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.     

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.     

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.     

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.     

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.     

结合模拟网络编码技术的选择式中继转发机制

针对时分半双工的单向传输中继协同系统,提出一种结合模拟网络编码(ANC,analog net-work coding)技术的选择式中继转发机制,中继站根据其对当前帧及上一帧发端数据的循环冗余校验结果,在四种可选方案中自适应切换转发策略,既避免误码传播,又保证分集增益最大化。ANC以符号级线性叠加为基本形式,同时引入星座旋转,使进行ANC的两帧数据功率均等且保持完全的区分度。接收机采用自适应的线性检测算法,以最低的解码复杂度有效去除帧间干扰。理论分析及仿真结果表明,同选择式解码转发机制相比,结合ANC的选择式中继转发机制在误块率及吞吐量性能上均具有显著优势,且发端至中继站间链路质量越好,优势越明显。     

Secrecy Outage of a Cognitive Radio Network with Selection of Energy Harvesting Relay and Imperfect CSI

Wireless Personal Communications - This paper investigates the physical layer security of an underlay cognitive radio network with relay selection scheme under threats of an eavesdropper. We...     

传输层网络编码性能分析

底层网络随机丢包导致的传输控制协议(TCP)传输性能恶化的问题由来已久.为了保障TCP的吞吐量在无线网络环境下依然能够保持在较好的性能,通过分析传输层网络编码(TCP/NC)协议的基本原理,分别利用NS-2搭建了软件仿真平台和Wi-Fi开发板搭建了硬件仿真平台.在2种平台上分别测试了传输层网络编码的性能并且分析了TCP的拥塞窗口和吞吐量性能.实验结果表明:传输层网络编码能够有效克服底层的随机丢包带来的影响,提升TCP吞吐量.     

双向中继信道中物理层网络编码的性能分析

针对双向中继信道,文章研究采用放大转发协议的物理层网络编码的性能.在考虑直传链路下,给出了3时隙网络编码的可达速率.在高信噪比条件下,推导了 3时隙物理层网络编码方案和2时隙物理层网络编码方案的中断概率近似表达式.通过仿真,验证了理论分析结果.同时,对3时隙物理层网络编码方案中继节点的功率分配因子进行了优化,在中继节点处于不同位置下分节点等功率和不同功率对不同方案进行了最大和速率的仿真,结果表明3时隙物理层网络编码可以利用网络的非对称性提高性能.     

Adaptive Modulation and Coding for Performance Enhancement of Vehicular Communication

With the advancements and increase in the transportation system in the current scenario, making transports intelligent is an important aspect for enhancing the safety, security and related commercial applications. Vehicular ad-hoc network has been evolved for the implementation of intelligent transportation systems. Vehicular scenario comprising of multipath fading, interference, dispersion and mobility distort the communication among the vehicles and between vehicles and surroundings. This work implements adaptive modulation and coding technique in the existing vehicular communication transmission process. Simulations were carried out for different transmission schemes with different code rate over several wireless channels for varying signal-to-noise ratio for performance evaluation. The results of this simulation testify that the proposed technique serves better than fixed transmission scheme in terms of bit error rate and spectral efficiency. Adaptive modulation together with turbo coding shows an approximate gain of 10 dB signal-to-noise ratio relative to fixed schemes.

     

Robust Uniform Channel Decomposition and Power Allocation for MIMO Systems with Imperfect CSI

In point to point MIMO systems, uniform channel decomposition (UCD) has been proven to be optimal in bit error rate (BER) performance and strictly capacity lossless when perfect channel state information (CSI) are assumed to be available at both the transmitter and the receiver side. However, in practice, CSI can be obtained at the transmitter if there is reciprocity between the forward and reverse channels in time division duplex (TDD) systems or can be conveyed from the receiver to the transmitter via a feedback channel. In any case, channel estimation error is inevitable. In this paper, a novel robust UCD scheme and corresponding optimal robust power allocation are proposed, which are capable of improving the BER performance in the context of imperfect CSI compared with the conventional UCD scheme and the robust precoding scheme proposed by Amir D. Dabbagh and David J. Love. Simulation results show that the MIMO channel capacity of the proposed robust UCD scheme is higher than that of the conventional UCD scheme. By deriving and analyzing the MIMO channel capacity lower bound of the robust UCD scheme, we prove that our proposed robust UCD scheme is capacity lossless in a channel estimation error existing MIMO system.     

Beamforming in Dual-Hop AF Relaying with Imperfect CSI and Co-channel Interference

This letter studies the joint effects of imperfect channel state information (CSI) and co-channel interference (CCI) on a dual-hop variable gain amplify-and-forward (AF) relay network with beamforming. The source and destination are both equipped with multiple antenna, while the relay has a single antenna. Specifically, the analytical expressions for the outage probability and average symbol error rate of the considered AF relaying are derived. Moreover, the asymptotic analysis at high SNR is also presented to reveal the diversity order and array gain of the relay system. Finally, computer simulations are given to confirm the validity of the proposed theoretical analysis and quantify the combined influence of imperfect CSI and CCI on the system performance.     

PSO Based Sum Rate Optimization for MU-MIMO Linear Precoder with Imperfect CSI

It is well known that if the perfect CSI is available at the BS, achieving the maximum sum throughput is equivalent to minimizing the product of mean square error matrix determinants (PDetMSE). Due to the presence of background noise in the estimated signal, the channel estimation errors are unavoidable. Hence, in this paper, it is assumed that the imperfect CSI is available at the BS and the channel estimation error variance is known at the transmitter. It is shown that maximizing the achievable sum rate is not exactly equal to minimizing the PDetMSE if the channel estimation error variance is included in the system design. Particle Swarm Optimization algorithm is used here to solve the sum rate maximization problem under the imperfect CSI. The simulation results compare the proposed system, which considers the channel estimation error variance as an integral part of the system design, with an existing system which assumes the perfect CSI at the transmitter side.     

Joint Transmission Rate Control and Opportunistic Network Coding Over Wireless Networks

Existing opportunistic network coding architectures (e.g., COPE) rely on pseudobroadcast to deliver a coded packet to multiple receivers in a single transmission. Only the primary receiver acknowledges the reception by MAC-layer acknowledgements (synchronous ACKs) and the other receivers receive the coded packet by overhearing and acknowledge the reception by asynchronous ACKs, which are usually piggybacked in outgoing data packets. In realistic wireless networks, this mechanism may cause unnecessary retransmissions if asynchronous ACKs are dropped due to packet losses or arrive late and thus compromise the throughput gain brought by network coding. In this paper, we propose a framework of joint rate control and code selection (ORC) to address this issue, aiming at improving the performance gain of opportunistic network coding in wireless networks. The framework of ORC consists of two mechanisms: (1) Rate control: the optimal transmission rate for coded packets is selected by formulating the rate control process as a Finite Horizon Markov Decision Process. (2) Code selection: based on the results of rate selection, the packet combination for forming the coded packet is determined. Numerical results show that ORC can substantially improve the performance gain of opportunistic network coding compared with COPE.     

一种新的基于部分网络编码的机会路由机制

网络编码能够提升无线网络传输性能,网络中的节点若采用传统的全网络编码,必须等待所有的数据包到达后才能进行解码,而这将造成网络的延迟。通过将部分网络编码和机会路由相结合,提出了一种新的路由协议(ORoPNC),该协议可以降低网络编码延迟,提高网络的稳定性。同时,设计了一种新的转发策略——ETXoEC。在这一策略下,转发节点的选取决定于当前链路状态和节点的剩余能量。仿真结果表明,网络的延迟降低了25%左右,能量消耗也得到了较好的平衡,整个网络的稳定性得到进一步提高。