Network coding with diversity and outdated channel state information

Physical-layer network coding （PNC） has the potential to significantly improve the throughput of wireless networks where the channels can be modeled as additive white Gaussian noise （AWGN） channel. As extending to mul- tiple channels, this technique requires both amplitude and phase compensation at each transmitter and will lead to inef- ficient systems yielding no diversity even with perfect channel state information （CSI）. In order to avoid these limita- tions, we apply network coding with diversity （NCD） to achieve a form of selection diversity and extend NCD to coop- erative multiple access channels in this paper. However, in practical wireless communication systems, the CSI could become outdated due to the difference between the CSI used in the relay selection and data transmission phases. Hence, the selected relay may not be the best one during data transmission phase due to the dynamic change in the wireless channels. Therefore, we first explore the relation between the present and past CSIs. Exploiting this relationship, the NCD scheme with outdated CSI is investigated based on the past CSI. To evaluate the performance of this scheme, an information-theoretic metric, namely the outage capacity, is studied under this condition.

Performance analysis of amplify-and-forward cooperative diversity with multiple-antenna nodes via analog network coding

Network coding (NC), which works in the network layer, is an effective technology to improve the network throughput, by allowing the relay to encode the information from different users and ensuring the destination to retrieve the desired information. Employing network coding technique in a cooperative network can improve the network performance further. In this paper, we introduce analog network coding (ANC) to a simple two-user cooperative diversity network, which adopts amplify-and-forward (AF) mode and all nodes use multiple antennas. The impact of the number of antenna on the system achievable rate is investigated. And the bit error rate (BER) performances of the traditional relay cooperative network and the cooperative network based on analog network coding under different propagation conditions are discussed. The simulation results show that the performance of the traditional cooperative network has improved significantly due to the employ of network coding.

DIVERSITY-AND-MULTIPLEXING TRADEOFF AND THROUGHPUT OF SUPERPOSITION CODING RELAYING STRATEGY

While the Network Coding cooperative relaying (NC-relaying) has the merit of high spectral efficiency,Superposition Coding relaying (SC-relaying) has the merit of high throughput. In this paper,a novel concept,coded cooperative relaying,is presented,which is a unified scheme of the NC-relaying and SC-relaying. For the SC-relaying strategy which can be considered one-way coded relaying scheme with multi-access channel,the close-form solution of the outage probabilities of the basic signal and additional signal are obtained firstly. Secondly,the Diversity-and-Multiplexing Tradeoff (DMT) characteristics of basic signal and additional signal are investigated entirely as well as the optimal close-form solutions. The compared numerical analysis shows the evaluation error of throughput based on the close-form solution is about 0.15 nats,which is within the acceptable error range. Due to the mutual effect between the both source signals,the available maximal values of the two multiplexing gains are less than 1.

FREQUENCY-TIME BLOCK CODE FOR FREQUENCY DIVERSITY IN UWB-OFDM SYSTEMS

The Ultra-WideBand Orthogonal Frequency Division Multiplexing (UWB-OFDM) approach is a promising physical-layer technique for short-range, high data-rate wireless networks. As the occupied band-width increases, however, its implementation becomes more and more difficult. In order to make it easier to achieve a UWB-OFDM system, a complexity-reduced Frequency diversity (F-diversity) scheme, Fre-quency-Time Block Code (FTBC), is presented in this paper. The FTBC halves the sampling rate required by other F-diversity techniques so as to cut down the cost of UWB-OFDM systems with F-diversity to a certain extent.

Network Coding Cooperation Performance Analysis in Wireless Network over a Lossy Channel, M Users and a Destination Scenario

Network coding (NC), introduced at the turn of the century, enables nodes in a network to combine data algebraically before either sending or forwarding them. Random network coding has gained popularity over the years by combining the received packet randomly before forwarding them, resulting in a complex Jordan Gaussian Elimination (JGE) decoding process. The effectiveness of random NC is through cooperation among nodes. In this paper, we propose a simple, low-complexity cooperative protocol that exploits NC in a deterministic manner resulting in improved diversity, data rate, and less complex JGE decoding process. The proposed system is applied over a lossy wireless network. The scenario under investigation is as follows: M users must send their information to a common destination D and to exchange the information between each others, over erasure channels;typically the channels between the users and the destination are worse than the channels between users. It is possible to significantly reduce the traffic among users and destination, achieving significant bandwidth savings, by combining packets from different users in simple, deterministic ways without resorting to extensive header information before being forwarded to the destination and the M users. The key problem we try to address is how to efficiently combine the packets at each user while exploiting user cooperation and the probability of successfully recovering information from all users at D with k < 2M unique linear equations, accounting for the fact that the remaining packets will be lost in the network and there are two transmission stages. Simulation results show the behaviour for two and three transmission stages. Our results show that applying NC protocols in two or three stages decreases the traffic significantly, beside the fact that the proposed protocols enable the system to retrieve the lost packets rather than asking for ARQ, resulting in improved data flow, and less power consumption. In fact, in some protocols the ARQ dropped from the rate 10ˉ1 to 10ˉ4, because of the proposed combining algorithm that enables the nodes to generate additional unique linear equations to broadcast rather than repeating the same ones via ARQ. Moreover, the number of the transmitted packets in each cooperative stage dropped from M (M - 1) to just M packets, resulting to 2 M packets instead 2 (M2 - 1) when three stages of transmission system are used instead of one stage (two cooperative stages).

Two-Phase Bidirectional Dual-Relay Selection Strategy for Wireless Relay Networks

In this article,we introduce a new bi-directional dual-relay selection strategy with its bit error rate(BER)performance analysis.During the first step of the proposed strategy,two relays out of a set of N relay-nodes are selected in a way to optimize the system performance in terms of BER,based on the suggested algorithm which checks if the selected relays using the maxmin criterion are the best ones.In the second step,the chosen relay-nodes perform an orthogonal space-time coding scheme using the two-phase relaying protocol to establish a bi-directional communication between the communicating terminals,leading to a significant improvement in the achievable coding and diversity gain.To further improve the overall system performance,the selected relay-nodes apply also a digital network coding scheme.Furthermore,this paper discusses the analytical approximation of the BER performance of the proposed strategy,where we prove that the analytical results match almost perfectly the simulated ones.Finally,our simulation results show that the proposed strategy outperforms the current state-of-the-art ones.

A Beamforming Technique Using Rotman Lens Antenna for Wireless Relay Networks

Rotman lens,which is a radio frequency beam-former that consists of multiple input and multiple output beam ports,can be used in industrial,scientific,and medical applications as a beam steering device.The input ports collect the signals to be propagated through the lens cavity toward the output ports before being transmitted by the antenna arrays to the destination in order to enhance the error performance by optimizing the overall signal to noise ratio(SNR).In this article,a low-cost Rotman lens antenna is designed and deployed to enhance the overall performance of the conventional cooperative communication systems without needing any additional power,extra time or frequency slots.In the suggested system,the smart Rotman lens antennas generate a beam steering in the direction of the destination to maximize the received SNR at the destination by applying the proposed optimal beamforming technique.The suggested optimal beamforming technique enjoys high diversity,as well as,low encoding and decoding complexity.Furthermore,we proved the advantages of our suggested strategy through both theoretical results and simulations using Monte Carlo runs.The Monte Carlo simulations show that the suggested strategy enjoys better error performance compared to the current state-of-the-art distributed multiantenna strategies.In addition,the bit error rate(BER)curves drawn from the analytical results are closely matching to those drawn from our conducted Monte Carlo simulations.

网络卷积协同通信新系统及性能

提出一种新的协同通信系统——网络卷积协同通信系统.新方案借鉴网络编码的思想,对协同用户自身要传输的数据和需要转发的同伴数据进行相关卷积编码,这样整个协同通信方案可等效为一个卷积编码器,在获得分集增益的同时可获得编码增益,提高系统的误码性能.在假设协同用户间信道理想的情况下,理论推导出系统误码率性能的上界.理论分析和仿真结果表明,网络卷积协同通信系统在协同用户间信道理想,且误比特率为10^-3时,较编码协同通信和无协同通信系统分别约有8～9 dB和11～13 dB的增益.

协作通信中联合信道-网络编码的性能分析与资源分配

针对无线网络中用户到协作节点和目的节点的上行链路不可靠的问题，研究了协作通信系统中具有特定协作节点的协作方案．在用户到协作节点的上行链路不可靠的情况下，将信道编码、网络编码同时引入到协作通信系统，建立了基于联合信道一网络编码的协作通信机制，

非对称协作分集通信中网络编码的应用

该文提出了网络编码在非对称三点协作传输系统中的应用。通过协作分集技术和网络编码技术的联合运用,不但可得到无线通信传输系统的分集增益,也可得到系统的编码增益。该文设计的方案,充分考虑无线通信环境的差异性,利用非对称调制方式,在保证较差通信环境中取得通信可靠性的同时,在较优链路采取较高速率进行传输,利用较优链路传输更多的信息,实现系统资源的充分利用。在方案的具体实现中,通过在中继链路的中继节点加入已知信息实现网络编码,使得系统的译码性能得到增加。仿真结果表明,将网络编码技术应用于非对称协作分集通信中,相对比非协作传输方案可增加分集增益,降低系统的误比特率。跟传统对称传输系统相比,可充分利用系统资源,提升了系统传输容量。

一种基于空时码的协作网络编码技术及其性能分析

该文提出了一种基于空时码的协作网络编码技术(Cooperative Network Coding based on Space-Time code,ST-CNC),该技术将协作分集技术和网络编码技术有机结合,能够克服无线信道衰落,提高系统资源利用率和网络吞吐。推导了采用ST-CNC的两跳链状网络中端到端信息交换的误比特率,分析了该技术带来的分集增益和网络编码增益。结果表明:相对于传统的多跳链路的数据交互策略,该技术能够带来明显的性能增益。最后通过仿真验证了分析结果的正确性。

适用于无线双向中继信道的机会协作网络编码

提出的一种机会协作网络编码(OCNC),将协作分集技术和网络编码技术有机结合,能克服无线信道衰落,提高系统资源利用率和网络吞吐.针对无线双向中继信道中端到端信息交换的情形,分别分析了3步、2步OCNC的误比特率(BER)性能和获取的网络编码增益,结果表明,相对于传统的数据交换方案,3步、2步机会协作网络编码在获得全分集(获得的分集阶数为参与协作的节点数)的同时,也分别获得了4/3倍和2倍的渐近网络编码增益,由于多个协作节点的机会中继,OCNC的网络编码增益在中间信噪比(SNR)区域更为突出.

一种新型的多址接入中继协作方案

现有多址中继协作方案的编码增益有限且用户之间不能相互辅助,为此,文中提出了一种结合网络与信道编码的多址中继协作方案:在中继端利用网络编码将不同用户的编码冗余同时转发,目的端通过对某个用户信息的正确译码恢复出其他用户的编码冗余.通过对译码错误事件概率的分析,推导了该方案的中断率与误码率近似值表达式.仿真结果表明,随着信噪比的提升,文中方案可获得比编码协作更好的中断率和误码率性能,同时信噪比较高的用户还可辅助提升信噪比较低的用户的性能.

联合LDPC码和网络编码的协作通信技术

结合信道编码和网络编码的思想,提出了一种在两用户协作情况下联合LDPC(low-density parity-check)码和网络编码的协作分集方案,该方案在接收端通过基于整体H矩阵的置信传播算法实现LDPC码和网络编码的联合译码,并对该方案在瑞利慢衰落信道下的性能进行了MATLAB仿真。仿真结果表明:与编码协作和不协作方案相比,所提方案在系统误码率性能上有着明显地改善。

线性网络编码在协作通信中的应用

协作通信是提高无线网络链路可靠性的最有效方法之一。文中将线性网络编码引入多用户协作通信系统中,提出新的中继转发方法。在中继转发阶段,参与协作的用户将机会侦听到的来自其它协作用户的数据和自身的数据进行线性网络编码,并转发出去。理论分析和仿真表明,与原有的基于异或编码方式的转发方法相比,本文的方法能获得更高的空间分集度,更低的系统中断概率。

基于网络编码的用户协作分集系统性能分析

针对非协作通信和传统协作通信系统不能达到高天线分集增益的问题,提出基于网络编码的用户协作系统模型。研究了基于网络编码不同协作用户的天线分集增益,并分析非协作机制、传统用户协作机制和基于网络编码用户协作机制的中断概率。理论分析和系统仿真表明,基于网络编码的用户协作系统能显著降低系统中断概率,获得更大的分集增益,且协作用户数越多,系统分集度越好。

多中继去噪重传物理层网络编码自适应分集策略

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。理论推导了基于解噪重传协议的系统容量,根据容量解析式给出了系统和容量最大化的2个条件表达式,提出了一种最大化系统和容量的自适应分集策略。在瑞利衰落信道环境下,通过理论分析给出所有中继链路特性均属于同一情况下的中断概率闭合解析式,同时也理论推导了一般放大重传和直接传输系统中断概率解析式。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非自适应系统、一般放大重传和直接传输系统相比有较大优势。

物理层网络编码分组的机会中继

为提升物理层网络编码方案的抗衰落性能,该文提出了一种基于物理层网络编码的机会中继方案(Opportunistic Relaying based-on Physical-layer Network Coding,PNC-OR),该方案利用物理层网络编码的基本思想、有效提升网络吞吐的同时,通过中继节点的分布式选择,也能够使系统获得多用户分集增益,提高了系统的抗衰落性能。针对双向无线中继信道中端到端信息交换的情形,推导了准静态衰落环境下PNC-OR中多个目的节点接收信息的和容量。数值结果显示:和机会中继、传统网络编码两种方案相比,PNC-OR具有更高的频谱效率,并且随着中继节点的增多,频谱效率也越高。

一种协作网络编码方案的功率优化分配方法

该文针对传统双路无线中继系统中的源和中继采用等功率发送,导致系统资源利用率低的问题,提出一种译码转发-空时协作网络编码方案的功率优化分配方法。该方法以最小化两源用户中断概率中的较大者为目标,并利用中断概率的高阶近似解,通过迭代计算获得最优功率分配因子。所提功率优化分配方法计算复杂度低且仅需信道的平均增益信息。仿真结果表明,与平均功率分配方法相比,所提功率优化分配方法使系统的中断概率和误码率性能均得到有效提升。