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Practical Physical Layer Network Coding for Two-Way Relay Channels: Performance Analysis and Comparison
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This paper investigates the performance of practical physical-layer network coding (PNC) schemes for two-way relay channels. We first consider a network consisting of two source nodes and a single relay node, which is used to aid communication between the two source nodes. For this scenario, we investigate transmission over two, three or four time slots. We show that the two time slot PNC scheme offers a higher maximum sum-rate, but a lower sum-bit error rate (BER) than the four time slot transmission scheme for a number of practical scenarios. We also show that the three time slot PNC scheme offers a good compromise between the two and four time slot transmission schemes, and also achieves the best maximum sum-rate and/or sum-BER in certain practical scenarios. To facilitate comparison, we derive new closed-form expressions for the outage probability, maximum sum-rate and sum-BER. We also consider an opportunistic relaying scheme for a network with multiple relay nodes, where a single relay is chosen to maximize either the maximum sum-rate or minimize the sum-BER. Our results indicate that the opportunistic relaying scheme can significantly improve system performance, compared to a single relay network.
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... Relaying is usually combined with network coding to improve the transmission efficiency of bidirectional wireless relay systems [1]. Among other types of network coding, Physical Layer Network Coding (PLNC) has been considered in End-to-End (E-to-E) systems to boost frequency utilization; this is one of the key problems with wireless communication systems [2][3][4]. Multiple Input Multiple Output (MIMO) E-to-E relay systems used with PLNC and it is already being implemented and analyzed to improve the transmission rate and diversity order [5][6][7]. Error correction coding has been introduced with network coding for performance enhancement [8][9][10][11][12]. ...
To accomplish the targets of Beyond Fifth-Generation (B5G) networks, considerable spectral efficiency, wide coverage, better reliability, and energy efficiency are the main objectives. In order to enhance the performance of the Orthogonal Frequency Division Multiplexing (OFDM) signal in terms of Bit Error Rate (BER), powerful channel coding, such as polar coding, must be considered. In addition, a Massive Multi-Input Multi-Output (MMIMO) combined with OFDM can support better performance and spectral efficiency. On the other hand, Physical Layer Network Coding (PLNC) can increase system throughput. This paper explores the integration of Polar-Coded OFDM (PCOFDM) with MMIMO and PLNC to enhance transmission reliability and throughput. A two-way relay transmission scenario is considered at millimeter Wave (mmWave) frequencies. The consequences of the extensive simulation assessments for Multilevel Quadrature Amplitude Modulation (M-QAM) demonstrated that refinements in throughput and BER can be performed using PCOFDM, with PLNC having enough antenna elements in the massive MIMO system at the base station (the relay node). In any case of the number of antenna elements utilized in the user terminal, the BER achievement of PCOFDM-MMIMO with PLNC surpassed that of a similar system without polar code (antenna elements used in the base station are 128 and 256).
... Over relay networks, relay nodes do not simply store the data received from source nodes, but they can process the data prior to forwarding them to destination nodes. Specif-ically, the network coding (NC) concept, which was originally proposed in [3], has been applied at the relay nodes to improve the throughput of wireless relay networks [4,5]. The incoming data packets from the source nodes can be subjected to random linear NC (RLNC) operations by the relay nodes. ...
The image transmission over wireless media experiences not only unavailable performance loss caused by the environment and hardware issues, but also information leakage to eavesdroppers who can overhear and attempt to recover the images. This paper proposes a secure cooperative relaying (SCR) protocol for the image communications in wireless relay networks (WRNs) where Alice sends high-resolution (HR) images to Bob with the assistance of a relaying user named Relay, and in the presence of an eavesdropper named Eve. In order to enhance the security of the image communications, random linear network coding (RLNC) is employed at both Alice and Relay to conceal the original images from Eve with RLNC coefficient matrices and reference images in the shared image datastore. Furthermore, the original HR images are downscaled at Alice to save transmission bandwidth and image super-resolution (ISR) is adopted at Bob due to its capability to recover the HR images from their low-resolution (LR) version, while still maintaining the image quality. In the proposed SCR protocol, Bob can decode both the original images transmitted from Alice over the direct link and the images forwarded by Relay over the relaying links. Simulation results show that the SCR protocol achieves a considerably higher performance at Bob than at Eve since Eve does not know the coefficient matrices and reference images used at Alice and Relay for the RLNC. The SCR protocol is also shown to outperform the counterpart secure direct transmission protocol without the relaying links and secure relaying transmission without the direct link. Additionally, an increased scaling factor can save the transmission bandwidth for a slight change in the image quality. Moreover, the impacts of direct, relaying and wiretap links are evaluated, verifying the effectiveness of the SCR protocol with the employment of Relay to assist the image communications between Alice and Bob in the WRNs.
... In addition, Q 1,Ω ∈ C T × T and Q 2,Ω ∈ C T × T denote an upper part and a lower part of the orthogonal matrix Q Ω . By substituting the equation in (6) for that in (5), the precoded signal can be simplified as, ...
This paper proposes overloaded multiple input multiple output (MIMO) bi-directional communication with physical layer network coding (PLNC) to enhance the transmission speed in heterogeneous wireless multihop networks where the number of antennas on the relay is less than that on the terminals. The proposed overloaded MIMO communication system applies precoding and relay filtering to reduce computational complexity in spite of the transmission speed. An eigenvector-based filter is proposed for the relay filter. Furthermore, we propose a technique to select the best filter among candidates eigenvector-based filters. The performance of the proposed overloaded MIMO bi-directional communication is evaluated by computer simulation in a heterogeneous wireless 2-hop network. The proposed filter selection technique attains a gain of about 1.5 dB at the BER of 10⁻⁵ in a 2-hop network where 2 antennas and 4 antennas are placed on the relay and the terminal, respectively. This paper shows that 6 stream spatial multiplexing is made possible in the system with 2 antennas on the relay.
... Known interference (KI) from another radio is more complicated to cancel than SI due to oscillator inaccuracies [5] and methods to do so are scarce [6]. Still, information theoretical works often assume perfect KIC [7], [8] somewhat negligently. ...
Physical layer security is a sought-after concept to complement the established upper layer security techniques in wireless communications. An appealing approach to achieve physical layer security is to use cooperative jamming with interference that is known to and suppressible by the legitimate receiver but unknown to, and hence not suppressible by, the eavesdropper. Suppressing known interference (KI), however, is challenging due to the numerous unknowns, including carrier and sampling frequency offsets, that impact its reception. This letter presents a measurement campaign that captures this challenge and then demonstrates the feasibility of solving that challenge by cancelling the KI using the frequency offsets least mean squares (FO-LMS) algorithm. Results show that KI suppression directly improves processing the signal-of-interest and that cooperative jamming effectively provides security at the physical layer.
In this article, we consider a two-way communication system empowered by a reconfigurable intelligent surface (RIS), consisting of passive reflective elements, in the presence of transceiver hardware impairments (HIs). To exploit the existence of a direct link between the end communication nodes, we utilize two time slots for their information exchange. We particularly analyze the instantaneous end-to-end signal-to-noise-plus-distortion-ratios (SNDRs) under HIs. The exact distribution of the magnitude of the end-to-end channel coefficients of the studied RIS-empowered communication system is derived under HIs and Nakagami-m fading channels. Using different settings for the level of HIs and the transmit powers at the end nodes, we also deduce novel exact and upper bound analytical expressions for the overall outage probability (OOP). For the high signal-to-noise ratio regime, an asymptotic OOP analysis is derived, which unveils the system’s diversity order. The presented numerical and simulation results corroborate our derived analytical findings, and demonstrate the impact of different system and channel parameters on the system’s OOP performance.
While Chap. 2 shows the great potential of the PLS technology in ensuring secure wireless communication, this chapter introduces how the PLS technology can be applied to achieve covert communication in wireless systems. In particular, we focus on two-hop relay systems and examine the covertness performance of such systems under various PLS techniques. In Sect. 3.1, we investigate the interplay between legitimate nodes and malicious wardens in a two-hop two-way relay system and show the covertness performance with an emphasis on the scaling law results of covert throughput. Different from the relays considered in Sect. 3.1, Sect. 3.2 focuses on the case of FD relays that can switch between the FD mode and the HD mode. Since the timeliness of CSI is vital for covert communication, Sect. 3.3 therefore explores the impact of outdated CSI on the covertness performance of the relay systems.
Full-duplex (FD) communication is a potential game changer for future wireless networks. It allows for simultaneous transmit and receive operations over the same frequency band, a doubling of the spectral efficiency. FD can also be a catalyst for supercharging other existing/emerging wireless technologies , including cooperative and cognitive communications, cellular networks, multiple-input multiple-output (MIMO), massive MIMO, non-orthogonal multiple access (NOMA), millimeter-wave (mmWave) communications, unmanned aerial vehicle (UAV)-aided communication, backscatter communication (Back-Com), and reconfigurable intelligent surfaces (RISs). These integrated technologies can further improve spectral efficiency, enhance security, reduce latency, and boost the energy efficiency of future wireless networks. A comprehensive survey of such integration has thus far been lacking. This paper fills that need. Specifically, we first discuss the fundamentals, highlighting the FD transceiver structure and the self-interference (SI) cancellation techniques. Next, we discuss the coexistence of FD with the above-mentioned wireless technologies. We also provide case studies for some of the integration scenarios mentioned above and future research directions for each case. We further address the potential research directions, open challenges, and applications for future FD-assisted wireless, including cell-free massive MIMO, mmWave communications, UAV, BackCom, and RISs. Finally, potential applications and developments of other miscellaneous technologies, such as mixed radio-frequency/free-space optical, visible light communication, dual-functional radar-communication, underwater wireless communication, multiuser ultra-reliable low-latency communications, vehicle-to-everything communications, rate splitting multiple access, integrated sensing and communication, and age of information, are also highlighted.
Space-air-ground integrated network (SAGIN), as a three-tiered architecture that assimilates satellite systems, aerial, and terrestrial communication networks, has become an intensive research domain in the present era of communications. SAGIN-based communication models are developed to enhance the user’s quality of experience (QoE). Besides providing noteworthy benefits in various applications and services, SAGIN has unprecedented challenges because of its self-organized, unpredictable, and heterogeneous nature. Relaying equipment in SAGIN can be a very low-orbit satellite, a base station (BS), and an unmanned vehicle assisting a pair of mobile users’ communications. Thus, developing a robust device-to-device (D2D) direct and relaying communication model concerning channel distribution is crucial. Based on this concern, this article proposes a relay-aided D2D multiple–input and multiple–output (MIMO) scheme (RAS) for enhancing the optimal energy efficiency (EE) as a function of spectral efficiency (SE). The proposed model derives a relay-based amplify-and-forward (AF) MIMO multihop communication system for implementation. The proposed computations of optimal EE and SE for D2D MIMO show that the approximation provided by a random matrix approximation is constrained to a specific signal-to-noise ratio (SNR) range when the optimal SE and EE are derived using Gaussian quadrature and a hypergeometric function.
In this paper, bi-directional traffic between two nodes communicating via a relay node is considered. A novel relaying method based on joint data packet encoding in conjunction with exploitation of a priori known information is presented. Moreover, a specially crafted method for combining of the direct and relayed radio signal is suggested. The proposed scheme enables a reduced number of transmissions, whereby enhancing aggregate throughput. Evaluation, where optimal power and rate settings are derived, shows that the proposed method enhances the throughput up to 33% as compared to a (traditional) four-phase bi-directional protocol under a system energy constraint, both with and without the proposed combining method
We show that mutual exchange of independent information between two nodes in a wireless network can be effi-ciently performed by exploiting network coding and the physical-layer broadcast property offered by the wireless medium. The proposed approach improves upon conventional solutions that separate the processing of the two unicast sessions, corresponding to information transfer along one direction and the opposite direction. We propose a distributed scheme that obviates the need for synchronization and is robust to random packet loss and delay, and so on. The scheme is simple and incurs minor overhead.
In this summary, we consider bi-directional communication between a transmitter and receiver
communicating via a relay station. We present a novel communication method based on joint data packet
encoding in conjunction with exploitation of a priori known information that enables reduced number of
transmissions, whereby enhancing aggregate throughput.
In a three-node wireless relay network, two nodes, BS1 and BS2, exchange information through a relay node, RL. Suppose time division duplex is used, physical network coding (PNC) uses two time slots for the information exchange instead of four time slots needed by the conventional method. In the first time slot, both BS1 and BS2 transmit simultaneously to RL. The relay node, RL does a PNC mapping based on the received signal and broadcast the mapped signal back to BS1 and BS2 simultaneously during the second time slot. The nodes, BS1 and BS2 are able to decode their desired information based on the received mapped signal and the signal which they had transmitted during the first time slot. In this paper, we analyze the average BER of the information exchanged between the two nodes in Rayleigh fading environments. We also derive the average BER of the mapped signal at the relay during the first time slot. With the derived BER of the mapped signal at RL, we propose to use power control at BS1 and BS2 to minimize the instantaneous BER of the mapped signal at RL. The proposed technique improves the BER of the desired information decoded at the two nodes. The solution turns out to be channel inversion based power control at both BS1 and BS2. The proposed power control technique improves both the average BER of the mapped signal at RL and the desired information at BS1 and BS2.
This paper considers a wireless relay network where two nodes S1 and S2 exchange their information through a relay node RL. It is assumed that both S1 and S2 are equipped with single antenna and RL is equipped with multi-antennas. Based on the principle of physical layer network coding (PNC), we study the optimal design for the analogue relaying, also known as amplify-and-forward (AF), at RL so as to maximize the sum- rate of bi-directional information exchange between S1 and S2. Optimal solution for the multi-antenna linear processing at RL is presented and low-complexity suboptimal schemes are proposed. Simulation results show that the proposed methods perform better than the conventional zero-forcing (ZF) and minimum- mean-squared-error (MMSE) -based linear relaying, and the performance gain is very significant when the two channels from S1 and S2 to RL are highly correlated.
This paper considers a wireless relay network where two nodes S1 and S2 exchange their information through a relay node RL. It is assumed that both S1 and S2 are equipped with single antenna and RL is equipped with multi-antennas. Based on the principle of physical layer network coding (PNC), we study the optimal design for the analogue relaying, also known as amplify-and-forward (AF), at RL so as to maximize the sum- rate of bi-directional information exchange between S1 and S2. Optimal solution for the multi-antenna linear processing at RL is presented and low-complexity suboptimal schemes are proposed. Simulation results show that the proposed methods perform better than the conventional zero-forcing (ZF) and minimum- mean-squared-error (MMSE) -based linear relaying, and the performance gain is very significant when the two channels from S1 and S2 to RL are highly correlated.
The purpose of this introductory chapter is to provide several measures of performance related to practical communication system design and to begin exploring the analytical methods by which they may be evaluated. While the deeper meaning of these measures will be truly understood only after their more formal definitions are presented in the chapters that follow, the introduction of these terms here serves to illustrate the various possibilities that exist, depending on both need and relative ease of evaluation.
In this paper, we derive tight upper and lower bounds for the average sum rate of two-way amplify-and-forward (AF) half-duplex relaying, which show that two-way AF half-duplex relaying can significantly mitigate the spectral efficiency loss of conventional one-way AF half-duplex relaying. We then extend the AF half-duplex two-way relaying to the case where source and destination terminals both transmit Alamouti's orthogonal space time block code (OSTBC) utilizing two antennas and relay has only one antenna. We derive both upper and lower bounds for the average sum rate as well as an upper bound for the pair-wise error probability (PEP) for the proposed OSTBC scheme. We also find the optimal power allocation for both two- way relaying schemes analytically. Our theoretical analysis and numerical simulation results show that higher average sum rate compared to the single antenna case and diversity order of two are achieved by the proposed OSTBC scheme.