Performance analysis of linear receivers in a MIMO relaying system

We investigate the performance of linear receivers in a cooperative system which consists of a source, a decodeand- forward (DF) relay and a destination that are all multiantenna nodes. The relay uses zero-forcing (ZF) equalization whereas the destination employs maximum ratio combining (MRC) as well as ZF techniques. Considering that perfect channel state information is available at the relay and destination, and the fading is Rayleigh, we derive a closed-form approximate expression for the outage probability of the post-receiver signalto- noise ratio (SNR) of each data stream at the destination and analyze the diversity order. The validity of the outage probability expression is confirmed with the numerical results.     

Distributed Adaptive Power Allocation for Wireless Relay Networks

In this paper, we consider a 2-hop wireless diversity relay network. We explore transmit power allocation among the source and relays to maximize the received signal to noise ratio (SNR) at the destination. We consider two relay protocols, "amplify and forward" (AAF) and "decode and forward" (DAF) and design the respective power allocations for both uneeded and coded systems. For a 2-hop relay system with one relay node, we derive a closed-form power allocation solution and, based on it, we propose a relay activation condition. If and only if the fading channel coefficients satisfy this condition, the relay transmits the signals to the destination; otherwise, the relay will stay in the idle state. For a system with more than one relay node, general closed-form power allocation solutions based on an exact SNR expression are difficult to derive; we hence, calculate a SNR upper bound and derive a sub-optimum power allocation solution based on this bound. The simulation results show that for a 2-hop diversity relay channel with one relay node the proposed adaptive power allocation (APA) scheme yields about 1- 2 dB SNR gains compared to the equal power allocation. This SNR gain increases monotonically as the number of relays increases     

Performance of Transmit Antenna Selection and Maximal-Ratio Combining in Dual Hop Amplify-and-Forward Relay Network over Nakagami-m Fading Channels

In this paper, we study end-to-end performance of transmit antenna selection (TAS) and maximal ratio combining (MRC) in dual hop amplify-and-forward relay network in flat and asymmetric Nakagami-m fading channels. In the network, source and destination communicate by the help of single relay and source-destination link is not available. Source and destination are equipped with multiple antennas, and relay is equipped with single antenna. TAS and MRC are used for transmission at the source and reception at the destination, respectively. The relay simply amplifies and forwards the signal sent by the source to the destination by using channel state information (CSI) based gain or fixed gain. By considering relay location, for CSI based and fixed relay gains, we derive closed-form cumulative distribution function, moments and moment generating function of end-to-end signal-to-noise ratio, and closed-form symbol error probability expression. Moreover, asymptotical outage probability and symbol error probability expressions are also derived for both CSI based and fixed gains to obtain diversity order of the network. Analytical results are validated by the Monte Carlo simulations. Results show that diversity order is minimum of products of fading parameter and number of antennas at the end in each hop. In addition, for optimum performance the relay must be closer to the source when the diversity order of the first hop is smaller than or equal to that of the second hop.     

Outage Performance of Dual-Hop AF Relay Channels with Co-Channel Interferences over Rayleigh Fading

This paper studies the outage performance of a dual-hop amplify-and-forward (AF) relay fading channel in an interference-limited environment. The relay and destination nodes are corrupted by multiple co-channel Rayleigh interferences. New exact closed-form expressions for the outage probability for channel-state-information (CSI)—assisted relay, in which gain is dependent on previous hop CSI and interference, are derived. Monte Carlo simulations are performed to verify the obtained theoretical results. For the cases where the number of interferers at the relay and the destination node is equal, we derive novel expressions for outage probability upper and lower bounds.     

Outage performance of MIMO relay channels with maximal ratio transmission

The outage performance of a multiple-input multiple-output (MIMO) relay system over slow frequency-nonselective fading channels, where maximal ratio transmission is adopted at both the source and relay transmitters whereas maximal ratio combining is used at relay and destination receivers, is investigated. A closed-form expression for the outage probability is presented. Numerical results are presented to verify the analysis.     

Performance Analysis of Incremental Amplify-and-Forward Relaying Protocols with Nth Best Partial Relay Selection Under Interference Constraint

In this paper, we investigate two incremental amplify-and-forward relaying protocols in cognitive underlay networks. In the proposed protocols, whenever the secondary destination cannot receive the secondary source’s signal successfully, it requests a retransmission from one of M secondary relays. In the first protocol, we assume that a secondary relay with the Nth best channel gain to the secondary source is used to forward the received signal to the secondary destination. In the second protocol, relying on the quality of channels between the secondary relay and secondary destination and between the secondary relay and primary user, the Nth best relay is chosen for the retransmission. We derive exact closed-form expressions of the outage probability and average number of time slots for both protocols over Rayleigh fading channel. Finally, these mathematical expressions are then verified by Monte Carlo simulations.     

Cooperative Communication Protocols in Wireless Networks: Performance Analysis and Optimum Power Allocation

In this paper, symbol-error-rate (SER) performance analysis and optimum power allocation are provided for uncoded cooperative communications in wireless networks with either decode-and-forward (DF) or amplify-and-forward (AF) cooperation protocol, in which source and relay send information to destination through orthogonal channels. In case of the DF cooperation systems, closed-form SER formulation is provided for uncoded cooperation systems with PSK and QAM signals. Moreover, an SER upper bound as well as an approximation are established to show the asymptotic performance of the DF cooperation systems, where the SER approximation is asymptotically tight at high signal-to-noise ratio (SNR). Based on the asymptotically tight SER approximation, an optimum power allocation is determined for the DF cooperation systems. In case of the AF cooperation systems, we obtain at first a simple closed-form moment generating function (MGF) expression for the harmonic mean to avoid the hypergeometric functions as commonly used in the literature. By taking advantage of the simple MGF expression, we obtain a closed-form SER performance analysis for the AF cooperation systems with PSK and QAM signals. Moreover, an SER approximation is also established which is asymptotically tight at high SNR. Based on the asymptotically tight SER approximation, an optimum power allocation is determined for the AF cooperation systems. In both the DF and AF cooperation systems, it turns out that an equal power strategy is good, but in general not optimum in cooperative communications. The optimum power allocation depends on the channel link quality. An interesting result is that in case that all channel links are available, the optimum power allocation does not depend on the direct link between source and destination, it depends only on the channel links related to the relay. Finally, we compare the performance of the cooperation systems with either DF or AF protocol. It is shown that the performance of a systems with the DF cooperation protocol is better than that with the AF protocol. However, the performance gain varies with different modulation types and channel conditions, and the gain is limited. For example, in case of BPSK modulation, the performance gain cannot be larger than 2.4 dB; and for QPSK modulation, it cannot be larger than 1.2 dB. Extensive simulation results are provided to validate the theoretical analysis.     

Asymptotic performance analysis of untrusted relay system with full-duplex jamming destination

The cooperative relay technique in the field of physical layer security is widely concerned by the academic community,due to the advantages of increasing the network capacity and expanding the network coverage.However,cooperative relays may play as untrusted nodes in some certain circumstances.Based on this,to enhance the secrecy performance of untrusted relay systems,a novel full-duplex destination jamming (FDJ) scheme was proposed in the Rayleigh fading channel.In order to maximize the system’s secrecy capacity,a switchable split-optimal antenna selection (OAS) scheme was proposed for a multiple-antenna destination,the power allocation optimization scheme between the source and destination was designed,and the corresponding closed-form expressions of secrecy performance were given.In the large-scale antennas analysis,the closed-form expressions of the ergodic achievable secrecy rate and the optimal power allocation factor of instantaneous secrecy capacity for the FDJ-OAS scheme were derived.Furthermore,based on different asymptotic cases,the asymptotic analyses of secrecy outage probability for the FDJ-OAS scheme were significantly analyzed.Simulation results show that the analytical curves match well with the Monte-Carlo simulation results.It is concluded that the diversity order of the FDJ-OAS scheme is proportional to the number of antennas and antenna diversity can be achieved,which reveals the advantages of the proposed FDJ-OAS scheme.     

Outage performance of two-hop multi-antenna co-operative relaying in rayleigh fading channel

Performance of co-operative relaying employing infrastructure based fixed relays having multiple antennas has been investigated. A closed-form expression of outage probability for such a system has been derived when the relay performs selection combining and the destination performs MRC combining of signals. The effect of relay placement on the system performance has also been studied.     

An opportunistic cooperation scheme and its BER analysis

The cooperative communication technology proposed in recent years enables network nodes to share their antennas to achieve diversity gain. In this paper, an efficient variation scheme on opportunistic cooperation is proposed by using an outage criterion, in which the cooperation mode will be adopted only when the channel from source to relay does not occur outage event. We derive a closed-form BER (bit error rate) expression for the proposed scheme over Rayleigh fading channels, showing that the full diversity is achieved by the new scheme. Also, the BER performance of the known coded cooperation is presented for the purpose of comparison with our scheme. Numerical results illustrate the superiority of the proposed scheme over the coded cooperation in terms of BER performance. It is pointed out that the corresponding BER advantage of the proposed scheme comes at the expense of increasing system overhead since the new scheme needs some feedback from relay to both source and destination.     

A Threshold-Free LLR-Based Scheme to Minimize the BER for Decode-and-Forward Relaying

In cooperative communications, the problem of error propagation has a detrimental effect on the diversity order of the wireless system. To mitigate such an effect, we present a relaying scheme that is based on the absolute value of the log-likelihood ratio (LLR) of the received message signals at both the relay node and the destination node. The calculated LLR values are then compared to each other and based on the result of the comparison, a decision is made on whether or not to activate the relay node. The proposed scheme does not rely on any threshold, and is thus simple in nature. A closed-form expression is derived for the bit-error-rate (BER) of the proposed scheme. The theoretical developments are validated by simulations. As a means for performance measurement, the proposed scheme is compared to its counterparts and is shown to provide a better BER performance at a much lower complexity. Furthermore, a closed-form expression of the outage probability is also derived.     

协作干扰下的非可信中继与全双工目的节点系统的遍历安全容量分析

研究了一种非可信放大转发中继与全双工目的节点相结合的传输模型。为提升系统安全性能,提出了全双工目的节点干扰(full duplex-destination based jamming,FD-DBJ)策略。同时结合半双工目的节点干扰策略以及放大转发中继策略对比分析系统安全性能。在瑞利衰落信道下,通过合理的近似分析推导出三种策略遍历安全容量的近似闭合表达式。分析与仿真结果显示,在高信噪比下,理论分析曲线与蒙特卡洛仿真结果基本吻合,并对三种策略的性能进行对比,凸显出FD-DBJ策略的性能优越性。并分析了FD-DBJ传输策略的最优功率分配因子。      

Capacity Analysis of Opportunistic Cooperative Networks under Adaptive Transmission over Rayleigh Fading Channels

In this paper, opportunistic cooperative amplify-and-forward networks in conjunction with three different adaptive policies, namely optimal simultaneous power and rate adaptation (OPRA), constant power with optimal rate adaptation (OPA) and truncated channel inversion with fixed rate (TIFR), are investigated and compared in terms of Rayleigh channel capacity where the source adapts its rate and/or power level according to channel conditions while the best relay simply amplifies and then forwards the received signals. Furthermore, the effect of diversity combining on the network is studied by investigating two cases of maximal ratio combining (MRC) and selection combining (SC) equipped at the destination. To this end, the mathematically tractable form of the upper and lower bound of the end-to-end effective signal-to-noise ratio (SNR) is provided and then used to derive the closed-form expression of the Shannon capacity. Our results are verified through comparison with Monte Carlo simulations in some representative scenarios where we also illustrate that, among them, for an arbitrary number of cooperative relays, OPRA slightly outperforms ORA, which, in turn, outperforms TIFR.     

Adaptive Cooperative Decode-and-Forward Transmission with Power Allocation Under Interference Constraint

In this paper, we examine an adaptive decode-and-forward cooperative protocol under interference constraint. In the proposed protocol, relying on the obtained instantaneous signal-to-noise ratios (SNRs), a direct link or relay link is used to transmit data from the secondary source to the secondary destination. In addition, once the relay link is used, the secondary source and relay must adapt their transmit power to maximize the instantaneous SNR of this link. To evaluate the performance of the proposed protocol, we derive closed-form lower-bound and upper-bound expressions for the outage probability over Rayleigh fading channel. Finally, various Monte-Carlo simulations are presented to verify our analysis and compare the performance of the proposed protocol with that of the direct transmission protocol in underlay cognitive network.     

MMSE based joint Tomlinson-Harashima source and linear relay precoder design in non-regenerative MIMO relay system

This paper proposes a joint nonlinear transceiver design scheme based on minimum mean square error(MMSE) criterion for non-regenerative multiple input multiple output(MIMO) relay system.The proposed scheme decomposes the error covariance matrix,reformulates the original joint design problem as two separate optimization problems,and then provides a closed-form solution with only local channel state information(CSI) available at the source and destination.Performance evaluation shows that the proposed scheme significantly outperforms linear schemes,and has a competitive performance compared with existing global CSI based nonlinear schemes,both iterative and non-iterative.     

同信道干扰条件下的多天线放大转发中继中断概率分析

该文研究了基于波束形成技术的双跳多输入多输出(MIMO)放大转发(AF)中继系统的中断概率,该系统在发射端、中继端和接收端都配置了多根天线。假设每条链路的发射端采用最大比传输(MRT)技术,接收端采用最大合并比(MRC)技术,该文得出了中继端受到同信道干扰时的信干噪比(SINR),推导了基于固定增益中继方案的中断概率(OP)闭合表达式。计算机仿真结果不仅验证了性能分析的有效性,而且还分析了关键参数对系统性能的影响以及配置多天线带来的好处。     

Three-phase two-way relaying with imperfect channel estimation and asymmetric traffic requirements: performance analysis and optimization

We study the effect of imperfect channel estimation (ICE) and asymmetric traffic requirements (ATRs) on the performance of bidirectional relaying with a direct link by employing three-phase analog network coding under Nakagami-m fading. Under such a realistic scenario, a tight lower bound on the overall outage probability is derived in closed-form, while a useful expression is presented for the asymptotically low outage regime. We also deduce the tight closed-form expression for the ergodic sum-rate. Furthermore, we formulate and solve analytically three optimization problems viz., relay power allocation under fixed location of the relay, relay position with fixed relay power allocation, and joint optimization of relay power allocation and location. Our results reveal that for given ICE, the optimal relay location offers significant system performance enhancement under ATRs, whilst the optimal relay power allocation has a more noticeable impact under symmetric traffic. It is also shown that the joint optimization of relay power allocation and location can further enhance the system performance, regardless of ATRs and ICE. Above all, based on the direct link quality, we show that the considered scheme outperforms its two-phase counterpart, even in the low signal-to-noise ratio regime.

     

Secure communication in untrusted relay selection networks with wireless energy harvesting

In this paper, we consider the secrecy performance of an energy-harvesting relaying system with Kth best partial relay selection where the communication of a multi-antenna source-destination pair is assisted via single-antenna untrusted relays. To protect confidential source messages from untrusted relays, transmit beamforming and destination jamming signals are used. The relays are energy-constrained nodes that use the power-splitting policy to harvest energy through the wireless signals from both the source and destination. For performance evaluation, closed-form expressions of the secrecy outage probability and average secrecy capacity (ASC) are derived for Nakagami-m fading channels. The analytical results are confirmed via Monte Carlo simulations. Numerical results provide valuable insights into the effect of various system parameters, such as relay location, number of relays, and power splitting ratio, on the secrecy performance. Specifically, the maximum ASC is achieved when the relay is located between the source and destination.

     

Peroformance analysis of decode-and-forward MIMO relay channels with OSTBCs

Performance analysis is presented for multiple-input multiple-output(MIMO) relay channels employing transmit antenna diversity with orthogonal space-time block codes(OSTBCs),where the source and the destination are equipped with Ns and Nd antennas,and communicate with each other with the help of a multiple-antenna relay operating in decode-and-forward(DF) mode.Over independent,not necessarily identical Rayleigh fading channels,exact closed-form symbol error rate(SER) expressions are derived for various digi...     

多用户分集与能量受限非可信中继系统遍历安全性能分析

研究了一种能量受限的非可信中继与多用户分集技术相结合的两跳链路安全网络通信模型。为提升系统安全性能，本文采用混合时间-功率分配中继(time-power splitting-based relaying, TPSR)协议,并结合机会调度策略(opportunistic scheduling strategy, OSS)从多用户分集网络中选择一个最佳目的节点作为信息接收端。基于随机选择(random selection, RS)策略，该文中利用低复杂度的高斯Q函数分析系统的安全性能以及在协作中继上进行能量采集活动不中断的条件下推导了系统的遍历安全速率(ergodic secrecy rate, ESR)的近似闭合表达式。此外，将提出的OSS与RS通信方案下性能进行对比，证明本文所提出的OSS更适用于分布式多用户选择网络。