Cooperative Relay Selection Mechanism in Multi-Hop Networks

In this paper, we consider a three-hop relay system based on interference cancellation technique in Underlay cognitive radio (CR) network. Although underlay CR has been shown as a promising technique to better utilize the source of primary users (PUs), its secondary performance will be severely degraded. On one hand, by adapting the Underlay spectrum sharing pattern, secondary users (SUs) would observe the strict power constraints and be interfered by primary users. On the other hand, limited transmit power results in limited transmission range, which greatly degrade the secondary transmission capacity. To solve the problems above, we propose an interference cancellation protocol for multi-hop wireless communication networks in underlay CR, which could develop the long-distance transmission performance and improve the transmission efficiency significantly. As simulation results shows, proposed scheme significantly reduce the secondary outage probability and increase the secondary diversity than the traditional cases.     

Outage Capacity Analysis for Cognitive Non-Orthogonal Multiple Access Downlink Transmissions Systems in the Presence of Channel Estimation Error

In this paper, we propose a downlink cognitive non-orthogonal multiple access (NOMA) network, where the secondary users (SUs) operate in underlay mode. In the network, secondary transmitter employs NOMA signaling for downlink transmission, and the primary user (PU) is interfered by the transmission from SU. The expressions for the outage probabilities are derived in closed-form for both primary and secondary users in the presence of channel estimation error. Numerical simulation results show that the channel estimation error and the inter-network interference cause degradation of the downlink outage performance. Also the power allocation and the location have a significant impact on the outage probability. The numerical experiments demonstrate that the analytic expressions of the outage probabilities match with the simulation results.     

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。     

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.     

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.     

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.     

Comparative performance study of one or multiple receivers schemes for FSO links over gamma–gamma turbulence channels

Terrestrial free space optical telecommunication systems offer license-free very high bandwidth access characteristics with significantly low installation and operational cost. On the other hand, the performance of such a system depends strongly on the weather conditions in the area between the transmitter and the receiver due to the fact that the transmission media is the atmosphere. A very significant phenomenon which decreases a FSO links' performance is atmospheric turbulence. In order to counterbalance this reduction, in this work, we consider a free space optical system with a multiple receivers' scheme and diversity in space that operates under weak to strong atmospheric turbulence conditions modeled by the gamma–gamma distribution. We derive closed form mathematical expressions for the estimation of the outage probability and the average bit error rate of the multiple receivers' system. Additionally, we compare the performance capabilities of the single point to point link with those of the spatial diversity scheme under the assumption that the total aperture surface of the receivers of the latter is the same as the aperture surface of the single receiver of the former. Moreover, we demonstrate numerical results for a variety of common practical cases for both cases, with and without, spatial diversity.     

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.     

Outage capacity and outage rate performance of MIMO free-space optical system over strong turbulence channel

Abstract

In this paper, we investigate outage capacity, outage probability, and outage rate performance of multiple-input multiple-output (MIMO) free-space optical system operating over strong turbulence channels. The MIMO optical system employs intensity modulation direct detection with on-off signaling, and equal gain combining technique at the receiver. We derived novel closed-form expressions for three system metrics, namely, outage capacity, outage probability, and outage rate. Expressions derived here are based on the generalized Gamma–Gamma channel model, which is based on scintillation theory that assumes that the irradiance of the received optical wave is modeled as the product of small-scale and large-scale turbulence eddies. The results are evaluated for different values of received signal-to-noise ratios, strong turbulence conditions, and several values of transmit/receive diversity.     

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.     

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。     

Second-order statistics of dual-hop transmission with an amplify-and-forward relay over Rician and Weibull fading channels

The level-crossing rate (LCR) and average fade duration (AFD) are the second-order statistics that are useful for the design of adaptive transmission and coding systems over wireless fading channels. These second-order statistics are analyzed for dual-hop transmissions with a fixed-gain amplify-and-forward relay, where the Rician and Weibull fading channels are considered. To evaluate the LCR and AFD, we also derived the lower and upper bounds on the LCR and AFD which are useful when the exact closed-forms of the LCR and AFD are difficult to obtain. To illustrate the performance of the dual-hop relay channel, numerical results of the outage probability, the LCR and AFD are presented.     

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.     

Performance study of terrestrial multi-hop OFDM FSO communication systems with pointing errors over turbulence channels

Abstract

The free-space optical communication systems attract significant research and commercial interest the last few years, due to their high performance and reliability characteristics along with their, relatively, low installation and operational cost. Moreover, due to the fact that these systems are using the atmosphere as propagation path, their performance is varying according to its characteristics. Here, we present the performance analysis of a serially relayed radio-on-free-space-optical (RoFSO) communication system which employs the orthogonal frequency division multiplexing technique, with a quadrature amplitude modulation scheme, over atmospheric turbulence channels modelled by either the Gamma–Gamma or the Gamma distribution model. For this RoFSO communication link, we derive closed-form mathematical expressions for the estimation of its average bit error rate and outage probability, taking into account the relays’ number, the atmospheric turbulence and the pointing errors effect. Furthermore, for realistic parameter values, numerical results are presented using the derived mathematical expressions, which are verified through the corresponding numerical simulations.     

Joint power allocation and relay positioning in multi-relay cooperative systems

The authors consider a dual-hop multi-relay cooperative relay system in this study. Both decode-and-forward (DF) and amplify-and-forward (AF) protocols are considered. Under different relay selection strategies, the authors derive closed-form outage probability expressions. With the second-order channel statistics, the authors propose to jointly optimise power allocation (PA) and relay positions in order to minimise the system outage probability. Simulation results show that the proposed adaptive allocation algorithms significantly outperform fixed allocation algorithms. With the proposed joint optimisation algorithm, AF relaying outperforms DF relaying when multiple relays are selected to help. When only the best relay is selected to help, DF relaying is shown to have better performance.     

An Adaptive Power Allocation Scheme for Performance Improvement of Cooperative SWIPT NOMA Wireless Networks

Future wireless networks demand high spectral efficiency, energy efficiency and reliability. Cooperative non-orthogonal multiple access (NOMA) with simultaneous wireless information and power transfer (SWIPT) is considered as one of the novel techniques to meet this demand. In this work, an adaptive power allocation scheme called SWIPT based adaptive power allocation (SWIPT-APA-NOMA) is proposed for a power domain NOMA network. The proposed scheme considers the receiver sensitivity of the end users while calculating the power allocation coefficients in order to prevent wastage of power allocated to user in outage and by offering priority to any one of the users to use maximum harvested power. A detailed analysis on the bit error rate (BER) performance of the proposed scheme is done and closed form expression is obtained. Simulations have been carried out with various parameters that influence the receiver sensitivity and the results show that the network achieves better outage and BER performance using the proposed scheme. It is found that the proposed scheme leads to a ten-fold decrease in transmit power for the same error performance of a fixed power allocation scheme. Further, it offers 96.06% improvement in the capacity for a cumulative noise figure and fading margin of 10 dB.     

BER analysis of space-time diversity in CDMA systems over frequency-selective fading channels

The performance of direct-sequence code division multiple access (DS-CDMA) using space-time spreading system, over frequency-selective fading channels, is investigated. The underlying transmit diversity scheme, previously introduced in the literature, is based on two transmit and one receive antenna. It was shown that when employed in flat fast-fading channels, the received signal quality can be improved by utilising the spatial and temporal diversities at the receiver side. We study the problem of multiuser interference in asynchronous CDMA systems that employ transmit/receive diversity using space-time spreading. To overcome the effects of interference, a decorrelator detector is used at the base station. Considering binary phase-shift keying transmission, we analyse the system performance in terms of its probability of bit error. In particular, we derive the probability of error over frequency-selective Rayleigh fading channels for both fast and slow-fading channels. For the fast-fading channel, both simulations and analytical results show that the full system diversity is achieved. On the other hand, when considering a slow-fading channel, we show that the scheme reduces to conventional space-time spreading schemes where the diversity order is half of that of fast-fading.     

Social-Aware Based Secure Relay Selection in Relay-Assisted D2D Communications

Relay-assisted transmission could effectively enhance the performance of Device-to-Device (D2D) communications when D2D user equipments (UEs) are too far away from each other or the quality of D2D channel is not good enough for direct communications. Meanwhile, security is one of the major concerns for proximity services. The secure relay selection problem for D2D communications underlaying cellular network is studied in this paper. Firstly, we define a relay selection area and derive the closed-form of outage probability in D2D links using a Poisson Point Process (PPP) method. Next, in the defined relay selection area, we propose a secure relay selection scheme for the relay-assisted D2D communication system by exploiting the social relation as a security factor. Simulation results show that the scheme based on social relation can greatly improve the security performance of relay-assisted D2D communications.     

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。     

Performance analysis of multiple-input multipleoutput singular value decomposition transceivers during fading and other cell interference

A generalised method is derived to compute the error probabilities of singular value decomposition (SVD)-based receivers for a multiple-input multiple-output (MIMO) system with uncoded transmission. The method can be used for a wide class of flat fading environments, including independent and identically distributed (i.i.d.) and semi-correlated Rayleigh and i.i.d. Ricean channels. Although the method is applied to equal-power binary phase shift keying, it can easily be extended to higher-order M-ary phase shift keying (M-PSK) and M-ary quadrature amplitude modulation (M-QAM) signal constellations and adaptive 'water-filling' schemes. The error probability curves derived from closed-form formulas and simulations demonstrate very close agreement. The error performances of channel inversion, minimum mean square error and zero forcing receivers are compared with the SVD receiver for a single-user system. The impact of multiple users is considered by studying the performance of an adaptive MIMO SVD transmission scheme operating in a cellular environment. In particular, the effect of inter-cell interference on the performance of the scheme is quantified, modelling the interference as increased Gaussian noise. A number of cellular layouts are examined and the impact of the resulting singal-to-interference and noise ratio on the constellation sizes that can be supported, the BER and so on is considered. The primary metric used for our performance analysis is the error-free transmission rate, which is derived for our adaptive system. For the cellular scenarios considered, it can be found that the effect of interference is considerable and the performance of the adaptive MIMO SVD scheme is only marginally better than that provided by conventional diversity methods.