Performance for Device-to-Device Communication with Three-Time-Slot Two-Way Amplify-and-Forward Relay Protocol

Multi-hop device-to-device(D2D) communication can significantly improve the system performance. This paper studied the outage performance of D2 D communication assisted by another D2 D user using three-timeslot two-way amplify-and-forward relaying protocol over Rayleigh fading channels. Considering the co-channel interference from cellular user at the D2 D node,the approximate expression for the overall outage probability was derived. Furthermore,a power allocation optimum method to minimize the outage probability was developed,and the closed form expression for the optimal power allocation coefficient at the relay was derived. Simulation results demonstrate accuracy of the derived outage probability expressions. Simulation results also demonstrate that the outage performance can be improved using the proposed optimal power allocation method.

PERFORMANCE ANALYSIS OF TWO-WAY AMPLIFY-AND-FORWARD RELAYING SYSTEM WITH MULTIPLE INTERFERERS AT THE RELAY

In this paper,we investigate the performance of the two-way Amplify-and-Forward(AF) relaying systems in an interference-limited Rayleigh fading environment.More specifically,assuming the presence of Rayleigh faded multiple interferers at the AF relay and noisy sources,an approximate closed-form expression for the Overall Outage Probability(OOP) and an integral expression for the average Symbol Error Probability(SEP) are derived.The analysis results are verified through com-parison with the Monte Carlo simulation results.

Greedy Algorithm Applied to Relay Selection for Cooperative Communication Systems in Amplify-and-Forward Mode

Using a relaying system to provide spatial diversity and improve the system performance is a tendency in the wireless cooperative communications. Amplify-and-forward （AF） mode with a low complexity is easy to be implemented. Under the consideration of cooperative communication systems, the scenario includes one information source, M relay stations and N destinations. This work proposes a relay selection algorithm in the Raleigh fading channel. Based on the exhaustive search method, easily to realize, the optimal selection scheme can be found with a highly complicated calculation. In order to reduce the computational complexity, an approximate optimal solution with a greedy algorithm applied for the relay station selection is proposed. With different situations of the communication systems, the performance evaluation obtained by both the proposed algorithm and the exhaustive search algorithm are given for comparison. It shows the proposed algorithm could provide a solution approach to the optimal one.

Asymptotic analysis of multi-branch two-way amplify-and-forward relaying in Nakagami-m fading with arbitrary fading parameter

Two-way relay networks have received lots of attention, thanks to its ability to overcome the loss in the spectral efficiency due to half-duplex transmission. Asymptotic performance analysis can provide valuable insights in- to practical system designs. However, this is a gap in two-way relay network. In this paper, the asymptotic performance is studied for multi-branch dual-hop two-way amplify-and-forward （AF） relaying networks in independently but not necessarily identically distributed （i.n.i.d.） Nakagami-m fading channels, with arbitrary m 〉 5. The approximate prob- ability density function （PDF） of the instantaneous dual-hop link power at high SNR region is derived. Then we present the asymptotic outage probability expression, and analyze the diversity order and coding gain. Simulations are per- formed to verify the tightness of the presented analysis at medium and high SNR regions.

Parameter Optimization for Amplify-and-Forward Relaying Systems with Pilot Symbol Assisted Modulation Scheme

Cooperative diversity is a promising technology for future wireless networks. In this paper, we consider a cooperative communication system operating in an amplify-and-forward (AF) mode with a pilot symbol as-sisted modulation (PSAM) scheme. It is assumed that a linear minimum mean square estimator (LMMSE) is used for the channel estimation at the receiver. A simple and easy-to-evaluate asymptotical upper bound (AUB) of the symbol-error-rate (SER) is derived for uncoded AF cooperative communication systems with quadrature amplitude modulation (QAM) constellations. Based on the AUB, we propose a criterion for the parameter optimization in the PSAM scheme. We discuss how the pilot spacing and the length of the Wiener ?lter should be chosen under the constraint of a tradeoff between pilot overhead, estimation accuracy, and receiver complexity. We also formulate an power allocation problem for the considered system. It is shown that the power allocation problem can optimally be solved by means of a gradient search method. Numerical simulations are presented to verify the correctness of the theoretical results and to demonstrate the benefits of the parameter optimization.

Outage Performance of Opportunistic Amplify-and-Forward Relaying over Asymmetric Fading Environments

This letter analyzes the outage probability of opportunistic amplify-and-forward relaying over asymmetric and independent but non-identically distributed (i.n.d) fading environments. The work investigates the scenarios where cooperative nodes are located at different geographical locations. As a result, the different signals are affected by different i.n.d fading channels, one may undergo Rician fading distribution and others may undergo Rayleigh fading distribution. In this letter, a lower bound of the outage probability for various asymmetric fading environments is derived at high SNR by applying the initial value theorem. The analytical model is validated through Monte-Carlo simulation results.

The Influence of LOS Components on the Statistical Properties of the Capacity of Amplify-and-Forward Channels

Amplify-and-forward channels in cooperative networks provide a promising improvement in the network coverage and system throughput. Under line-of-sight (LOS) propagation conditions in such cooperative networks, the overall fading channel can be modeled by a double Rice process. In this article, we have stud-ied the statistical properties of the capacity of double Rice fading channels. We have derived the analytical expressions for the probability density function (PDF), cumulative distribution function (CDF), level- crossing rate (LCR), and average duration of fades (ADF) of the channel capacity. The obtained results are studied for different values of the amplitudes of the LOS components in the two links of double Rice fading channels. It has been observed that the statistics of the capacity of double Rice fading channels are quite dif-ferent from those of double Rayleigh and classical Rice fading channels. Moreover, the presence of an LOS component in any of the two links increases the mean channel capacity and the LCR of the channel capacity. The validity of the theoretical results is confirmed by simulations. The results presented in this article can be very useful for communication system designers to optimize the performance of cooperative networks in wireless communication systems.

Imperfect Channel State Information of AF and DF Energy Harvesting Cooperative Networks

Wireless information and powered transfer networks(WIPT) has recently been implemented in 5th generation wireless networks. In this paper, we consider half-duplex relaying system in which the energy constrained relay node collects energy via radio frequency(RF) signals from the surrounding resources. Regarding energy harvesting protocol, we propose power time switching-based relaying(PTSR) architecture for both amplify-and-forward(AF) and decode-and-forward(DF). Especially, we reveal the analytical expressions of achievable throughput, ergodic capacity and energy-efficient in case of imperfect channel state information(CSI) for both AF and DF network. Through numerical analysis, we analyse the throughput performance, energy-efficient and ergodic capacity for different parameters, including power splitting ratio and energy harvesting time. Moreover, we also depict the performance comparison between AF and DF network with perfect and imperfect CSI. The results in numerical analysis reveal that the result of AF relaying network is less significant than DF relaying network in the various scenarios.

OPTIMAL POWER ALLOCATION WITH AF AND SDF STRATEGIES IN DUAL-HOP COOPERATIVE MIMO NETWORKS

Dual-hop cooperative Multiple-Input Multiple-Output (MIMO) network with multi-relay cooperative communication is introduced. Power allocation problem with Amplify-and-Forward (AF) and Selective Decode-and-Forward (SDF) strategies in multi-node scenario are formulated and solved respectively. Optimal power allocation schemes that maximize system capacity with AF strategy are presented. In addition, optimal power allocation methods that minimize asymptotic Symbol Error Rate (SER) with SDF cooperative protocol in multi-node scenario are also proposed. Furthermore, performance comparisons are provided in terms of system capacity and approximate SER. Numerical and simulation results confirm our theoretical analysis. It is revealed that, maximum system capacity could be obtained when powers are allocated optimally with AF protocol, while minimization of system's SER could also be achieved with optimum power allocation in SDF strategy. In multi-node scenario, those optimal power allocation algorithms are superior to conventional equal power allocation schemes.

Modified Cooperative Subchannel Allocation Algorithms and PSO Based Power Allocation for an Alamouti Decode and Forward Relaying Protocol in Multiuser OFDMA Systems

The present work is a discussion on the performance analysis of Modified Cooperative Subchannel Allocation (CSA) Algorithms which is used in Alamouti Decoded and Forward (Alamouti DF) Relaying Protocol for wireless multi-user Orthogonal Frequency Division Multiplexing Access (OFDMA) systems. In addition, the performance of approximate Symbol Error Rate (SER) for the Alamouti DF Relaying Protocol with the Cooperative Maximum Ratio Combining Technique (C-MRC) is analyzed and compared with SER upper bound. The approximate SER is asymptotically tight bound at higher Signal-to-Noise Ratio (SNR). From the asymptotic tight bound approximate SER, Particle Swarm Optimization (PSO) based Power Allocation (PA) is determined for the Alamouti DF Relaying Protocol. The simulation results suggested that the Modified Throughput based Subchannel Allocation Algorithm achieved an improved throughput of 6% to 33% compared to that of existing cooperative diversity protocol. Further, the Modified Fairness based Subchannel Allocation Algorithm rendered fairness of 7.2% to 17% among the multiuser against the existing cooperative diversity protocol.

基于定向天线的多中继节点的AF协同通信系统性能分析

研究了基于定向天线的多中继节点放大转发协同通信技术。首先,从理论上推导了全向发送-全向接收(without beamforming transmit-receive,N-BF),定向发送-全向接收(beamforming transmit-without beam-forming receive,T-BF)以及定向发送-定向接收(beamforming transmit-beamforming receive,TR-BF)3种模式下信道容量及其中断概率。然后,结合具体的数值仿真对不同模式下的信道容量和中断概率分别进行了详细的分析比较。结果表明,TR-BF性能最优,TR-BF以及T-BF相比N-BF而言,系统受噪声影响更小。

协同分集下AF与DF比较

在慢衰落信道中,协同分集是一种新的空间分集方式,其本质是利用分布用户的单天线形成一个虚拟的多天线系统,即形成虚拟MIMO。在其协同方式中,有AF模式和DF模式(编码协同是DF模式的一种特殊情况)。该文针对AF与DF两种基本协同方式进行了详细的比较,并在对称信道和非对称信道下进行了系统的仿真。理论分析和仿真结果表明:在相同的条件下,AF模式相对于DF模式有较大的优势是因为AF模式较DF模式有较大的阵列增益,虽然两者有相同的分集增益,但DF有更大的灵活性。

两跳OFDM-AF接力系统中的子载波配对技术

分析了基于放大前传的两跳正交频分复用接力系统.针对因信号在两跳过程中被置于相同子载波传输而限制系统性能的问题,提出了子载波配对技术,并采用匈牙利算法提出了最优配对方案.进一步提出了基于子带的子载波配对方案.仿真结果表明,子载波配对技术能为系统带来约5dB的增益;基于子带的子载波配对增益略低,但能大大降低信令开销.

一种AF-MIMO中继系统中的混合协作方案

为了提升协作通信系统中放大转发方案的系统性能,提出了一种新的基于选择中继的混合协作方案.中继节点根据正确解码与否被分为两个集合P和Q,系统分别从两个集合中挑选在目的节点处具有最高信噪比的中继节点进行放大转发.推导出了新方案信道容量的闭式表达式.仿真结果表明,新方案的误码率性能和信道容量均优于传统的基于选择中继的放大转发方案.

基于最优中继集合选择的HDAF算法

为减少协作通信系统资源消耗,提出了一种基于混合译码放大前传（hybrid decode-amplify-and-forward,HDAF）的中继选择算法。该算法以降低系统的中断概率和最小化总功率为目标,采用等效信道增益参数排序的方法,得到了最优中继集合的选择算法。该算法既保证通信过程更可靠,不易中断,又减少多余中继节点的使用,节省资源。仿真结果表明,采用最优中继集合选择算法,在10~30dB的信噪比范围内,HDAF协作方式的中断概率要小于放大转发（amplify-and-forward,AF）和译码转发（decode-and-forward,DF）协作方式。该算法与功率分配相结合,在相同中断概率条件下,源节点所需功率比AF和DF协作方式少1~4dBm,节约了系统资源的消耗。

MIMO-AF协作中继网络中发送预编码器的优化

本文首先利用中继节点和目标节点在第一时隙中的接收信噪比之和最大准则,推导出优化问题并解得优化的预编码器矢量。然后又利用目标节点最大比合并后的接收信号信噪比最大准则,推导出性能更佳的预编码器优化问题,但由于表达式复杂不能得到闭式解。为此本文提出了两种次优解决方法,分别是梯度下降迭代法和近似求解法。仿真结果表明,提出的两种准则优化预编码器方法都能有效改进系统性能,且因后者更能直接反映接收端情况,效果更好。两种次优的解优化方法能够获得几乎相同的系统性能,但梯度下降法采用迭代运算,计算量比较大,而近似求解法在性能不损失的情况下大大降低了计算复杂度。

多节点AF协作通信系统中的信道估计方法

依据频率选择性衰落信道下基于正交频分复用技术的多节点放大转发协作通信系统,提出一种基于叠加导频的分段式信道估计方法。该方法采用双块状导频,分别记录级联链路和第2段链路状态信息,并估计相应的信道状态信息,计算出第1段链路信道状态信息。仿真结果表明,该方法能够获得2段链路的信道状态信息,减小信道估计导频开销和时隙周期,提高信道估计的实时性。

矿井巷道AF协作通信系统建模及信道容量优化

针对矿井巷道复杂受限环境中电磁波传播多径衰落问题,基于多波模信道模型,建立了矿井巷道放大转发(amplifying-and-forwarding,AF)协作通信系统模型,分别推导出矿井巷道单中继和多中继AF协作通信系统的信道容量公式。考虑矿井巷道内的本质安全要求,在系统总功率和各节点功率双重受限的条件下,以信道容量为优化准则,分别提出了矿井巷道AF协作通信系统单中继和多中继环境的功率分配方法,并进行了仿真比较。实验证明,本方法能够显著提升系统的信道容量;系统总功率的大小影响功率分配方法对信道容量的优化效果和优化幅度:在一定总功率范围内,功率分配方法对信道容量的优化效果随着总功率的增加而减小,功率分配方法对信道容量的优化幅度随着总功率的增加而增加。

同频干扰环境下双向AF中继性能分析及参数优化

双向中继(two-way relaying,TWR)作为提高中继网络频谱效率的一种有效手段,近年来受到广泛关注。本文研究同频干扰环境下三时隙TWR策略的中断概率性能,中继采用放大转发(amplify-and-forward,AF)策略。首先,理论推导了策略中断概率下界的闭合表达式和高信噪比下的渐进表达式。仿真表明,理论结果能够匹配策略的实际中断概率性能。根据理论结果,以最小化中断概率为目标对中继节点功率分配和中继位置参数进行优化。提出三种优化问题,即(1)给定中继位置,中继功率分配优化问题,(2)给定中继功率分配方案,中继位置优化问题,(3)联合优化中继功率分配和中继位置。仿真结果表明,联合优化能够实现最优的中断概率性能。

基于AF协作的多中继M2M通信系统的SER性能分析

基于移动端对移动端(M2M)信道衰落服从重叠Nakagami-m分布的假设,研究M-PSK调制下移动放大转发(AF)中继对M2M系统的性能影响。利用矩母函数(MGF)方法,推导了多AF中继辅助M2M通信(MAF-M2M)系统的误符号率(SER)性能下界表达式,并结合近似概率密度函数(PDF)方法,给出了更为逼近的近似SER表达式。结果表明,目的端采用最大比合并时,AF中继可以明显改善不同m参数信道下M2M通信系统性能。计算机仿真结果验证了性能界和近似SER的正确性。