A New Approach for Inter-cell Interference Randomization based on Cell/Sector-specific Interleaver Pattern

Document Number: IEEE S802.16m-07_218,

Date Submitted:2007-11-13

Source:Yunzhou Li, Xibin Xu, Xin Su, Xiaofeng Zhong, Shidong ZhouE-mail:{liyunzhou, xuxb, suxin, zhongxf, zhousd}@tsinghua.edu.cnTsinghua Univ.

Re:TGm Call for comments on SDD, IEEE 802.16m-07/040

Abstract:This document proposes a new approach to randomize inter-cell interference based on cell/sector-specific interleaver pattern.

Purpose:This contribution proposes a new approach to randomize inter-cell interference based on cell/sector-specific interleaver pattern. Meanwhile, some simulation results to verify the advantages of the new approach are presented in this contribution, too.

Notice:This document does not represent the agreed views of the IEEE 802.16 Working Group or any of its subgroups. It represents only the views of the participants listed in the “Source(s)” field above. It is offered as a basis for discussion. It is not binding on the contributor(s), who reserve(s) the right to add, amend or withdraw material contained herein.

Release:The contributor grants a free, irrevocable license to the IEEE to incorporate material contained in this contribution, and any modifications thereof, in the creation of an IEEE Standards publication; to copyright in the IEEE’s name any IEEE Standards publication even though it may include portions of this contribution; and at the IEEE’s sole discretion to permit others to reproduce in whole or in part the resulting IEEE Standards publication. The contributor also acknowledges and accepts that

this contribution may be made public by IEEE 802.16.

Patent Policy:The contributor is familiar with the IEEE-SA Patent Policy and Procedures:

<http://standards.ieee.org/guides/bylaws/sect6-7.html#6> and <http://standards.ieee.org/guides/opman/sect6.html#6.3>.Further information is located at <http://standards.ieee.org/board/pat/pat-material.html> and <http://standards.ieee.org/board/pat >.

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Outline

• The traditional approaches to randomize the inter-cell interference

• The proposed approach to ICI

• What is the benefit from cell-specific interleaving?

• The performance of IDMA and principle

• Conclusion & Proposal to 802.16m SDD

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The traditional approaches to inter-cell interference

• The randomization of ICI is necessary

• The traditional approaches to ICI include:

Cell-specific scrambling (3GPP downlink)

Frequency Hopping

etc.

• Channel coding process

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The proposed approach to ICI

•The cell-specific interleaving Coded bit-level interleaving

Don’t need channel interleaver

Mapping To

OFDMASubchannels

Data to transmit in PHY

burst

Randomizer

FECCell/sector-

specificBit-interleaver

Repetition

Modulation

•Generation and allocation of cell-specific interleaver patternsA pseudo-random method is proposed in C80216m-07_218r1.doc to generate the cell-specific interleaver pattens

An interleaver patten is completely determined by its generation seed and the length of the interleaver.

The seeds can be reused between “far-spaced” cells in a manner similar to that of frequency reuse in a cellular system. A detailed method is given in C80216m-07_218r1.doc

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What is the benefit from cell-specific interleaving?

• cell-specific scrambling and cell-specific interleaving (IDMA) basically have the same performance for the receiver without iterative detection.

• cell-specific interleaving obviously outperforms cell-specific scrambling in BER performance when iterative multi-user detection is used in receiver.

• The benefit from cell-specific interleaving is very important for broadcasting, for which other ICI mitigating techniques, such as beamforming or ICI coordinating can’t be implemented.

• Moreover, saving energy by reducing RF operating

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The performance of IDMA and principle

• Simulation conditions:

Rayleigh channel,

Three Users (K=3)

QPSK,

convolutional code with constraint length=5

Iteration times= 3

0 2 4 6 8 10 1210

-6

10-5

10-4

10-3

10-2

10-1

100

SNR (dB)

BE

R

R=1/4, K=1R=1/2, K=1R=1/4, K=3R=1/2, K=3

• Conlusion:

In conclusion, the BER performance of multi-user system based on IDMA is approaching that of single user system

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The performance of IDMA and principle

•Assumption:

channel coefficient

BPSK for two users

System Model

1,0,1 khk

Best case: 1,1 10 bb

1100 shshrsimplifytosetherenoise 0,:

Modulation symbol for b1

Modulation symbol for b2

Signal overlapping

User 1 User 21100 shshr

Easily to detect for b0 and b1!

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The performance of IDMA and principle

Modulation symbol for b1

Modulation symbol for b2

Signal overlapping

User 1 User 21100 shshr

difficultly to detect for b0 and b1!

0,1 10 bbworst case:

worst case:

But, if the prior information about b0 and/or b1 is derived from FEC decoder , it is easily to further increase the certainty about b0 and b1

0,1 10 bb

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The performance of IDMA and principle

•Based on the results presented by the published papers about IDMA and iterative multi-user detection, we can draw the following conclusions:User-specific interleaving is more helpful than user-specific scrambling to refine the certainty of coded bits of all users.

Rayleigh channel is more favorable to reduce the iterative times of detection for the IDMA-OFDM system, due to the inconsistent fluctuations of the channels of different users

0 10 20 30 40 50 60 700.4

0.6

0.8

1

1.2

1.4

1.6

1.8

subcarrier index

ampl

itude

channel of user0

channel of user1

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Conclusion and Proposal to 802.16m SDD

[ The following text proposal is suggested by this contribution:

cell/sector-specific interleaving shall be considered in SDD as an approach to randomize and mitigate the inter-cell interference

]