Source and Channel Coding for Cooperative Relaying

User cooperation is a powerful tool to combat fading and increase robustness for communication over wireless channels. Although it is doubtless a promising technique for enhancing channel reliability, its performance in terms of average source distortion is not clear since source-channel separation theorem fails under the most common nonergodic slow-fading channel assumption, when channel state information (CSI) is only available at the receiving terminals. This work sheds some light on the end-to-end performance of joint source-channel coding for cooperative relay systems in the high signal-to-noise ratio (SNR) regime. Considering distortion exponent as a figure of merit, we propose various strategies for cooperative source and channel coding that significantly improve the performance compared to the conventional scheme of source coding followed by cooperative channel coding. We characterize the optimal distortion exponent of a full-duplex relay channel for all bandwidth ratios. For the half-duplex relay channel, we provide an upper bound which is tight for small and large bandwidth ratios. We consider the effect of correlated side information on the distortion exponent as well.     

Cooperative Decode-and-Forward Relaying for Secondary Spectrum Access

We propose a two-phase protocol based on cooperative decode-and-forward relaying for a secondary system to achieve spectrum access along with a primary system. The primary and secondary systems comprise of a transmitter-receiver pair, PT-PR and ST-SR, respectively. In the first transmission phase, PT transmits the primary signal to PR, which is also received by ST and SR, where it is decoded. At ST, the primary signal is regenerated and linearly combined with the secondary signal by assigning fractions alpha and (1 - alpha) of the available power to the primary and secondary signals respectively. This combined signal is then broadcasted by ST in the second transmission phase. We show that as long as ST is located within a critical radius from PT, there exists a threshold value for alpha above which the outage probability of the primary system will be equal to or lower than the case without spectrum sharing. We also determine the outage probability achieved by the secondary system. Theoretical and simulation results confirm the efficiency of the proposed spectrum sharing scheme.     

Opportunistic Relaying for MIMO Amplify-and-Forward Cooperative Networks

We consider a wireless relay network with multiple antenna terminals over Rayleigh fading channels, and apply distributed space-time coding (DSTC) in amplify-and-forward (A&F) mode. The A&F scheme is used in a way that each relay transmits a scaled version of the linear combination of the received symbols. It turns out that, combined with power allocation in the relays, A&F DSTC results in an opportunistic relaying scheme, in which only the best relay is selected to retransmit the source’s space-time coded signal. Furthermore, assuming the knowledge of source-relay CSI at the source node, we design an efficient power allocation which outperforms uniform power allocation across the source antennas. Next, assuming M-PSK or M-QAM modulations, we analyze the performance of the proposed cooperative diversity transmission schemes in a wireless relay networks with the multiple-antenna source and destination. We derive the probability density function (PDF) of the received SNR at the destination. Then, the PDF is used to determine the symbol error rate (SER) in Rayleigh fading channels. We derived closed-form approximations of the average SER in the high SNR scenario, from which we find the diversity order of system R min{N _s , N _d }, where R, N _s , and N _d are the number of the relays, source antennas, and destination antennas, respectively. Simulation results show that the proposed system obtain more than 6 dB gain in SNR over A&F MIMO DSTC for BER 10^?4, when R = 2, N _s  = 2, and N _d  = 1.     

Outage-based Decision Strategies for Coded Cooperative Relaying Schemes

Two cooperation decision strategies based on the instantaneous signal-to-noise ratio (SNR) differences between source-destination, source-relay, and relay-destination channels are considered for coded cooperative relaying systems. Upper bounds on outage probability at the destination for the coded cooperative relaying schemes are first derived and exhaustive search is then used for SNR difference values and partitioning to minimize the outage probability for a given range of the SNR differences. Numerical results confirm the performance enhancement offered by the proposed schemes.     

Cooperative Fading Regions for Decode and Forward Relaying

Cooperative transmission protocols over fading channels are based on a number of relaying nodes to form virtual multi-antenna transmissions. Diversity provided by these techniques has been widely analyzed for the Rayleigh fading case. However, short range or fixed wireless communications often experience propagation environments where the fading envelope distribution is meaningfully different from Rayleigh. The main focus in this paper is to investigate the impact of fading distribution on performances of collaborative communication. Cooperative protocols are compared to co-located multi-antenna systems by introducing the concept of cooperative fading region. This is the collection of fading distributions for which relayed transmission can be regarded as a competitive option (in terms of performances) compared to multi-antenna direct (noncooperative) transmission. The analysis is dealt with by adopting the information theoretic outage probability as the performance metric. Cooperative link performances at high SNR are conveniently expressed here in terms of diversity and coding gain as outage parameters that are provided by the fading statistics of the channels involved in collaborative transmission. Advantages of cooperative transmission compared to multi-antenna are related to the propagation environment so that the analysis can be used in network design.      

Outage Performance for IDF Relaying Mobile Cooperative Networks

Cooperative communication is a key technique in fifth generation (5G) mobile wireless networks. In this paper, we study the transmit antenna selection (TAS) in mobile cooperative networks. We derive the exact closed-form outage probability (OP) expressions for two TAS schemes. Based on the derived OP expressions, the impact of power allocation on OP performance is evaluated. Then we obtain that the Monte-Carlo simulation results and the analysis results match very well. The OP performance is affected by the power-allocation parameter.     

一种基于自适应网络卷积编码的协作中继方法

在无线衰落信道环境中,协作中继是一种增加额外分集增益的有效方法,而网络编码可以用来提高网络吞吐量。网络编码采用XOR(异或)来混合两个源端的信息包,其稳健性差并且每个中继只能服务两个源端。该文提出一种自适应网络卷积编码协作中继方法,在中继端采用卷积编码方法代替XOR来混合两个或多个源端的信息包,混合后的信息可以看作是卷积编码器的一路输出,然后将其转发给目的端。当信道处于深度衰落时,该文提出了一种宽松自适应网络卷积编码协作中继方法,放松了中继参与转发的条件。该文提出的中继方法稳健性好,可以自适应匹配变化的无线网络拓扑结构,并且减少了网络编码协作中继方法所需要的中继个数。理论分析和仿真结果表明所提出的中继方法相比网络编码协作中继方法在性能上有大幅提高,尤其是随着协作节点数目增加,可保证系统获得稳定的额外满分集增益。     

New Solutions for Cooperative Relaying Implementation of OSTBC with 3/4 Code Rate

In this paper we propose two new cooperative relaying schemes which enable distributed implementation of the orthogonal space time block coding (OSTBC) with 3/4 code rate. These proposed schemes are compared with cooperative relaying scheme with virtual OSTBC and 1/2 code rate. The considered schemes are used for creating virtual 4 × 1 multiple input–single output (MISO) channel, and include one base station with two antennas, two relay stations each with a single antenna and one mobile station with a single antenna. Obtained results show that in the case of the same bit rate the proposed schemes provide better bit error rate (BER) performances than virtual OSTBC with 1/2 code rate. On the other side, for the same symbol constellations the proposed schemes have almost identical BER performances as virtual OSTBC with 1/2 code rate, but with a benefit of 1.5 times increased code rate.     

MIMO协同中继技术概述

无线协同中继技术可以提供更高数据速率,扩大覆盖面积,提高频谱效率,对抗衰落,增强系统的鲁棒性。文中研究了协同中继技术产生的背景,探讨了现有的各种协同中继方案,并对它们的性能进行了比较。着重介绍了MIMO协同中继的发展情况,并指出发展趋势和值得研究的问题。     

Full-Duplex Relaying Schemes for Cooperative NOMA Networks with SWIPT

Wireless Personal Communications - Existing security approaches for safeguarding data exchange among the sensor nodes are investigated in presence of apriori information of an adversary in...     

中继蜂窝网络下行协作网络编码中继方法

In this paper, we first overview some traditional relaying technologies, and then pre-sent a Network Coding-Aware Cooperative Relaying (NC2R) scheme to improve the performance of downlink transmission for relay- aided cellular networks. Moreover, sys-tematic performance analysis and extensive simulations are performed for the proposed NC2R and traditional relaying and non-relaying schemes. The results show that NC2R outperforms conventional relaying and non-relaying schemes in terms of blocking probability and spectral efficiency, especially for cell-edge users. Additionally, the location selections for relays with NC2R are also dis-cussed. These results will provide some insights for incorporating network coding into next-generation broadband cellular relay mo-bile systems.     

Wireless Mesh Networks and Cooperative Relaying Technologies

The Wireless Mesh Network (WMN) has become a focus in research of wireless broadband communications . In a switching technologies - based wireless Mesh network, the entire network is regarded as an IP subnet, so it cannot be applied in situations where large coverage is required . The use of cooperative relaying technologies can improve the transmission rate and reliability of wireless link; while the wireless Mesh network, once integrated with cooperative relaying technologies and routing technologies , can improve its spectrum efficiency and cover a wide area . However, there are many problems to be solved with respect to standardization, key technologies research and industrialization. Therefore , the application of cooperative relaying technologies in wireless Mesh networks is still a great challenge .     

Hybrid Digital-Analog Relaying for Cooperative Transmission Over Slow Fading Channels

Hybrid digital-analog coding schemes have been proposed in source-channel coding to increase the robustness toward channel mismatch, in the absence of transmitter channel state information (CSIT). Recognizing that the same kind of robustness is needed at the relay in a three-node relay network, we propose several novel relaying protocols based on hybrid digital-analog transmission. We compare the performance of the new schemes with traditional digital-only (decode-and-forward or compress-and-forward) or analog-only (amplify-and-forward) relaying, as well as to performance bounds corresponding to genie-aided compress-and-forward relaying. Our new protocols achieve significant gains in terms of achievable expected rates, and they are able to close in on the performance bounds. In particular, we conclude that the best overall performance is obtained by an adaptive combination of decode-and-forward and hybrid digital-analog relaying.      

MIMO Cooperative Diversity with Scalar-Gain Amplify-and-Forward Relaying

We analyze diversity performance of scalar fixed- gain amplify-and-forward (AF) cooperation in multiple-input multiple-output (MIMO) relay channels with ns source antennas, nR relay antennas, and nD destination antennas. We first derive the exact symbol error probability (SEP) for maximum likelihood decoding of orthogonal space-time block codes with M-ary phase-shift keying modulation over such channels and then characterize the effect of MIMO cooperative diversity on SEP behavior in a high signal-to-noise ratio regime. We show that the simple scalar-gain AF cooperation can create the diversity order d_AF les n_Sn_D + n_Sn_Rn_D/max{n_S, n_R, n_D} with the equality if 2max{n_S, n_R,n_D} ges n_S + n_R + n_D - 1. This finding reveals that the number of relay antennas greater than or equal to n_S + n_D - 1 is required to achieve the additional diversity order n_Sn_D by scalar-gain AF relaying. We also present the asymptotic SEP as the number of relay antennas tends to infinity.     

协作中继中联合乘积码的网络编码应用

在协作中继系统中应用网络编码可以提高网络的吞吐量,基于异或的网络编码并没有很好的纠错能力.提出了一种基于乘积码的网络编码方式,中继联合各个接收端的信息块,转发一次冗余块编码以提高各个接收端解码能力.理论和仿真曲线都证明了相对于简单的异或型网络编码,基于乘积码的网络编码可以提供更好的性能.     

Multicast Network Security with Asymmetric Cooperative Relaying

International Journal of Wireless Information Networks - This paper exhibits the confidentiality performance study of a cooperative multicast network consisting of $${\mathcal {K}}$$ asymmetric...     

最佳中继协作通信系统的功率分配算法

 为提高基于最佳中继选择的协作通信系统的性能,提出了以最小化系统中断概率为目标的功率分配算法.首先建立了系统的优化模型并证明了待解的优化问题实质是凸优化问题,由此提出了最优功率分配算法并给出了算法步骤.其次,在此基础上提出了一种有效的次最优功率分配算法,该算法计算简单且仅需已知各个中继节点的平均信道状态信息,无需在传输中实时更新,因而不增加系统的额外开销.仿真结果表明,本文提出的最优算法和次最优算法所得到的功率分配方案与穷举搜索方法的结果非常接近;与等功率分配方案相比,这两种算法均能显著提高系统的中断概率性能.     

An Efficient Adaptive Distributed Space-Time Coding Scheme for Cooperative Relaying

A non-regenerative dual-hop wireless system based on distributed Alamouti space-time coding is considered. It is assumed that each relay retransmits an appropriately scaled space-time coded version of its received signal. The main goal of this paper is to find a scaling function for each relay to minimize the outage probability. In the high signal-to-noise ratio (SNR) regime for the relay-destination link, it is shown that a threshold-based scaling function (i.e., the relay remains silent if its channel gain with the source is less than its predetermined threshold) is optimum from the outage probability point of view. Numerical results demonstrate a dramatic performance improvement as compared to the case that the relay stations forward their received signals with full power even for finite SNR scenarios.     

Timing Synchronization for Cooperative Communications with Detect and Forward Relaying

A non-data-aided near maximum likelihood (NDA-NML) symbol timing estimator is presented, which is applied to a cooperative communication system with a source, relay and destination. A Cramer rao bound (CRB) for the estimator for asymptotically low signal-to-noise (SNR) ratio case is derived. The timing complexity of the NDA-NML estimator is derived and compared with the correlation based data-aided maximum likelihood (DA-ML) estimator. It is demonstrated that the complexity of the NDA-NML estimator is much less than that of correlation based DA-ML estimator. The bit-error-rate (BER) performance of this system operating in a detect-and-forward (DAF) mode is studied where the channel state information (CSI) is available at the receiver and the symbol timings are estimated independently for each channel. SNR combining (SNRC) and equal ratio combining (ERC) methods are considered. It is found that timing estimation error has a significant effect on BER performance. It is also found that for large timing error the benefit of cooperative diversity could vanish. It is demonstrated that significant gains can be made with both combining methods with cooperation and timing estimation, where the gains are the same for both estimators.