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A Unified Discretization Approach to Compute-Forward: From Discrete to Continuous Inputs

IEEE TRANSACTIONS ON INFORMATION THEORY 2023年第1期69卷 1-46页

作者： Pastore, Adriano Lim, Sung Hoon Feng, Chen Nazer, Bobak Gastpar, Michael Ctr Tecnol&x00F2 Telecomunicac Catalunya CTTC CERCA g Castelldefels Spain Hallym Univ Sch Informat Sci Chunchon South Korea Univ British Columbia Sch Engn Kelowna BC Canada Boston Univ Dept Elect & Comp Engn Boston MA USA Ecole Polytech Fed Sch Comp & Commun Sci CH-1015 Lausanne Switzerland

Compute-Forward is a coding technique that enables receiver(s) in a network to directly decode one or more linear combinations of the transmitted codewords. Initial efforts focused on Gaussian channels and derived achievable rate regions via nested lattice codes and single-user (lattice) decoding as well as sequential (lattice) decoding. Recently, these results have been generalized to discrete memoryless channels via nested linear codes and joint typicality coding, culminating in a simultaneous-decoding rate region for recovering one or more linear combinations from K users. Using a discretization approach, this paper translates this result into a simultaneous-decoding rate region for a wide class of continuous memoryless channels, including the important special case of Gaussian channels. Additionally, this paper derives a single, unified expression for both discrete and continuous rate regions via an algebraic generalization of R & eacute;nyi's information dimension.

关键词： Decoding Lattices Receivers Codes Entropy Linear codes Source coding compute-forward physical-layer network coding multiple-access channel information dimension entropy

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network-Coded Multiple Access on Unmanned Aerial Vehicle

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IEEE JOURNAL ON SELECTED AREAS IN COMMUNICATIONS 2018年第9期36卷 2071-2086页

作者： Pan, Haoyuan Liew, Soung Chang Liang, Jiaxin Shao, Yulin Lu, Lu Chinese Univ Hong Kong Dept Informat Engn Hong Kong Hong Kong Peoples R China Chinese Acad Sci Ctr Space Utilizat Key Lab Space Utilizat Technol & Engn Ctr Space Utilizat Beijing 100094 Peoples R China Univ Chinese Acad Sci Beijing 100049 Peoples R China

This paper presents the first network-coded multiple access (NCMA) downlink system on unmanned aerial vehicle (UAV). The use of UAV as a mobile aerial base station has received much attention in the 5G community in the context of highly mobile and flexible-configurable communication systems. As UAVs are limited by their flight time in the air, achieving high spectral and power efficiency while they are inflight is of great importance. Non-orthogonal multiple access (NOMA) is a promising technique to increase the spectral and power efficiency. Conventional NOMA downlink that makes use of superposition coding in combination with successive interference cancellation (SIC) decoding does not work well in scenarios where the channel conditions of different downlink users are not readily available at the transmitter side. This is the case, for example, in the UAV scenario in which the UAV transmitter moves quickly, causing the channel conditions to vary in a very dynamic manner. This paper investigates a new NOMA downlink architecture, referred to as network-coded multiple access. In the absence of channel information, an NCMA transmitter allocates equal power to the superposed signals of different downlink users. A key challenge is how to achieve high NOMA throughput under such equal power allocation. Toward this end, NCMA makes joint use of physical-layer network coding (PNC) and multiuser decoding (MUD) together with a new superposition coding scheme, referred to as NCMA-based superposition coding. In NCMA-based superposition coding, equal powers are allocated to the signals of different users, but a relative phase offset between the signals is introduced to optimize PNC and MUD decodings. To demonstrate the feasibility and advantage of the NCMA downlink, we implemented our designs on a software-defined radio and UAV. Our experimental results show that NCMA is robust against varying channel conditions. Moreover, the throughput of NCMA can outperform the state-of-the-art

关键词： Non-orthogonal multiple access physical-layer network coding network-coded multiple access unmanned aerial vehicle implementation

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network-Coded Multiple Access

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IEEE TRANSACTIONS ON MOBILE COMPUTING 2014年第12期13卷 2853-2869页

作者： Lu, Lu You, Lizhao Liew, Soung Chang Chinese Univ Hong Kong Inst Network Coding Hong Kong Hong Kong Peoples R China Chinese Univ Hong Kong Dept Informat Engn Hong Kong Hong Kong Peoples R China

This paper proposes and experimentally demonstrates a first wireless local area network (WLAN) system that jointly exploits physical-layer network coding (PNC) and multiuser decoding (MUD) to boost system throughput. We refer to this multiple access mode as network-coded multiple access (NCMA). Prior studies on PNC mostly focused on relay networks. NCMA is the first realized multiple access scheme that establishes the usefulness of PNC in a non-relay setting. NCMA allows multiple nodes to transmit simultaneously to the access point (AP) to boost throughput. In the non-relay setting, when two nodes A and B transmit to the AP simultaneously, the AP aims to obtain both packet A and packet B rather than their network-coded packet. An interesting question is whether network coding, specifically PNC which extracts packet A circle plus B, can still be useful in such a setting. We provide an affirmative answer to this question with a novel two-layer decoding approach amenable to real-time implementation. Our USRP prototype indicates that NCMA can boost throughput by 100 percent in the medium-high SNR regime (>= 10 dB). We believe further throughput enhancement is possible by allowing more than two users to transmit together.

关键词： network coding physical-layer network coding multi-user detection multiple access implementation

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On Lattice-Based Broadcasting for Massive-User MIMO: Practical Algorithms and Optimization

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IEEE TRANSACTIONS ON WIRELESS COMMUNICATIONS 2024年第11期23卷 16544-16558页

作者： Qiu, Xinzhe Yang, Tao Thompson, John Beihang Univ Sch Elect & Informat Engn Beijing Peoples R China Shenzhen Inst Beihang Univ Shenzhen 518063 Peoples R China Univ Edinburgh Inst Digital Commun Sch Engn Edinburgh EH9 3JL Scotland

This paper studies a lattice-based broadcasting (LBC) scheme for a single-cell downlink system. The base station (BS) has N antennas and the K user-equipments (UEs) have a single-antenna. The system is referred to as massive-user MIMO (mU-MIMO) when K is very large. At the transmitter side, the BS encodes the messages for the UEs with state-of-the-art channel codes and q-PAM modulation. We suggest a codeword-level precoding, which transforms the K UEs' coded sequences by an invertible integer matrix A(-1) over Z(q), resulting in K codeword-level precoded (CLP) streams. Then, the CLP streams undergo a linear signal-level precoding (SLP) with regularized integer-forcing, and the resultant signals are transmitted via the N antennas of BS. The operations of CLP and SLP are both linear. At the receiver side, each UE attempts to compute an integer-combination (ICB) of the K CLP streams w.r.t. the integer matrix A, which turns out to be its desired message thanks to the CLP. For computing the ICB, we put forth new soft detection algorithms, which efficiently calculate the a posteriori probability of ICB over the lattice. The complexity is shown to be (much) less than O(Kq), which is suited for large values of K. Further, we develop a particle swarm based approach that jointly optimizes A and the power allocation matrix. Numerical results demonstrate dramatically enhanced performance over baseline schemes including regularized zero-forcing and vector perturbation precoding, for both slow and fast fading channels.

关键词： Streams Precoding Lattices Downlink Codes Vectors Broadcasting Multi-user MIMO massive access coded modulation lattice compute-forward physical-layer network coding soft detection channel coding precoding broadcast channel

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network-Coded Multiple Access with High-Order Modulations

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IEEE TRANSACTIONS ON VEHICULAR TECHNOLOGY 2017年第11期66卷 9776-9792页

作者： Pan, Haoyuan Lu, Lu Liew, Soung Chang Chinese Univ Hong Kong Dept Informat Engn Hong Kong Hong Kong Peoples R China Chinese Univ Hong Kong Inst Network Coding Hong Kong Hong Kong Peoples R China

This paper presents the first network-coded multiple access (NCMA) system prototype operated on high-order modulations up to 16-QAM. NCMA jointly exploits physical-layer network coding (PNC) and multiuser decoding (MUD) to boost throughput of multipacket reception systems. Direct generalization of the existing NCMA decoding algorithm, originally designed for BPSK, to high-order modulations, will lead to huge performance degradation. The throughput degradation is caused by the relative phase offset between received signals from different nodes. To circumvent the phase offset problem, this paper investigates an NCMA system with multiple receive antennas at the access point, referred to as MIMO-NCMA. We put forth a low-complexity symbol-level NCMA decoder that, together with MIMO, can substantially alleviate the performance degradation induced by relative phase offset. To demonstrate the feasibility and advantage of MIMO-NCMA for high-order modulations, we implemented our designs on software-defined radio. Our experimental results show that the throughput of QPSK MIMO-NCMA is double that of both BPSK NCMA and QPSK MUD at SNR = 10 dB. For higher signal-to-noise ratios at which 16-QAM can be supported, the throughput of MIMO-NCMA can be as high as 3.5 times that of BPSK NCMA. Overall, this paper provides an implementable framework for high-order modulated NCMA.

关键词： High-order modulation implementation multiple access multi-user detection network-coded multiple access physical-layer network coding

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Optimal DoF Region for the Asymmetric Two-Pair MIMO Two-Way Relay Channel

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IEEE TRANSACTIONS ON SIGNAL PROCESSING 2017年第7期65卷 1700-1711页

作者： Liu, Kangqi Tao, Meixia Yuan, Xiaojun Shanghai Jiao Tong Univ Dept Elect Engn Shanghai 200240 Peoples R China ShanghaiTech Univ Sch Informat Sci & Technol Shanghai 201210 Peoples R China

In this paper, we study the optimal degrees of freedom (DoF) region for the two-pair MIMO two-way relay channel (TWRC) with asymmetric antenna setting, where two pairs of users exchange information with the help of a common relay. Each user i is equipped with M-i antennas, for i = 1, 2, 3, 4, and the relay is equipped with N antennas. First, we prove the converse of the DoF region by using the cut-set theoremand the genie-message approach. Then, we present new transmission schemes to achieve the optimal DoF region at different antenna configurations. Due to the asymmetric data exchange, where the two users in each pair can communicate a different number of data streams, we not only need to form the network-coded symbols but also need to process the additional asymmetric data streams at the relay. This is realized through the joint design of relay compression matrix and source precoding matrices. After obtaining the optimal DoF region, we study the optimal sum DoF by solving a linear programing problem. Our DoF analysis reveals that in the asymmetric antenna setting, some antennas at certain source nodes are redundant and cannot contribute to enlarge the DoF region. It is also found that there is no loss of optimality in terms of the sum DoF by enforcing symmetric data exchange within each user pair.

关键词： Multiple-input multiple-output two-way relay channel interference alignment physical-layer network coding signal alignment degrees of freedom

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OFDM Modulated PNC in V2X Communication: An ICI-Aware Approach Against CFOs and Time-Frequency-Selective Channels

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IEEE ACCESS 2019年 7卷 4880-4897页

作者： Situ, Zhenhui Ho, Ivan Wang-Hei Wang, Taotao Liew, Soung Chang Chau, Sid Chi-Kin Hong Kong Polytech Univ Dept Elect & Informat Engn Hong Kong Peoples R China Hong Kong Polytech Univ Res Inst Sustainable Urban Dev Hong Kong Peoples R China Shenzhen Univ Coll Informat Engn Shenzhen 518060 Peoples R China Chinese Univ Hong Kong Dept Informat Engn Hong Kong Peoples R China Australian Natl Univ Res Sch Comp Sci Canberra ACT 0200 Australia

This paper studies the application of physical-layer network coding (PNC) in vehicleto-everything communications to accommodate the time-critical nature of vehicular ad-hoc networks (VANETs). The idea can theoretically reduce the transmission latency by 50%, thus alleviating the short contact time issues caused by high-speed vehicle motion. Conventional studies of PNC primarily considered static networks. In highly mobile networks like VANETs, the carrier frequency offsets (CFOs) due to high-speed motion will lead to inter-carrier interference (ICI) in orthogonal frequency division multiplexing (OFDM) systems. Moreover, the vehicular environment with time-frequency-selective channels further undermines accurate channel estimation for multiple users. It is also worth noting that the CFO that exists in OFDM modulated PNC cannot be completely eliminated through CFO tracking and equalization as in conventional point-to-point transmissions. These critical issues can significantly increase the bit error rate at the receiver. To address these challenges, this paper proposes an ICI-aware approach that jointly achieves accurate channel estimation, signal detection, and channel decoding. We express the channel estimation and detection and decoding as two optimization problems and resolve them with the expectation-maximization algorithm and the belief propagation algorithm, respectively. The proposed approach can efficiently mitigate the negative effect of ICI by exploiting both pilot and data tones in channel estimation, detection, and decoding. Both simulation and experiment are conducted to evaluate the proposed approach, and the results reveal that the proposed algorithm outperforms the benchmark that simply treats ICI as Gaussian noise.

关键词： V2X communication physical-layer network coding time-frequency-selective channel inter-carrier interference

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Achievable Rate Regions for Two-Way Relay Channel Using Nested Lattice coding

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IEEE TRANSACTIONS ON WIRELESS COMMUNICATIONS 2014年第10期13卷 5607-5620页

作者： Smirani, Sinda Kamoun, Mohamed Sarkiss, Mireille Zaidi, Abdellatif Duhamel, Pierre CEA LIST Commun Syst Lab F-91191 Gif Sur Yvette France Univ Paris Est Marne la Vallee LIGM F-77454 Marne La Vallee 2 France Supelec CNRS LSS F-91192 Gif Sur Yvette France

This paper studies a Gaussian two-way relay channel where two communication nodes exchange messages with each other via a relay. It is assumed that all nodes operate in half-duplex mode without any direct link between the communication nodes. A compress-and-forward relaying strategy using nested lattice codes is first proposed. Then, the proposed scheme is improved by performing layered coding: A common layer is decoded by both receivers, and a refinement layer is recovered only by the receiver that has the best channel conditions. The achievable rates of the new scheme are characterized and are shown to be higher than those provided by the decode-and-forward strategy in some regions.

关键词： Compress-and-forward Gaussian channel lattice codes physical-layer network coding side information two-way relay channel

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Signal technique for friend or foe detection of intelligent malicious user in cognitive radio network

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INTERNATIONAL JOURNAL OF AD HOC AND UBIQUITOUS COMPUTING 2019年第1期32卷 29-42页

作者： Sabuj, Saifur Rahman Hamamura, Masanori BRAC Univ Dept Elect & Elect Engn Dhaka 1212 Bangladesh Kochi Univ Technol Grad Sch Engn Kami 7828502 Japan

In cognitive radio networks, security issues arise when intelligent malicious users can attack and decrease the permitted channel for unlicensed users (secondary users). In this paper, we propose a novel scheme, based on friend or foe (FoF) detection technique with physical layer network coding, to enable discrimination between secondary users and intelligent malicious users. Theoretical expressions are derived for probabilities of detection of secondary user, miss detection, and false alarm. In addition, the effectiveness of the proposed approach is evaluated by theoretical analysis and Monte Carlo simulation. Furthermore, an algorithm is proposed for distinguishing between secondary user and intelligent malicious user. Finally, based on the outcome of simulation of probabilities and normalised cross-correlation, it is determined that the proposed scheme outperforms in terms of orthogonal frequency-division multiplexing (OFDM) signal compared with quadrature phase-shift keying (QPSK) signal over cognitive radio network.

关键词： cognitive radio network friend or foe detection physical-layer network coding cross-correlation

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Practical Power-Balanced Non-Orthogonal Multiple Access

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IEEE JOURNAL ON SELECTED AREAS IN COMMUNICATIONS 2017年第10期35卷 2312-2327页

作者： Pan, Haoyuan Lu, Lu Liew, Soung Chang Chinese Univ Hong Kong Dept Informat Engn Hong Kong Hong Kong Peoples R China Chinese Acad Sci Technol & Engn Ctr Space Utilizat Beijing 100864 Peoples R China Chinese Univ Hong Kong Inst Network Coding Hong Kong Hong Kong Peoples R China

This paper is a theoretical-plus-experimental investigation of practical 5G strategies for power-balanced non-orthogonal multiple access (NOMA). By allowing multiple users to share the same time and frequency, NOMA can scale up the number of served users and increase spectral efficiency compared with existing OMA. Conventional NOMA schemes with successive interference cancellation (SIC) do not work well when users with comparable received powers transmit together. To allow power-balanced NOMA (more exactly, near power-balanced NOMA), this paper investigates a new NOMA architecture, named network-coded multiple access (NCMA). A distinguishing feature of NCMA is the joint use of physical-layer network coding (PNC) and multiuser decoding to boost NOMA throughputs. We first show that a simple NCMA architecture in which all users use the same modulation, referred to as rate-homogeneous NCMA, can achieve substantial throughput improvement over SIC-based NOMA under near power-balanced scenarios. Then, we put forth a new NCMA architecture, referred to as rate-diverse NCMA, in which different users may adopt different modulations commensurate with their relative SNRs. A challenge for rate-diverse NCMA is the design of a channel-coded PNC system. This paper is the first attempt to design channel-coded rate-diverse PNC. Experimental results on our software-defined radio prototype show that the throughput of rate-diverse NCMA can outperform the state-of-the-art rate-homogeneous NCMA by 80%. Overall, rate-diverse NCMA is a practical solution for near power-balanced NOMA.

关键词： Non-orthogonal multiple access physical-layer network coding network-coded multiple access 5G systems edge users implementation

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