Physical Layer Network Research Articles

Maximum Throughput Gain of Compute-and-Forward for Multiple Unicast

Compute-and-Forward (CF), also known as reliable physical layer network coding, is a technique that provides the possibility of exploiting the features of broadcast and superposition in wireless networks. It has been shown that the throughput for multiple unicast traffic can be significantly boosted by CF. In this letter, the limit of such improvement is investigated by comparing the performance of CF with the traditional routing-based transmission schemes. For networks characterized by local interference and half-duplex constraints, it is proven that the throughput gain of CF over traditional routing, expressed by an improvement factor, is upper bounded by 3K, where K is the number of unicast sessions. Furthermore, a class of networks is presented for which an improvement by a factor of K/2 is feasible by applying CF. Hence, the throughput gain of CF is at most on the order of K for any network, and a gain in that order is indeed achievable for some networks.

Research on Physical Layer Network Coding Technology in Wireless Network

Recently, Network coding has been proved to be the breakthrough in the research field of network and communication. It is an effective technique to increase network capacity and improve the robustness and reliability of networks. In this paper, there is application of network coding in wireless network. In order to improve the reliability and the throughput of wireless network, we do extensive research on network coding incorporated with the multicast communication in WLAN, the routing optimization in multi-hop network and the retransmission efficiency for wireless broadcast system, and focus on the protocol design and the theory for the performance analysis. On the basis of introduction on basic idea and method of network coding, we proposes a new physical layer network coding scheme for two-way relay channel model based on a belief propagation approach. Then we make performance analysis through numerical simulation.

Power Allocation and Relay Selection for Two-Way Relaying Systems by Exploiting Physical-Layer Network Coding

In this paper, we study the power allocation and relay selection strategy for two-way relaying systems using physical-layer network coding (PNC), in which two information symbols can be exchanged in two time slots. Our approach is based on maximizing the objective rate under a total power budget consumed by the transmission of the two information symbols. Two optimization objectives, namely, the minimum of the achievable rates of the two directions and the sum rate of the system, are considered here. Since the objectives are not continuously differentiable functions, we propose a method based on a suboptimal solution to solve the original problems. It is shown that the main problems have closed-form solutions, and the strategies can be implemented in a distributed manner. The numerical results verify the effectiveness of our proposal.

An Optimal Power Allocation for the Two-Way Relay System Using Physical-Layer Network Coding

In this letter, an optimal power allocation in the two-way relay channel of four transmission nodes employing the physical-layer network coding (PNC) protocol is proposed to improve the network sum-rate of the two-way relay system. The optimal power allocation is obtained by maximizing the network sum-rate of the PNC protocol under a sum-power constraint in a Rayleigh fading channel environment. Analytical and simulation results show that the proposed power allocation can improve the network sum-rate. Furthermore, compared with the equal power allocation scheme, the proposed power allocation scheme can achieve much higher network sum-rate performance.

Common-Channel Optical Physical-Layer Network Coding

We propose and experimentally demonstrate a coherent optical physical-layer network coding scheme on polarization-multiplexed differential quaternary phase-shift keying (PM-DQPSK) signals, in which the two PM-DQPSK signal components in the network-coded signal occupy the same channel and cannot be separated by conventional means of demultiplexing. In the scheme, network coding at intermediate nodes is realized by combining the two PM-DQPSK signals with a coupler. For network decoding at terminal nodes, one of the signal components is reconstructed and subtracted from the network-coded signal to obtain the other signal component. From its known bit sequence, waveform reconstruction of the signal to be subtracted is implemented by a lookup table. Carrier phase estimation for the reconstructed waveform utilizes the property that DQPSK signals have constant modulus at the sampling point. Experimental results show that, for 12-GBd PM-DQPSK signals, network decoding at a bit error rate of 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-3</sup> can be achieved, with 2.1-dB optical signal-to-noise ratio penalty relative to back-to-back transmission.

Design and Analysis of Multi-Level Physical-Layer Network Coding for Gaussian Two-Way Relay Channels

In this paper, we propose a multi-level physical-layer network coding (MPLNC) scheme that optimizes the relay performance for both symmetric and asymmetric traffic in a Gaussian two-way relay channel. The proposed MPLNC scheme enables each source to employ multiple linear binary codes for encoding, one per modulation level, and the relay node to decode superimposed network codewords at each modulation level. We first derive the achievable rate for the transmission of arbitrary constellations and then prove that MPLNC with multistage decoding (MPLNC/MSD) can achieve the achievable rate if binary code rates are properly chosen for both sources. Furthermore, the design criteria for the proposed MPLNC scheme is investigated, which includes the rate design rule and the labeling strategy. Moreover, we derive the error exponent and an upper bound of the overall error probability for MPLNC. Our analysis and simulation results show that MPLNC/MSD has a significant performance advantage in comparison to the existing bit-interleaved coded modulation (BICM)-based PLNC scheme.

Efficient routing on two layer degree-coupled networks

Traffic dynamics of multiplex networks is one of the new research topics since many systems are proved not to be composed of only a single layer network. Here we focus routing strategies on a two layer degree-coupled network that is composed of a logical layer network and a physical layer network. In this paper, three routing strategies are proposed. Increasing coupling randomness between inter-layer nodes decreases the traffic capacity of the system, which is the result of increase of repeated routing on central nodes. Further, we show that a weighting logical layer network cannot enhance traffic capacity significantly, while avoiding passing through those heavy traffic nodes could notably promote traffic capacity than the performance of a similar strategy in a traditional one layer network.

MIMO Physical Layer Network Coding Scheme in Two-Way Relay Networks

To enhance the ber performance of pseudo physical-layer network coding (ppnc) scheme, a new scheme called pseudo physical-layer soft network coding (ppsnc) scheme is proposed, ppsnc adopts soft information not hard decision information, and its ber performance is better than ppnc. Meanwhile ppsnc has no synchronization problem compared with physical-layer network coding (pnc) scheme. At the same time, we also discuss the performance of ppsnc in mimo environment. The simulation results show that mimo-ppsnc outperforms the other schemes.

Transmission of 16-QAM OFDM Signal with Secure Strategy Technique in DD-OOFDM Systems

The physical layer of optical access network is vulnerable to various attacks. As the dramatic increase of users and network capacity, the issue of physical-layer security becomes more and more important. This paper proposes a physical-enhanced secure strategy for DD-OOFDM system by employing frequency domain chaos scrambling. The FEC coding can also improve the system performance and will not influence the encrypt process. A 2.5Gb/s 16QAM LDPC-OFDM data with Logistic mapped chaos scrambling are successfully transmitted over 40km SSMF. The results show that security sequences protect the system from attacker and keep a good performance for legal receiver.

Advanced Applications of Wireless Sensor Network Using Sensor Cloud Infrastructure

It is our pleasure to publish a special issue on advanced applications of wireless sensor network using sensor cloud infrastructure. This special issue contains seven high quality research papers related to the growing technologies of recent wireless sensor networks and sensor cloud infrastructure. The paper “Sensor resource sharing approaches in sensorcloud infrastructure” by Y. Lim and J. Park presents a survey on sensor-cloud infrastructure (SCI) and discusses technical issues of SCI such as architecture, sensor description methods, middleware based on publish/subscribe data exchange model, and case studies. The paper “Multiple wide tables with vertical scalability in multitenant sensor cloud systems” by K. Ma and B. Yang proposes the multitenant multiple wide tables with vertical scalability by analyzing the features of multitenant data and shows the effectiveness of the proposed method by the experiments. The paper “Semantic reasoning with contextual ontologies on sensor cloud environment” by K. Park et al. presents a massive contextual events handling scheme on a big data framework based on a context-aware inference model with the contextual ontologies and shows that the proposed collaboration framework allows many cooperating parties to collaborate with each other by sharing constituent entities. The paper “Modeling and analysis on congestion control for data transmission in sensor clouds” by J. Huang et al. proposes an Improved Random Early Detection (IRED) algorithm that meets sensor cloud networking requirements better and develops a queueing model coupled with an analysis technique to evaluate the performance of the proposed congestion control scheme. The paper “Agriculture sensor-cloud infrastructure and routing protocol in the physical sensor network layer” by K. Kimet al. proposes an agriculture sensor-cloud infrastructure to provide various services efficiently and to process largescale sensor data effectively and evaluates the proposed techniques by simulation experiments. The paper “Competition-based device-to-device transmission scheduling to support wireless cloud multimedia communications” byR. Yao et al. presents a new algorithm to improve the data transmission quality for a mobile multimedia cloud network (MMCN) in a cloud device-to-device (D2D) communication and demonstrates the simulation results to show the effects of the proposed algorithm. The paper “Towards an environmental measurement cloud: delivering pollution awareness to the public” by F. Dominguez et al. proposes a cloud platform with a federated two-layer architecture which integrates an environmental sensor network with a sensor web, in order to offer geographical environmental data to the public and also to serve as a test bed for scientific research on noise and air pollution. We hope that the papers of this issue contribute to the progress of research and the development of Wireless Sensor Networks.

Providing Secrecy With Structured Codes: Two-User Gaussian Channels

Recent results have shown that structured codes can be used to construct good channel codes, source codes, and physical layer network codes for Gaussian channels. For Gaussian channels with secrecy constraints, however, efforts to date rely on Gaussian random codes. In this paper, we advocate that structure in random code generation is useful for providing secrecy as well. In particular, a Gaussian wiretap channel in the presence of a cooperative jammer is studied. Previously, the achievable secrecy rate for this channel was derived using Gaussian signaling, which saturated at high signal-to-noise ratio (SNR), owing to the fact that the cooperative jammer simultaneously helps by interfering with the eavesdropper, and hurts by interfering with the intended receiver. In this paper, a new achievable rate is derived through imposing a lattice structure on the signals transmitted by both the source and the cooperative jammer, which are aligned at the eavesdropper but remain separable at the intended receiver. We prove that the achieved secrecy rate does not saturate at high SNR for all values of channel gains except when the channel is degraded.

Joint Channel Estimation and Channel Decoding in Physical-Layer Network Coding Systems: An EM-BP Factor Graph Framework

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.

레일레이 페이딩 채널에서 전이중 양방향 중계 네트워크의 성능 분석

전이중(full-duplex) 양방향(two-way) 중계 네트워크는 전이중 방식을 사용하는 중계기에서 중첩 부호화(superposition coding) 혹은 물리 계층 네트워크 부호화(physical layer network coding)를 사용하여 기존 반이중(half duplex) 중계기를 사용하는 양방향 중계 네트워크에 비해 높은 주파수 효율을 제공한다. 본 논문에서는 전이중 양방향 중계 네트워크를 고려하여 전이중 방식에서 필연적으로 발생하는 루프간섭 신호의 영향을 살펴보았다. 여기에서 사용자 및 중계기는 루프간섭 신호를 제거하기 위해 루프간섭 신호를 추정한다. 하지만 루프간섭 신호를 추정할 때, 추정 오류가 발생하여 수신 신호에서 루프간섭 신호를 완벽하게 제거하기는 어렵다. 모의실험에서는 불능 확률(outage probability)을 통해 이로 인해 발생할 수 있는 성능 변화를 분석하였다.

Combining Cooperation and Physical Layer Network Coding to Achieve Reliable Multicast

A novel cooperative scheme based on Physical layer Network Coding (PNC) for short range communication (SRC) networks is presented in this paper. We investigate a scenario of overlapping networks with multicast traffic and propose a technique for the leverage of inter-network cooperation. Our main goal is to exploit the characteristics of PNC in a solution for cooperative SRC networks, where energy efficiency is improved without degrading Quality of Service (QoS). The performance of our proposed cooperative scenario is highly energy efficient and it also presents high throughput. Comparing our scheme with a conventional protocol we show that it presents better performance. We analytically present the throughput, the delay and the energy efficiency of the neighbouring networks and we validate the mathematical analysis through extensive simulations. In addition, we provide an assessment of the impact of the capture effect on the proposed approach. Our proposal is inspired by recent patents in telecommunications that focus on interference cancellation. Keywords: Multicast, cooperative networks, network coding, energy efficiency.Multicast, cooperative networks, network coding, energy efficiency.Multicast, cooperative networks, network coding, energy efficiency.

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.

Hexagonal Constellations for Adaptive Physical-Layer Network Coding 2-Way Relaying

We focus on a constellation design for adaptive physical-layer network coding strategy in a wireless 2-way relay channel. It is well known that 4QAM constellations require extended-cardinality network coding adaptation to avoid all singular channel parameters at the Multiple-Access (MA) stage. The cardinality extension is undesirable since it introduces redundancy decreasing the data rates at the broadcast stage. In this paper, we target a design of constellations avoiding all the singularities without the cardinality extension. We show that such a constellation is 4-ary constellation taken from hexagonal lattice (4HEX) which keeps comparable error performance at the MA stage as 4QAM, however without the cardinality extension. The similar properties has been found also by unconventional 3HEX and 7HEX constellations.

Medium access control: A physical layer network-coded approach

This paper investigates the medium access control (MAC) stratifies for communication systems. Since the signals are naturally superposed in public medium, we introduce physical layer network coding into MAC system and propose the physical layer network coded MAC (PNC-MAC) to utilize the collisions occurring in the MAC process. The implicit expressions of the throughput and average delay of the system operated with the new algorithm are derived in an iterative way. To show the performance of the algorithm, we compare the throughput and average delay induced by the new algorithm with current schemes via simulations. The results show that when operated with our proposed PNC-MAC, MAC system can achieve a larger throughput while the frames bear shorter average delay. Moreover, in many users case, the throughput increases slightly while the average delay ascends drastically.

Design and Study of Cognitive Network Physical Layer Simulation Platform

Cognitive radio technology has received wide attention for its ability to sense and use idle frequency. IEEE 802.22 WRAN, the first to follow the standard in cognitive radio technology, is featured by spectrum sensing and wireless data transmission. As far as wireless transmission is concerned, the availability and implementation of a mature and robust physical layer algorithm are essential to high performance. For the physical layer of WRAN using OFDMA technology, this paper proposes a synchronization algorithm and at the same time provides a public platform for the improvement and verification of that new algorithm. The simulation results show that the performance of the platform is highly close to the theoretical value.

Joint CPFSK Modulation and Physical-Layer Network Coding in Two-Way Relay Channels

Joint CPFSK Modulation and Physical-Layer Network Coding in Two-Way Relay Channels

Optimal Energy-Efficient Power Allocation and Outage Performance Analysis for Cognitive Multi-Antenna Relay Network Using Physical-Layer Network Coding

In this paper, we investigate power allocation scheme and outage performance for a physical-layer network coding (PNC) relay based secondary user (SU) communication in cognitive multi-antenna relay networks (CMRNs), in which two secondary transceivers exchange their information via a multi-antenna relay using PNC protocol. We propose an optimal energy-efficient power allocation (OE-PA) scheme to minimize total energy consumption per bit under the sum rate constraint and interference power threshold (IPT) constraints. A closed-form solution for optimal allocation of transmit power among the SU nodes, as well as the outage probability of the cognitive relay system, are then derived analytically and confirmed by numerical results. Numerical simulations demonstrate the PNC protocol has superiority in energy efficiency performance over conventional direct transmission protocol and Four-Time-Slot (4TS) Decode?and-Forward (DF) relay protocol, and the proposed system has the optimal outage performance when the relay is located at the center of two secondary transceivers.