [SRS is always

disabled in FDD RL20 and

before.]

PUCCH: Physical UL Control Channel

M d l ti S h




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

Physical

channel

Modulation

PDSCH QPSK,

16QAM,

64QAM

PMCH QPSK,

16QAM,64QAM

PBCH QPSK

PDCCH,

PCFICH

QPSK

PHICH BPSK

PUSCH QPSK,16QAM,

64QAM

PUCCH BPSK

and/or

QPSK

M d l C t t




Module Contents

• OFDM Basics



• OFDM Weaknesses






• RRM Overview

• VoIP in LTE

DL R f Si l O h d




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

S h i ti Si l O h d




Synchronization Signals Overhead

Primary Synchronization Signal (PSS)

- occupies 144 Resource Elements per frame (20 timeslots); i.e. (62 subcarriers + 10empty Resource Elements) x 2 times/frame

Example: 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 SSS

PSS0.5ms = 1 slot

Normal CP

Extended CP

PSS & SSS frame + slot

structure in time domain

(FDD case)

checking for SSS

at 2 possible positions

CP length

PDCCH PCFICH & PHICH h d (1/2)




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 Channel

Region (1-3 OFDM symbols*)

1 2 s u b c a r r i e r s

F r e q

u e n c y

TimeData Region

One subframe (1ms)

PDCCH, PCFICH & PHICH overhead (1/2)

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

PDCCH PCFICH & PHICH overhead (2/2)




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 byControl 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

PBCH Overhead




PBCH Overhead

Occupies (288* – x) Resource Elements (REs) per 20 timeslots per transmit antenna

The 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%

7 2

s u b c a r r i e r s

Repetition Pattern of PBCH = 40 ms

one radio frame = 10 ms

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

UL Demodulation Reference Signal Overhead (1/2)




UL Demodulation Reference Signal Overhead (1/2)

Demodulation ReferenceSignal (DRS)

• The DRS is sent on the 4th OFDM symbol of each RBoccupied by the PUSCH.

PUCCH

PUCCH

PUSCH

UL DRS Overhead (2/2)




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

PRACH Overhead




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 durationsand defining if PRACH preambles can be send in any radio frame or only in evennumbered 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 RACHdensity: 1 (RACH resource reserved once per frame)

Channel BW PRACH Overhead

1.4 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 %

PUCCH Overhead




PUCCH Overhead

PUCCH

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

domain per TTI Channel 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

T o t a l U L

B a

n d w i t h

PUCCH

PUCCH

PUSCH

1 subframe = 1ms

F r e q u e n c y

1

2 s u b c a r r i e r s

Physical Layer Overhead Example




Physical Layer Overhead Example

Example of overhead:

• DL 2Tx – 2RX• UL 1TX - 2RX

• PRACH in every frame

• 3 OFDM symbols for PDCCH

Module Contents




Module Contents

• OFDM Basics



• OFDM Weaknesses





• Frequency Variants• RRM Overview

• VoIP in LTE

LTE Measurements




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





Module Contents




Module Contents

• OFDM Basics



• OFDM Weaknesses






• VoIP in LTE

LTE Frequency Variants in 3GPP – FDD




LTE Frequency Variants in 3GPP FDD

1

2

34

5

7

8

9

6

2x25

2x75

2x60

2x60

2x70

2x45

2x35

2x35

2x10

824-849

1710-1785

1850-1910

1920-1980

2500-2570

1710-1755

880-915

1749.9-1784.9

830-840

BW[MHz] Uplink [MHz]

869-894

1805-1880

1930-1990

2110-2170

2620-2690

2110-2155

925-960

1844.9-1879.9

875-885

Downlink [MHz]

10 2x60 1710-1770 2110-2170

11 2x25 1427.9-1452.9 1475.9-1500.9

1800

2600

900

US AWS

UMTS core

US PCS

US 850

Japan 800

Japan 1700

Japan 1500

Extended AWS

Europe Japan Americas

788-798 758-768

777-787 746-756

Japan 800

US700

2x10

2x1013

12 2x18 698-716 728-746

14 US700

US700

815 – 830 860 – 875

704 – 716 734 – 746

2x15

2x1217

18

US700

Band

UHF (TV)832 – 862 791 – 821

830 – 845 875 – 890

2x30

2x1519

20

Japan 800

1626.5 – 1660.5 1525 – 15592x3424

1447.9 – 1462.9 1495.9 – 1510.92x1521

LTE Frequency Variants - TDD




LTE Frequency Variants TDD

33

34

35

36

37

39

40

38

1x20

1x60

1x15

1x20

1x40

1x60

1x100

1x50

1910 - 1930

1850 - 1910

2010 - 2015

1900 - 1920

1880 - 1920

1930 - 1990

2300 - 2400

2570 - 2620

BW[MHz] Frequency[MHz]

UMTS TDD 1

UMTS TDD 2

US PCS

US PCS

US PCS

Euro midle gap 2600

China TDD

China TDD

Band

Module Contents




Module Contents

• OFDM Basics




• OFDM Weaknesses





• VoIP in LTE

RRM building blocks & functions




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 anadequate QoS (if applicable)

•RRM located in eNodeB

•MIMO Ctrl., LA & schedulers act on TTI basis.

LTE RRM: Scheduling (1/5)




LTE RRM: Scheduling (1/5)

• Motivation

– Bad channel condition avoidance

OFDMA

The part of total available

channel experiencing badchannel condition (fading)

can be avoided during

allocation procedure.

CDMA

Single Carrier transmission

does not allow to allocateonly particular frequency

parts. Every fading gap

effects the data.

Scheduler (UL/DL) (2/5)




Scheduler (UL/DL) (2/5)

• 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 retransmission

2. Random access procedure

3. Signaling radio bearer with or without data radio bearer

4. Scheduling request

5. Conversational voice data

6. Data radio bearer

• Downlink:

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

based on CQI with resources assigned in a fair manner

Downlink Scheduler (3/5)




( )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 CandidateSet 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 scheduling for 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 scheduling of UEs according to simple criteria

- > Determination of Candidate Set 2

Start

End

Frequency domain scheduling of UEs / bearers

- > PRB / RBG allocation to UEs / bearers

Uplink Scheduler (4/5)




p ( )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), 15 UEs

(15MHz) and 16 UEs (20MHz)

Frequency Domain:

• Uses a random function to assure equal distribution of PRBs over the available frequencyrange (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

RL30Uplink Scheduler (5/5)




• Flexi eNodeB takes into account the noise and interference measurements together withthe UE Tx power density (= UE TX power per PRB) when allocating PRBs in thefrequency domain

• Cell edge users are assigned to frequency sub-bands with low measured inter-cellinterference

• Up to 10% gain for cell edge users in low and medium loaded networks

• Easier to implement than channel aware scheduling (no sounding reference signal used)

Improvement in UL coverage by optimizing the cell edge performance

eNode Bmeasuredinterference

subband with lowinterference

subband with highinterference

subband with mediuminterference

PRBs


p ( )IAS: Interference Aware Scheduler UL

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




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



Link Adaptation / AMC for PUSCH (3/6)




p ( )

Functionality

• UL LA is active by default but can be deactivated by O&M parameters. If not active,the ini t ial 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 measurementsfrom 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 BLERsituations, 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)

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




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

p p ( )

MCS: Modulation & Coding Scheme

TBS: Transport Block Size

ATB: Automatic Transmission Bandwidth

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


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

P e r i o d i c C Q I ( P U C C H )

Ap e r i o d i c C Q I s ( P U S C H )

UL grant + CQI indicator


Benefits

• Not so many periodic CQIs on PUCCH

needed

• Allow frequent submission of more detailed

reports (e.g. MIMO, frequency selective

parts)

LTE RRM: Power Control (1/5)




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 doesn’t 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


Power Control (2/5) RL30




Downlink Power Boosting for Control Channels

• Offsets determine power shifts for subcarriers which carry PCFICH/PHICHor cell-specific Reference Signal

Benefits:

• Better PCFICH detection avoids throughputdegradation due to lost subframes

• Higher reliability of PHICH avoidsunnecessary retransmissions causingcapacity degradation and additional UEpower consumption

• Better channel estimation avoids throughputdegradation and improves HO performance

Cons:

• Small degradation on PDSCH subcarriers:Subcarrier power boosting only allowed ifthe excess power is withdrawn from theremaining subcarriers


Example of Reference Signals

power boosting



Power Control (4/5)




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 α

• α: Path loss compensation factor. Three values:

– α= 0, no compensation of path loss

– α= 1, full compensation of path loss (conventional compensation)

– α ≠ { 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 dBmi f i PL j j P i M P i P TF PUSCH PUSCH CMAX PUSCH



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&RL30: up to 840 active users in 20MHz• Handover RAC cases have higher priority than normal access to the cell

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




Transmit diversity for 2 antennas

Benefit: Diversity gain, enhanced cell coverage

• Each Tx antenna transmits the same stream of data with Receiver getsreplicas 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

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




S1

S2

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

Precoding

Map ontoResource

Elements

Map onto

Resource

Elements

OFDMA

OFDMA

Modulation

Modulation

Code word1

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

Precoding (3/5)




• Precoding generates the signals for each antenna port

• Precoding is done multiplying the signal with a precoding matrix selected from apredefined 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 SpatialMultiplexing & precoding

Pre-coding codebook for 2 Tx antenna case





LTE RRM: Connection Mobility ControlHandover Types




Handover Types

• Intra-RAT handover

– Intra eNodeB and Inter eNodeB handover

– Above handovers can also be Inter-frequency handovers (RL20) i.e. to support different

frequency bands and deployments within one frequency band but with different center

frequencies

– Data forwarding over X2 for inter eNodeB HO

– HO via S1 interface (RL20): HO in case of no X2 interface configured between serving

eNB and target eNB

• Inter-RAT handover

– LTE to WCDMA: RL30

– WCDMA to LTE: RL40

– LTE to CDMA2000: RL40 (CDMA2000 to LTE not assigned)

– LTE GSM and GSM LTE: not assigned

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-GW

P-GW


A reliable and lossless mobility

Intra LTE Handover via S1

RL20




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


• Admission Control gives priority to HO

related access over other scenarios• Blacklists

Inter Frequency Handover

RL20




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 deploymentin different frequency bands as wellas for LTE deployments within onefrequency band but with differentcenter frequencies

• Blacklists


Inter RAT Handover to WCDMARL30




Inter RAT Handover to WCDMA

• Coverage based inter-RAT PS handover

• Only for multimode devices supportingLTE and WCDMA

• Event triggered handover based on DLmeasurement RSRP (reference signalreceived power)

• Operator configurable RSRP threshold

• Network evaluated HO decision

• Target cells are operator configurable

• An ANR functionality may be appliedoptionally


• Blacklisting

• eNB initiates handover via EPC



Module Contents




• OFDM Basics




• OFDM Weaknesses

• SC-FDMA

• LTE Air Interface Physical Layer




• VoIP in LTE

VoIP in LTE RL20




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

Single Radio Voice Call Continuity (SR-VCC) In RL40 Plan




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



Documents

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