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Asynchronous physical-layer network coding: Symbol Misalignment Estimation and Its Effect on Decoding

IEEE TRANSACTIONS ON WIRELESS COMMUNICATIONS 2017年第10期16卷 6881-6894页

作者： Shao, Yulin Liew, Soung Chang Lu, Lu Chinese Univ Hong Kong Dept Informat Engn Hong Kong Hong Kong Peoples R China Chinese Acad Sci Technol & Engn Ctr Space Utilizat Beijing Peoples R China Chinese Univ Hong Kong Inst Network Coding Hong Kong Hong Kong Peoples R China

In asynchronous physical-layer network coding (APNC) systems, the symbols from multiple transmitters to a common receiver may be misaligned. Knowledge of the amount of symbol misalignment, hence its estimation, is important to PNC decoding. This paper addresses the problems of symbol-misalignment estimation and optimal PNC decoding given the misalignment estimate, assuming the APNC system uses the root-raised-cosine pulse to carry signals (RRC-APNC). Our contributions are as follows. First, we put forth an optimal symbol-misalignment estimator that makes use of double baud-rate samples. Second, we devise optimal RRC-APNC decoders in the presence of non-exact symbol-misalignment estimates. In particular, we show how to whiten the colored noise in the double baud-rate samples to simplify the design of optimal decoders. Third, we investigate the decoding performance of various estimation-and-decoding schemes for RRC-APNC. Extensive simulations show that: 1) our double baud-rate estimator yields substantially more accurate symbol-misalignment estimates than the baud-rate estimator does;the mean square error gains are up to 8 dB and 2) an overall estimation-and-decoding scheme in which both estimation and decoding are based on double baud-rate samples yields much better performance than other schemes. Compared with a scheme in which both estimation and decoding are based on baud-rate samples, the double baud-rate sampling scheme yields 4.5 dB gains on symbol error rate performance in an additive white Gaussian noise channel, and 2 dB gains on packet error rate performance in a Rayleigh fading channel.

关键词： physical-layer network coding asynchronous PNC pulse shaping symbol misalignment estimation sum-product algorithm noise whitening

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Carrier sensing range analysis in a general IEEE 802.11 network with physical-layer network coding

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WIRELESS COMMUNICATIONS & MOBILE COMPUTING 2015年第18期15卷 2206-2218页

作者： Lin, Shijun Shi, Jianghong Xiamen Univ Dept Commun Engn Xiamen Peoples R China

In this paper, we investigate the carrier sensing range (CSR) of a general 802.11 network with physical-layer network coding (PNC). We aim to derive a sufficient CSR that can prevent the hidden-node collisions in a general 802.11 PNC network. The analysis includes two steps. First, we analyze the six link-to-link interference cases in an 802.11 PNC network to show that the mutual interference will be most severe when each node in the network initiates a two-hop end node link. Second, we consider the worst interference case that all concurrently transmitting links in the network are two-hop end node links and placed in the densest manner and develop a closed-form expression of a sufficient CSR that prevents the hidden-node collisions in a PNC network. From the analysis results, we find that to prevent the hidden-node collisions, the CSR in PNC network should be bigger than the one in traditional non-network-coding network. Furthermore, we carry out extensive simulations to find out the throughput gain of PNC scheme in a general wireless network when considering the impact of CSR. Simulation results show that compared with the non-network-coding scheme, PNC scheme has throughput gain when a large proportion (i.e., 90%) of links in the network are two-hop links and the link density has little effect on the throughput gain of PNC scheme. Copyright (C) 2014 John Wiley & Sons, Ltd.

关键词： physical-layer network coding carrier sensing range analysis throughput gain

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DNF-SC-PNC: a new physical-layer network coding scheme for two-way relay channels with asymmetric data length

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WIRELESS networkS 2019年第7期25卷 3727-3734页

作者： Yang, Hongjuan Li, Bo Liu, Gongliang Liu, Xin Peng, Xiyuan Harbin Inst Technol Weihai Sch Informat & Elect Engn Weihai Peoples R China Harbin Inst Technol Auto Test & Control Inst Harbin Peoples R China Dalian Univ Technol Sch Informat & Commun Engn Dalian Peoples R China

To improve the bit error rate (BER) performance of physical-layer network coding (PNC) in data length asymmetric two-way relay channels (TWRC), a new PNC scheme named combined denoise-and-forward and superposition coded physical-layer network coding (DNF-SC-PNC) is proposed, and the decoding algorithm of the scheme is improved. In the new scheme, the mixed information is denoised and superposed at the relay node, which will be broadcasted to the destination nodes. The destination nodes can use successive interference cancellation (SIC) or likelihood rate (LLR) algorithm for decoding. Theoretical analysis and simulation results show that DNF-SC-PNC can provide better BER performance and better throughput rate performance when the data length is asymmetric. Furthermore, we also proved that LLR algorithm can provide better performance than SIC algorithm in data length asymmetric TWRC.

关键词： physical-layer network coding Asymmetric data length SIC algorithm LLR algorithm

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Combined orthogonal physical-layer network coding over fading two-way relay channels

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INTERNATIONAL JOURNAL OF COMMUNICATION SYSTEMS 2014年第12期27卷 4265-4279页

作者： Li, Bo Chong, Peter Han Joo Wang, Gang Yang, Hongjuan Guan, Yongliang Harbin Inst Technol Commun Res Ctr Harbin 150080 Peoples R China Nanyang Technol Univ Sch Elect & Elect Engn Singapore 639798 Singapore

This paper proposes a new physical-layer network coding (PNC) scheme, named combined orthogonal PNC (COPNC), for fading two-way relay channels. The scheme is based on orthogonal PNC (OPNC). In the scheme, the two source nodes employ orthogonal carriers, and the relay node makes an orthogonal combining of the two information bits rather than exclusive or (XOR), which is employed in most PNC schemes. The paper also analyzes the bit error rate (BER) performance of PNC, OPNC, and COPNC for Rayleigh fading model. Simulation results for Rayleigh and Nakagami-m fading channels show that COPNC can provide outstanding BER performance compared with PNC and OPNC, especially when the uplink channel conditions are asymmetric. The results in Nakagami-m channels also imply that COPNC will provide higher BER gain with more severe fading depth. Potential works about COPNC are also presented in this paper. Copyright (c) 2013 John Wiley & Sons, Ltd.

关键词： two-way relay channels physical-layer network coding combined physical-layer network coding orthogonal combining

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Joint Channel Estimation and Channel Decoding in physical-layer network coding Systems: An EM-BP Factor Graph Framework

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IEEE TRANSACTIONS ON WIRELESS COMMUNICATIONS 2014年第4期13卷 2229-2245页

作者： Wang, Taotao Liew, Soung Chang Chinese Univ Hong Kong Dept Informat Engn Hong Kong Hong Kong Peoples R China

This paper addresses the problem of joint channel estimation and channel decoding in physical-layer network coding (PNC) systems. In PNC, multiple users transmit to a relay simultaneously. PNC channel decoding is different from conventional multi-user channel decoding: specifically, the PNC relay aims to decode a network-coded message rather than the individual messages of the users. Although prior work has shown that PNC can significantly improve the throughput of a relay network, the improvement is predicated on the availability of accurate channel estimates. Channel estimation in PNC, however, can be particularly challenging because of 1) the overlapped signals of multiple users;2) the correlations among data symbols induced by channel coding;and 3) time-varying channels. We combine the expectation-maximization (EM) algorithm and belief propagation (BP) algorithm on a unified factor-graph framework to tackle these challenges. In this framework, channel estimation is performed by an EM subgraph, and channel decoding is performed by a BP subgraph that models a virtual encoder matched to the target of PNC channel decoding. Iterative message passing between these two subgraphs allow the optimal solutions for both to be approached progressively. We present extensive simulation results demonstrating the superiority of our PNC receivers over other PNC receivers.

关键词： physical-layer network coding expectation-maximization belief propagation factor graph message passing

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Unsaturated Throughput Analysis of physical-layer network coding Based on IEEE 802.11 Distributed Coordination Function

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IEEE TRANSACTIONS ON WIRELESS COMMUNICATIONS 2013年第11期12卷 5544-5556页

作者： Lin, Shijun Fu, Liqun Xiamen Univ Dept Commun Engn Xiamen Fujian Peoples R China Chinese Univ Hong Kong Inst Network Coding Shatin Hong Kong Peoples R China

In this paper, we investigate the throughput performance of physical-layer network coding (PNC) under the IEEE 802.11 distributed coordination function (DCF). We consider the wireless network that two client groups communicate with each other across one relay node, and focus on the unsaturated network case. The difficulty in modeling the relay systems under the IEEE 802.11 DCF is that the minimum contention window sizes of the client nodes and the relay node may be different, which makes the traditional throughput analysis methods for the non-relay wireless networks inapplicable. Fortunately, we find that the relay system can be decomposed into four parts and respectively modeled. Analytical results show that the throughput gain of PNC scheme is heavily affected by the probability that a transmitted network-coding (NC) packet contains the information of two packets. The implication is that the throughput benefit of PNC is more significant for bidirectional isochronous traffic with rate requirements. We further derive an approximate closed-form solution of the optimal transmission probability of client nodes that maximizes the PNC network throughput. We validate our analytical model through extensive simulations and discuss the relationship between the PNC network throughput and other system parameters, such as the minimum contention window sizes of both the client nodes and the relay node.

关键词： physical-layer network coding IEEE 802.11 DCF unsaturated throughput analysis

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Asynchronous physical-layer network coding

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IEEE TRANSACTIONS ON WIRELESS COMMUNICATIONS 2012年第2期11卷 819-831页

作者： Lu, Lu Liew, Soung Chang Chinese Univ Hong Kong Dept Informat Engn Shatin Hong Kong Peoples R China

A key issue in physical-layer network coding (PNC) is how to deal with the asynchrony between signals transmitted by multiple transmitters. That is, symbols transmitted by different transmitters could arrive at the receiver with symbol misalignment as well as relative carrier-phase offset. A second important issue is how to integrate channel coding with PNC to achieve reliable communication. This paper investigates these two issues and makes the following contributions: 1) We propose and investigate a general framework for decoding at the receiver based on belief propagation (BP). The framework can effectively deal with symbol and phase asynchronies while incorporating channel coding at the same time. 2) For unchannel-coded PNC, we show that for BPSK and QPSK modulations, our BP method can significantly reduce the asynchrony penalties compared with prior methods. 3) For QPSK unchannel-coded PNC, with a half symbol offset between the transmitters, our BP method can drastically reduce the performance penalty due to phase asynchrony, from more than 6 dB to no more than 1 dB. 4) For channel-coded PNC, with our BP method, both symbol and phase asynchronies actually improve the system performance compared with the perfectly synchronous case. Furthermore, the performance spread due to different combinations of symbol and phase offsets between the transmitters in channel-coded PNC is only around 1 dB. The implication of 3) is that if we could control the symbol arrival times at the receiver, it would be advantageous to deliberately introduce a half symbol offset in unchannel-coded PNC. The implication of 4) is that when channel coding is used, symbol and phase asynchronies are not major performance concerns in PNC.

关键词： physical-layer network coding network coding synchronization

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Modulated Retro-Reflector-Based physical-layer network coding for Space Optical Communications

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IEEE ACCESS 2021年 9卷 44868-44880页

作者： Jia Yanmei Lyu Congmin Shen Pengfei Lu Lu Univ Chinese Acad Sci Sch Aeronaut & Astronaut Beijing 100049 Peoples R China Chinese Acad Sci Technol & Engn Ctr Space Utilizat Key Lab Space Utilizat Beijing 100094 Peoples R China

We propose a Modulated Retro-Reflector (MRR) based physical-layer network coding (PNC) framework for space two-way relay (TWR) optical communications. MRR PNC simplifies the end node's design by replacing pointing, acquisition and tracking mechanisms which require large size, weight, and power (SWaP) consumption. Each end node modulates its data on top of the interrogating beam from the relay node so that the two end nodes' frequencies are synchronized and there is no carrier frequency offset between the two end nodes and the relay. However, the transmitted signal based on the interrogating beam and twice the channel fading leads to noise aggregation. We analyze the impact of this noise aggregation by deriving the bit error rate (BER) for MRR PNC and performing simulations in Gamma-Gamma fading channels. The simulation results show that MRR PNC has a 3 dB optical signal noise ratio penalty compared with MRR "point-to-point" systems. The overall system throughput of MRR PNC is 99% higher than the traditional non-network-coded scheme in the >= 6 dB (for BPSK, >= 9 dB for QPSK) signal noise ratio regime. We propose using low-density parity-check (LDPC) codes to mitigate the problem of the degradation of the BER caused by the noise aggregation in MRR PNC. Our simulation results show that a rate 1/2 LDPC code can achieve 2 dB coding gain on BER 10(-3). We show that the asynchrony penalty is 3 dB on BER 10(-3) compared with a synchronous system. The implication is that when channel coding is used, the system can still work. Our findings show that MRR PNC can double the system throughput while keeping low values of SWaP, is feasible for space TWR optical communications.

关键词： Relays Laser beams Throughput Bit error rate Modulation network coding High-speed optical techniques physical-layer network coding two-way relay channel modulated retro-reflector MRR PNC MRR ANC throughput

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Implementation of Short-Packet physical-layer network coding

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IEEE TRANSACTIONS ON MOBILE COMPUTING 2023年第1期22卷 284-298页

作者： Ullah, Shakeel Salamat Liew, Soung Chang Liva, Gianluigi Wang, Taotao CU Coding Hong Kong Peoples R China Chinese Univ Hong Kong Dept Informat Engn Hong Kong Peoples R China German Aerosp Ctr DLR Inst Commun & Networking D-82234 Wessling Germany Shenzhen Univ Coll Elect & Informat Engn Shenzhen 518060 Peoples R China

This paper presents the implementation and experimental evaluation of a short-packet physical-layer network coding (PNC) system. Implementation of short-packet PNC systems is challenging. First, short packets may have only a few pilot symbols for synchronization and channel estimation purposes. Increasing the number of pilots increases the overhead;decreasing the number of pilots, on the other hand, degrades the packet error rate performance. Second, many short-packet systems are meant for applications with very stringent delay requirements. Employing advanced but complex PNC channel decoding may result in unacceptable delay due to the processing delay. This work presents a low-complexity and low-overhead physical-layer design of OFDM-based short-packet PNC systems, implemented over the software-defined radio platform. Our design makes use of only a small number of pilots (without separate OFDM preamble symbols) to address issues such as slot synchronization, packet detection, carrier frequency offsets, and mismatched channel state information. Our design employs reduced-complexity XOR channel decoding based code-aided parameter estimation (that includes synchronization and channel estimation) to compensate for the limitations imposed by having a small number of pilots. This is the first demonstration that provides a practical framework for applying PNC to short-packet communications.

关键词： physical-layer network coding short-packet transmissions software-defined radios code-aided parameter estimation XOR channel decoding

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Identification of superposed modulations for two-way relaying MIMO systems with physical-layer network coding

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IET COMMUNICATIONS 2017年第2期11卷 225-231页

作者： Ben Chikha, Wassim Chaoui, Slim Attia, Rabah Carthage Univ Tunisia Polytech Sch SERCOM Lab La Marsa 2078 Tunisia

The automatic modulation identification of a detected signal represents an essential task for an intelligent receiver and plays an important role in demodulating the intercepted signals for several communication systems. In this study, the authors propose an efficient algorithm of superposed modulations identification dedicated for two-way relaying multiple-input multiple-output systems with physical-layer network coding (PLNC). The aim of this work is to identify a pair of sources modulations from the superposed constellation, when PLNC is applied. For this purpose, the authors use the higher order statistics-based features in conjunction with genetic algorithm and information theory as a features selection method and the random forests as a classifier. Simulations are provided to assess the accuracy of the proposed algorithm through the average probability of correct identification for different modulation scheme pairs. It is shown that the algorithm achieves high-modulation identification in acceptable signal-to-noise ratio level at different relay position.

关键词： feature selection genetic algorithms higher order statistics radio receivers signal detection relay networks (telecommunication) network coding MIMO communication two-way relaying MIMO system superposed modulation identification physical-layer network coding automatic modulation identification signal detection intelligent receiver two-way relaying multiple-input multiple-output system PLNC source modulation superposed constellation relay position signal-to-noise ratio level random forest feature selection method information theory genetic algorithm higher order statistics-based feature

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