异步协同系统频选信道下基于线性预处理的DSTC结构设计

在协同中继系统中,应用分布式空时码(Distributed Space Time Coding, DSTC),可以在有效提高系统效率的同时获得全协同分集。但是,各中继节点的异步传输和节点间的多径衰落会破坏空时码字的结构,使之不能获得全分集。本文针对两中继的异步协同系统,提出了一种频率选择性信道下的基于线性预处理的DSTC传输结构。在此传输结构中,源节点对发送数据块进行预处理后发送给中继节点,中继节点对接收信号进行简单的共轭重排等处理,使得在目的节点形成DSTC的结构。其中,为抵抗异步传输和多径衰落引入的符号间干扰(Inter-symbol Interference, ISI),在源节点处和中继节点处均加入循环前缀(Cyclic Prefix, CP)。于是目的节点对接收到的信号进行DFT处理后,可以运用ML算法对数据信息进行检测。理论分析和仿真表明,当存在定时误差和节点间为频率选择性信道时,目的节点运用ML检测算法该传输结构可获得全空间分集和全多径分集。然后,本文考虑了信道各径延迟为整数倍符号周期的情况,并且证明了该传输结构的分集增益只与节点间信道的有效信道长度有关。      

A Proposed H-STCDD Scheme in Cooperative Communication System

In this paper, the hierarchical space time cyclic delay diversity (H-STCDD) scheme is proposed. Proposed scheme uses hierarchical modulation and achieves approximately full rate. It also uses a cyclic delay diversity scheme, which improves the benefit of channel coding particularly in high SNR environment between source to relay and source to destination. According to simulation result, proposed scheme has up to 2.2 dB better BER performance than conventional cooperative scheme at BER of 10^?3 and has similar BER performance with the STCDD scheme particularly in high SNR environment between source to relay and source to destination. Throughput of the proposed scheme is better than those of other cooperative schemes. Therefore proposed scheme is more efficient than other cooperative scheme and can be efficiently used in high SNR environment between source to relay and source to destination.     

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.     

Cooperative quadrature physical layer network coding in wireless relay networks

This paper proposes a cooperative quadrature physical layer network coding (CQPNC) scheme for a dual‐hop cooperative relay network, which consists of two source nodes, one relay node and one destination node. All nodes in the network have one antenna, and the two source nodes transmit their signals modulated with quadrature carriers. In this paper, a cooperative quadrature physical layer network coded decode‐and‐forward (DF) relay protocol (CQPNC‐DF) is proposed to transmit the composite information from the two source nodes via the relay node to the destination node simultaneously to reduce the number of time slots required for a transmission. The proposed CQPNC‐DF relay protocol is compared with time‐division multiple‐access amplify‐and‐forward (TDMA‐AF), TDMA‐DF, cooperative network coded DF (CNC‐DF) and cooperative analog network coded AF (CANC‐AF) relay protocols to demonstrate its effectiveness in terms of bit error rate (BER) and system throughput under different propagation conditions. The simulation results reveal that the proposed CQPNC‐DF relay protocol can significantly improve the network performance. Compared with two TDMA schemes and CNC‐DF, the proposal can provide up to 100% and 50% throughput gains, respectively. Moreover, no matter what the scene, the proposed scheme always has the lowest BER in the low SNR region. Copyright © 2013 John Wiley & Sons, Ltd.     

A Unified Cross-Layer Framework for Resource Allocation in Cooperative Networks

Node cooperation is an emerging and powerful solution that can overcome the limitation of wireless systems as well as improve the capacity of the next generation wireless networks. By forming a virtual antenna array, node cooperation can achieve high antenna and diversity gains by using several partners to relay the transmitted signals. There has been a lot of work on improving the link performance in cooperative networks by using advanced signal processing or power allocation methods among a single source node and its relays. However, the resource allocation among multiple nodes has not received much attention yet. In this paper, we present a unified crosslayer framework for resource allocation in cooperative networks, which considers the physical and network layers jointly and can be applied for any cooperative transmission scheme. It is found that the fairness and energy constraint cannot be satisfied simultaneously if each node uses a fixed set of relays. To solve this problem, a multi-state cooperation methodology is proposed, where the energy is allocated among the nodes state-by-state via a geometric and network decomposition approach. Given the energy allocation, the duration of each state is then optimized so as to maximize the nodes utility. Numerical results will compare the performance of cooperative networks with and without resource allocation for cooperative beamforming and selection relaying. It is shown that without resource allocation, cooperation will result in a poor lifetime of the heavily-used nodes. In contrast, the proposed framework will not only guarantee fairness, but will also provide significant throughput and diversity gain over conventional cooperation schemes.     

Spectrally Efficient Incremental Relaying for Coverage Expansion in Cellular Networks with Heterogeneous Path Loss Conditions

In this paper we propose a cooperative scheme in which fixed relays operate with a higher spectral efficiency than the source. The relay transmits L times faster than the source with L times the spectral efficiency, reducing the loss inherent to the orthogonal cooperation. We assume a large scale path loss model which is capable of handling with heterogeneous conditions between the nodes of the network: the source, the relay and the base-station antennas can be at different heights. Our results show that the proposed scheme consumes less energy while achieving up to 3 dB of gain, in terms of throughput, when compared to the baseline cooperative scheme. In addition, a coverage area analysis shows that the proposed scheme increases considerably the cell area when compared to the non-cooperative transmission and to the baseline cooperative scheme. Finally, we show that the proposed scheme, with a single relay, outperforms in the high signal to noise ratio region the regular cooperative scheme using multiple relays.     

Minimum Error Probability Cooperative Relay Design

In wireless networks, user cooperation has been proposed to mitigate the effect of multipath fading channels. Recognizing the connection between cooperative relay with finite alphabet sources and the distributed detection problem, we design relay signaling via channel aware distributed detection theory. Focusing on a wireless relay network composed of a single source-destination pair with L relay nodes, we derive the necessary conditions for optimal relay signaling that minimizes the error probability at the destination node. The derived conditions are person-by-person optimal: each local relay rule is optimized by assuming fixed relay rules at all other relay nodes and fixed decoding rule at the destination node. An iterative algorithm is proposed for finding a set of relay signaling approaches that are simultaneously person-by-person optimal. Numerical examples indicate that the proposed scheme provides performance improvement over the two existing cooperative relay strategies, namely amplify-forward and decode-forward     

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.     

协作通信中的自适应分级调制与功率分配

基于分级调制的中继协作技术可以很好地利用无线信道的广播特性和中继节点的位置优势来对抗信道衰落.本文提出一种自适应的协作方法,这种方法根据中继的相对位置,选择最优的分级调制星座图以及源与中继之间的功率分配比例,以使目的节点接收的数据误码率最小.仿真结果表明优化星座图和优化源与目的节点之间的功率分配比例都可以获得可观的性能提升.当中继位于源与目的节点的中点附近时,在消耗相同能量带宽资源的条件下,这种最优化的协作方法比非协作系统有3-4dB的性能增益.     

Improving energy efficiency of incremental relay based cooperative communications in wireless body area networks

In this paper, we investigate the energy efficiency of an incremental relay based cooperative communication scheme in wireless body area networks (WBANs). We derive analytical expressions for the energy efficiency of direct and cooperative communication schemes taking into account the effect of packet error rate. The following communication scenarios specific to a WBAN are considered: (i) in‐body communication between an implant sensor node and the gateway, and (ii) on‐body communication between a body surface node and the gateway with line‐of‐sight (LOS) and non‐LOS channels. The results reveal a threshold behavior that separates regions where direct transmission is better from regions where incremental relay cooperation is more useful in terms of energy efficiency. It is observed that, compared with direct communication, incremental relay based cooperative communication schemes improves the energy efficiency significantly. Further, cooperation extends the source‐to‐destination hop length over, which energy efficient communication can be achieved as compared with direct communication. We also observe that, for both direct as well as cooperative transmission schemes in error prone channels, an optimal packet size exists that result in maximum energy efficiency. Copyright © 2013 John Wiley & Sons, Ltd.     

A Non-Orthogonal Selection Cooperation Protocol with Interference in Multi-Source Cooperative Networks

This work proposes a non-orthogonal selection cooperation scheme with interference for multi-source and single destination cooperative networks. In our model, the source nodes can cooperate for one another, i.e., each source node plays the dual role of a source and a relay, thus there is no need for relays. In addition, the source nodes can be continuously transmitted and without dedicated timeslots for cooperative transmissions, which can save system resources and improve spectral efficiency. However, by this way, it will introduce interference with the non-orthogonal transmission mechanism. To overcome this problem, we use general reception scheme in source nodes and successive interference cancellation technology in the destination node, which can reduce the effect of interference effectively. For interference-limited networks, we also derive the theoretical upper bound and lower bound of outage probability of our method. Through the outage probability analysis and comparison, the results show that the spectral efficiency is improved while the system still keeps acceptable transmission reliability.

     

乘法运算的模拟网络编码中继方法

当前无线网络编码中继采用异或运算和叠加运算实现,该文提出一种基于乘法运算的网络编码中继方案。该方案中继节点对接收到的两个源节点信号直接相乘,然后放大转发,从而实现网络编码。与异或运算的网络编码相比,该方案采用模拟技术实现,降低了中继节点网络编码的复杂度;同时该方案将接收信号与本地信号相乘实现网络译码,译码算法比叠加运算的方案简单。理论分析表明该方案的分集增益与未经网络编码的中继系统相同;仿真结果表明,该方案与现有的网络编码中继协作方案性能相当。     

一种超宽带模拟合并转发协作通信系统

针对频率选择性衰弱信道下协作通信系统信道估计复杂的问题,提出了一种模拟合并放大转发超宽带(UWB)协作通信方案.该方案在源节点处对发送符号进行实数分布式空时编码并附加传输参考,在中继节点处利用传输参考对多径分量进行模拟合并,从而构建了一种改进型非正交放大转发协作通信系统.仿真结果证明,相对于无协作通信系统,模拟合并转发...     

Performance Analysis and Optimal Power Allocation for Space–Time and Amplify-and-Forward Cooperative System

In this paper, we consider a space?Ctime and amplify-and-forward (ST-AF) cooperative system which consists of two-antenna source, single-antenna relay and destination. Source transmits Alamouti space?Ctime coding symbols to destination with cooperation of relay which adopts AF strategy. Closed-form symbol error rate (SER) is derived for the ST-AF system with PSK signals. Moreover, a SER approximation is developed to show the asymptotic performance of the ST-AF cooperative system in medium and high SNR regimes. For comparison, the SER approximation of another cooperative space?Ctime coding (C-STC) scheme is also derived. Theoretical analysis shows that the ST-AF can obtain more diversity gain and achieve higher diversity order than C-STC. Statistical optimal power allocation (OPA) algorithm for the ST-AF cooperative system is presented based on the SER performance. It turns out the OPA only depends on the channel links related to the relay, not depend on the direct link between source and destination. Finally, numerical simulations validate the theoretical analysis.     

Decode-to-cooperate: a sequential alamouti-coded cooperation strategy in dual-hop wireless relay networks

An optimal cooperation strategy, decode-to-cooperate, is proposed and investigated for performance improvements in dual-hop wireless relay networks. Based on decode-and-forward (DF) strategy with multiple relay selection, we design a novel scheme such that the source node keeps transmitting sequentially and the selected relays cooperate by transmitting the decoded signal using distributed Alamouti coding. We exploit the multipath propagation effect of the wireless channel to achieve lower probability of error and introduce optimum power allocation and relay positioning. We analyze the scenario when the source to destination direct link is not available and derive a closed form expression for symbol error rate (SER), its upper bound and an asymptotically tight approximation to exploit the performance gain by selecting the optimum relays in a multiple-relay cooperation scheme. Moreover, asymptotic optimum power allocation (based on the SER approximation) and optimal relay positioning are also considered to further improve the SER. The proposed relay selection scheme outperforms cooperative (DF) and non-cooperative schemes by more than 2 dB.     

Protocol design and data detection for two‐way relay networks with fractional asynchronous delays

In wireless two‐way relay systems, it is difficult to achieve perfect timing synchronization among different nodes. In this paper, we investigate relaying protocol design and data detect schemes for asynchronous two‐way relaying systems to combat the intersymbol interference caused by asynchronous transmission. We consider fractional asynchronous delays and two schemes are proposed based on cyclic prefixed single carrier block transmission, namely, the receiver frequency domain equalization scheme and relay synchronization and network coding (RSNC) scheme. In the receiver frequency domain equalization scheme, the relay simply amplifies the received signal and forwards to the two source nodes, and fractionally spaced frequency domain equalizer (FS‐FDE) is employed at the receiver to recover the transmit data. In the RSNC scheme, the asynchronous signals are resynchronized with an FS‐FDE at the relay node. The output signals of FS‐FDE are then demodulated and network coded before forwarding to the two source nodes. In this RSNC scheme, data detection at the source nodes is the same as that in synchronous networks because the asynchronous signals have already been synchronized at the relay node. Simulation results show that the performance of both schemes is almost the same as in the perfect synchronized two‐way relaying systems. Copyright © 2012 John Wiley & Sons, Ltd.     

A cooperative phase steering scheme in multi-relay node environments

We propose a decode-and-forward (DF) based cooperative phase steering scheme and analyze its outage probability. The cooperative phase steering scheme is to make the received signals from multiple relay nodes co-phased at a destination node by pre-adjusting the phase differences.With a reasonable amount of feedback information from a destination node, the cooperative phase steering scheme circumvents the drawbacks of conventional cooperative diversity techniques such as maximal ratio combining (MRC) reception, maximal ratio transmission (MRT), and opportunistic relay selection schemes. Our analytical and simulation results show that the cooperative phase steering scheme outperforms the opportunistic relay selection scheme and approaches the MRT scheme known as a theoretically optimal cooperative diversity technique. It is also shown that cooperative phase steering has sufficient robustness to phase incoherence.     

Throughput maximization of ad-hoc wireless networks using adaptive cooperative diversity and truncated ARQ

We propose a cross-layer design which combines truncated ARQ at the link layer and cooperative diversity at the physical layer. In this scheme, both the source node and the relay nodes utilize an orthogonal space-time block code for packet retransmission. In contrast to previous cooperative diversity protocols, here cooperative diversity is invoked only if the destination node receives an erroneous packet from the source node. In addition, the relay nodes are not fixed and are selected according to the channel conditions using CRC. It will be shown that this combination of adaptive cooperative diversity and truncated ARQ can greatly improve the system throughput compared to the conventional truncated ARQ scheme and fixed cooperative diversity protocols. We further maximize the throughput by optimizing the packet length and modulation level and will show that substantial gains can be achieved by this joint optimization. Since both the packet length and modulation level are usually discrete in practice, a computationally efficient algorithm is further proposed to obtain the discrete optimal packet length and modulation level.     

WSN中一种基于能量效率的协同中继传输方案

本文针对分簇无线传感器网络,提出了一种基于能量效率的协同中继传输方案,该方案中源簇头根据源到邻簇头之间的信道状态信息选择最优中继节点;协同传输数据时,目的节点接收到两个时隙的信号后进行最大比合并,并根据设定的接收信噪比门限范围在确认帧中给中继节点反馈功率调整信息,以减少重传次数或降低中继节点的发射功率,在不增加开销的情况下可以减少系统总的能量消耗。文章利用概率密度函数推导了基于部分信道状态信息选择中继协同的误符号率闭式表达式,最后通过蒙特卡洛仿真进行了验证。结果表明:误符号率的理论推导值与仿真值一致,在相同的接收信噪比门限时,本文所提方案能够明显提高系统的能效性。      

Partner selection strategies in cooperative wireless networks with optimal power distribution

There have been several results that illustrate the best performance that a network can get through cooperation of relay nodes. For practical purposes, not all nodes in the network should be involved at the same time in every transmission. Therefore, optimal partner selection protocols in cooperative wireless networks are believed to be the first important thing that should be paid attention to. This problem in our article is considered in the context of regenerative nodes and non-altruistic cooperation （no pure relay exists; all nodes have their own data to transmit）. For each transmission, the protocol must provide the user （source node） a ＇best partner＇ （relay node） to cooperate with （for network simplicity and less transmission signals here, assume that each user has only one cooperative node）. A criterion is essentially needed when defining what a ＇best partner＇ is; in this article, two factors, i.e, the successful transmission probability and the transmission power, are considered. Three optimal partner selection strategies with different goals are proposed and analyzed respectively. The simulation results show that these are all supposed to be good tradeoffs between power consumption and transmission performance.