认知选择协同分集任意信噪比中断概率的分析

选择中继已被证明是一种有效和实用的协作分集方法.但是,现有的分析主要集中在渐进高信噪比(SNR)区域,因此,研究认知选择协同分集系统任意信噪比的中断概率具有现实意义.推导了瑞利衰落信道选择中继协议的中断概率解析式,并进行了仿真.仿真结果表明,选择中继协议在任意信噪比情况下,增加中继节点可降低中断概率,而解码中继协议(DF)在低、中信噪比情况下不一定降低中断概率;同时,选择中继协议的中断性能和分集增益随频谱空穴检测能力的提高而增强.     

低信噪比下增强型解码转发协作的性能分析

研究了接收节点将其译码状态反馈给其他节点这一增强性手段对解码转发协作的性能改善情况.推导了低信噪比条件下,增量中继、选择中继的中断概率和吞吐量表达式,给出了中断概率的三阶近似式.结合增量中继、选择中继的各自优点,提出了一种联合中继模式.理论分析和数值仿真表明,提出的联合中继模式在中断概率和吞吐量2个方面性能优越.     

机会协同通信系统的中继公平性研究

为提高机会协同通信系统的中继选择公平性,提出了以不影响系统中断性能为目标的协同方案。在建立了协同通信系统模型的基础上,提出机会协同方案,并引入比例公平算法对机会协同方案进行改进;分别对2种方案下的中继选择概率与系统中断概率进行了分析,根据定义的公平因子表征中继公平性与理想公平上限。仿真结果表明,提出的基于比例公平的机会协同方案,显著改善了中继选择的公平性,在大信噪比条件下趋近理想公平上限,同时保持了系统中断性能。     

基于Alamouti编码与发射天线选择的MIMO中继系统中断性能分析

为增加网络覆盖范围、保持网络的高吞吐量,研究了使用发射天线选择的MIMO中继系统的中断概率性能。在多输入多输出中继系统中,分别以最大化中继和目标上的接收信噪比为准则在源、中继上选择发射天线,推导了系统中断概率的封闭表达式,并进一步分析了该系统的分集阶数。蒙特卡罗仿真实验证实了理论推导的正确性。     

放大转发方式下中继选择策略的性能分析

研究了几种主要的协同中继选择策略;通过仿真对比了在放大转发方式（Amplifier-and-forward AF）下全部协同、部分协同、机会中继的中断概率性能;最后归纳总结了中继节点数目、信噪比及目标信息速率对上述中继选择策略中断概率性能的影响情况。     

双向协作系统的中继选择和功率分配策略

针对瑞利衰落信道下双向多中继协作通信系统,为了降低中断概率,提出了一种基于最小化中断概率的中继选择策略和功率分配方案。首先联合考虑两条链路的中继节点处信噪比和信道增益实现双链路中继选择,然后推导出一种新的最优中继下双向放大转发协作中断概率的近似表达式上界,并利用凸优化求解得到使中断概率最小的最优功率分配解。仿真结果表明,与现有策略相比,提出的策略能够明显降低系统中断概率和误码率,显著提高系统性能。     

Two-way中继系统的中继选择算法分析

为了提升双向AF中继系统总速率和降低系统中断概率,提出了一种最小中断概率的中继算法MOP,介绍了现有的两种中继选择算法,利用通信系统的性能指标(信噪比、中断概率、信道容量)展开分析。仿真结果表明,所提出最小中断概率中继选择算法可明显降低系统中断概率,在提升系统总速率的性能与最大化容量中继算法接近,有效地改善了系统性能。     

基于冗余前置的机会编码协同中继策略

对于多节点的协同网络,机会编码协同总是选择最佳中继参与协同,能够取得优越的中断概率性能。为了进一步提高中断概率性能,提出了基于冗余前置的机会编码协同中继策略,并对其在瑞利平坦慢衰落信道条件下的中断概率性能进行了计算机仿真。结果表明,所提策略的中断概率性能明显优于机会编码协同中继策略,若所要求的中断概率为10-3,当潜在协同中继数目为7,协同等级为0.5,目标信息速率为1 bit/s/Hz的条件下,所提策略较机会编码协同中继策略可以获得1.9 dB的信噪比增益。     

能量收集全双工中继网络中的中继策略研究

本文针对双跳全双工多中继系统,研究了在中继节点能量受限情况下的中继选择方案。在该文中,中继工作方式为放大转发（Amplify-and-Forward, AF）,且中继通过收集源节点提供的能量来对源节点信息进行转发。整个通信过程分为两阶段,能量收集阶段与信息传输阶段,即采用的是时域分割方案。为了获得较好的性能与复杂度折中,本文分别研究了三种不同的中继选择策略,即最佳中继选择方案和两种次优中继选择方案。针对所提的三种方案,推导分析了其系统中断概率的理论值和下边界,以及系统的有效吞吐量。最后,利用蒙特卡洛仿真验证了理论分析的正确性,且仿真结果表明最佳中继选择方案的性能优于两种次优的中继选择方案,但其实现的复杂度高。      

基于中断概率的协作通信中继选择与功率分配算法

研究了功率受限情况下多中继协作通信网络的中继选择和功率优化问题。在AF网络中,提出了一种低复杂度中继选择与功率分配算法,其目标是在总功率一定的条件下使系统的中断概率最小。本算法对源节点和所有潜在中继节点进行功率分配,结合当前信噪比选择最优的中继集合,通过最速下降法求出使系统中断概率最低的功率分配因子。该算法不需要知道大量瞬时信道信息、不需要系统在等功率条件下进行中继选择,只需求得中继节点排列矩阵便可根据当前信噪比自适应获得最优中继节点集合。仿真结果表明,在相同条件下,该算法明显优于不同中继节点集合下几种算法的中断性能,并且与传统的SAF及AAF算法相比,有效降低了中断概率,提升了系统性能和功率效率。     

基于截短ARQ协议的协作分集系统吞吐量研究

研究协作分集通信系统的跨层设计使系统吞吐量最大化.首先推导基于截短ARQ协议的协作分集和两跳系统的吞吐量理论表达式,揭示数据包长度和调制方式对系统吞吐量的影响,在此基础上用自适应技术优化系统性能,采用连续二维优化求出了吞吐量的最大值,进而提出了实用的二维离散吞吐量优化算法,该算法的优化结果与吞吐量最大值相差很小,最后提出了计算量更小的一维离散优化算法,且其吞吐量性能损失也很小.     

A cooperative-ARQ protocol with frame combining

This article presents a low coordination overhead cooperative Automatic Repeat reQuest (ARQ) scheme with an integrated frame combiner, which exploits space diversity and cooperation between neighbouring nodes. A comparison between cooperation with and without frame combiner is also performed. In channels with a strong Line of Sight (LOS) component and low Signal-to-Noise ratio (SNR), the efficiency of the proposed protocol is many times higher than for other ARQ schemes. For non-LOS scenarios, the cooperative ARQ without frame combiner achieves the best efficiency results, and the overhead introduced by the frame combiner mechanism leads to results that can be even below the classical ARQ mechanism. In AWGN channels, the saturation throughput of the proposed scheme integrated into a IEEE 802.11 DCF based MAC is also studied. When the number of active stations is high, the cooperative ARQ without frame combiner shows to be the best option, while for light network loads, the presented scheme performs better.     

MBC中的Ⅰ型HARQ改进方案

在流星突发通信中,为确保数据有效可靠地传输,通常采用前向纠错与自动重传请求相结合的方法,即HARQ。传统I型HARQ效率较低,难以满足大数据量通信。为了有效利用流星信道,建立了流星突发通信模型,提出了一种基于分集合并的Ⅰ型HARQ方案,推导出了有效信噪比公式,讨论了信噪比改善系数和最大重传次数,并进行了仿真。仿真结果表明,该方案可有效提高可靠性,增加吞吐量。     

自适应调制混合ARQ系统中低时延冗余递增策略的研究

冗余递增混合ARQ能提供较高的数据通过率,但也带来了较大的传输时延。该文提出一种具备低时延冗余递增策略的混合ARQ系统并与自适应调制系统相结合,不但根据不同的接收信噪比,选取不同的调制方式,而且还选择不同的冗余递增策略。仿真和计算结果表明,与采用固定冗余递增策略的自适应调制混合ARQ系统相比,该系统在保证较高的数据通过率的前提下,大大降低了系统传输时延。     

无线传感器网络中基于放大转发的机会协同ARQ协议吞吐量及能效分析

提出了一种基于放大转发的机会协同自动重传请求协议,在提供可靠传输的同时获得了高能效。给出了一种基于马尔科夫链的吞吐量模型和一种能量效率分析模型,分别分析了所提协议的吞吐量和能效性能。Monte Carlo仿真表明理论分析与实际仿真所得到的系统吞吐量性能基本一致,且仿真结果还表明该协议相比传统ARQ协议具有更高的吞吐量和能效性能。     

Throughput Analysis for Parallel ARQ over Correlated MIMO Channels

We treat the throughput analyses of parallel ARQ schemes over correlated MIMO channels with adaptive modulation and coding (AMC). To describe the packet transmission over multiple parallel logic channels, we extend the existing burst- error model for single channel to multiple parallel logic channels. Based on such a packet error model, we derive the throughput of different parallel ARQ protocols. Moreover, to describe the temporally correlated physical channel fading, we generalize the existing Markov model for single channel to multiple parallel channels for MIMO systems. Then we develop a method for calculating the packet-level model parameters from the parameters of the physical-layer model and the MIMO transceiver. Using the above hierarchical throughput analysis framework, we investigate the potential throughput gain or throughput loss of parallel ARQ over the conventional serial ARQ in MIMO systems. Our results reveal that as SNR increases, parallel ARQ can achieve higher throughput gain or less throughput loss compared to serial ARQ; parallel SW can achieve throughput gain in most of the MIMO scenarios but increasing the number of antennas does not always bring higher gain; parallel GBN with large number of antennas and independent buffers can achieve throughput gain; parallel SR incurs throughput loss.     

Throughput maximization of ad-hoc wireless networks using adaptive cooperative diversity and truncated ARQ

We propose a cross-layer design which combines truncated ARQ at the link layer and cooperative diversity at the physical layer. In this scheme, both the source node and the relay nodes utilize an orthogonal space-time block code for packet retransmission. In contrast to previous cooperative diversity protocols, here cooperative diversity is invoked only if the destination node receives an erroneous packet from the source node. In addition, the relay nodes are not fixed and are selected according to the channel conditions using CRC. It will be shown that this combination of adaptive cooperative diversity and truncated ARQ can greatly improve the system throughput compared to the conventional truncated ARQ scheme and fixed cooperative diversity protocols. We further maximize the throughput by optimizing the packet length and modulation level and will show that substantial gains can be achieved by this joint optimization. Since both the packet length and modulation level are usually discrete in practice, a computationally efficient algorithm is further proposed to obtain the discrete optimal packet length and modulation level.     

Cooperative ARQ protocol for correlated wireless channels

A novel Automatic repeat ReQuest （ARQ） protocol called cooperative ARQ is presented in this letter, where a relay terminal is requested to retransmit an erroneously received packet, instead of the source terminal. The data link layer Packet Error Rate （PER） performance of cooperative ARQ is derived in correlated wireless channel. The results show that even though the relay-destination channel is worse than the sourcedestination channel, the new protocol outperforms the traditional one as long as the average SNR of the relaydestination channel is better than a certain threshold. It is also demonstrated that a second order diversity gain can be achieved with the cooperative ARQ protocol.     

ARQ strategies for relay cooperative systems

We propose two novel automatic repeat request (ARQ) strategies for relay cooperative systems over Rayleigh fading channel one uses relay ARQ and the other destination ARQ. The BER performance of these two strategies is derived in fast block fading. Numerical analysis and simulation show the systems can get more performance gain when the inter-channel (the source to the relay) quality is bad in the relay ARQ strategy. In the destination ARQ strategy, when the uplink qualities of the source and relay to the destination are poor, the average received SNR of the destination is much low, the systems performance can be improved efficiently.     

An Adaptive Hybrid ARQ Scheme

A hybrid ARQ in which the transmitter adaptively selects an FEC code according to the channel condition is presented and analyzed. The code is selected according to the past transmissions and acknowledgements by an algorithm which is a generalization of that in [1]. The throughput is obtained as a function of the frame error rate for a general system employing the adaptive hybrid ARQ with acknowledgements that arrive instantly on an error-free return channel. The throughput is obtained as a function of the signal-to-noise ratio for an example quad rate system employing convolutional codes with non-coherent frequency shift keying over the uncorrelated Rayleigh fading channel. This allows the best choice for the parameters of the algorithm to be made. In the case that the channel bit errors are independent, the generalization offers performance improvement of less than 10% over that in [1]. But when the channel errors are bursty, as in the case of Rayleigh fading with finite bit interleaving, the generalization offers throughput improvement as high as 24%. We go on to consider incorporating code combining with the adaptive scheme to form an adaptive memory hybrid ARQ. Simulation of a system using complementary punctured convolutional codes with 4 code rates shows that 2-level code combining can extend the adaptive scheme's useful throughput into the low SNR region by approximately 4 dB.