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Discussion on some details for the simulation of IMT-A

China Communications Standards Association

CJK-B3G #20 in Zhangjiajie China, 8-10 April 2009

Qin Fei

qinfei@datangmobile.cn

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Content

Introduction

Polarized antenna modeling

Inter-cell interference modeling

Smart antenna pattern

Preliminary Geometry Distribution

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Introduction

IMT.EVAL give a good guideline on the modeling and evaluation of IMT-Advanced.

This document focus on some important details which not defined in IMT.EVAL, but will very important in system level simulation.

Purpose of this document is to raising those issues for discussion and to exchange views, trying to get common understanding if possible.

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Polarized antenna modeling

IMT-A system will support more antenna elements number, up to 8.

Dual-polarized antenna is a good solution to minimal the antenna size and make it easy to implementation in engineering.

Polarized antenna will be an important antenna configuration in the evaluation of IMT-A.

Polarized antenna channel impulse response formula are not clearly defined in IMT.EVAL.

Polarization power loss should be correctly considered in the simulation.

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Polarized antenna modeling - Channel impulse response

The SCM channel model for the polarized antenna are defined in the IMT.EVAL. The formula of the channel impulse response is given as following:

Where, the Frx,u,V , Frx,u,H , Ftx,s,V , Ftx,s,H are the channel response vector projected on the V and H direction including the antenna gain at the MS and BS sides. See the following figure1.

The formulas for these values Frx,u,V , Frx,u,H , Ftx,s,V , Ftx,s,H are not clearly defined.

tjjdjd

F

F

jj

jj

F

FPt

mnmnumns

mnHstx

mnVstx

hhmn

hvmn

vhmn

vvmn

T

mnHurx

mnVurxM

mnnsu

,,1

0,1

0

,,,

,,,

,,1

,1

,

,,,

,,,

1,,

2expsin2expsin2exp

expexp

expexp

H

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In Fig. 1, the transmitted signal in each antenna is divided into the v-component and h-component. At the receiving antenna, the signals include the v-component and h-component, and the cross-talk between each component.

Fig.1 Polarization impulse response

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vFUE

hFUEhvFk ,

UE1

vhFk ,UE

1

vFBS

hFBS

Polarized antenna modeling - Channel impulse response

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The projections of the 4 components are the function of tilt angle of MS antenna and BS antenna, and also the AOA and AOD. It can be given as

where

mnHstx

mnVstx

hhmn

hvmn

vhmn

vvmn

T

mnHurx

mnVurx

F

F

jj

jj

F

F

,,,

,,,

,,1

,1

,

,,,

,,,

,

,

expexp

expexp

,

,

T

mnmnBS

mnBST

mnHurx

mnVurx

CosSinG

CosG

F

F

)()()(

)()(

),(

),(

,,

,

,,,

,,,

)()()(

)()(

),(

),(

,,

,

,,,

,,,

mnmnMS

mnMST

mnHstx

mnVstx

CosSinG

CosG

F

F

Polarized antenna modeling - Channel impulse response

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Polarized antenna modeling – Polrization power loss

The introduction of the polarized antenna channel model will decrease the channel response power that can be called polarization power loss. According to the channel model for polarized antenna system, the polarization power loss for the nth path can be given as:

For example, the BS antenna is ±45°cross-polarized, the UE antenna is vertical, the AoD and AoA is 0°, and the polarization power loss of the nth path is:

For all N paths, the mean polarization power loss is:

M

k

kM

m mnmnmn

mn

n

1 ,

2,

222,

2221

,222122

)(cos)(cos)(sin)(sin)(cos)(cos)(sin

)(cos)(sin)(cos)(cos)(cos

Lp

111

5.05.0M

00.5

00.5

Lp

kk

M

m

n

N

nnn LpP

1

Lp

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In system simulations, usually the channel from a MS to a far away BS with weak interference will not be modeled.

In this case, the weak interference is considered as white noise with equal power considering the large scale fading.

So, when calculating the power of the weak interference, the polarization power loss must be added to the large scale fading and path loss.

The polarization power loss should also be considered when calculating the Geometry in the simulation.

If the polarization power loss is ignored, the performance of polarized antenna system in the simulation will be lower than the correct value.

The performance loss is decided by the number of neighbors which are considered as white noise.

Polarized antenna modeling – Polrization power loss

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Inter-cell interference modeling

Method 1: Establish SCM channel model for the UE to all 57 neighbor sectors to calculate the SINR. Simulation efficiency is very low! CPU and Memory exhausting!

Method 2: Establish UE to the strongest (ordered by large scale fading) N cell’s SCM channel response, N=3 to 6. The other cells interference are modeling with Rayl fading plus pathloss and shadow fading.

Method 3: Establish UE to the strongest (ordered by large scale fading) N cell’s SCM channel response, N=3 to 6. The other cells interference are considered as AWGN only take into the large scale fading( pathloss and shadow fading) when calculating the power.

Method4:Establish UE to the anchor cell’s SCM channel response. All the neighbour cells interference are considered as AWGN or Raly.

Simulation efficiency: Method1<Method2<Method3<Method4 Accuracy:Method1>Method2>Method3>Method4 Selection by the simulation requirement, but Method2 is preferred.

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Smart Antenna Pattern

Cause the different antenna structure, the unit gain pattern is different from the traditional 70 degree 3 sector pattern.

The unit gain pattern of smart antenna is wider than 70 degree; usually, two patterns are suggested.

1)the idea model of the unlimited baffle-board model, about 120 degree, Fig. 2.

2)the measurement pattern, about 90 degree, Fig.3. The sector gain pattern is composed by proper sector beamforming weight for

different unit gain pattern。 For example, the sector beamforming weight for 4+4 polarized antenna array

is

w = [-0.2421 + 0.3241i, -0.4938 + 0.8696i, -0.4938 + 0.8696i, 0.2603 - 0.5622i] for unit pattern 1), Fig.2;

w = [0.35, 1, 1, -0.6] for unit pattern 2). Fig.3.

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The 120 degree Unit gain pattern, the composed sector gain pattern(4 antenna with 0.5 lamda spacing) and the traditional 70 degree pattern are showed as the following figure 2.

Smart Antenna Pattern

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The 90 degree Unit gain pattern, the composed sector gain pattern(4 antenna with 0.5 lamda spacing) and the traditional 70 degree pattern are showed as the following figure 3.

Smart Antenna Pattern

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Preliminary Geometry Distribution

ITU Urban Macro VS 3GPP Case1(Both ISD = 500)

-5 0 5 10 15 20 250

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

Geomety(dB)

CDF

— Case1, Am = 25— Uma, SF Cr— Uma, No SF Cr

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