lte air interface dimensioning -...

1 © Nokia Siemens Networks 2008 Customer Confidential

LTE Air Interface Dimensioning

Stockholm, 26.01.2009

Piotr GodziewskiNetwork Engineering


Meeting Agenda

• Link budget target

• Transmitting end modeling

• Receiver end modeling

• Resource allocation modeling

• Required Signal to Interference Margin (SINR)

• System overhead


Link budget target

• Estimating maximum allowable path loss for single radio link

PathLossmax_DL

PathLossmax_UL

R

Antenna gain, feeder/cable losses, noise figures, etc.

Transmitter/receiver end modeling

Clutter type, propagation model, channel model, etc.

Propagation environment

User data rate, system overhead, cell load, coverage reliability, BLER etc.

Requirements


Transmitting end modeling

• EIRP – Effective Isotropic Radiated Power

MIMObodyTMAinsfeederantennaantennaTx GLLLGPEIRP +−−−+= _

TX power per antenna connector (DL 8/20/40/60 W license based control)(UL 23±2 dBm)

Antenna gain

Feeder loss (0 dB in UL with Tower Mounted Amplifier)(0 dB in DL with feederless solution,RRH or System Module close to the antenna)

TMA insertion loss (DL only) (~0.5 dB with Tower Mounted Amplifier)

Body loss (UE only) (0 dB for PC cards/laptops/etc.)

Total power increase due to single stream MIMO (TX diversity technique)(3 dB in DL for 2TX diversity, if not already considered in SINR)


Receiving end modeling

• OFDM receiver sensitivity

SINRNFRBkHzHzdBmSRx ++⋅⋅⋅+−= )#1215log(10/174

Thermal Noise Density

Number of Physical Resource Blocks (DL: all available in the channel)(UL: allocated for transmission)

Noise figure (HW specific)

SINR (Signal to Interference Ratio)

DL: total TX power is shared between all subcarriersUL: total TX power is focused on allocated PRBsSensitivity must be modified in this way if we assume total TX power for the total channel in EIRP formula

OFDMA/SC-FDMA

3GPP allows for 15 kHz and 7.5 kHz

Subcarrier bandwidth


Resource allocation modeling

• Basic rules (3GPP 36.213 Dec2008)– Separate MCS set for DL and UL– TBS mapping table– TBS mapping rules for dual-stream

▪ 1 ≤ #RB ≤ 55 take TBS for one-layer and multiply by 2

▪ 56 ≤ #RB ≤ 110 use specific mapping table

…

One-layer mapping



• Transport Block– Number of user data bits transmitted to single

user during one TTI (1 ms)– Transport Block is defined for two

consecutive Physical Resource Blocks in time domain

EffectiveUserThroughput = 384 / (100% - 10%) = 427 kbps

MCS = 10-16QAM TBS index = 9

…search for TBS ≥ EffectiveUserThroughput

[#RB=3 and TBS=456] is the smallest possible configuration

456 bits / TTI = 456 bits / 1 ms = 456 kbps ≥ 427 kbps

…done!



• Effective coding rate– Denotes coding rate applied on PDSCH/PUSCH with respect to the allocated

resource blocks, TBS and overheads

Number of allocated resource blocks

Number of resource elements per RB (84 for normal CP)(72 for extended CP)

Total number of resource elements within 1 ms (TTI)

Percentage of system overhead

Transport Block Size (depends on MCS/#RB combination)

orderMoverheadRERBTBSCR

⋅−⋅⋅⋅=

)1(2##

Modulation order (QPSK=2, 16QAM=4, 64QAM=6)



• Example coding rates– DL MCS set– TBS for #RB=50

▪ 10 MHz bandwidth,all resource blocks allocated

– 23% system overhead▪ PRACH in every subframe▪ 3 OFDM symbols for signaling▪ Reference Signal at one antenna port

• Impact on– SINR interpolation


Required Signal to Interference Ratio (SINR)

• Target SINR– Obtained from link level simulations– OFDM specific channel models– Considered antenna schemes:

▪ Downlink• 1Tx-2Rx• 2Tx-2Rx TX div.• 2Tx-2Rx Spatial Multiplexing

▪ Uplink• 1Tx-2Rx• 1Tx-4Rx

– Possible outcomes form▪ SINR value refers to the given

number of allocated resource blocks and MCS (modulation and coding scheme)

- Suitable for large channel bandwidths- Correlation between UE and eNB antennas in case of multi antenna systems- Doppler spread considered (Doppler frequency)- Large number of taps

EPA / ETU / EVA

light

UEcarrierDoppler v

vff ⋅=

EPA 5Hz:Doppler frequency=5Hz for 1800MHz and 3km/h



• Samples for DL 2Tx-2Rx

SINR within the one and the same MCS are worse for low number of resource blocks.Turbo coding efficiency decreases rapidly for small amount of input data (related to correlation increase between input and output bits of turbo coder)

Turbo coding degradation

Since there is practically no turbo coding degradation for #RB>25 it is possible to assume “flat” distribution of SINR for #RB>25

#RB>25



• Example– MCS-10 and #RB=3

SINR values for specific coding rates(known from simulation assumptions)

…6.57 dB does not refer to effective codingrate from link budget calculations

Additional interpolation needed(coding rate offset consideration)

General procedure for SINR estimation


System overhead

• Downlink– Synchronization signals – occupies two last OFDM symbols in timeslot

0 and 10 in every radio frame (72 subcarriers per symbol)

Radio frame(20 timeslots)

Timeslot 0 and 10

72 subcarriers in OFDM symbol dedicated for synchronization signal


System overhead

• Downlink– Reference signal – configuration depends on the chosen antenna

scheme

Res

ourc

e bl

ock

= 12

sub

carr

iers

1TX antenna


System overhead


scheme

2TX antenna


System overhead


scheme

Res

ourc

e bl

ock

= 12

sub

carr

iers

4TX antenna


System overhead

• Downlink– PBCH (Physical Broadcast Channel) – 72 subcarriers in four OFDM

symbols per radio frame– PDCCH (Physical Downlink Control Channel) – up to four OFDM

symbols per subframe

4 symbols only in case of 1.4 MHz bandwidth (10 RBs)

Assume 3 symbols per subframe for standard macro/micro cell planning


System overhead

• Uplink– Reference signal for PUSCH – 4th OFDM symbol in every resource

block dedicated for PUSCH transmission (3rd symbol in case of extended CP)

Timeslot

REs occupied by PUSCH reference signal


System overhead

• Uplink– PRACH (Physical Random Access Channel) – six resource blocks– PUCCH (Physical Uplink Control Channel) – single PUCCH occupies

two resource blocks in two consecutive timeslots (one RB per onetimeslot)

Subframe

Resource block

...

Sys

tem

cha

nnel

Note:From the link budget point of view, reference signal for PUCCH does not need to be considered separately since it is included in the resources occupied by PUCCH


System overhead

• Example figures– DL 2Tx-2Rx– UL 1Tx-2Rx– PRACH in every subframe– 3 OFDM symbols for PDCCH– CQI mode 2-0


Thank you for attention

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