基于网络编码的协作HARQ协议

该文基于网络编码技术提出了一种新的协作HARQ协议。在中继节点的协助下两个用户与基站进行通信。中继节点响应基站的重传请求,对两用户的增加冗余帧采用物理层网络编码即信号重叠调制技术进行处理,然后发送至基站。基站对接收信号采用多用户联合检测以及联合软判决译码。在平坦瑞利衰落信道下,该网络编码协作HARQ协议较传统的非协作HARQ协议可获得较大的性能改善,其性能接近没有采用网络编码的协作HARQ协议,且需要较少的硬件和带宽资源。     

乘法运算的模拟网络编码中继方法

当前无线网络编码中继采用异或运算和叠加运算实现,该文提出一种基于乘法运算的网络编码中继方案。该方案中继节点对接收到的两个源节点信号直接相乘,然后放大转发,从而实现网络编码。与异或运算的网络编码相比,该方案采用模拟技术实现,降低了中继节点网络编码的复杂度;同时该方案将接收信号与本地信号相乘实现网络译码,译码算法比叠加运算的方案简单。理论分析表明该方案的分集增益与未经网络编码的中继系统相同;仿真结果表明,该方案与现有的网络编码中继协作方案性能相当。     

一种基于补偿校正的网络编码和信道编码联合设计

将信道编译码中性能较优的LDPC码运用到网络编码和信道编码联合设计,提出一种接收端补偿校正的网络编码和信道编码联合设计方案,该方案在中继节点进行解调和译码后硬判决,以降低中继节点处理数据的复杂性,然后进行网络编码而不考虑编码数据中存在的误码,通过接收节点对中继硬判决信息的错误概率进行补偿和校正来获取最大似然接收。仿真实验表明,提出的网络编码和信道编码联合设计方案不但降低了中继节点处理数据的复杂性,同时提高了传输系统的可靠性。     

基于软门限LDPC码的中继信道容量实现

LDPC（Lowdensity parity code）码是逼近香农界的信道码。为了逼近香农界,其优化一般采用硬门限准则。但当信道容量小于编码码率时,LDPC无法正确译码。因此,提出从软门限的角度优化LDPC码,使得在码率超过信道容量时,接收端仍可以部分译码,并将该LDPC码用于单中继信道中,解决使用解码前传（DF,decode and forward）的中继信道容量瓶颈问题,进而提高信道容量。还考虑中继节点使用Slepian-Wolf信源编码,降低中继节点到目的节点的信道质量要求的同时,仍能保证无失真译码。     

双中继协作通信的功率分配改进方案

为克服信息处于深度衰落情况下单中继协作困难,减少多中继协作目的端信号处理的复杂度,给出了双中继节点参与协作通信的功率分配方案。两个中继节点分别采用放大转发(AF)、译码转发(DF)以及混合译码放大转发(HDAF)3种协作方式进行通信。在满足一定的中断概率和节点功率限制情况下,利用MATLAB软件中的Fmincon优化函数,得到了各节点的最小发射功率。数值分析表明,在相同条件下,两个中继节点采用HDAF协作方式比采用AF协作方式、DF协作方式消耗的系统总功率分别少4~9 dBm、0.5~1 dBm,最大限度地节约了系统功率的消耗。     

一种信道编码与物理层网络编码的联合设计

基于正交振幅调制（QAM）设计了一种信道编码与物理层网络编码的联合实施方案,该方案巧妙的引入了一种去噪映射机制,即重新安排QAM调制的星座映射,中继节点对接收数据去噪后直接映射为对应数字比特流的异或。同时,利用卷积码和MAC-XOR网络编码（Network Coding, NC）的线性性质,使得中继节点只需直接估计网络编码的码字,因此中继节点的解调/译码的复杂度减少50%。在此基础上对该方案的误比特率性能进行分析。仿真结果表明了该方案的有效性,即与已有的物理层网络编码方法相比,在没有增加译码复杂度的基础上,该方案的信道容量有了显著提高。      

基于译码前传协作中继网络的类准正交线性分散码

提出了一种基于译码前传协作中继网络的类准正交线性分散码,该码的码字矩阵实部和虚部可以分解成满足准正交设计的实码字矩阵;对接收端的译码考虑了2种方式,一种是对总的接收信号进行快速最大似然译码,另一种是对经过中继和未经过中继的接收信号分别进行快速最大似然译码;分析了2种方式的计算复杂度,对2种方式的信道容量、中断概率和误比特率等特性进行了仿真对比,结果表明,在相同条件下,方式2比方式1信道容量更高,中断概率和误比特率更低,但计算复杂度更高.     

有载波频偏的PNC与LDPC码的联合设计

双向中继信道中采用物理层网络编码技术时,多址接入阶段的非同频现象会造成系统严重的性能损失.物理层网络编码与信道编码的联合设计可以在很大程度上改善系统性能并降低设备复杂度,但目前大多数PNC与信道编码的联合设计只考虑完全同步的情况.本文提出在物理层网络编码多址接入阶段存在载波频偏情况下的双节点均值频率补偿法和单节点完全频率补偿法PNC与LDPC的联合设计,在中继节点处通过分别设计对应的频率补偿滤波器,重新分析译码判决门限与噪声分布情况.仿真结果表明,本文提出的有载波频偏条件下的两种PNC与LDPC的联合设计相比于传统的物理层网络编码有很好地性能表现.     

MARC中联合BICM-ID和网络编码设计及性能分析

联合网络信道编码是将网络编码和信道编码联合处理,通过联合处理网络信道编码可以增加带有噪声信道的分集数,从而进一步提高网络容量。结合联合网络信道编码的思想,基于比特交织编码调制迭代译码(BICM-ID)设计了两种应用于多址接入中继信道(MARC)环境中的联合网络信道编码方案,并对这两种方案进行了仿真比较。仿真结果表明:在译码之前对解调后的软信息直接进行网络译码相比于对译码后的外信息进行网络译码能更加有效地利用中继信道传输的冗余信息。     

基于非正规LDPC码的中继协作通信及其联合迭代译码的性能研究

 本文构造了一种适用于中继协作通信的非正规LDPC系统码,并将双非正规LDPC系统码应用于中继协作系统中. 提出了目的点接收机基于双LDPC码联合Tanner图的对多路接收信号进行联合迭代译码的新算法. 理论分析和数值模拟表明本文所提出的新方法将高效信道编码和协作技术有机地结合起来以充分实现编码协作所具有的潜在分集和编码增益,与非协作系统相比可显著地提高系统性能.     

An achievable rate region of cooperative multiple-access channels with hybrid CF and DF cooperation

In this letter, we derive an achievable rate region of a two-user cooperative multiple-access (CMA) channel where one user performs decode-and-forward (DF) cooperation and the other user performs Wyner-Ziv-type compress-and-forward (CF) cooperation. The proposed rate region is achieved using a communication scheme that applies block Markov coding at each user and backward decoding at destination. Numerical results show that for some channel scenarios, the proposed hybrid CF and DF cooperation scheme enlarges the rate region achieved by the pure DF-based cooperation scheme.     

Cooperation Strategies and Resource Allocations in Multiuser OFDMA Systems

Cooperative communication and orthogonal frequency-division multiplexing (OFDM) technology are both promising candidates for next-generation wireless communication systems. In this paper, we investigate cooperation strategies and resource-allocation algorithms for multiuser cooperative orthogonal frequency-division multiple-access (OFDMA) systems. There are two major contributions of this paper. First, we propose a novel cooperation strategy for the OFDMA system. When there are two users in the system, the strategy achieves the capacity region upper bound for decode-and-forward (DF) cooperation. When there are multiple users in the system, the strategy can achieve near upper-bound performance in certain network topologies. Moreover, the strategy always outperforms those that are previously proposed for cooperative OFDMA systems. The second contribution is that we develop novel centralized resource-allocation algorithms for cooperative OFDMA systems. The advantages of the algorithms are that they not only simultaneously solve relay, power, and subcarrier allocation but also have complexity that increases only linearly with the number of subcarriers in the systems.      

Decode-to-cooperate: a sequential alamouti-coded cooperation strategy in dual-hop wireless relay networks

An optimal cooperation strategy, decode-to-cooperate, is proposed and investigated for performance improvements in dual-hop wireless relay networks. Based on decode-and-forward (DF) strategy with multiple relay selection, we design a novel scheme such that the source node keeps transmitting sequentially and the selected relays cooperate by transmitting the decoded signal using distributed Alamouti coding. We exploit the multipath propagation effect of the wireless channel to achieve lower probability of error and introduce optimum power allocation and relay positioning. We analyze the scenario when the source to destination direct link is not available and derive a closed form expression for symbol error rate (SER), its upper bound and an asymptotically tight approximation to exploit the performance gain by selecting the optimum relays in a multiple-relay cooperation scheme. Moreover, asymptotic optimum power allocation (based on the SER approximation) and optimal relay positioning are also considered to further improve the SER. The proposed relay selection scheme outperforms cooperative (DF) and non-cooperative schemes by more than 2 dB.     

A Hybrid Adaptive Relay Technique for Cooperative Communication System

Cooperative communication will increase the channel capacity, when the communicating terminals exceed more than two. Therefore, a relay is termed, as three-terminal unit is a fundamental for user cooperation. The cooperation provides throughput enhancement, reliability, and coverage improvement for wireless communication. Relay technique plays a vital role in cooperative communication in terms of increasing coverage range as well as spectral efficiency. In existing techniques Amplify Forward increase the noise and Decode Forward increase the computational cost of the receiver. In order to overcome the above limitation, a hybrid adaptive relay technique is proposed for cooperative communication system, which will initially check the channel quality of the end user received SNR. When the receiver does not able to decode the message, then the user will choose relay signal. We derived a closed form expression to find the outage probability and channel capacity for the Rayleigh fading channel. Finally, simulation results show the performance of proposed adaptive relay technique in comparison with traditional relay technique by considering both perfect and imperfect CSI.     

一种基于协作网络编码DF与AF的机会协作方案

在协作网络编码的解码转发方案的基础上,提出了基于协作网络编码DF与AF的机会协作通信方案,在这个方案中,用户根据与协作伙伴间的瞬时信道状态信息,决定如何处理接收到的协作伙伴的信息.若信道状态信息满足用户能够正确解码的要求,则采用协作网络编码DF方案,对接收到的信息与本地信息进行叠加发送给基站,否则采用AF方案,对接收到的信息进行放大,转发给基站.并研究得到了该方案的中断概率,通过仿真论证得到,该方案能够有效的降低系统的中断概率.     

散射通信的协作分集技术研究

对协作分集进行简单介绍,提出了将协作分集应用到散射通信中的方案,分析了协作分集在散射通信中的应用可行性。并对其中的放大转发和译码转发在只有一个中继节点的情况下进行仿真,仿真结果证明在大信噪比时译码转发的性能优于放大转发。且协作分集应用到散射通信中在相同的信噪比下,误码率更低,提高了系统性能。利用协作分集技术对散射通信进行组网,较直接组网设备复杂度低,易于实现。     

Using Orthogonal and Quasi-Orthogonal Designs in Wireless Relay Networks

Distributed space-time coding was proposed to achieve cooperative diversity in wireless relay networks without channel information at the relays. Using this scheme, antennas of the distributive relays work as transmit antennas of the sender and generate a space-time code at the receiver. It achieves the maximal diversity when the transmit power is infinitely large. This paper is on the design of practical distributed space-time codes (DSTCs). We use orthogonal and quasi-orthogonal designs which are originally used in the design of space-time codes for multiple-antenna systems. It is well known that orthogonal space-time codes have full diversity and linear decoding complexity. They are particularly suitable for transmissions in the network setting using distributed space-time coding since their ldquoscale-freerdquo property leads to good performance. Our simulations show that they achieve lower error rates than the random code. We also compare distributed space-time coding to selection decode-and-forward using the same orthogonal designs. Simulations show that distributed space-time coding achieves higher diversity than selection decode-and-forward (DF) when there is more than one relay. We also generalize the distributed space-time coding scheme to wireless relay networks with channel information at the relays. Although our analysis and simulations show that there is no improvement in the diversity, in some networks, having channel information at the relays saves both the transmission power and the transmission time.     

Cooperative lattice coding and decoding in half-duplex channels

We propose novel lattice coding/decoding schemes for half-duplex outage-limited cooperative channels. These schemes are inspired by the cooperation protocols of Azarian et al. and enjoy an excellent performance-complexity tradeoff. More specifically, for the. relay channel, we first use our lattice coding framework to generalize Yang and Belfiore implementation of the non-orthogonal amplify and forward cooperation protocol. This generalization is shown to offer significant performance gains while keeping the decoding complexity manageable. We then devise a novel variant of the dynamic decode and forward protocol, along with a lattice-coded implementation, which enjoys a near-optimal diversity-multiplexing tradeoff with a low encoding/decoding complexity. Finally, for the cooperative multiple-access channel, we present a lattice-coded implementation of the non-orthogonal amplify and forward protocol and demonstrate its excellent performance-complexity tradeoff. Throughout the paper, we establish the performance gains of our proposed protocols via a comprehensive simulation study     

Distributed space-time coding scheme with differential detection and power allocation for cooperative relay network

By introducing orthogonal space-time coding (STC) scheme in wireless cooperative relay network, two distributed differential STC (DSTC) schemes based on the amplify-and-forward (AF) and decode-and- forward (DF) methods are, respectively, developed. The scheme performance is investigated in symmetric and asymmetric wireless relay networks. The presented schemes require no channel information at both relay terminals and destination terminal, and have linear decoding complexity when compared with the existing scheme. Moreover, they are suitable for the application of different constellation modulations and DSTC schemes, and thus provide more freedoms of design. Besides, the power allocations between source and relay terminals are jointly optimized to minimize the system pairwise error probability for symmetric and asymmetric networks, and two practical methods are presented to solve the complicated optimized problem from asymmetric network. Simulation results show that the scheme with DF method has better performance than that with AF method due to no amplification of noise power, but the performance superiority will decrease at high SNR due to the error propagation of decoding at the relays. Furthermore, the distributed DSTC schemes with optimal power allocation have better performance than those with conventional fixed power allocation.