Physical Layer Network Research Articles

Practical NOMA-Based Coordinated Direct and Relay Transmission

This letter puts forth a practical non-orthogonal multiple access (NOMA)-based coordinated direct and relay transmission (CDRT) scheme, referred to as network-coded multiple access CDRT (NCMA-CDRT). We consider a two-user uplink scenario, where a near user communicates directly to a base station (BS), whereas a far user needs the assistance of a decode-and-forward relay. While prior NOMA-CDRT studies focused extensively on theoretical analysis, its superiority has not been well investigated through practical communication schemes. In particular, successive interference cancellation (SIC), a predominant NOMA decoding technique, does not work well if transmitters with comparable received powers transmit together. We investigate NCMA-CDRT to tackle this practical issue. A distinguishing feature of NCMA-CDRT is the joint use of physical-layer network coding (PNC) and multiuser decoding at both the relay and the BS. We design packet relaying strategies that can forward the PNC packets decoded at the relay to boost system throughput. Experiments on software-defined radio indicate that the total throughput of NCMA-CDRT significantly outperforms the SIC-based NOMA-CDRT. Overall, NCMA-CDRT is a viable solution for cooperative NOMA systems.

Full‐duplex ambient backscatter with physical layer network coding

Ambient backscatter which utiliees the ambient radio-frequency signals to enable transmissions between battery-less devices has attracted considerable attention in academia and industry. This study addresses the questions of full-duplex (FD) and self-interference cancellation (SIC) for ambient backscatter which adopts dual-antenna structure to achieve persistent information transmission and energy harvesting. The authors construct the physical-layer network coding (PNC) mapping principle of on–off keying in the dual-antenna structure and propose the PNC-based FD algorithm to eliminate the self-interference in the information domain. Furthermore, the bit-error-ratio and throughput performances are analysed under conventional half-duplex mode and the proposed FD mode, respectively. In order to facilitate system complexity and reduce power consumption, they design a hardware prototype to achieve SIC which consists of low-power passive analogue components. Numerical results are provided to confirm the theoretical studies. Circuit simulations demonstrate that the circuit is commendably consistent with the design concept.

The Resilience of Massive MIMO PNC to Jamming Attacks in Vehicular Networks

In this article, we investigate the resilience of Massive MIMO Physical Layer Network Coding (PNC) to jamming attack in both sub-6 GHz and millimeter-Wave (mmWave) systems in vehicular networks. Massive MIMO generally is resilient to jamming attacks, and we investigate the impact that PNC has on this resilience, if combined with Massive MIMO. The combination of Massive MIMO and PNC has shown a significant improvement in the bit error rate (BER) in our previous investigation. The corresponding framework is analysed against a barraging attack from a jammer, where the jamming channel is not known to the base station (BS), and the jammer can use any number of transmit antennas. Over Rayleigh channel, our simulation results reveal that Massive MIMO PNC performs better in the lower signal-to-noise ratio (SNR) regions to jamming attacks and this is achieved at twice the spectral efficiency. A similar performance is observed over mmWave channel.

Outage Performance of Downlink Full-Duplex Network-Coded Cooperative NOMA

This letter studies the impact of network-coded multiple access (NCMA) on the outage performance of full-duplex cooperative non-orthogonal multiple access (NOMA). In particular, we propose a network-coded cooperative NOMA (NC-CNOMA) strategy, under which user devices utilize physical-layer network coding (PNC) to demodulate signals with greater probability. The exact analytical expression of the outage probability is derived to evaluate the performance of the proposed scheme. The provided simulation results validate our analysis and the proposed NC-CNOMA scheme outperforms the conventional cooperative NOMA with regard to outage performance.

A Throughput Efficient Multi-Stage Technique for Binary Multiway Relaying

We consider binary multiway relaying with $N$ nodes where each node demands messages of all other nodes and can only communicate via a relay. The nodes use binary transmissions. We propose two schemes requiring a maximum of $2\lceil \frac {N}{2} \rceil + 2$ channel uses (CUs) for full data exchange, which is lesser than previously published schemes for many values of $N$ . Physical layer network coding is employed at the relay with message dependent node transmissions. The schemes have lower decoding complexities, better bit error rates, and are more energy efficient compared to other schemes requiring nearly same number of CUs.

Signal-Aligned Network Coding for Multicell Processing With Limited Cooperation

In this paper, we propose a signal-aligned network coding (SNC) scheme for K-user time-varying multiple-input multiple-output (MIMO) interference channels with limited receiver cooperation. We assume that the receivers are connected to a central processor via wired cooperation links with individual limited capacities. Our SNC scheme determines the precoding matrices of the transmitters so that the transmitted signals are aligned at each receiver. The aligned signals are then decoded into noiseless integer combinations of messages, also known as network-coded messages, by physical-layer network coding. The key idea of our scheme is to ensure that independent integer combinations of messages can be decoded at the receivers. Hence the central processor can recover the original messages of the transmitters by solving the linearly independent equations. We prove that our SNC scheme achieves full degrees of freedom (DoF) by utilizing signal alignment and physical-layer network coding. Simulation results show that our SNC scheme outperforms the compute-and-forward scheme in the finite SNR regime of the two-user and the three-user cases. The performance improvement of our SNC scheme mainly comes from efficient utilization of the signal subspaces for conveying independent linear equations of messages to the central processor.

Transmit power minimisation for full‐duplex two‐way relaying systems with asymmetric packet‐rates and quality‐of‐service requirements

This study solves the transmit power minimisation problem subject to a target quality-of-service constraint of a full-duplex (FD) two-way decode-and-forward relaying system with asymmetric packet-rates, where the two-way relaying system can operate in two different styles, i.e. half-duplex sources with full-duplex relaying (HDS-FDR) and full-duplex sources with full-duplex relaying (FDS-FDR) styles. For the FDS-FDR style, the relay node can use two strategies to handle the received signals from the sources, namely, physical-layer network coding (PNC) and physical-layer superposition coding (PSC), both of which are referred to as FDS-FDR-PNC and FDS-FDR-PSC styles, respectively. By transforming the transmit power minimisation problem into a two-stage problem, optimum power control (OPC) techniques are developed for the HDS-FDR, FDS-FDR-PNC and FDS-FDR-PSC styles, respectively, giving closed-form solutions for individual transmit power at the relay and the sources. Computer simulations are conducted and the results validate the proposed OPC techniques. It is shown that the FDS-FDR-PNC style performs best in terms of energy saving when the two sources' packet-rates are moderately asymmetric or symmetric. For the case that the packet-rates are strongly asymmetric, the FDS-FDR-PSC style can save more energy than the other two styles.

C-RAN-Type Cluster-Head-Driven UAV Relaying With Recursive Maximum Minimum Distance

In this letter, a Cloud Radio Access Network-type cluster-head-driven uplink model for multiple-antenna Unmanned Aerial Vehicles (UAV) relaying schemes is presented, which enables joint Maximum Likelihood symbol detection in the UAV cluster-head and the selection of UAV sources to communicate with each other aided by UAV-based relays. A relay selection technique, named Cluster-Head-Driven Best-Link (CHD-Best-Link), which employs cluster-head buffers and physical-layer network coding, is devised. A recursive maximum minimum distance relay selection strategy that exploits time-correlated channels and equips the CHD-Best-Link scheme is also developed. Simulations illustrate that CHD-Best-Link has superior average delay and bit error rate performances to that of previous schemes.

Precoded Physical Layer Network Coding with Coded Modulation in MIMO-OFDM Bi-Directional Wireless Relay Systems

Precoded Physical Layer Network Coding with Coded Modulation in MIMO-OFDM Bi-Directional Wireless Relay Systems

Non-coherent multi-symbol detection of PR-CPM for deep space relay satellites with physical-layer network coding

The demand for wireless spectrum and data transmission has increased dramatically with the rapid growth of deep-space exploration and communication. The satellite relay communication is an essential technique to solve the issues above. The method of combining Physical-layer Network Coding (PNC) with Continuous Phase Modulation (CPM) on relay satellites can improve communication efficiency and perform the collection and transmission of space data effectively. Partial-Response CPM (PR-CPM) signals possess excellent spectrum and power characteristics and are suitable for deep-space communications with limited bandwidth and massive data transmission. In this paper, a partial response non-coherent multi-symbol detection algorithm is proposed based on the Maximum-Likelihood principle. The proposed algorithm fully utilizes the memory properties of PR-CPM signals and makes decisions on specified symbols by observing a number of symbols each time. Simulation results indicate that the performance gain under the Bit Error Rate of 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">−4</sup> is about 2 dB when 5 symbols are inspected, compared with the case where the observation length is 3.

Timely Information Update With Nonorthogonal Multiple Access

This article studies information freshness in information update systems with nonorthogonal multiple access (NOMA). Information freshness is characterized by age of information (AoI), defined as the time elapsed since the generation of the last successfully received update. Conventional orthogonal multiple access (OMA) systems, say time-division multiple access (TDMA) systems, lead to high average AoI when a large number of users take turns to transmit their latest samples to a common receiver over a wireless medium. In contrast to OMA, NOMA allows multiple users to transmit simultaneously. Although NOMA could lead to higher packet error rates (PER) due to the wireless interference among users, we show that higher PERs do not always lead to a higher average AoI. Specifically, our experiments on software-defined radio indicate that NOMA with conventional multiuser decoding (MUD) techniques leads to higher PERs but lower average AoI than OMA does in the high SNR regime. Furthermore, to improve the AoI performance in the medium SNR regime, we combine MUD with physical-layer network coding (PNC), a technique that turns wireless interference into useful network-coding information. PNC works well even when the SNRs of different NOMA users do not differ much. This article is the first attempt to apply PNC to information update systems. Experiments show that the combined use of PNC and MUD reduces the average AoI significantly in a practical network setting. Overall, PNC-enabled NOMA is a promising solution to information update systems.

Joint Optimization of Energy-Harvesting-Powered Two-Way Relaying D2D Communication for IoT: A Rate–Energy Efficiency Tradeoff

Device-to-device (D2D) communication is a key enabling technology to facilely realizing the Internet of Things (IoT) due to its spectral and energy efficiencies features. Exploiting the physical-layer network coding (PNC) and energy harvesting (EH) technology, two-way relaying (TWR) D2D communication can achieve significant performance for IoT in terms of data rate and energy efficiency (EE). In this article, we investigate the EH-aided TWR D2D communication sharing the uplink (UL) spectrum of the traditional cellular networks. We assume that the D2D transmitters, receivers, and participating relays can collect renewable energy (RE) from natural resources. Also, the relays are considered to be powered by radio-frequency (RF) signals utilizing the power splitting (PS) protocol. Subject to the Quality of Service (QoS), power, subchannel assignment, EH, and maximum practical power constraints, two nonconvex mixed-integer nonlinear programming (MINLP) problems are formulated. The two problems provide a tradeoff on either maximizing the TWR D2D link (TDL) rate or its EE depending on the IoT application needs. Based on the particle swarm optimization (PSO) algorithm, we propose the rate and EE tradeoff EH-based algorithm (REET-EH) to deal with these problems. The proposed algorithm can optimally perform the resource allocation (RA), PS factors determination, power allocation (PA), and relay selection processes. The numerical results investigate the performance of the REET-EH algorithm and show its consistency over several parameters. Also, the results illustrate that our proposed algorithm improves the system performance compared with other state-of-the-art algorithms with regard to the D2D link rate and EE.

Relay denoising mapping approach design and performance analysis for heterogeneous physical‐layer network coding with high‐order modulation

In recent years, considerable studies have been devoted to physical-layer network coding (PLNC) in a two-way relay channel (TWRC) network with the symmetric channel. However, it may not be appropriate for the asymmetric channel in which the source-to-relay channels are not equally strong and the two sources may utilise different modulation. In this study, the authors studied the heterogeneous PLNC design in the asymmetric TWRC network with high-order modulation and proposed a relay denoising mapping approach to reduce the decoding error probability. Firstly, they put forward a cluster maximisation algorithm to enlarge one cluster by sucking the neighbour points, which satisfy the exclusive law. Then, based on this algorithm, they designed the heuristic nearest-neighbour denoising mapping (HNDM) approach. The HNDM algorithm divides the nearest neighbour superimposed constellation points into the same cluster as far as possible. Points in the same cluster are coded into a new symbol by a specific mapping that achieves a many-to-one mapping. Performance results are provided in terms of symbol error rate. Under diversity channel conditions, the performances of 16-quadrature amplitude modulator (16-QAM)-8-phase-shift keying and 16-QAM-quadrature phase-shift keying are evaluated.

Flexible Cloud/User-Centric Entanglement and Photon Pair Distribution With Synthesizable Optical Router

The practical roll-out of quantum communication technologies in optical networks and the adoption of novel quantum applications demand the distribution of single or entangled photons. Flexibility and dynamicity are paramount for the provision of quantum resources, in order to scale with the number of users and to meet the demand of complex network architectures. We present a quantum network architecture that features this degree of reconfigurability, without being restricted to a rigid physical-layer network based on purely passive multiplexing componentry. We leverage spectral assets of photon-pair sources, from the short-wavelength band to the L-band, and agile spatial switching at a remote optical network node, in order to realize a flexible distribution map that features different flavors, reaching from cloud-centric to user-centric quantum connectivity. Photon pair distribution is experimentally demonstrated between five users in a 17-km reach, tree-shaped optical network, with high visibility entanglement shared between three users of the network. Simultaneous distribution of photons to more than one user is enabled and the delivered photon rate can be dynamically adjusted. Penalty-free operation is confirmed for integrating a co-existing classical control channel within the quantum.

Design and Analysis of Three-Way Relay Network Coding Schemes Based Differential Chaos Shift Keying Communication System

In this paper, a three-way relay network coding schemes based differential chaos shift keying (DCSK) communication system are investigated. Two schemes of physical layer network coding (PLNC) schemes are proposed to communicate between three users. In the first scheme, three users send their information’s using DCSK modulation in different time slots to the relay, then two encoded bits are extracted from the received bits. After that, the relay broadcast the two encoded bits to three users using DCSK modulation in different time slots. To improve the throughput, energy and spectral efficiency of scheme-1, a new model of PNC scheme is developed based on multiple access DCSK (MA-DCSK) and quadrature chaos shift keying (QCSK) systems. In the first phase, the users send their information’s via MA-DCSK, while in the second phase, the relay broadcast the two encoded bits using QCSK system. In both schemes, the BER analytics are derived and compared with the simulated results under AWGN and multipath Rayleigh fading channel. Furthermore, throughput, link bandwidth and energy efficiency are also derived and compared for two schemes.

Channel-Aware Adaptive Physical-Layer Network Coding Over Relay-Assisted OFDM-VLC Networks

In this article, we propose and experimentally demonstrate the full-duplex channel-aware adaptive physical-layer network (APNC) coding over orthogonal frequency division multiplexing (OFDM) based visible light communication (VLC) to boost the capacity of relay-assisted VLC networks. The network encoding is realized by detecting signals coming from different terminal nodes simultaneously with a single photodiode at the relay node, which then achieves the amplify-and-forward function. At the receiver of each terminal node, the desired signal can be reconstructed by applying the corresponding APNC decoding to the detected interfered signal from the relay node. The use of adaptively loaded OFDM not only addresses the inherent frequency fading issue in VLC systems but also relaxes the synchronization issue at the relay node. The detailed principles of the proposed full-duplex channel-aware APNC scheme are presented, and its performance is experimentally investigated in a two-way-relay (TWR) VLC network. Experimental results show that the proposed scheme exhibits superior BER performance to other existing network scheduling schemes. For a TWR-VLC network with a fixed 600-Mb/s throughput, we achieve around two orders of magnitude reductions in the bit-error-rate (BER) by using the proposed channel-aware APNC scheme compared to other schemes, and BERs of 3.96 × 10−4 and 5.32 × 10−4 are attained for the two transmission links in the TWR network, respectively.

Information modeling for cyber-physical production system based on digital twin and AutomationML

Production systems play an important role in intelligent manufacturing. A large number of manufacturing resources are designed and developed with virtual (digital) ones, which will be associated with the physical ones throughout their lifecycle. With the recent emergence of information and communications technologies (ICTs), such as internet of things, big data, virtual reality, artificial intelligence, and 5G, the interconnection and interaction between physical resources and virtual ones become possible in production systems. Digital twin (DT) shows great potential to realize the cyber-physical production system (CPPS) in the era of Industry 4.0. In this paper, we present our vision on integrating various physical resources into CPPS via DT and AutomationML. To elaborate on how to apply ICTs, this paper firstly explores a generic architecture of CPPS based on DT. DT is a virtual and authoritative representation of physical manufacturing resource, since DT includes various models and manufacturing big data of resource. The proposed architecture is illustrated in detail as follows: (1) physical layer, (2) network layer, (3) virtual layer, and (4) application layer. A case of expert fault diagnose for aircraft engine is presented using the proposed information fusion in the architecture. Secondly, this paper proposes an approach of information modeling for CPPS based on AutomationML. Various manufacturing services can be encapsulated and defined in the standardized format (AutomationML), and then the corresponding virtual manufacturing resources (DTs) will be integrated into CPPS. Finally, this paper describes a case of information modeling for blisk machining and demonstrates the modeling approach in real-life scenarios for support manufacturing resource sharing via DT. Furthermore, the conclusion and further work is briefly summarized.

Spatial-modulated physical-layer network coding based on block Markov superposition transmission for maritime relay communications

As an alternative to satellite communications, multi-hop relay networks can be deployed for maritime long-distance communications. Distinct from terrestrial environment, marine radio signals are affected by many factors, e.g., weather conditions, evaporation ducting, and ship rocking caused by waves. To ensure the data transmission reliability, the block Markov superposition transmission (BMST) codes, which are easily configurable and have predictable performance, are applied in this study. Meanwhile, the physical-layer network coding (PNC) scheme with spatial modulation (SM) is adopted to improve the spectrum utilization. For the BMST-SM-PNC system, we propose an iterative algorithm, which utilizes the channel observations and the a priori information from BMST decoder, to compute the soft information corresponding to the XORed bits constructed by the relay node. The results indicate that the proposed scheme outperforms the convolutional coded SM-PNC over fast-fading Rician channels. Especially, the performance can be easily improved in high spatial correlation maritime channel by increasing the memory m.

Novel Secure Group Data Exchange Protocol in Smart Home with Physical Layer Network Coding.

Smart homes have been shown to be one of the most important applications of Internet of Things (IoT); however, security issues are still the main drawback to be improved, especially facing the problem of terminal power constraint and distributed network architecture. In this paper, we propose a novel secure group data exchange protocol in smart homes with physical layer approaches which retains the benefit of key sharing needless and lightweight computation. As the core technique, nested lattice physical layer network coding is conduct in each sensor node to form a summed data at a home router. With such summed data, the untrusted home router attack and external eavesdropper attack can be resistant. Performance has been analyzed for the proposed protocol in terms of time slot cost, security resistance, and secrecy capacity. Finally, simulations have been conducted to demonstrate the theoretical analysis.

Mapping Obfuscation-Based PHY Security Scheme for Resource-Constrained Wireless Sensor Network

ABSTRACT Wireless sensor network (WSN) physical layer (PHY) uses M-ary spread spectrum (MaSS). This paper explores MaSS and emphasizes that based on the implementation approach; the technology has the potential to provide security at the PHY of wireless devices. The MaSS parameters, namely, spreading sequences and symbol to sequence mapping logic, can be obfuscated for security implementation. In this paper, we have focused our analysis on obfuscating mapping logic, i.e. Mapping Obfuscation (MO). Mathematical analysis reveals that an eavesdropper with processing speed in the order of 1018 operations/sec can intercept and decode short length (maximum 8–10 bytes) packets in <100 s. Simulation exposes that the eavesdropper can achieve a success rate of 50% for short-length packets if its signal-to-noise ratio exceeds −1 dB. An attacker has only one check metric for mapping sequence detection that is correct frame check sequence (FCS) detection. However, FCS detection may be misleading; if packet-embedded FCS and eavesdropper-generated FCS are the same for the wrong mapping sequence. For MO-based MaSS, false FCS detection probability is 30 times more than valid FCS detection probability. To reduce false FCS probability attacker need to analyse multiple radio frequency (RF) packets for detecting a valid mapping key; this increases the computation time. For MO-based PHY security, correct mapping sequence identification by exhaustive search demands cluster-based parallel processing.