非理想载波同步物理层网络编码误比特性能分析

采用相干检测的物理层网络编码系统的误比特性能与载波同步精度密切相关,收发双方的载波同步误差将引起系统性能恶化。本文研究了残余载波同步误差对采用相同星座和正交星座BPSK信号的两种物理层网络编码双向中继系统误比特性能的影响。首先基于最大似然准则推导了存在残余载波同步误差时中继节点及源节点处接收信号的判决区域,然后运用Craig极坐标法分析了系统多址接入、广播阶段及总的端到端误比特性能,得出了精确的误比特率表达式,文中的分析方法可推广到采用其他调制方式的物理层网络编码系统。计算机仿真表明:文中的理论分析与仿真结果完全吻合,所推导的理论公式可以效地评估BPSK调制物理层网络编码系统的误比特性能;正交星座系统对载波同步误差更为敏感,相同的同步误差对正交星座系统的性能恶化更为严重。      

过时信道状态信息下的机会式中继选择系统的安全性能分析

在 Nakagami m衰落信道下,目的端和窃听者采用最大比合并策略,本文研究了在机会式自适应解码转发中继选择安全协作系统中的安全性能。由于实际信道中的反馈延迟,最优的合法中继选择基于合法信道反馈的过时信道状态信息。为了评价机会式中继选择在改善安全性能上的表现,分别推导了准确的正安全容量概率和准确的安全中断概率闭合表达式。此外,针对两种不同情况, 推导了形式简单的渐近表达式,并明确给出安全分集阶数和安全阵列增益。理论分析和数值仿真表明,增加中继个数和目的节点的天线数能够改善安全中断概率的性能表现,且在信道状态信息过时的条件下,系统的安全分集阶数与中继数无关。      

物理层网络编码机会中继及中断性能分析

该文研究了频率非选择性瑞利衰落信道中的物理层网络编码系统容量问题。基于放大转发机制提出了一种基于最大最小互信息准则的机会中继策略。在瑞利衰落信道环境下,从双向通信的角度,通过理论分析得出其中断概率解析式,同时推导了理想物理层网络编码和传统直接传输系统的中断概率解析式。通过理论分析,发现在某些节点发射功率条件下,系统中断概率将完全取决于单向链路。在此基础上完成了数值仿真实验,结果表明所提策略的中断性能与理想物理层网络编码和传统直接传输相比有了显著的提高。     

Opportunistic Scheduling for Wireless Network Coding

This letter addresses a scheduling problem for wireless network coding (WNC). In our previous work, we have theoretically shown that the optimum number of nodes to be included into a network?coded packet as well as its transmission rate depends on time?varying link condition between a transmitting node and receiving nodes [1]. Based on this observation, this letter designs practical scheme which opportunistically selects scheduled nodes, packets to be coded and an employed modulation level according to time?varying channel conditions and packet length. The numerical results show that the proposed opportunistic scheduling can improve the overall throughput as compared with non?opportunistic approach.     

机会式网络编码的系统中断性能

该文在两用户通过一个中继节点的协作向基站传送数据的无线通信环境下,研究了基于网络编码的中继策略。与通常的用户到中继的信道是可靠的这一假设不同,该文假设所有的信道都存在衰落现象,比较了复制重传中继策略、确定性网络编码策略和机会式网络编码策略对系统中断概率的影响。仿真结果说明了机会式网络编码中继策略具有较好的性能。     

非理想信道信息下双向多中继选择系统性能分析

该文在双向多中继选择系统中,分析了采用自适应调制的基于三时隙时分广播(TDBC)中继传输协议的系统性能,给出了存在信道估计误差时,系统的端到端信干噪比表达式,然后通过不等式缩放将表达式转化为多个服从指数分布变量和的形式,求出了其上界的分布,并利用该分布推导出了系统平均频谱效率的上界闭式表达式。通过仿真可以看出,理论分析结果与蒙特卡洛仿真结果相吻合,随着信道估计误差的增加,系统的平均频谱效率降低,并会由于自干扰不能完全被消除而出现平台。为了降低信道估计误差对系统性能的影响,该文进一步提出了一种中继端最优的功率分配策略。     

Outage Performance of Cognitive AF Relay Networks with Imperfect CSI Based on Geometrical Analysis

This paper studies the outage performance of a cognitive Amplify-and-forward (AF) relay network subject to Rayleigh fading.Under the condition of imperfect Channel state information (CSI) estimations of the links from the secondary system to the Primary user (PU),the closed-form upper and lower bounds of the outage probability are derived through a geometrical analysis method.An asymptotic analysis of the outage probability is also derived in the high Signal-to-noise ratio (SNR) regime to gain additional insights on the system.The simulation results corroborate our theoretical analysis,and the effectiveness of the geometrical analysis method is verified with the conventional approach as a benchmark.The asymptotic results are very tight with the analytical lower bound in the high SNR regime.It also can be observed from the simulation results that the impact of the number of relays as well as the imperfect CSI on the outage probability and the diversity order.     

网络编码机会协同中继中断概率分析

采用机会,给出了在译码转发方式下基于网络编码的双向多中继系统平均中断概率表达式,通过Monte Carlo仿真,验证了理论分析的正确性。随后分析了功率分配因子与信噪比和中继节点个数在不同情形下的系统中断性能,指出了功率分配因子与系统总功率和中继节点的内在关系。仿真结果表明,在双向多中继系统中采用网络编码和机会中继时,功率分配因子取值在0.6或0.6附近时能够获得最优的系统中断性能。     

Cooperative Diverse Opportunistic Network Coding for Wireless Networks

Wireless Personal Communications - Opportunistic network coding (ONC) increases communication networks’ throughput by XORing two or more packets together. However, it has shown that ONC...     

Performance Analysis of Space-Time Coded CDMA System Over Nakagami Fading Channels with Perfect and Imperfect CSI

In this paper, the performance of multiuser CDMA systems with different space time code schemes is investigated over Nakagami fading channel. Low-complexity multiuser receiver schemes are developed for space-time coded CDMA systems with perfect and imperfect channel state information (CSI). The schemes can make full use of the complex orthogonality of space-time coding to obtain the linear decoding complexity, and thus simplify the exponential decoding complexity of the existing scheme greatly. Moreover, it can achieve almost the same performance as the existing scheme. Based on the bit error rate (BER) analysis of the systems, the theoretical calculation expressions of average BER are derived in detail for both perfect CSI and imperfect CSI, respectively. As a result, tight closed-form BER expressions are obtained for space-time coded CDMA with orthogonal spreading code, and approximate closed-form BER expressions are attained for space-time coded CDMA with quasi-orthogonal spreading code. Computer simulation for BER shows that the theoretical analysis and simulation are in good agreement. The results show that the space-time coded CDMA systems have BER performance degradation for imperfect CSI.     

中继协作无线网络中不完美反馈下基于网络编码的重传方案

无线广播网络传输过程中,目的节点反馈信息丢失或部分丢失导致发送节点不能了解目的节点的真实接收状态.为提高不完美反馈下无线网络的重传效率,本文提出中继协作无线网络中不完美反馈下基于网络编码的重传方案.本方案基于部分可观察马尔科夫决策过程对不完美反馈下的重传过程进行建模.发送节点根据系统观测状态和最大置信度更新系统估计状态,根据数据包发送顺序,优先选择最早丢失且能够恢复最多丢包的编码包重传.目的节点缓存不可解编码包以提升编解码机会.重传过程中源节点关注目的节点请求包需求,相同情况优先选择传输可靠性较高的中继节点,以提升传输有效性.仿真结果表明,在不完美反馈下相对于传统方案,本方案可有效提高重传效率.     

Partial Relay Selection in Energy Harvesting Based NOMA Network with Imperfect CSI

The wireless body area network (WBAN) can effectively modify the health and lifestyle monitoring specifically where multiple body parameters are measured using biomedical sensor devices. However, power consumption and reliability are crucial issues in WBAN. Cooperative Communication usually prolongs the network lifetime of WBAN and allows reliable delivery of bio-medical packets. Hence, the main aim of this investigation is to propose a novel protocol Cooperative Energy efficient and Priority based Reliable routing protocol with Network coding (CEPRAN) to enhance the reliability and energy efficiency of WBAN using cooperative communication method. Firstly, to identify a relay node from the group of sensor nodes for data forwarding, an enhanced Cuckoo search optimization algorithm is proposed. Secondly, Cooperative Random Linear Network Coding approach is incorporated into the relay node to improve the packet transfer rate. CEPRAN is implemented in Ns-3 simulator and the experimental results prove that the proposed protocol outperforms the existing SIMPLE Protocol.

     

Computing Coding Solutions for Opportunistic Network Coding Used in Wireless Mesh Networks

Wireless Personal Communications - Wireless mesh networks represent a key architecture on which several communication systems are relaying. Implementations of these networks which apply...     

On the Performance of Cellular Two-Way Relay Systems with Analog Network Coding and Multiuser Diversity

We consider a cellular two-way relaying system in which a multi-antenna base station (BS) communicates bidirectionally with one of several single-antenna mobile stations (MSs) via a single-antenna relay using analog network coding. We employ MS selection coupled with beamforming at the BS so as to maximize the end-to-end signal-to-noise ratios. In the considered system, the target rates at the sources can generally be different owing to the asymmetric traffic flow in opposite directions. With such a general setup, we perform an overall system outage probability analysis over Rayleigh fading channels. For more insights, we derive a closed-form asymptotic expression for overall outage probability and an upper bound expression for ergodic sum-rate of the system. Based on these expressions, we show that the system achieves a performance gain, and a diversity order of minimum of the number of BS antennas and the number of MSs. Moreover, we address the problem of optimization of relay location in order to minimize the overall system outage under asymmetric traffic conditions. Finally, we provide numerical and simulation results to corroborate the theoretical analysis and the advantages offered by the proposed scheme.     

Opportunistic Relay Selection with Outdated CSI: Outage Probability and Diversity Analysis

In this paper, we analyze the outage probability and diversity order of opportunistic relay selection in a scenario based on decode and forward and where the available channel state information (CSI) is outdated. The study is conducted analytically by obtaining a closed-form expression for the outage probability, which is defined as the probability that the instantaneous capacity is below a target value. We derive high-SNR approximations for the outage probability. By doing so, we demonstrate that the diversity order of the system is reduced to 1 when CSI is outdated, being this behavior independent of the level of CSI accuracy. A physical explanation for this extreme loss of diversity is provided along with numerical results to support the analytical study.     

无线多跳网络中一种基于网络编码的机会路由

近年来机会路由和网络编码是两种利用无线信道广播特性提高网络性能的新兴技术。相比传统的静态路由决策,机会路由利用动态和机会路由选择减轻无线有损链路带来的影响。网络编码可以提高网络的资源利用率。但编码机会依赖于多个并发流所选路径的相对结构。为了创造更多的网络编码机会和提高网络吞吐量,本文提出了一种基于流间网络编码的机会路由(ORNC)算法。在ORNC中,每个分组转发的机会路径选择是基于网络编码感知的方式进行的。当没有编码机会时,采用背压策略选择下一跳转发路径以平衡网络负载。仿真结果表明本文提出的ORNC算法能够提高无线多跳网络的吞吐量。     

Robust Tomlinson-Harashima Precoders for Multiuser MISO Downlink with Imperfect CSI

In this paper, we consider robust non-linear precoding for the downlink of a multiuser multiple-input single-output (MISO) communication system in the presence of imperfect channel state information (CSI). The base station (BS) is equipped with multiple transmit antennas and each user terminal is equipped with a single receive antenna. We propose two robust Tomlinson-Harashima precoder (THP) designs. The first design is based on the minimization of the total BS transmit power under constraints on the mean square error (MSE) at the individual user receivers. We show that this problem can be solved by an iterative procedure, where each iteration involves the solution of a pair of convex optimization problems that can be solved efficiently. A robust linear precoder with MSE constraints can be obtained as a special case of this robust THP. The second design is based on the minimization of a stochastic function of the sum MSE under a constraint on the total BS transmit power. We formulate this design problem as an optimization problem that can be solved by the method of alternating optimization, the application of which results in a second-order cone program that can be numerically solved efficiently. Simulation results illustrate the improvement in performance of the proposed precoders compared to other robust linear and non-linear precoders in the literature.     

基于不完美CSI的认知反向散射通信吞吐量最大化算法

为了提高频谱传输效率和抑制信道不确定性影响,该文提出一种基于不完美信道状态信息的认知反向散射通信吞吐量最大化算法。首先,考虑主基站最大发射功率、传输时间、用户服务质量、有界信道不确定性等约束,建立了联合优化主基站波束、传输时间、反射系数的多变量耦合的非线性鲁棒吞吐量最大化模型。其次,利用最坏准则、S-Procedure、连续凸近似和交替优化方法,将原问题转换为凸优化问题,并提出一种基于迭代的鲁棒资源分配算法。仿真结果表明,与非鲁棒算法对比,所提算法具有较好的吞吐量和鲁棒性,且中断概率减小2.39%。     

Multiuser MIMO Transceiver Design for Uplink and Downlink with Imperfect CSI

This paper considers a joint linear transmitter and receiver design for multi-user multiple-input multiple-output (MU-MIMO) systems using total mean square error (TMSE) criterion, subject to a total transmit power constraint assuming imperfect channel state information. Both the uplink and downlink MU-MIMO systems, which is employed with improper constellations such as binary phase shift-keying and $M$ -ary amplitude shift-keying are considered. A minimum TMSE design is formulated as a nonconvex optimization problem under a total transmit power constraint and the closed-form optimum linear precoder and decoder for both the downlink and uplink MU-MIMO systems with improper modulation are determined by solving this nonconvex optimization problem. A novel contribution in this paper is to derive a closed-form optimum linear precoder and decoder for both the downlink and uplink MU-MIMO systems with improper modulation by solving the nonconvex optimization problem under total power constraint. The simulation results show that the performance of the proposed design is improved over the previous design.     

无线传感器网络中利用随机网络编码的低能耗可靠机会路由

无线传感器网络中节点大多采用电池供电,让节点以低能耗将采集的数据传递到信宿,对无线传感器网络有效运行极为重要.该文提出了能量有效的可靠机会路由EROR（Energy-efficient Reliable Opportunistic Routing）,它利用结合节点剩余能量和链路上收发双方的总能耗的转发代价,选择转发节点集合（简称“转发集”）、主转发节点和协助转发节点,让节点调节发射功率并利用随机线性编码把数据包分片编码发送到转发集,进而以多跳方式把数据可靠低能耗地传递到信宿.仿真结果表明：在网络生存时间和能耗方面,EROR比已有路由策略CodePower更优.