Performance Of Physical Layer Network Coding Research Articles

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

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.

Channel-Coded Physical-Layer Network Coding With OFDM Modulation

This paper addresses the carrier frequency offset (CFO) problem in OFDM modulated physical-layer network coding (PNC) operated in a two-way relay channel (TWRC). CFO, caused by node-motion induced Doppler shifts and/or asynchronous oscillators, induces inter-carrier interference (ICI) between OFDM subcarriers and hence, degrades PNC performance. To mitigate the CFO/ICI effect in PNC, this paper considers channel-coded PNC and focuses on the receiver design at the relay. CFO compensation, signal detection, and channel decoding are the three basic signal processing blocks at the relay node. For the latter two, we consider both a joint and a separate design. For the joint design, we construct a factor graph to integrate channel coding with ICI, and then, propose a scheme based on belief propagation. For the separate design, two low-complexity schemes differing in channel decoding are proposed. Our simulation results, using repeat-accumulate channel codes, reveal that (1) a CFO compensation approach that amounts to positioning the relay’s oscillator frequency at the middle of the received frequencies from the two end nodes is bit error rate (BER)-optimal for all the three schemes; (2) the joint design is superior at low SNR and/or high CFO levels; and (3) more importantly, with the joint design, for low-to-medium CFO levels, the BER of the channel-coded PNC is comparable with that of traditional point-to-point communications without CFO, thus manifesting itself as a promising technique in OFDM modulated TWRC with practical CFO constraints.

The Performance of Physical-Layer Network Coding in Asymmetric Rayleigh Fading Two-Way Relay Channels

Up to now, most of the researches about physical-layer network coding (PNC) are based on symmetric two-way relay channels. In this paper, we mainly study PNC in asymmetric two-way relay Rayleigh fading channels and classify the systems into five asymmetric cases. So as to describe the asymmetric cases, we introduce the asymmetric factors. We simulate the bit error rate (BER) performance of PNC in both symmetric and asymmetric cases with asymmetric factors fixed. After that we analyze the BER performance of PNC with one of the asymmetric factors is variable when two channels are relatively unreliable. Finally, we give the conditions that one kind of asymmetric scenario transforming to other kind. Also, in the matter of anti-noise performance, uplink asymmetry has worst performance and the phase asymmetry-downlink is the best case.

Reliable Physical-Layer Network Coding Supporting Real Applications

This paper presents the first reliable physical-layer network coding (PNC) system that supports real TCP/IP applications for the two-way relay network (TWRN). Theoretically, PNC could boost the throughput of TWRN by a factor of 2 compared with traditional scheduling (TS) in the high signal-to-noise (SNR) regime. Although there have been many theoretical studies on PNC performance, there have been relatively few experimental and implementation efforts. Our earlier PNC prototype, built in 2012, was an offline system that processed signals offline. For a system that supports real applications, signals must be processed online in real-time. Our real-time reliable PNC prototype, referred to as RPNC, solves a number of key challenges to enable the support of real TCP/IP applications. The enabling components include: 1) a time-slotted system that achieves $\mu s$ -level synchronization for the PNC system; 2) reduction of PNC signal processing complexity to meet real-time constraints; 3) an ARQ design tailored for PNC to ensure reliable packet delivery; and 4) an interface to the application layer. We took on the challenge to implement all of the above with general-purpose processors in PC through an SDR platform rather than ASIC or FPGA. With all of these components, we have successfully demonstrated image exchange with TCP and two-party video conferencing with UDP over RPNC. Experimental results show that the achieved throughput approaches the PHY-layer data rate at high SNR, demonstrating the high efficiency of the RPNC system.

Physical-Layer Network Coding Scheme over Asymmetric Rayleigh Fading Two-Way Relay Channels

To improve the bit error rate (BER) performance of physical-layer network coding (PNC) in asymmetric two-way relay channels (TWRC), in this paper, we study a new PNC scheme named bi-quadrature physical-layer network coding (BQ-PNC) for Rayleigh flat fading TWRC. In BQ-PNC scheme, the two users employ quadrature carriers and the relay node use quadrature combining rather than XOR which is very common in other PNC schemes. We give the BER analysis of BQ-PNC and simulate the performance. Theoretical and simulation results show that the proposed scheme can significantly enhanced the BER performance, either in symmetric or asymmetric cases. Especially for uplink asymmetric TWRC, BQ-PNC can provide more than 4 dB gain compared with PNC scheme.

Physical-Layer Network Coding in Two-Way Heterogeneous Cellular Networks With Power Imbalance

The growing demand for high-speed data, quality of service (QoS) assurance and energy efficiency has triggered the evolution of 4G LTE-A networks to 5G and beyond. Interference is still a major performance bottleneck. This paper studies the application of physical-layer network coding (PNC), a technique that exploits interference, in heterogeneous cellular networks. In particular, we propose a rate-maximising relay selection algorithm for a single cell with multiple relays based on the decode-and-forward strategy. With nodes transmitting at different powers, the proposed algorithm adapts the resource allocation according to the differing link rates and we prove theoretically that the optimisation problem is log-concave. The proposed technique is shown to perform significantly better than the widely studied selection-cooperation technique. We then undertake an experimental study on a software radio platform of the decoding performance of PNC with unbalanced SNRs in the multiple-access transmissions. This problem is inherent in cellular networks and it is shown that with channel coding and decoders based on multiuser detection and successive interference cancellation, the performance is better with power imbalance. This paper paves the way for further research in multi-cell PNC, resource allocation, and the implementation of PNC with higher-order modulations and advanced coding techniques.

양방향 중계채널에서 중계기 다중안테나가 물리계층네트워크 코딩의 성능에 미치는 영향

양방향 중계채널에서 중계기 다중안테나가 물리계층네트워크 코딩의 성능에 미치는 영향

Cooperative mechanism for PNC two-hop slotted ALOHA network

In this paper, we propose a buffer-information-aided (BIA) request to send (RTS)/clear to send (CTS) mechanism to improve the throughput performance of physical-layer network coding (PNC) in a slotted-ALOHA two-hop relay network. In the proposed BIA mechanism, the relay node collects the information of the destination address of the first several packets at the sending buffers of the client nodes, and determines the transmission client nodes at the next time slot. Therefore, the collision probability can be decreased and the proportion of PNC transmissions among the total transmissions is improved. Simulation results show that compared with the traditional RTS/CTS mechanism, the proposed cooperative mechanism can greatly improve the PNC network throughput.

BER Analysis of Physical-Layer Network Coding in the AWGN Channel With Burst Pulses

The essential idea behind physical-layer network coding (PNC) is to superimpose signals so as to improve throughput. Current studies focus mainly on PNC over the AWGN or Rayleigh channels without consideration of burst pulses. This paper aims to evaluate the bit error rate (BER) performance of classical PNC, over a mixed channel that considers the combined effects of Gaussian noise and burst pulses. Besides, this paper explores the use of the Reed-Solomon (RS) codes to improve the BER performance of PNC over the mixed channel. Simulation results show that burst pulses deteriorate the BER significantly, and the RS codes are able to compensate for substantial BER performance degradation.

Physical-Layer Network Coding Systems With MFSK Modulation

Physical-layer network coding (PNC) is an attractive technique because it can significantly enhance the throughput of a wireless network with a relatively simple implementation, as compared with conventional network coding (NC) schemes. In this paper, we first investigate PNC with frequency shift keying (FSK) through the derivation of its bit-error rate (BER) and capacity, as well as the impact of imperfect synchronization to the overall performance. Based on the discussions on PNC with 2FSK, we then further expand the analysis to PNC with M-ary FSK (MFSK). Theoretical results indicate that the BER performance of PNC with 2FSK is a bit worse than that of PNC with 2PSK. As the constellation dimension M increases, the BER performance of PNC with M-ary FSK improves at the expense of bandwidth efficiency degradation.

The Feasibility of Mobile Physical-Layer Network Coding with BPSK Modulation

This paper considers applying physical-layer network coding (PNC) to orthogonal frequency division multiplexing (OFDM) modulated mobile ad-hoc networks (MANETs) to resolve the outstanding issue of short contact time between nodes due to their mobility. Ideally, PNC enables data exchange twice as fast as the traditional scheduling, and thus, it is a potential performance booster in MANETs. However, the application of PNC in MANETs is challenged by the carrier frequency offset (CFO) problem inherently caused by node-motion-induced Doppler shifts and asynchronous oscillators. CFO induces intercarrier interference (ICI) that degrades PNC performance. In this paper, we investigate the CFO/ICI impact on the signal-to-interference-and-noise ratio (SINR) and bit error rate (BER) in the signal detection of PNC in a two-way relay channel (TWRC) based on binary phase-shift keying (BPSK) modulation. We find that PNC with power control suffers, at most, a 3 dB SINR penalty compared with generic point-to-point communications in both the flat-fading and the frequency-selective channels. We also find that a belief propagation (BP) algorithm could be employed in the signal detection of PNC to effectively tackle ICI and reduce its impact on the BER of PNC. For CFO compensation in PNC, we propose a method that amounts to positioning the relay's local oscillator frequency at the middle of the received frequencies from the two end nodes in the TWRC. Importantly, we show that 1) this compensation method can theoretically maximize the worst SINR in PNC and that 2) in the case of similar CFO of the two uplinks in TWRC, it allows PNC to achieve a BER at the relay close to that in the ideal case, i.e., in point-to-point communications without CFO. Overall, this paper demonstrates that mobile PNC is feasible in general, laying the foundation for future studies.

Error Performance of Physical-Layer Network Coding in Multiple-Antenna Two-Way Relay Systems With Outdated CSI

In this paper, we study the impact of outdated channel state information (CSI) on the error rate performance in multiple-antenna two-way decode-and-forward (DF) relay systems, where physical-layer network coding (PNC) is adopted. We consider two variations of relay selection, namely, single best relay selection (S-RS) and multiple successfully-participated relay selection (MSP-RS). Under perfect and outdated CSI assumptions, closed-form expressions for the end-to-end system symbol error probability (SEP) are derived for the S-RS scheme, along with the asymptotic SEP expressions in high SNR regions for the MSP-RS scheme. By both analytical and simulation results, it is clearly shown that a full cooperative diversity gain can be achieved with perfect CSI. The results also manifest that the S-RS scheme can achieve only the transmit diversity gain with outdated CSI. On the other hand, the MSP-RS scheme can achieve a full cooperative diversity gain even if the CSI is outdated at the expense of high complexity.

Building Blocks of Physical-Layer Network Coding

This paper investigates the fundamental building blocks of physical-layer network coding (PNC). Most prior work on PNC focused on its application in a simple two-way-relay channel (TWRC) consisting of three nodes only. Studies of the application of PNC in general networks are relatively few. This paper is an attempt to fill this gap. We put forth two ideas: a general network can be decomposed into small building blocks of PNC, referred to as the PNC atoms, for scheduling of PNC transmissions; and we identify nine PNC atoms, with TWRC being one of them. Three major results are as follows. First, using the decomposition framework, the throughput performance of PNC is shown to be significantly better than those of the traditional multi-hop scheme and the conventional network coding scheme. For example, under heavy traffic volume, PNC can achieve 100% throughput gain relative to the traditional multi-hop scheme. Second, PNC decomposition based on a variety of different PNC atoms can yield much better performance than PNC decomposition based on the TWRC atom alone. Third, three out of the nine atoms are most important to good performance. Specifically, the decomposition based on these three atoms is good enough most of the time, and it is not necessary to use the other six atoms.

Error Performance of Physical-Layer Network Coding in Multiple-Antenna TWRC

In this paper, the error performance of physical-layer network coding (PNC) is studied in multiple-antenna two-way relay channels (TWRCs), where two users exchange their messages with the help of a relay. We assume that the TWRC system uses binary phase-shift keying (BPSK) modulation and that all channels are Rayleigh faded. In particular, we consider a general system model where two users may have different numbers of antennas and different average signal-to-noise ratios (SNRs) to the relay. Considering a TWRC with multiple antennas at both users and the relay [referred to as multiple-input multiple-output (MIMO)-TWRC], we derive the upper and lower bounds on the uplink error probability of PNC based on maximum-likelihood (ML) detection. In this scheme, a transmit antenna selection (TAS) strategy is applied at two users, where each user selects the strongest transmit antenna for transmission. Furthermore, we also present the upper and lower bounds for two special cases, namely, the single-input multiple-output (SIMO)-TWRC with single-antenna users and the multiple-antenna relay and the multiple-input single-output (MISO) TWRC with multiple-antenna users and the single-antenna relay. Then, the diversity order is investigated for the schemes. We show that the PNC with TAS outperforms the PNC with space-time block codes (STBCs) significantly. The numerical results also demonstrate that our bounds are very tight to the Monte Carlo simulation.

On the Optimal Design and Performance of Linear Physical-Layer Network Coding for Fading Two-Way Relay Channels

The design of a reliable physical-layer network coding (PNC) scheme for practical fading two-way relay channels is a challenging task. This is because the signals transmitted by two users arrive at the relay with varied amplitudes and a relative carrier-phase offset, which will impair the performance of PNC. This paper studies a linear PNC scheme for fading two-way relay channels where the transmitters lack the channel state information. In this scheme, the relay computes and broadcast some finite-set integer combinations of two users' messages. The coefficients for the integer combinations used at the relay are carefully designed to minimize the error probability. This scheme can be viewed as a practical embodiment of the compute-and-forward concept. We develop a new LPNC design criterion called minimum set-distance maximization. Using this criterion, we derive an explicit expression for the optimized integer coefficients that minimizes the error probability of LPNC. The optimized integer coefficients turn out to resemble the fading channel coefficients. We further derive a closed-form expression on the average error probability performance over a complex-valued Rayleigh fading two-way relay channel, which shows that our designed LPNC scheme approaches the optimal error performance at a high SNR. Numerical results show that our designed LPNC outperforms existing schemes by more than 5 dB at a medium-to-high SNR regime.

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

SUMMARYThis 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 © 2013 John Wiley & Sons, Ltd.

Performance of Physical-layer Network Coding in Asymmetric Rayleigh Fading Two-way Relay Communication Systems

Performance of Physical-layer Network Coding in Asymmetric Rayleigh Fading Two-way Relay Communication Systems