LTE Air Interface

LTE RPESS LTE Air Interface

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

• • • • • • • • • • • • 3

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

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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 4

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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 5

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Fourier Transform amplitude

Time Domain

fs 

Ts

1 Ts

Inverse Fourier Transform

time

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 multipath propagation environments as it simplifies handling of inter-symbol interference.

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spectral power density

The rectangular Pulse Frequency Domain

fs

frequency f/fs

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.

Multiple Access Methods TDMA • Time Division

User 2

User 1

User 3

User ..

OFDMA

FDMA

CDMA

• Frequency Division

• Code Division

• Frequency Division • Orthogonal subcarriers

f

f

t

t

f

f

t

f

f

t

f

OFDM is the state-of-the-art and most efficient and robust air interface 7

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f

OFDM Basics • Transmits hundreds or even thousands of separately modulated radio

signals using orthogonal subcarriers spread across a wideband channel

Total transmission bandwidth 15 kHz in LTE: fixed

Orthogonality: The peak ( centre frequency) of one subcarrier … …intercepts the ‘nulls’ of the neighbouring subcarriers

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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

bandwidth

frequency 9

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OFDM versus coventional FDM • OFDM allows a tight packing of small carrier - called the subcarriers - into a given

Power Density

Power Density

frequency band.

Frequency (f/fs)

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Saved Bandwidth

Frequency (f/fs)

Fast Fourier Transform (FFT) • • • •

FFT is a method for calculating the Discrete Fourier Transform (DFT) and it is and fundamental element in OFDM IFFT = Inverse FFT. FFT/IFFT allows to move between time & frequency domain representations. FFT & IFFT are blocks included in an OFDMA system: – FFT in the Receiver – IFFT in the Transmitter

T

FFT 1/T

time

T

FFT time

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frequency

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0

frequency

LTE Air Interface Specifications The LTE radio interface is standardised in the 36-series of 3GPP Release 8. The detailed physical layer structure is described in 5 physical layer specifications. LTE is standardised in the 36-series of 3GPP Release 8: TS 36.1xx Equipment requirements (terminals, eNodeB) TS 36.2xx Layer 1 (physical layer) specifications TS 36.3xx Layer 2 and 3 specifications TS 36.4xx Network signalling specifications TS 36.5xx User equipment conformance testing

OFDMA SCFDMA Subcarriers eNodeB

Frequency

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Physical layer specifications: TS 36.201 Physical layer; General description TS 36.211 Physical channels and modulation TS 36.212 Multiplexing and channel coding TS 36.213 Physical layer procedures TS 36.214 Physical layer; Measurements

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 13

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Multi-Path Propagation & Inter-Symbol Interference (ISI)

+ Tt

BTS

Time 0

Ts Time 0 Tt

Ts+Tt

ISI

Inter Symbol Interference 14

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Multi-Path Propagation & the Guard Period 2 1 3

Time Domain

Tg

TSYMBOL

1

Guard Period (GP) time

TSYMBOL 2

Guard Period (GP) TSYMBOL

time

Guard Period (GP)

3

time 15

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Propagation delay exceeding the Guard Period 2 1 3

Time Domain T SYMBO

4

Tg

L

1

Delay spread > Tg  ISI

time 2 time 3 time

Tg: Guard period duration ISI: Inter-Symbol Interference

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The Cyclic Prefix •

OFDM symbol

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 the following symbol to locate the start of the symbol and begin then with decoding.

OFDM symbol

OFDM symbol

OFDM symbol

Cyclic prefix

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Part of symbol used for FFT processing in the receiver

The OFDM Signal

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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 19

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OFDM Plain OFDM

•

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.

1 UE 1

20

... subcarrier

•

time

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2 UE 2

3 UE 3

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common info (may be addressed via Higher Layers)

... ... ...

OFDMA®

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

• •

time ... 2 ... 2 ...

1

1

2

1

1

1

2

1 . . . 1

1 . . . 1

1 . . . 1

2

such block is simply a set of some subcarriers over some time.

1

1

1

3

3

3

3

3 ...

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

3

3

3

3

3 ...

3

3

3

3

3 ...

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.

subcarrier

1

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

• •

Orthogonal Frequency Multiple Access OFDMA®

2 ... . . . . . . ... ...

Resource Block (RB) 1 UE 1 21

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3 UE 3

common info (may be addressed via Higher Layers)

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 22

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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).

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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.

I3 I1 I4 I0

f0 24

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f1

f2

f3

f4

ICI = Inter-Carrier Interference

∆P

Doppler in OFDM and Loss of Orthogonality • Doppler effect (shift): Change in frequency of a wave due to the relative motion of source and receiver. • Symbols are distorted in the time domain ▪ Frequency shifts make symbol detection inaccurate ▪ MCS schemes with high number of bits per subcarrier are not suitable for MSs moving at high speed ▪ More difficult to support high data rates ▪ Doppler only impacts SINRs at the higher range i.e. > 20dB ICI in the absence of orthogonality

It reduces orthogonality • The frequency domain subcarriers are shifted causing inter-carrier interference (ICI) • Frequency shift in the subcarriers limits the SNR values • The nulls of interferers and peaks of signals will not coincide

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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 26

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Subcarrier types Data subcarriers: used for data transmission – Reference Signals: ▪ used for channel quality and signal strength estimates. ▪ They don’t occupy a whole subcarrier but they are periodically embedded in the stream of data being carried on a data subcarrier.

Null subcarriers (no transmission/power): ▪ DC (centre) subcarrier: 0 Hz offset from the channel’s centre frequency ▪ Guard subcarriers: Separate top and bottom subcarriers from any adjacent

channel interference and also limit the amount of interference caused by the channel. Guard band size has an impact on the data throughput of the channel.

Guard (no power)

Guard (no power) DC (no power) data

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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

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OFDMA Parameters in LTE • • • •

Frame duration: Subframe duration (TTI): Subcarrier spacing: Sampling Rate:

1.4MHz

10ms created from slots and subframes. 1 ms ( composed of 2 x 0.5 slots) Fixed to 15kHz ( 7.5 kHz defined for MBMS) Varies with the bandwidth but always factor or multiple of 3.84 to ensure compatibility with WCDMA by using common clocking

3 MHz

Frame Duration

1010ms ms

Subcarrier Spacing

15 kHz

Sampling Rate ( MHz) Data Subcarriers

CP length © Nokia Siemens Networks

10 MHz

15 MHz

20 MHz

1.92

3.84

7.68

15.36

23.04

30.72

72

180

300

600

900

1200

Normal CP=7, extended CP=6

Symbols/slot

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5 MHz

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

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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 30

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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

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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

requirements (power amplifier)

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OFDMA

• Reduced PAPR means lower RF hardware

SC-FDMA

multipath 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 mathematical description of the time domain representation of an SC-FDMA symbol.

SC-FDMA and OFDMA Comparison (1/2) • OFDMA transmits data in parallel across multiple subcarriers • SC-FDMA transmits data in series employing multiple subcarriers • In the example: – OFDMA: 6 modulation symbols ( 01,10,11,01,10 & 10) are transmitted per OFDMA symbol, one on each subcarrier

– SC-FDMA: 6 modulation symbols are transmitted per SC-FDMA symbol using all subcarriers per modulation symbol. The duration of each modulation symbol is 1/6th of the modulation symbol in OFDMA

OFDMA 33

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SC-FDMA

SC-FDMA and OFDMA Comparison (2/2)

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Uplink Air Interface Technology SC-FDMA • User multiplexing in frequency domain (in OFDMA the user multiplexing is in

sub-carrier domain) • One user always continuous in frequency • Smallest UL bandwidth, 12 subcarriers: 180 kHz (same for OFDMA in DL) • Largest UL bandwidth: 20 MHz (same for OFDMA in DL) – Terminals are required to be able to receive & transmit up to 20 MHz, depending on the frequency band though

Receiver

f

User 1

f f

User 2 35

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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 36

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LTE Physical Layer - Introduction • 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 FDD

..

Frequency band 1..

..

Frequency band 2..

TDD

Single frequency band

..

Downlink 37

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..

Uplink

LTE Physical Layer Structure – Frame Structure (FDD) • 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

0.5 ms slot

- 1 slot = 7 (normal CP) or 6 OFDM symbols (extended CP)

sy0 sy1 sy2 sy3 sy4 sy5 sy6

10 ms frame s0

s1

s2 s3

s4

s5

s6 s7

…..

s18 s19

s: slot

0.5 ms slot

SF0 38

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SF: SubFrame

SF1

SF3

SF2

1 ms sub-frame

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…..

SF9

Sy: symbol

LTE Physical Layer Structure – Frame Structure (TDD) 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

radio frame 10 ms SF #0

...

SF #2

SF #4

subframe

SF #0

DwPTS GP UpPTS

UL/DL carrier

DwPTS GP UpPTS

f SF #2

...

SF #4

subframe half frame

Downlink Subframe Uplink Subframe

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DwPTS: Downlink Pilot time Slot UpPSS: Uplink Pilot Time Slot GP: Guard Period to separate between UL/DL

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time

Subframe structure & CP length • 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 = 5.21μs;

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

Short cyclic prefix:

 ‘sampling time’ of the overall channel  basic Time Unit  = 32.5 nsec

5.21 s Long cyclic prefix: = Data

Ts =

16.67 s

Subcarrier spacing X max FFT size

Copy

= Cyclic prefix 40

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1 sec

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Resource Block and 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 Subcarrier 1

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

180 KHz

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

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).

Subcarrier 12 0 1 2 3 4 5 6 0 1 2 3 4 5 6 1 slot

1 slot

1 ms subframe

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Resource Element

Physical Resource Blocks

12 subcarriers ..

Resource block

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

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•

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

1 ms subframe or TTI

0.5 ms slot

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

.. Frequency

Time

•

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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)

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Channel bandwidth (MHz)

1.4

3

5

10

15

20

Number of subcarriers

72

180

300

600

900

1200

Number of resource blocks

6

15

25

50

75

100

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DL Physical Resource Block • 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

12 subcarriers ..

..

• Reference signals are modulated to identify the cell to which they belong. 1 ms subframe • or TTI

0.5 ms slot

DL reference signal

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

Time

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

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

• 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

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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)

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UL Physical Resource Block: DRS & SRS • The Demodulation Reference 12 subcarriers ..

..

Note: when the subframe contains the PUCCH, the Demodulation Reference Signal is embedded in a different way

Frequency 1 ms subframe or TTI

0.5 ms slot Time Sounding Reference Signal on last OFDM symbol of 1 subframe; Periodic or aperiodic transmission

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Demodulation Reference Signal in subframes that carry PUSCH

RA41202EN10GLA0 PUCCH: Physical UL Control Channel

Signal is transmitted in the third SC-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 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 SCFDMA symbol of subframes that carry neither PUSCH nor PUCCH data.

Modulation Schemes • 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

Physical channel

Modulation

PDSCH

QPSK, 16QAM, 64QAM

PMCH

QPSK, 16QAM, 64QAM

6 bits/symbol

PBCH

QPSK

64QAM

PDCCH, PCFICH

QPSK

b0 b1b2b3 b4 b5 Im

PHICH

BPSK

PUSCH

QPSK, 16QAM, 64QAM

PUCCH

BPSK and/or QPSK

64QAM: QPSK:

16QAM:

2 bits/symbol

4 bits/symbol

QPSK

16QAM

b0 b1

b0 b1b2b3

01

00

Im

Im

11

10Re

1111

Re 0000

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Re

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 49

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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 %

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* with 1/2/4 Antenna Ports RA41202EN10GLA0

PRB: Physical Resource Block

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/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 10ms Radio frame 2

3

4

5

7

8

1ms Subframe

1

2

3 2

4 3

5 4

PSS & SSS frame + slot structure in time domain (FDD case) 51

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6 5

10

SSS PSS

0.5ms = 1 slot 1

9

7

Normal CP

6

Extended CP checking for SSS at 2 possible positions

 CP length

PDCCH, PCFICH & PHICH overhead (1/2) The combination of PDCCH, PCFICH & PHICH occupies the first 1, 2 or 3 symbols per TTI* One subframe (1ms)

Resource Elements reserved for 12 subcarriers

Frequency

Reference Symbols (2 antenna port case)

Control Channel

Data Region

Region (1-3 OFDM symbols*) 52

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

Time

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%

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

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%

72 subcarriers

one radio frame = 10 ms

Repetition Pattern of PBCH = 40 ms PBCH 54

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RA41202EN10GLA0

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

UL Demodulation Reference Signal Overhead (1/2) Demodulation Reference Signal (DRS) • The DRS is sent on the 4th OFDM symbol of each RB occupied by the PUSCH.

PUCCH

PUSCH

PUCCH

55

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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

56

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 %

© Nokia Siemens Networks

* for normal CP RA41202EN10GLA0

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

57

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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 %

RA41202EN10GLA0

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%

58

12 subcarriers

Total UL Bandwith

Frequency

PUCCH

© Nokia Siemens Networks

PUSCH

PUCCH 1 subframe = 1ms RA41202EN10GLA0

Time

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

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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 60

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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. – – – –

61

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

© Nokia Siemens Networks

CSI: Channel State Information (received power per PRB) RA41202EN10GLA0 TA: Timing Advance

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

RSRQ ( Reference Signal Received Quality) • Defined as the ratio N×RSRP/(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

Note: 3GPP has open issues on these e.g. measurement bandwidth on RSSI

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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 setting

Received Interference Power: • Received interference power, including thermal noise, within one PRBs bandwidth Thermal 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

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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 64

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LTE Frequency Variants in 3GPP – FDD E-UTRA band

Total [MHz]

Uplink [MHz]

Downlink [MHz]

Europe

Japan

Americas

1

2x60

1920-1980

2110-2170

UMTS core

2

2x60

1850-1910

1930-1990

US PCS

3

2x75

1710-1785

1805-1880

1800

4

2x45

1710-1755

2110-2155

US AWS

5

2x25

824-849

869-894

US 850

6

2x10

830-840

875-885

7

2x70

2500-2570

2620-2690

Japan 800 2600

8

2x35

880-915

925-960

9

2x35

1749.9-1784.9

1844.9-1879.9

10

2x60

1710-1770

2110-2170

11

2x25

1427.9-1452.9

1475.9-1500.9

12

2x18

698-716

728-746

US700

13

2x10

777-787

746-756

US700

14

2x10

788-798

758-768

US700

900 Japan 1700 Extended AWS Japan 1500

Band 15 – 16: reserved

65

17

2x12

704 – 716

734 – 746

18

2x15

815 – 830

860 – 875

19

2x15

830 – 845

875 – 890

20

2x30

832 – 862

791 – 821

© Nokia Siemens Networks

* „digitalRA41202EN10GLA0 dividend“

US700 Japan 800 Japan 800 UHF (TV)*

LTE Frequency Variants - TDD

66

E-UTRA band

Total [MHz]

Frequency [MHz]

33

1x20

1900 - 1920

UMTS TDD 1

34

1x15

2010 - 2015

UMTS TDD 2

35

1x60

1850 - 1910

US PCS

36

1x60

1930 - 1990

US PCS

37

1x20

1910 - 1930

US PCS

38

1x50

2570 - 2620

39

1x40

1880 - 1920

China TDD

40

1x100

2300 - 2400

China TDD

© Nokia Siemens Networks

RA41202EN10GLA0

Euro midle gap 2600

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 67

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RRM building blocks & functions Overview

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 eNodeB

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LTE RRM: Scheduling (1/4)

• Motivation – Bad channel condition avoidance

69

CDMA

OFDMA

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

The part of total available channel experiencing bad channel condition (fading) can be avoided during allocation procedure.

© Nokia Siemens Networks

RA41202EN10GLA0

Scheduler (UL/DL) (2/4) • • • • • •

Cell-based scheduling (separate scheduler per cell) Scheduling on TTI basis (1ms) Resource assignment in time and frequency domain (UL/DL) Proportional Fair (PF) resource assignment among UEs Priority for SRB (Signalling Radio Bearers) over DRB (Data Radio Bearers) Priority handling (UL/DL) for

• Random Access procedure • Signalling • HARQ re-transmission • Uplink: • Scheduler controls UEs & assigns appropriate grants per TTI • Channel unaware UL scheduling based on random frequency allocation (Channel-aware UL scheduling foreseen for RL30 & it will be SW licensed)

• Downlink: • Channel aware DL scheduling - Frequency Domain Packet Scheduling (FDPS) based on CQI with resources assigned in a fair manner

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RL09

RL09

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 Start

– Time Domain Scheduling: Parameter MAX_#_UE_DL decides how many UEs are

Pre-Scheduling: Select UEs eligible for scheduling

allocated in the TTI being scheduled

-> Determination of Candidate Set 1

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

Time domain scheduling of UEs according to simple criteria -> Determination of Candidate Set 2 Frequency domain scheduling of UEs/bearers -> PRB/RBG allocation to UEs/bearers End

71

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Feature ID(s): LTE45

RL09

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)

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

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Feature ID(s): LTE45

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

RL09

Optimizing air interface efficiency • 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 bits per byte -> 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

Feature ID(s): LTE31 73

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RA41202EN10GLA0

RL09

Link Adaptation / AMC for PDSCH (2/6) Procedure: START

• 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 reporting from UE , shall be determined for the PRBs assigned to UE as indicated by the DL scheduler

Retrieve Default MCS

no

Dynamic AMC active?

HARQ retransmission?

no Use Default MCS

Determine avaraged CQI value for allocated PRBs

Determine MCS

END

74

© Nokia Siemens Networks

yes

Use the same MCS as for initial transmission

Link Adaptation / AMC for PUSCH (3/6)

RL09

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)

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

Uplink

Downlink

– fast

– slow periodical

▪ 1 TTI

▪ ~30ms

– channel aware

– channel partly aware

▪ CQI based

▪ average BLER based

– MCS selection

– MCS adaptation

– output

– output

– up to 64QAM support

– up to 16 QAM support

▪ +/- 1 MCS correction

▪ 1 out of 0-28

▪ MCS ▪ ATB

▪ MCS ▪ TBS

76

© Nokia Siemens Networks

MCS: Modulation & Coding Scheme TBS: Transport Block Size RA41202EN10GLA0 ATB: Automatic Transmission Bandwidth

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

RL09

Optimize the DL performance 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

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RA41202EN10GLA0

Feature ID(s): LTE30

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

•

78

Allow frequent submission of more detailed reports (e.g. MIMO, frequency selective parts)

© Nokia Siemens Networks

RA41202EN10GLA0

Feature ID(s): LTE767

RL10

RL09

LTE RRM: Power Control (1/4) Improve cell edge behaviour, reduce inter-cell interference & power consumption

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

Feature ID(s): LTE27 79

© Nokia Siemens Networks

RA41202EN10GLA0

RL09

Power Control (2/4) Improve cell edge behaviour, reduce inter-cell interference and power consumption

Uplink: • UL PC is a mix of Open Loop Power Control & Closed Loop Power Control: PPUSCH (i )  min{PCMAX ,10 log10 ( M PUSCH (i ))  P0 _ PUSCH ( j )   ( j )  PL  TF (i )  f (i )}[dBm]

• 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

•

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 80

© Nokia Siemens Networks

2) SINR measurment 3) Setting new power offset

4) TX power level adjustment with the new offset 1) Initial TX power level

Feature ID(s): LTE27<E28

RL09

Power Control (3/4) Uplink (cont.): • UL PC is a mix of Open Loop Power Control & Closed Loop Power Control: PPUSCH (i )  min{PCMAX ,10 log10 ( M PUSCH (i ))  P0 _ PUSCH ( j )   ( j )  PL  TF (i )  f (i )}[dBm]

• 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<E28 81

© Nokia Siemens Networks

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 α UL SINR

Conventional Power Control: α=1

UE Tx Power

If Path Loss increases by 10 dB the UE Tx power increases by 10 dB 82

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RA41202EN10GLA0

UL SINR

UE Tx Power

Fractional Power Control: α ≠ { 0 ,1} If Path Loss increases by 10 dB the UE Tx power increases by < 10 dB

LTE RRM: Radio Admission Control (RAC)

RL09

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 • RL09: All RRC connection setup request are admitted by default to avoid RAC complexity

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LTE RRM: MIMO / Antenna Control (1/5)

RL09

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.

• • • •

84

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

© Nokia Siemens Networks

Spatial multiplexing (MIMO) for 2 antennas (2/5) Two code words (S1+S2) are transmitted in parallel to 1 UE  double peak rate

Benefit: Doubles peak rate compared to 1Tx antenna

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

• Can be open loop or closed loop depending

S2

if the UE provides feedback

• Spatial multiplexing with 2 code words • Supported physical channel: PDSCH S1 Layer Mapping

•

85

2 code words transferred when channel conditions are good

© Nokia Siemens Networks

Code word 1

Modulation

L1

Precoding × Scale

Code word 2

RA41202EN10GLA0

L2

×

OFDMA



Map onto Resource Elements

OFDMA

W1 ×

Modulation



Map onto Resource Elements

× W2

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 86

© Nokia Siemens Networks

RA41202EN10GLA0

DL adaptive open loop 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 • Open loop spatial multiplexing with 2

1 code word A is transmitted via 2 antennas to 1 UE; improves the LiBu A

code words

• Supported physical channel: PDSCH • Dynamic switch considers the UE specific

A B

link quality

• 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 Note: DL adaptive closed loop MIMO has been moved to RL20 Feature ID(s): LTE70

87

© Nokia Siemens Networks

LiBu: Link RA41202EN10GLA0 Budget

RL09

MIMO, DL channels & RRM Functionality (5/5) RRM MIMO Mode Control Functionality • Refers to switch between:  Tx Diversity (single stream)  MIMO Spatial Multiplexing (double stream)  1x1 SISO / 1x2 SIMO • Provided by eNB only for DL direction

In UL, Flexi eNodeB has 2Rx Div. :

• Maximum Ratio Combining Benefit: increase coverage by increasing the received signal strength and quality

Available MIMO options vs. channel type • Options for Transmit Diversity (2 Tx): – Control Channels – PDSCH • Options for Dual Stream (SM): – Only DL PDSCH • MIMO is SW feature Channel can be configured to use MIMO mode Channel cannot be configured to use MIMO mode

88

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LTE RRM: Connection Mobility Control (1/3) Handover Types • Intra-RAT handover – Intra eNodeB – Inter eNodeB  Data forwarding over X2

• High performance for 15…120 km/h • Optimized performance for 0…15 km/h  HO in case of no X2 interface configured between Serving eNB & Target eNB: HO via S1 interface – RL20

• Inter-RAT Handover – PS domain only – RL20: LTE  WCDMA – RL30: LTE  CDMA2000 – RL40: WCDMA  LTE – Not assigned: LTE  GSM; GSM  LTE

89

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RL09

Intra frequency handover via X2 (2/3) A reliable and lossless mobility • 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

X2

S-GW

MME

P-GW S1

Feature ID(s): LTE53 90

© Nokia Siemens Networks

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RL20

Inter RAT Handover to WCDMA (3/3) • Only for multimode devices supporting • • • • • • •

91

LTE & WCDMA Event triggered Handover based on DL measurement Reference Signal Received Power (RSRP) Operator configurable RSRP threshold Inter-RAT HO measurements only activated if there is not Intra-frequency neighbour cell Network evaluated HO decision eNB broadcasts IRAT cell selection information best target WCDMA cell may be selected when above the threshold eNB initiates Handover via EPC

© Nokia Siemens Networks

RA41202EN10GLA0

WCDMA

LTE

Iub RNC

S1 SGSN

S-GW P-GW

MME

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 92

© Nokia Siemens Networks

RA41202EN10GLA0

RL20

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 CS fallback Handover where LTE terminal will be moved to 2G/3G to make CS call The ultimate LTE voice solution will be VoIP + IMS (not RL10) CS Fallback handover

E-UTRAN

Paging in LTE

MME MSC-S

2G/3G RAN 93

© Nokia Siemens Networks

RA41202EN10GLA0

CS call setup in 2G/3G

MGW

RL30

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

Single Radio Voice Call Continuity (SR-VCC)

94

LTE VoIP

LTE VoIP

3G CS voice

3G CS voice

© Nokia Siemens Networks

RA41202EN10GLA0

3G CS voice

3G CS voice

LTE Voice Evolution

Data only LTE

LTE HSPA & I-HSPA 2G/3G

LTE HSPA & I-HSPA 2G/3G

LTE HSPA & I-HSPA

MSS

CS fallback handover

© Nokia Siemens Networks

CS/PS MGW

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MSS

VoIP SR-VCC

RA41202EN10GLA0

Evolution to IMS VoIP solution

Full IMS centric multimedia service architecture

Introduce NVS VoIP solution

Increased radio efficiency for voice service

MGW

95

IMS multimedia

Broadband LTE introduction

CS/PS

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Fast track LTE VoIP

PS

NVS

NVS

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IMS

VoIP SR-VCC