Cooperative transmission in wireless networks using incremental opportunistic relaying strategy

In this study, the authors develop a novel cooperative transmission scheme ? distributed opportunistic incremental decode and forward (DOIDF) that employs the incremental relaying (IR) strategy in opportunistic relaying (OR) protocols. By exploiting limited feedback from the destination, the proposed scheme starts the OR plan only when outage event happens in direct transmission (DT). The outage probability of DOIDF is derived in detail, and the results show that DOIDF can achieve the same space diversity order as multiple input single output (MISO) and single input multiple output (SIMO) systems, which is the upper limit of cooperative diversity. By analysing and comparing the approximate expression of outage probability of various protocols in high-signal-to-noise ratio (SNR) regime, the concept of system overhead factor (SOF), which reveals the effects of channel allocation in cooperative protocols on system performance, is proposed. Subsequent analysis and simulation results show that DOIDF outperforms corresponding OR schemes in outage probability, spectral efficiency and SNR gain over DT.     

Fast antenna subset selection algorithms for multiple-input multiple-output relay systems

The antenna subset selection technique balances the performance and hardware cost in the multipleinput multiple-output (MIMO) systems, and the problems on the antenna selection in MIMO relay systems have not been fully solved. This paper considers antenna selection on amplify-and-forward (AF) and decode-andforward (DF) MIMO relay systems to maximise capacity. Since the optimal antenna selection algorithm has high complexity, two fast algorithms are proposed. The selection criterion of the algorithm for AF relay is to maximise a lower bound of the capacity, but not the exact capacity. This criterion reduces algorithmic complexity. The algorithm for DF relay is an extension of an existing antenna subset selection algorithm for one-hop MIMO systems. The authors show the derivations of the algorithms in detail, and analyse their complexity in terms of numbers of complex multiplications. Simulation results show that the proposed algorithms for both cases achieve comparable performance to the optimal algorithm under various conditions, and have decreased complexity.     

Closed-form symbol error rate expression of decode-and-forward relaying using orthogonal space-time block coding

The authors investigate the symbol error rate (SER) performance of the cooperative decode-andforward (DF) relaying strategy with orthogonal space-time block coding (OSTBC) applied at all links of sourcerelay, source-destination and relay-destination. Only when one relay node is able to correctly decode the OSTBC codeword of the source, it will forward source information to the destination with the same OSTBC codeword. The exact SER expressions of DF relaying with OSTBC are presented for M-PSK and M-QAM modulations, respectively, over dissimilar Rayleigh fading channels. By virtue of the multinomial theorem and the law of total probability, the derived expressions are further deduced in closed form. Simulations demonstrate the proposed closed-form analytical results. It is pointed out that such results have seldom appeared in literatures before.     

Secrecy Outage Probability Analysis Based on Cognitive Decodeand-Forward Relaying

Wireless communications have to face to several different security issues in practice due to the nature of broadcast. The information theory is well known to provide efficient approaches to address security issues in wireless communications, which attracts much attention in both industry and academia in recent years. In this paper, inspired by information theory, we study the outage probability of the opportunistic relay selection based on cognitive decode-and-forward relaying with the secrecy consideration. Specifically, the closed-form expression of the outage probability is proposed. Moreover, the asymptotic performance evaluation on the basis of the analytical results is investigated. The simulation results show that the relay selection can reduce the outage probability in accordance with our theoretical analysis.     

M分布模型下多跳相干OFDM FSO系统的性能研究

本文在涵盖了从弱湍流到强湍流的所有信道条件,能够表征现有大多数湍流信道的M分布模型下,采用QPSK调制方式研究了多跳相干OFDM FSO系统的性能。系统在中继辅助链路的发射机和接收机之间使用DF中继协议。考虑大气湍流、路径损耗以及瞄准误差对大气信道衰落模型的联合作用,分别推导出系统的中断概率和误符号率的Meijer G形式的闭合表达式。通过仿真分析了中继链路长度、中继节点数以及子载波个数等关键因素对系统的中断性能和误符号率性能的影响。本研究为中继系统的实际应用奠定了理论基础。     

Cross-layer queuing analysis on multihop relaying networks with adaptive modulation and coding

Multihop relaying is one of the promising techniques in future generation wireless networks. The adaptive modulation and coding (AMC) mechanisms can be applied in order to increase the spectral efficiency of wireless multihop networks. However, most of these mechanisms concentrate on the physical layer without taking the queuing effects at the data link layer into account, whose performances are overestimated. Therefore the cross-layer analytical framework is presented in analysing the quality-of-service (QoS) performances of the decode-and-forward (DF) relaying wireless networks, where the AMC is employed at the physical layer under the conditions of unsaturated traffic and finite-length queue at the data link layer. Considering the characteristics of DF relaying protocol at the physical layer, the authors first propose modelling a two-hop DF relaying wireless channel with AMC as an equivalent Finite State Markov Chain (FSMC) in queuing analysis. Then, the performances in terms of queuing delay, packet loss rate and average throughput are derived. The numerical results show that the proposed analytical method can be efficiently applied for studying the issues including the relay deployment and the cross-layer design in the multihop relaying networks.     

Diversity analysis of smart relaying over Nakagami and Hoyt generalised fading channels

Signal transmission with the help of relay(s) in wireless networks can achieve spatial diversity without the need of having multiple attennas at the source and/or destination. Among various signal processing techniques proposed for the relays, the adaptive decode-and-forward (DF) relaying strategy, recently proposed by Wang et al. and generally referred to as smart relaying, has been shown to achieve the maximal spatial diversity even when imperfect detection is committed at the relays. The work by Wang et al., however, only considers Rayleigh fading channels. This paper extends the diversity analysis of the smart relaying technique to the important Nakagami and Hoyt generalised fading channels. Performance analysis proves that, at high signal-to-noise ratio, the maximal diversity order achieved by the smart relaying system under the Nakagami channel is m_SD + min{m_SR, m_RD}, where m_SR, m_RD and m_SD are the fading figures of the source?relay (S?R), relay?destination (R?D) and source?destination (S?D) links. Under the Hoyt fading channel, the diversity order is 2. The obtained results on the diversity order are shown to be insensitive to the quality of the R?D feedback channel.     

Two incremental relaying protocols for cooperative networks

The authors investigate a cooperative network with three terminals. By exploiting a simple two-bit feedback message from the destination, two incremental relaying protocols are proposed, namely incremental selection amplify-and-forward (ISAF) and joint incremental selection relaying (JISR) with an aim to balance the load between the source and the relay. The authors derive the asymptotic outage probabilities of the two new protocols and find them to be lower than that of the incremental amplify-and-forward (IAF) protocol, which has been identified as the best protocol so far. Moreover, the spectral efficiencies of ISAF and JISR match that of IAF. Simulation results have verified the asymptotic performance of the protocols and have shown that JISR outperforms ISAF and IAF over all signal-to-noise ratio values.     

OFDM水声通信下行非正交多址接入功率分配方法研究

针对基于功率域非正交多址接入（Power Domain Non-orthogonal Multiple Accesses,PD-NOMA）的正交频分复用（Orthogonal Frequency Division Multiplexing,OFDM）水声下行通信系统的功率分配问题,提出了一种基于中断概率的功率分配方法。用户节点在系统初始化阶段根据源节点广播的组网数据包获取水声信道的统计特征,源节点根据水下用户反馈的信道特征参数建立水下用户的中断概率模型,以最小化两用户的中断概率和为目标建立目标函数,在中断概率区域边界上遍历搜索最优的功率分配系数。仿真结果表明,该方法在保证公平性的条件下,有效降低了用户节点的中断概率,提高了系统的频谱利用率和误码性能。     

Throughput Analysis of HARQ Scheme Based on Full-Duplex Two-Way AF SWIPT Relay

The simultaneous wireless information and power transfer (SWIPT) relay system is one of the emerging technologies. Xiaomi Corporation and Motorola Inc. recently launched indoor wireless power transfer equipment is one of the most promising applications. To tap the potential of the system, hybrid automatic repeat request (HARQ) is introduced into the SWIPT relay system. Firstly, the time slot structure of HARQ scheme based on full duplex two-way amplify and forward (AF) SWIPT relay is given, and its retransmission status is analyzed. Secondly, the equivalent signal-to-noise ratio and outage probability of various states are calculated by approximate simplification. Thirdly, the energy harvesting power in each state is calculated. Finally, the energy harvested-throughput sum function is constructed to characterize the performance of energy harvesting and data transmission. Simulation results show that the proposed HARQ scheme has better energy harvested-throughput sum function than the traditional HARQ scheme. When P₂ = 22 dB, the maximum sum function is 54.86% (the proposed HARQ scheme) and 52.307% (the traditional HARQ scheme), respectively.     

Software reliability allocation of digital relay for transmission line protection using a combined system hierarchy and fault tree approach

Digital relay is a special purpose signal processing unit in which the samples of physical parameters such as current, voltage and other quantities are taken. With the proliferation of computer technology in terms of computational ability as well as reliability, computers are being used for such digital signal processing purposes. As far as computer hardware is concerned, it has been growing steadily in terms of power and reliability. Since power plant technology is now globally switching over to such computer-based relaying, software reliability naturally emerges as an area of prime importance. Recently, some computer-based digital relay algorithms have been proposed based on frequency-domain analysis using wavelet-neuro-fuzzy techniques for transmission line faults. A software reliability allocation scheme is devised for the performance evaluation of a multi-functional, multi-user digital relay that does detection, classification and location of transmission line faults.     

主用户链路深度衰落下的认知网络中继

针对主用户链路经历深度衰落而发生通信中断的问题,提出了一种认知网络对主用户进行"透明"中继的方案。在不改变主用户通信协议的前提下,该方案首先感知主用户的状态,以判断其是否需要中继服务。当主用户通信发生中断时,认知网络利用从用户的能量检测器选出一个最优的节点解码转发主用户信号。从中断概率角度证明了这种最优单节点中继具有与多节点中继相同的空间分集作用,能够提高主用户平均传输效率,有较大的中继信道容量。通过仿真分析,验证了其分集效果和传输效率的提升。     

Outage performance of cooperative relaying with dissimilar Nakagami-m interferers in Nakagami-m fading

The authors investigate the outage performance for decode-and-forward relaying schemes in the presence of dissimilar Nakagami-m interferers under non-identical Nakagami-m fading channels. A closed-form expression for the outage probability is derived under this scenario. Simulation results demonstrate our theoretical solutions.     

无线中继网络系统容量最大化中继选择机制

分析了基于用户频谱效率的中继选择算法的不足,基于最大流最小割定理,给出了系统容量最优化问题模型,分析了两跳中继网络接入链路和中继链路对系统容量的不同影响.基于链路权重因子,提出一种基于系统容量最大化的中继选择算法.对不同中继选择算法下的系统容量差异的理论与仿真分析结果表明,提出的系统容量最大化中继选择算法可以获得更优的系统容量性能,并对网络拓扑和节点个数具有良好的鲁棒性.     

Embedded Coded Relay System for Molecular Communications

With the emergence of the COVID-19 pandemic, the World Health Organization (WHO) has urged scientists and industrialists to explore modern information and communication technology (ICT) as a means to reduce or even eliminate it. The World Health Organization recently reported that the virus may infect the organism through any organ in the living body, such as the respiratory, the immunity, the nervous, the digestive, or the cardiovascular system. Targeting the abovementioned goal, we envision an implanted nanosystem embedded in the intra living-body network. The main function of the nanosystem is either to perform diagnosis and mitigation of infectious diseases or to implement a targeted drug delivery system (i.e., delivery of the therapeutic drug to the diseased tissue or targeted cell). The communication among the nanomachines is accomplished via communication-based molecular diffusion. The control/interconnection of the nanosystem is accomplished through the utilization of Internet of bio-nano things (IoBNT). The proposed nanosystem is designed to employ a coded relay nanomachine disciplined by the decode and forward (DF) principle to ensure reliable drug delivery to the targeted cell. Notably, both the sensitivity of the drug dose and the phenomenon of drug molecules loss before delivery to the target cell site in long-distance due to the molecules diffusion process are taken into account. In this paper, a coded relay NM with conventional coding techniques such as RS and Turbo codes is selected to achieve minimum bit error rate (BER) performance and high signal-to-noise ratio (SNR), while the detection process is based on maximum likelihood (ML) probability and minimum error probability (MEP). The performance analysis of the proposed scheme is evaluated in terms of channel capacity and bit error rate by varying system parameters such as relay position, number of released molecules, relay and receiver size. Analysis results are validated through simulation and demonstrate that the proposed scheme can significantly improve delivery performance of the desirable drugs in the molecular communication system.     

Performance Analysis of Relay Based NOMA Cooperative Transmission under Cognitive Radio Network

This paper proposes a hybrid spectrum accessing mechanism by using NOMA-based cooperative transmission and beam-forming technology. In this mechanism, the secondary user employs spectrum-sensing technology to detect the existence of the primary user. If the primary user does not exist, the secondary source user directly transmits data to the destination user. If the primary user exists, the secondary source user finds the optimal relay according to certain selection principle before transmitting data to the destination user through the chosen relay node. For the signal receiving stage, the secondary user takes use of beam-forming technology to receive the signal from both the secondary source and the secondary relay node. Meanwhile the interference from the primary user is cancelled out in the stage. Furthermore, the outage probability for secondary user in the proposed mechanism is theoretically derived. Finally, the simulation results show that compared with the traditional mechanism, the proposed system model can not only guarantee the continuity of secondary transmission, but also significantly reduce the outage probability of secondary transmission.     

Ergodic Capacity Evaluation of Multi-Hop Decode-and-Forward MIMO-OFDM Relaying Network

Spatial diversity plays a significant role in wireless communication systems, including the Fourth Generation (4G) and Fifth Generation (5G) systems, and it is expected to be a fundamental part of the future wireless communication systems as well. The Multiple-Input Multiple-Output (MIMO) technology, which is included in the IEEE 802.16j standard, still holds the most crucial position in the 4G spectrum as it promises to improve the throughput, capacity, spectral, and energy efficiency of wireless communication systems in the 2020s. This makes MIMO a viable technology for delay constrained medical and health care facilities. This paper presents an approximate closed-form expression of the ergodic capacity for the Decode-and-Forward (DF) protocol MIMO-Orthogonal Frequency Division Multiplexing (OFDM) relaying network. Although MIMO-OFDM is highly valuable for modern high-speed wireless communication systems, especially in the medical sciences, its performance degrades in multi-hop relay networks. Therefore, in this paper, an approximate closed-form expression is derived for an end-to-end ergodic capacity of multi-hop DF MIMO-OFDM wireless communication system has been presented. Monte-Carlo simulations are conducted to verify the performance of the presented analysis regarding the capacity (bits/s/Hz) for different SNR-dB values for single, 2 × 2, 4 × 4, and multi-hop DF MIMO-OFDM systems. The presented results provide useful insights for the research on the end-to-end ergodic capacity evaluation.     

Distributed truncated ARQ protocol for cooperative diversity networks

Automatic repeat request (ARQ) retransmission in user cooperative networks, which use amplify-and-forward as a relaying strategy is dealt with. In contrast to the conventional environments, where the source responds in a retransmission demand, in cooperative systems this requirement can also be satisfied by a relay node. In addition, if a relay node can be selected according to the instantaneous channel conditions, the source is not always the optimal responder. The problem under consideration here is to find the retransmission combination which optimises the performance under a given delay quality-of-service constraint. It will be shown that the optimal combination depends on the number of available relays, the total number of retransmissions and the average signal-to-noise ratio. We provide an analytical framework for the definition of the optimal combination in function of these three system parameters. Since the practical ad hoc networks are not centralised and do not have an external control, a distributed truncated ARQ protocol is further proposed to apply the decided retransmission combination.     

Performance of a QAM/FSO communication system employing spatial diversity in weak and saturation turbulence channels

In this paper, the bit error rate (BER) performance and outage probability of quadrature amplitude modulation free space optical (QAM/FSO) communications with spatial diversity in turbulent environments are investigated. The equal-gain combining (EGC) and selection combining (SelC) diversity techniques are considered to mitigate turbulence-induced signal fading in the proposed system. The average BER and outage probability expressions are derived for EGC diversity in weak and saturation turbulence channels. The results indicate that using EGC diversity can significantly improve the system performance compared to employing the SelC diversity or single monolithic aperture schemes. Specifically, approximately 4 and 9?dB lower signal-to-noise power ratios are required for the 1?×?4 EGC diversity system than for the 1?×?4 SelC and non-diversity systems at a BER of 10^?10. In addition, the use of diversity techniques also significantly decreases the outage probability. The proposed scheme can be helpful for establishing a spatial diversity FSO system with a low error rate and high transmission rate.     

Effective transmission opportunity allocation scheme for real-time variable bit rate traffic flows with different delay bounds

The medium access control of IEEE 802.11e defines a novel coordination function, namely, hybrid coordination function (HCF), which allocates transmission opportunity (TXOP) to stations taking their quality of service (QoS) requirements into account. However, the reference TXOP allocation scheme of HCF controlled channel access, a contention-free channel access function of HCF, is only suitable for constant bit rate traffic. For variable bit rate traffic, packet loss may occur seriously. The authors propose a TXOP allocation scheme to efficiently allocate bandwidth and meet the QoS requirements in terms of both delay bound and packet loss probability. To achieve high bandwidth efficiency, the authors take advantage of not only intra-flow multiplexing gain of traffic flows with large delay bounds, but also inter-flow multiplexing gain of multiple traffic flows with different delay bounds. According to numerical results obtained by computer simulations, the proposed TXOP allocation scheme results in much higher bandwidth efficiency than previous algorithms under the same constraints of delay bounds and packet loss probability.