Single Relay Selection for Bidirectional Cooperative Networks with Physical‐Layer Network Coding

To serve the growing demand of the bidirectional information exchange, we propose a single relay selection (RS) scheme for physical‐layer network coding (PNC) in a bidirectional cooperative network consisting of two sources and multiple relays. This RS scheme selects a single best relay by maximizing the bottleneck of the capacity region of both information flows in the bidirectional network. We show that the proposed RS rule minimizes the outage probability and that it can be used as a performance benchmark for any RS rules with PNC. We derive a closed‐form exact expression of the outage probability for the proposed RS rule and show that it achieves full diversity gain. Finally, numerical results demonstrate the validity of our analysis.     

Least Square Channel Estimation for Two‐Way Relay MIMO OFDM Systems

This letter considers the channel estimation for two‐way relay MIMO OFDM systems. A least square (LS) channel estimation algorithm under block‐based training is proposed. The mean square error (MSE) of the LS channel estimate is computed, and the optimal training sequences with respect to this MSE are derived. Some numerical examples are presented to evaluate the performance of the proposed channel estimation method.     

基于有限域网络编码的中继选择方法

针对采用有限域网络编码的多源多中继协作通信系统,提出一种以极大最小距离可分码作为网络编码的自适应中继选择方法,将网络编码技术与中继选择技术相结合来提高系统的复用增益。通过分析系统的中断概率性能,得到系统的分集复用折中,由此证明自适应中继选择方法能够在保持协作系统获得满分集增益的同时,使得系统的复用增益不低于1/2。仿真结果表明,自适应中继选择方法优于传统的网络编码协作方法。     

Decode‐and‐forward two‐way relaying protocol with one retransmission

This paper investigates the decode‐and‐forward two‐way relaying channel without direct link and proposes a protocol based on the physical‐layer network coding (PNC) protocol. The proposed protocol (termed ORT) introduces one retransmission into PNC, aiming at enhancing its outage performance. To manifest the merits of ORT, we compare it with PNC and the time‐division broadcast (TDBC) protocol, in terms of outage performance, expected rate, and diversity‐multiplexing tradeoff (DMT). Firstly, we derive the outage probability of the three protocols and then the expected rate. Secondly, asymptotic analysis is conducted to shed light on the diversity and coding gains. Finally, the DMT is obtained for the three protocols. The numerical results reveal the following: (i) that ORT performs better than PNC in both outage and expected rate performance when the nodes transmit with different powers. However, it has the same DMT performance with PNC; (ii) that ORT possesses improved DMT performance over TDBC whereas its expected rate is only better than the latter at medium to high signal‐to‐noise ratio. Copyright © 2012 John Wiley & Sons, Ltd.     

物理层安全中的最优中继选择及协同干扰策略

本文提出了一种以协同干扰为基础,结合了最优中继选择和功率分配的物理层安全方案.该方案针对分布式天线的场景,从中间节点中选择一个最佳的节点作为中继,剩余的其他节点作为协同干扰节点.中继节点使用放大转发策略.本文同时提出了协同干扰节点的波束成形算法.另外,我们还推导出了中继节点和协同干扰节点之间的功率分配的闭式解.最后,本文还给出了相关的仿真结果,证实了新提出的方案比传统方案能获得更高的安全容量.     

Performance of Two‐User Two‐Way Amplify‐and‐Forward Relaying Systems with Scheduling

In this paper, we study scheduling schemes for two‐user two‐way wireless relaying systems. Two transmission modes are considered: point‐to‐point direct transmission and two‐way amplify‐and‐forward relaying. An optimal scheduling scheme that opportunistically selects the best transmission mode for each user is proposed to minimize the sum bit error rate (BER). The performance lower bound of the optimal scheduling scheme is analyzed, and closed‐form expression of the lower‐bound BER is derived. However, for optimal scheduling, the scheduler requires the knowledge of channel state information (CSI) of all links. To reduce the feedback information of CSI, we also propose a suboptimal scheduling scheme that selects the transmission mode using only the CSI of two direct links. Simulation results show that there are 4 dB to 8 dB gains for the proposed optimal and suboptimal schemes over the fixed direct transmission and fixed two‐way relayed transmission scheme. The performance gap between the optimal and suboptimal scheduling schemes is small, which implies a good trade‐off between implementation complexity and system performance.     

非对称速率的双向中继信道物理层网络编码

本文提出了基于非对称速率的双向中继信道的物理层网络编码方案。本文所提方案联系实际无线通信信道的差异性,不但考虑了较差链路的最大传输性能以保证其传输的可靠性,而且在较优链路采取较高速率进行传输,从而充分利用较优链路来传输更多信息,增加通信系统的信道容量。为实现不对称速率传输,其基本思想是在较差链路中加入已知信息,通过已知信息可减小中继节点接收到的叠加信号的星座图,使得通信系统的译码性能得到提升。在中继节点,根据叠加信号的星座图对叠加信号进行联合解调,在节省了系统工作时隙的同时也减小了系统的复杂度。仿真结果表明了采用非对称速率传输不但可保证信息传输的可靠性,还可提高通信系统的信道容量,充分利用系统资源。      

一种基于TCM的信道编码与物理层网络编码的联合设计

该文在双向中继信道中基于网格编码调制(Trellis Coded Modulation, TCM)提出了一种信道编码与物理层网络编码的联合实施机制。该机制采用TCM,将编码和调制统一考虑,提高了编码序列的自由距离,从而获得更高的编码增益。此外,利用卷积码和MAC-XOR网络编码的线性性质,使得中继节点只要直接估计网络编码的码字,这样中继节点进行TCM译码的复杂度减少了50%。该机制同时考虑信道编码技术、调制技术以及物理层网络编码三者联合设计的问题,既提高信息传输率,又保证了可靠性。     

Combined orthogonal physical‐layer network coding over fading two‐way relay channels

This paper proposes a new physical‐layer network coding (PNC) scheme, named combined orthogonal PNC (COPNC), for fading two‐way relay channels. The scheme is based on orthogonal PNC (OPNC). In the scheme, the two source nodes employ orthogonal carriers, and the relay node makes an orthogonal combining of the two information bits rather than exclusive or (XOR), which is employed in most PNC schemes. The paper also analyzes the bit error rate (BER) performance of PNC, OPNC, and COPNC for Rayleigh fading model. Simulation results for Rayleigh and Nakagami‐m fading channels show that COPNC can provide outstanding BER performance compared with PNC and OPNC, especially when the uplink channel conditions are asymmetric. The results in Nakagami‐m channels also imply that COPNC will provide higher BER gain with more severe fading depth. Potential works about COPNC are also presented in this paper. Copyright © 2013 John Wiley & Sons, Ltd.     

基于接收信噪比和网络寿命的最优中继选择

为了增大网络寿命,降低误符号率,优化无直传链路协作通信系统的性能,本文提出基于接收信噪比和网络寿命的最优中继选择算法。由于网络寿命的问题无法直接求解,将其转化为中继节点剩余能量与目的节点达到接收信噪比门限时发射功率的比值。首先计算各个中继在目的节点的接收信噪比,将大于信噪比门限加入候选中继,然后依次计算候选中继的联合优化函数值并排序,值最大者即为最优中继。理论推导了系统误符号率的上下界,仿真表明理论值与仿真值较为吻合,验证了系统在保证较低误符号率的基础上延长了网络寿命。     

基于物理层网络编码的非对称中继系统性能分析

在无线通信研究中,网络编码因其可有效提升带宽利用率的特性得到了大量关注.但是,网络编码用于双向中继信道(TWRC)时,中继位置的不对称将造成系统性能的下降,故在源节点使用分层调制的方法来解决此问题.研究了分层调制和物理层网络编码的联合以及优化,并进行了系统仿真.仿真结果显示,在非对称中继信道下,通过与传统调制方案(CM...     

Denoising Mapping Utilizing Constellation Symmetry in Denoise‐and‐Forward Two‐Way Relay Channels

The denoising mapping with the closest‐neighbor clustering (CNC) method in denoise‐and‐forward two‐way relay channels is studied. Specifically, the symmetry of the constellations in source terminals A and B is utilized to reduce the complexity of the CNC method. The specific case considered first to illustrate how the constellation symmetry works in the CNC method is the quadrature phase‐shift keying constellation in A and B and the single‐antenna deployment in all terminals. This case study shows that an enormous complexity reduction can be achieved. Next, the result is extended to multiple‐antenna scenarios and square quadrature amplitude modulations.     

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.     

基于网络编码的感知无线网多中继机制

多中继感知协作通信技术是无线通信领域中,利用时空分集提升网络吞吐量的热门研究方向。该文首次提出了感知无线网中分布式译码转发后的中继冗余问题,并在理论与仿真上证明了现有传输协议不仅不足以支持多中继感知通信,而且由于其衍生了大量冗余而降低了网络吞吐量。针对该问题,该文提出了在缓存队列中结合随机网络编码的中继机制,从而有效地避免了中继冗余,使得多中继感知的吞吐量接近理想上界,减少缓存空间的占用,仿真结果表明该文提出的机制是一种高效实用的感知中继传输机制。     

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。      

Network coding‐based channel quality indicator reporting for two‐way multi‐relay networks

This paper considers channel quality indicator (CQI) reporting for data exchange in a two‐way multi‐relay network. We first propose an efficient CQI reporting scheme based on network coding, where two terminals are allowed to simultaneously estimate the CQI of the distant terminal‐relay link without suffering from additional overhead. In addition, the transmission time for CQI feedback at the relays is reduced by half while the increase in complexity and the loss of performance are negligible. This results in a system throughput improvement of 16.7% with our proposed CQI reporting. Upper and lower bounds of the mean square error (MSE) of the estimated CQI are derived to study performance behaviour of our proposed scheme. It is found that the MSE of the estimated CQI increases proportionally with the square of the cardinality of CQI level sets although an increased number of CQI levels would eventually lead to a higher data rate transmission. On the basis of the derived bounds, a low‐complexity relay selection (RS) scheme is then proposed. Simulation results show that, in comparison with optimal methods, our suboptimal bound‐based RS scheme achieves satisfactory performance while reducing the complexity at least three times in case of large number of relays. Copyright © 2012 John Wiley & Sons, Ltd.     

Outage Probability of Decode‐and‐Forward Relaying Systems with Efficient Partial Relay Selection in Nakagami Fading Channels

Recently, efficient partial relay selection (e‐PRS) was proposed as an enhanced version of PRS. In comparing e‐PRS, PRS, and the best relay selection (BRS), there is a tradeoff between complexity and performance; that is, the complexity for PRS, e‐PRS, and BRS is low to high, respectively, but vice versa for performance. In this paper, we study the outage probability for e‐PRS in decode‐and‐forward (DF) relaying systems over non‐identical Nakagami‐m fading channels, where the fading parameter m is an integer. In particular, we provide closed‐form expressions of the exact outage probability and asymptotic outage probability for e‐PRS in DF relaying systems. Numerical results show that e‐PRS achieves similar outage performance to that of BRS for a low or medium signal‐to‐noise ratio, a high fading parameter, a small number of relays, and a large difference between the average channel powers for the first and the second hops.     

网络编码系统中基于天线选择的安全传输技术研究

为提高模拟网络编码系统的安全传输容量,提出一种基于天线选择物理层安全传输方案;研究在准静态慢衰落信道条件下,源结节与中继结点的天线选择策略及其性能分析。该方案分别以最大信道容量和最大信道增益为目标,在最优选择准则基础上,提出简化的天线选择方法。数值仿真表明:联合主信道容量最大化(CMCCM)准则具有最优的性能曲线,但其运算复杂度也最大。相比于固定选择策略,CMCCM方案提供系统增益约5 d B。特别地,简化的独立信道增益最大化(ICGM)方案与CMCCM方案表现出接近的性能曲线。     

Optimal resource allocation for multiple network‐coded two‐way relay in orthogonal frequency division multiplexing systems

This paper studies optimal resource allocation for multiple network‐coded two‐way relay in orthogonal frequency division multiplexing systems. All the two‐way relay nodes adopt amplify‐and‐forward and operate with analog network coding protocol. A joint optimization problem considering power allocation, relay selection, and subcarrier pairing to maximize the sum capacity under individual power constraints at each transmitter or total network power constraint is first formulated. By applying dual method, we provide a unified optimization framework to solve this problem. With this framework, we further propose three low‐complexity suboptimal algorithms. The complexity of the proposed optimal resource allocation (ORA) algorithm and three suboptimal algorithms are analyzed, and it is shown that the complexity of ORA is only a polynomial function of the number of subcarriers and relay nodes under both individual and total power constraints. Simulation results demonstrate that the proposed ORA scheme yields substantial performance improvement over a baseline scheme, and suboptimal algorithms can achieve a trade‐off between performance and complexity. The results also indicate that with the same total network transmit power, the performance of ORA under total power constraint can outperform that under individual power constraints. Copyright © 2012 John Wiley & Sons, Ltd.