doc.: IEEE 802.11-13/0111r1

Zhanji Wu, et. Al.

January 2013

Submission

A Physical-layer Network Coding Relay scheme for IEEE 802.11

Date: 2013-01-11

Name Affiliations Address Phone Email Zhanji Wu Beijing University of

Post and Telecommunication (BUPT)

Xitucheng Road 10, Haidian district, Beijing, China

+86 10 62281058

wuzhanji@bupt.edu.cn

Gao Xiang Beijing University of Post and Telecommunication (BUPT)

Xitucheng Road 10, Haidian district, Beijing, China

+86 13811150845

gaoxiangbupt@gmail.com

Yang Fan Beijing University of Post and Telecommunication (BUPT)

Xitucheng Road 10, Haidian district, Beijing, China

+86 15901337957

bupt07yangfan@gmail.com

Wu Bin Institute of Microelectronics of the Chinese Academy of Sciences (IMECAS)

3 Beitucheng West Road, Chaoyang District, Beijing, PR China

wubin@ime.ac.cn

Yunzhou Li Tsinghua University Tsinghua Rd. Beijng, China

+86 10 62773363

liyunzhou@tsinghua.edu.cn

Zhendong Luo China Academy of Telecommunication Research (CATR)

No.52 Hua Yuan Bei Rd., Beijing, China

+86 10 62300171

luozhendong@catr.cn

Authors:

Slide1

doc.: IEEE 802.11-13/0111r1

Zhanji Wu, et. Al.

January 2013

Submission Slide2

Abstract

• Based on joint network coding and channel coding, a physical network coding (PNC) transmission scheme for a two-way relay system is proposed. By using the broadcast nature of the wireless medium and the linear property of LDPC codes, only two time slots are required for data transmission. In the first time slot, the two users send their own data to the relay at the same time. In the second time slot, the relay performs joint network decoding and channel decoding, and then forwards the encoded bits to the two users. Simulations results show that the proposed scheme outperforms the conventional decode-and-forward (DF) Relay in term of system throughput, which is increased up to 100%.

doc.: IEEE 802.11-13/0111r1

Zhanji Wu, et. Al.

January 2013

Submission Slide3

Background

• Device-to-device (D2D) communication is a more reasonable scheme for the traffic between a communicating STAs pair, which are closely located with limited interference to the WLAN network. D2D links have several advantages, such as low transport delay and high data rate.

• One drawback of direct D2D communication is the limited range, the relay is able to extend the communication range and improve the performance of wireless systems.

• Physical network coding (PNC) is a joint network and channel coding technique that can be used at the relay station to help cooperating users to improve the throughput.

doc.: IEEE 802.11-13/0111r1

Zhanji Wu, et. Al.

January 2013

Submission

• A Physical-layer Network Coding (PNC) scheme is proposed to further boost the throughput and capacity of the system.

Two way relay channel （ TWRC）

Slide 4

A R B

Time Slot 1

Time Slot 2

Time Slot 3

A R B

Time Slot 1

Time Slot 2

A R B

Time Slot 1

Time Slot 2

Time Slot 3

Time Slot 4

SA SB

SR SR

SA SB

SR SR SR SR

SA SB

Store-and-forward model Model of network coding based on bits XOR(3 time slots)

Physical-layer network coding model(2 time slots)

doc.: IEEE 802.11-13/0111r1

Zhanji Wu, et. Al.

January 2013

Submission

Diagram of 3-Phase PNC

Slide 5

Encoding Modulation

source bits sequence of user 1

Demodulation and Decoding

simple ARQ

Channel

No

Encoding Modulation

source bits sequence of user 2

Yes

Modulation

ChannelDemodulationDecoding1 2c cCalculate information bits of user 2

Simple ARQ

DemodulationDecoding1 2c cCalculate information bits of user 1

Simple ARQ

Broadcast phase

Multiple access phase

Relay

1 1 1y x n 1x

2xChannel Demodulation and Decoding

2 2 2y x n

1c

2c

simple ARQ

No

Yes

1 2c c

STA S1

STA S2

STA S1

STA S2

User Station

doc.: IEEE 802.11-13/0111r1

Zhanji Wu, et. Al.

January 2013

Submission

• Process flow of 3-phase conventional networking coding scheme : The information bits of STAs S1 and S2 are encoded by LDPC encoder

to produce codewords c1 and c2, respectively. And then, modulate to produce complex-valued symbols x1 and x2.

Symbols x1 and x2 are sent to relay node in two different time slots, respectively.

Relay demodulates and decodes the received symbols y1 and y2 to get the estimates c1 and c2, respectively. If the estimates do not satisfy the parity check matrix of LDPC, adopt ARQ protocol and chase combining.

If satisfied, Relay performs the network coding and modulates to broadcast for the two STAs in one time slot.

Each STA demodulates and decodes the received signal.

Process flow

Slide 6

1 2z c c

doc.: IEEE 802.11-13/0111r1

Zhanji Wu, et. Al.

January 2013

Submission

Diagram of 2-Phase PNC

Slide 7

Encoding Modulation

source bits sequence of user 1

Demodulation

1 2c c

simple ARQ

Channel

No

Encoding Modulation

source bits sequence of user 2

Yes

Modulation

ChannelDemodulationDecoding1 2c cCalculate information bits of user 2

Simple ARQ

DemodulationDecoding1 2c cCalculate information bits of user 1

Simple ARQ

Broadcast phase

Multiple access phase

Relay

1 2x x n

1x

2x

STA S1

STA S2

STA S1

STA S2 No

NoYes

Yes

Decoding

User Station

doc.: IEEE 802.11-13/0111r1

Zhanji Wu, et. Al.

January 2013

Submission

System Model of PNC

Slide 8

NOTESMultiple access (MA) phase: Two STAs send signals simultaneously in one timeslot to the relay.Broadcast phase: the relay decodes the superimposed signals and maps them to a network-coded (XOR) packet to broadcast to the two STAs.

Step1: Mutiple Access Phase

1C 2C

S2S1

R

1 2RC C C

S2S1

R

Step2: Broadcast Phase

1 2source node: S and S

relay node: R

doc.: IEEE 802.11-13/0111r1

Zhanji Wu, et. Al.

January 2013

Submission

• Process flow of 2-phase PNC scheme : The information bits of STAs S1 and S2 are encoded by the same LDPC

encoder to produce codewords c1 and c2, respectively. And then, modulate to produce complex-valued symbols x1 and x2.

Symbols x1 and x2 are sent to relay node at the same time in one time slot.

Relay demodulates the superimposed received signal to produce the LLRs of as LDPC decoder input, and then decodes by LDPC to get the z estimates . If the z estimates do not satisfy the parity check matrix of LDPC, adopt ARQ and chase combining. .

If satisfied, Relay modulates z and broadcasts to two STAs in one timeslot.

Each STA demodulates and decodes the received signal.

Process flow

Slide 9

1 2z c c

doc.: IEEE 802.11-13/0111r1

Zhanji Wu, et. Al.

January 2013

Submission

• In the MA phase, the STAs S1 and S2 send symbols x1 and x2 to relay node simultaneously. The AWGN channel and BPSK modulation is considered. The received superimposed signal of relay is , where n is the AWGN random complex variable with mean zero and variance .

• Define ,

• Assume L denotes the LLR of ,

Detection and decoding of relay for 2-phase PNC scheme

Slide 10

1 2y x x n 2

1 2x x

1 0

0

1 2c c 1 2x x 1 2,x x

2

1 2 1 21, 1 1, 1x x or x x

1 2 1 21, 1 1, 1x x or x x

1 2c c

2 2

( 0 | )log

( 2 | )

( | 0) ( 0)log

( | 2) ( 2) ( | 2) ( 2)

4 4log(cosh )

P yL

P y

P y P

P y P P y P

y

doc.: IEEE 802.11-13/0111r1

Zhanji Wu, et. Al.

January 2013

Submission

Simulation Parameters

Slide 11

Parameters ValuesChannel model AWGN

Coding (3,6) LDPC

Code rate ½

Length of codeword 1088

Modulation BPSK

Channel estimation Perfect CSI

doc.: IEEE 802.11-13/0111r1

Zhanji Wu, et. Al.

January 2013

Submission

-5 -4 -3 -2 -1 0 1 2 3 40

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1regular(3,6)LDPC-BPSK R=1/2 K=544bit

SNR (dB)

tp (

pack

et/t

imes

lot)

2-phase scheme

3-phase schemew.o. network coding (DF)

Throughput performance of two STAs

Slide 12

• We use term throughput (tp) to indicate the average number of correct received data packets in one time slot for two STAs.

• The tp performance of the proposed scheme is significantly improved.

• For SNR<-4 dB, the DF scheme is the best; for -4 dB<SNR<-1 dB, 3-phase PNC is the best, for SNR>-1dB, 2-phase PNC is the best, TP is increased up to 100%.where SNR = Es/ σ2.

doc.: IEEE 802.11-13/0111r1

Zhanji Wu, et. Al.

January 2013

Submission

Conclusions

• Network coding can significantly boost the throughput and capacity of the system.

• Compared to the conventional DF relay scheme, the throughput of the 2-phase PNC is increased up to 100%, and the throughput of the 3-phase PNC is increased up to 33%.

• The proposed scheme can be applied to two-way high-throughput scenarios, such as short-range video communication, short-range two-person interactive 3D game and data synchronization for local devices.

Slide 13

doc.: IEEE 802.11-13/0111r1

Zhanji Wu, et. Al.

January 2013

Submission

References

[1] K. Doppler, M. Rinne, C. Wijting, C. B. Ribeiro, and K. Hug, Device-to-device communication as an underlay to LTE-advanced networks. IEEE Communications Magazine. vol. 47, pp. 42-49, 2009.

[2] Xuanmin Lu, Qiaoyun Qiu, Heng Wu. A Joint Design of Network Coding and Channel Coding for Multiple Access Channel. Modern Electronics Technique. Vol.23, No.06, 2010.pp:52-55.

[3] S.Zhang, S.Liew. Channel Coding and Decoding in a Relay System Operated with Physical-Layer Networking Coding. IEEE Journal on Selected Areas in Communications, 2009, pp: 788–796.

[4] C. Hausl and J. Hagenauer, “Iterative network and channel decoding for the two-way relay channel,” in Proc. IEEE International Conference on Communication (ICC 2006), Istanbul, Turkey, Jun. 2006.

Slide 14