Interference mitigation in Z-channel and relay-assisted Z-channel: a diversity gain region perspective

This work considers the interference management in Z-channel and full-duplex decode-and-forward (FD DF) relay-assisted Z-channel. In the case of Z-channel, closed-form expressions for the achievable diversity gain regions (DGRs) with both single-user (SU) codes and multi-user (MU) codes are presented. The closed-form expression for the achievable DGR of the clustered FD DF relay-assisted Z-channel with SU codes is also presented. In the Z-channel, if the interference-free receiver is constrained to operate at optimal diversity multiplexing tradeoff (DMT), the SU codes are shown to achieve better DGR than MU codes. Furthermore, in the Z-channel, the SU codes achieve DGR outer bound at low multiplexing gain region, and MU codes can never achieve DGR outer bound. Also, we have shown that Z-channel with two co-located antennas at the interfering transmitter achieves better DGR compared to that of the clustered FD DF relay-assisted Z-channel with single antenna at the interfering transmitter.     

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.     

Outage Probability of Regenerative Protocols for Two-Source Two-Destination Networks

In this paper, the analytical expressions for the outage probability of different decode-and-forward (DF) relaying strategies for two-source two-destination networks are evaluated allowing an investigation of their effectiveness in energy saving to be determined. Each source node transmits data to an interested destination node with the help of the remaining source node in a cooperative DF manner. Specifically, we consider four DF protocols, including repetition DF (RDF), parallel DF (PDF), network coding-based RDF (NC-RDF), and dirty paper coding-like network coding-based PDF (DPC-NC-PDF). The closed-form expression of the outage probability for each protocol is derived at high signal-to-noise ratio. The results show that the DPC-NC-PDF protocol achieves the best performance while the NC-RDF protocol is better than both the RDF and PDF protocols with proper linear NC coefficients. All the DF protocols are shown to achieve diversity order one and the highest multiplexing gain is achieved with the NC-RDF and DPC-NC-PDF protocols. Finally, simulation results are presented to verify the analytical findings and show the system throughput comparison of various DF protocols.     

On the achievable diversity-multiplexing tradeoff in half-duplex cooperative channels

We propose novel cooperative transmission protocols for delay-limited coherent fading channels consisting of N (half-duplex and single-antenna) partners and one cell site. In our work, we differentiate between the relay, cooperative broadcast (down-link), and cooperative multiple-access (CMA) (up-link) channels. The proposed protocols are evaluated using Zheng-Tse diversity-multiplexing tradeoff. For the relay channel, we investigate two classes of cooperation schemes; namely, amplify and forward (AF) protocols and decode and forward (DF) protocols. For the first class, we establish an upper bound on the achievable diversity-multiplexing tradeoff with a single relay. We then construct a new AF protocol that achieves this upper bound. The proposed algorithm is then extended to the general case with (N-1) relays where it is shown to outperform the space-time coded protocol of Laneman and Wornell without requiring decoding/encoding at the relays. For the class of DF protocols, we develop a dynamic decode and forward (DDF) protocol that achieves the optimal tradeoff for multiplexing gains 0/spl les/r/spl les/1/N. Furthermore, with a single relay, the DDF protocol is shown to dominate the class of AF protocols for all multiplexing gains. The superiority of the DDF protocol is shown to be more significant in the cooperative broadcast channel. The situation is reversed in the CMA channel where we propose a new AF protocol that achieves the optimal tradeoff for all multiplexing gains. A distinguishing feature of the proposed protocols in the three scenarios is that they do not rely on orthogonal subspaces, allowing for a more efficient use of resources. In fact, using our results one can argue that the suboptimality of previously proposed protocols stems from their use of orthogonal subspaces rather than the half-duplex constraint.     

Spectrally-efficient relay selection with limited feedback

This paper addresses the multiplexing loss that occurs in relay networks due to causality of relays and the half-duplex constraint. We devise relay selection methods to recover the multiplexing loss in decode-and-forward (DF) relay networks, while requiring very little feedback (merely bits/relay). Two network topologies are studied: First the case is considered where a direct link is available between the source and destination, in addition to the relayed links. For this configuration, an incremental transmission scheme is proposed, and comprehensively analyzed, which uses limited feedback to improve both diversity as well as multiplexing gain. Then, the case without a direct link is considered, for which efficient non-orthogonal DF protocols are produced and analyzed. An interesting feature of the latter methods is unequal error protection capability via a family of embedded diversity-multiplexing (DMT) curves, which can be very useful for practical applications. Even considering this method's minimal DMT, a marked improvement over previous DF methods is observed, especially in high spectral efficiencies.     

Nakagami-m信道下全双工解码转发中继中断概率分析

研究存在残余自干扰（residual self-interference, RSI）条件下全双工解码转发中继的中断概率性能。在Nakagami-m信道下,推导了多跳解码转发（multi-hop decode-and-forward,MH-DF）策略和选择解码转发（selected decode-and-forward,SDF）策略的端到端中断概率闭合表达式和渐近表达式,分析了两种策略的可达分集度。结果显示,MH-DF策略的可达分集度为0,SDF策略的可达分集度由信道成型因子和中继功率伸缩方案决定。相比于MH-DF策略,SDF策略具有更优的中断概率性能和抗自干扰能力。      

On the Diversity Gain of AF and DF Relaying With Noisy CSI at the Source Transmitter

The problem of optimizing resource allocation over a half-duplex relay channel with noisy channel state information at the source transmitter (CSIT) is studied, with a focus on the asymptotically high signal-to-noise ratio (SNR) regime. A novel upper bound on the diversity-multiplexing tradeoff (DMT) is derived, taking into account the quality of the CSIT. It is shown that from a DMT perspective, the decode-and-forward (DF) protocol is strictly optimal over a certain range of the multiplexing gains. When the quality of the CSIT is sufficiently high, the DMT performance of the DF protocol with noisy CSIT equals that of the dynamic DF protocol shifted above by a constant diversity gain, which depends only on the quality of the CSIT about the source-destination link. When the quality of the CSIT reduces, DF relaying is still DMT-optimal, but only over a smaller range of the multiplexing gains. In an intermediate range of the multiplexing gains, nonorthogonal schemes provide some additional gains when the CSIT quality is sufficiently low. It is also shown that the DMT of the amplify-and-forward (AF) protocol is offset by a constant term depending on the quality of the CSIT of the source-destination link only.     

QoS-guaranteed multi-relay selection and power allocation optimization in cooperative systems

This paper investigates the relay selection and power allocation problem in multi-user based cooperative networks, where intermediate relay nodes help source forward information to destination using decode-and-forward (DF) relaying protocol. Specifically, we propose a novel multi-relay nodes selection strategy taking both instantaneous channel state information (I-CSI) and residual energy into consideration, by which 'emergence' diversity gain can be achieved and the imbalance of resource utilization can be overcome. Besides, using Largangian dual-primal decomposition and subgradient projection approach, an optimal power allocation algorithm at source and cooperative relay nodes is presented with the constraints of each user's individual quality of service (QoS) requirements and system total transmit power. Theoretical analysis and simulation results demonstrate that the proposed scheme can significantly improve energy efficiency, while guaranteeing a good balance between achievable data rate and average network lifetime with relatively low implementation complexity.     

Differential modulation for two-user cooperative diversity systems

This paper introduces a novel differential modulation scheme for a two-user cooperative diversity system which does not require channel state information at either the users or the destination. The performance of fixed decode-and-forward and selection relaying protocols is evaluated in both symmetric and asymmetric interuser-channel cases. The lower bound on the performance of the decode-and-forward protocol is given, while the exact bit-error probability of the selection relaying protocol is thoroughly derived. The decode-and-forward relaying protocol achieves a performance gain when the signal-to-noise ratios in the interuser channels are symmetric and sufficiently high. The selection relaying protocol shows a larger performance gain and does not exhibit an error floor like in the case of the decode-and-forward protocol. In addition, it is robust to the asymmetric interuser channels.     

Decode-and-Forward Relaying With Quantized Channel State Feedback: An Outage Exponent Analysis

The problem of resource allocation to maximize the outage exponent over a fading relay channel using the decode-and-forward protocol with quantized channel state feedback (CSF) is studied. Three different scenarios are considered: relay-to-source, destination-to-relay, and destination-to-source-and-relay CSF. In the relay-to-source CSF scenario, it is found that using merely one bit of CSF to control the source transmit power is sufficient to achieve the multiantenna upper bound in a range of multiplexing gains. In the destination-to-relay CSF scenario, the systems slightly outperform dynamic decode-and-forward (DDF) at high multiplexing gains, even with only one bit of feedback. Finally, in the destination-to-source-and-relay CSF scenario, if the source-relay channel gain is unknown to the feedback quantizer at the destination, the diversity gain only grows linearly in the number of feedback levels, in sharp contrast to an exponential growth for multiantenna channels. In this last scenario, a simple scheme is shown to perform close to the corresponding upper bound.      

Recovering Multiplexing Loss through Concurrent Decode-and-Forward (DF) Relaying

In this paper, we develop a novel digital cooperative diversity transmission protocol for a two-source scenario by combining the two sources’ two classic decode-and-forward (DF) relaying steps and using 2L + 1 time slots to transmit L codewords from each source. Assuming the relays can perfectly decode their associated source messages, we give an information-theoretic average achievable capacity region for this transmission scheme. Through diversity-multiplexing tradeoff analysis, we show that our so called concurrent DF relaying protocol can effectively recover the multiplexing loss induced by the half-duplex operation in the relays, while still obtaining some diversity gain. Numerical results reveal our scheme offers significant performance advantages over the classic DF relaying protocols, especially for high signal-to-noise ratio (SNR) and large frame length L regime.

具有大规模天线选择与功率分配的协作通信

在瑞利衰落信道下研究了采用前向译码转发协议的三节点协作模型,分析了中继分布大规模天线阵列时系统的可靠性能。为了有效地降低系统复杂度,同时又能获得大规模天线带来的分集增益,给出了中继选择合并(SC)与天线选择空间调制(SM)相结合的组合传输方案。为了进一步提高可靠性能,研究了SC/SM组合方案如何通过功率分配优化其误比特率性能。仿真分析表明,大规模中继SC/SM方案的功率分配能够有效改善系统的误比特率性能。     

Adaptive Decode-and-Forward Protocol Based Cooperative Spectrum Sensing in Cognitive Radio with Interference at the Secondary Users

In this paper a novel multiple-user cooperative spectrum sensing scheme (MCSS) based on hybrid relay is proposed to achieve the spatial diversity gain in detection of the primary user (PU) in a cognitive radio (CR) network. A practically important case where co-channel interference signals are present at the network is considered for the analysis. Closed-form expressions of detection probability \((\hbox {P}_{\mathrm{d}})\) and false alarm probability \((\alpha )\) for the proposed adaptive decode-and-forward based multiple-user cooperative spectrum sensing scheme (ADF-MCSS) using energy detector over Rayleigh fading sensing channels is derived in presence of co-channel interference at the secondary user which is far away from the PU. Further we extend the concept of two user amplify-and-forward (AF) and decode-and-forward (DF) cooperative spectrum sensing schemes in multiple-user scenario (i.e. AF-MCSS and DF-MCSS) over Rayleigh fading channels when the secondary user (which is far away from PU) is affected by interference. Closed-form expressions of AF-MCSS and DF-MCSS schemes over a Rayleigh fading channels are also evaluated and compared with that of proposed ADF-MCSS in presence of interference signals at the secondary user. Further the performance analysis of AF-MCSS, DF-MCSS and ADF-MCSS schemes are compared with the existing non-cooperative spectrum sensing schemes in presence of interference at the secondary user. Our analysis is validated by numerical and simulation results for multiple-user CR network. The impact of number of cooperative relays, SNR in sensing channel, energy of interference signal, false alarm on detection probability in proposed ADF, AF and DF schemes is shown.     

Performance of antenna selection schemes in dual hop full-duplex decode-and-forward relaying over Nakagami-m fading channels

In this paper, we investigate the outage performance of several antenna selection (AS) schemes in dual hop full-duplex (FD) multiple-input multiple-output (MIMO) relay networks in which the relay adopts decode-and-forward (DF) protocol over Nakagami-m fading channels. In the network, the source (S), destination (D) and relay (R) are assumed to be equipped with multiple antennas. We assume that the line-of-sight component between S and D cannot be established due to the poor fading environment conditions. For signal transmission-reception during the training period, only a single antenna at each node is selected according to selection techniques, and then with the help of an error-free feedback channel the selected antenna index is sent to the related node. Outage probability (OP) expressions related to AS schemes are obtained in closed forms and asymptotic OPs are also derived in order to get more meaningful insights into OP and diversity behaviour. The theoretical results are verified by Monte Carlo simulations. We show that performance of the FD relay can be significantly improved by using selection techniques compared to half-duplex (HD), especially at low signal-to-noise ratio (SNR) region. In addition, results show that the performance floor level meaning zero diversity at high SNR region, which is also confirmed by asymptotic analysis and is an inherent disadvantage of FD relay, can be decreased. Moreover, it is shown that the FD relay with AS schemes outperforms HD as the target rate increases for a certain value of SNR and residual self-interference power.     

基于用户协作的小区间干扰抑制方案

以长期演进（LTE）上行链路单载波频分多址（SC-FDMA）传输方案为基础,提出了一种基于用户协作的小区间干扰抑制传输方案。该方案采用译码转发中继工作方式,位于相邻小区边缘的两用户互为中继相互协作,在3个时隙内完成用户终端到基站的信息传输。仿真研究表明：该方案能够有效抑制小区间用户共信道干扰,同时充分利用用户协作所提供的空间分集增益提高小区边缘用户链路传输可靠性。此外,该方案所采用的块空时分组编码（B-STBC）能够很好地保持用户终端发射信号的低峰均比特性。     

Decouple-and-Forward Relaying for Dual-Hop Alamouti Transmissions

In this letter, decouple-and-forward (DCF) relaying for dual-hop Alamouti transmissions is proposed as enhanced amplify-and-forward (AF) relaying to achieve spatial diversity gain especially provided by a two-antenna relay. DCF relaying that consists of decoupling, re-encoding and amplifying needs a little more complicated relay than AF relaying but a less complicated one than decode-and-forward (DF) relaying. Assuming uncorrelated Rayleigh fading channels, we derive a probability density function (PDF) of end-to-end signal-to-noise ratio (SNR) for the DCF system and provide its bit error rate (BER) performance. Numerical investigation shows that the analysis provided in this letter is exact and in dual-hop Alamouti transmissions, DCF achieves BER close to DF and even better BER when SNR is low.     

On the energy efficiency of MIMO cooperative relaying networks

Cooperative relaying techniques can greatly improve the capacity of the multiple input and multiple output (MIMO) wireless system. The transmit power allocation (TPA) strategies for various relaying protocols have become very important for improving the energy efficiency. This article proposes novel TPA schemes in the MIMO cooperative relaying system. Two different scenarios are considered. One is the hybrid decode-and-forward (HDF) protocol in which the zero-forcing (ZF) process is operated on relays, and the other is the decode-and-forward (DF) protocol with relay node and antenna selection strategies. The simulation results indicate that the proposed schemes can bring about significant capacity gain by exploiting the nature of the relay link. Additionally, the proposed TPA scheme in the HDF system can achieve the same capacity as the equal TPA with fewer relay nodes used. Finally, the capacity gain with the proposed schemes increases when the distribution range of relay nodes expands.     

分组协同中继系统性能研究以及分组长度性能影响分析

针对AF(amplify-and-forward)和DF(decode-and-forward)2种转发模式,分析了分组协同中继通信系统在高信噪比下的误帧率性能,并研究了帧长对误帧率的影响。研究表明,以误帧率为准则,AF和DF模式都取得了相同的分集增益,但是编码增益不一样,并且编码增益与帧长有关。与现有的研究结论不一样,考虑到实际的分组长度,DF总是能够获得较AF更好的性能,帧越短DF的优势越明显;当帧长足够大时AF能够获得和DF相近的性能。还研究了最优的中继位置,对于AF系统,最优的中继位置总是位于源和目的节点中点处;而对于DF系统,当帧长增大时最优的中继位置将从靠近源处逐渐移至中点处。     

一种利用软信息网络编码在双向中继网络进行估计转发的方法

 在本文中,我们为双向中继网络(Two-way Relay Networks)设计了一种崭新的估计-转发(EF:Estimate-and-Forward)方法.在中继端信道解码后首先得到每一比特的对数似然比(LLR:Log-Likelihood Ratio),然后利用两个方向的比特LLR进行软信息网络编码,并借此构造出中继端的发送信号.因为此方法保留了两端比特信息的软信息并抑制了噪声,所以在任何条件下它的性能都要优于传统的放大-转发(AF:Amplify-and-Forward)方式和解码-转发(DF:Decode-and-Forward)方式,文中详细推导了三种转发方式的最大可达速率,得到EF方式下最大可达速率的上界和下界,还证明了EF方式较其它两种方式节省功率消耗,并通过仿真得到了速率曲线与误码率曲线,明确的验证了EF的优势.     

Superposition Coding and Analysis for Cooperative Multiple Access Relay System

The conventional straightforward relaying scheme named decode-and-forward (DF) protocol is used at relay to decode the data received from source and forward the decoded data to the destination to improve the spatial diversity gain. Although it is a simple scheme, the total resource efficiency is low for multiple sources. Superposition coding has been known as a spectral efficient technique in wireless networks. However, when it is applied to the uplink multiple access relay systems, it suffers from performance degradation caused by the power allocation between the symbols of multiple sources. In this paper, we propose to remedy this problem by using hierarchical modulation at the source node and superposition coding at the relay node to enhance the bit energy. We investigate how hierarchical modulation can be incorporated and optimized with superposition coding. Specially, we discuss the capacity behavior of the proposed scheme and compare with the baseline, namely the capacity behavior of the existing DF scheme and the capacity behavior of the superposition coding. Our results are encouraging in that superposed hierarchical modulation significantly improves the better block error rate and capacity performance in multiple access relay channels.