一种 1x2x4分布式空时编码异步协作方案

协作分集技术可以有效提高移动通信系统的容量和可靠性。近年来,分布式空时码（DSTC）被广泛应用到协作分集系统以实现空间分集增益。然而,时间异步和频率异步会使正交DSTC的码字结构受到破坏,严重影响系统性能。本文针对时间异步的协作通信系统,提出一种基于分布式Alamouti STBC的1x2x4异步协作方案。对这种方案进行了理论分析和算法推导,并且重新定义了中继节点归一化后的发射信号幅度。仿真结果表明该方案的误比特率性能具有明显优势,能在时间异步的协作通信系统中很好地发挥多天线接收性能。     

无线传感器网络中基于NDMA的跨层协作多包接收

本文研究了协作分集下的NDMA(网络辅助分集多址接入)机制,针对无线传感器网络特点和信道矩阵满秩性要求设计中继选择准则,提出了一个新的跨层协作多包接收机制.该机制在抗信道衰落的同时可有效限制数据包重传次数,从而大大提高多包接收的效率.对新机制的性能仿真以及该机制与NDMA、联合NDMA、时隙ALOHA之间的性能对比证实了新机制的有效性.     

一种1×2×4分布式空时编码异步协作方案

协作分集技术可以有效提高移动通信系统的容量和可靠性.针对时间异步的协作通信系统,提出一种基于分布式Alamouti STBC的1×2 ×4异步协作方案.对这种方案进行理论分析和算法推导,并且重新定义了中继节点归一化后的发射信号幅度.仿真结果表明,该方案的误比特率性能具有明显优势,能在时间异步的协作通信系统中很好地发挥多天线接收性能.     

基于协作通信的TD-VAA-SCDMA系统

协作通信解决了普通单天线移动终端的空间分集问题,使单天线移动终端在多用户环境中可共享其他终端的天线,从而得到多天线分集增益,改善了移动通信系统的性能.本文从协作通信的概念和原理出发,提出了一种基于协作通信的虚拟多天线(VAA)TD-SCDMA系统,探讨了该系统中各层的实现和面临的挑战.     

改善系统中断速率的一种新虚拟接收天线方案

在发射分集系统中,使用虚接收天线技术将时间分集转化为虚接收天线分集,以提高信道的秩,可以有效提高系统中断速率,这十分适用于某些需要能够在较低的中断概率下以一定的传输速率进行通信的系统。已有的研究是将同样的数据在两个时隙内重复发送以形成虚接收天线,而这使得传输效率下降了一半。为改善性能,提出了一种新的虚接收天线方案,不再简单地重复发送,而用一个时隙发送前两个时隙数据的和,从而提高传输效率。分析和仿真表明,新方案可以提供与重复发送方案相同的分集阶数,而且相对于重复发送方案,新方案可以更有效地提高系统中断速率,并且遍历容量也相应提高。     

基于多天线接收的空间分集盲均衡算法

基于多天线接收的空间分集技术与均衡技术相结合的空间分集均衡算法可以克服衰落带来的不利影响,有效提高通信系统接收端的性能。文中将多天线支路间的合并权值和均衡器的权值统一合并于盲均衡算法中的系数估计,形成一种新的空间分集盲均衡算法,该算法具有较小的实现复杂度和很好的均衡效果。通过仿真实验表明,在误符号率相同的条件下,本文提出的分集均衡算法比单路信号盲均衡算法所需信噪比低1 dB-2 dB。同时分析了多天线接收的支路信号间存在的相位差以及延迟对算法的性能影响。     

协作分集在Wimax中的应用研究

采用空间分集技术可以有效的对抗无线信道中的衰落。协作分集是一种新的空间分集技术，其原理是单天线的无线用户通过协作，811227共享他们的天线和资源从而形成一个虚拟的多天线系统。OFDM是Wimax中的关键技术，其将数据调制到各个子载波上发送。将协作分集引入到Wimax系统中，利用OFDM技术，可以有效地抵抗信道频率选择衰落的影响，使系统性能得到显著提高。     

一种基于协作MIMO的Relay-STBC-HARQ策略及其性能分析

在两跳协作通信中,第一跳增益来自接收分集,第二跳主要增益来自协作编码.利用协作中继节点的多天线构成的MIMO系统,构造一种新型的连续STBC编码,VBLAST-STBC混合解码的中继HARQ策略,可以同时有效获得HARQ的时间分集增益以及空时编码的分集增益与复用增益.理论分析与仿真结果表明,Relay-STBC-HARQ策略可以充分挖掘第一跳的分集增益以及第二跳的协作增益,不仅可以获得可靠性覆盖,而且可以在误码率、码率与时延间获得一种弹性平衡.     

空时码在DS-UWB系统的应用研究

直接序列超宽带(DS-UWB)通信技术是无线通信中的一个非常有发展前途的技术.为克服无线传输中多径衰落效应,针对DS-UWB系统,提出了一种将空时编码和Rake接收结合的方案,并进行性能分析和仿真.该方案建立在码片波形,使系统不仅获得空间分集,同时获得多径分集.仿真结果表明,基于这种方案的多天线系统的性能明显优于单天线系统.     

高速铁路移动通信系统多天线分集接收方案

在差分调制解调的信号模型下,提出了高铁场景下2种多天线分集接收模型——线性合并分集接收和统计合并分集接收,从而得出高铁场景下车地无线宽带通信较有效的分集接收方案,提升系统性能。数学分析和仿真结果表明,所提出的线性合并分集和统计合并分集都可以通过增加分集数来降低高速移动带来的误码率平层,统计合并分集的性能要优于线性合并分集,但是其接收机复杂度也比线性合并分集要高。在实际应用中可以根据QoS的要求在性能和复杂度之间进行折衷。     

一种无线Mesh网络中基于协同通信的多包接收方法

协同通信容许移动节点共享彼此的天线以构建虚拟多入多出系统,可有效获得空间分集增益。为利用虚拟多入多出信道的分集增益,该文提出了一种在无线Mesh网络上行链路中采用协同策略的多包接收方法。该方法中提出由发生冲突的Mesh终端及其协同节点构建虚拟多入多出信道,且多天线Mesh路由器通过串行干扰消除算法来快速分离冲突包。理论分析和仿真结果表明该方法可充分利用空间资源,相比NDMA和TDMA可有效提高系统的有效吞吐量并降低时延。     

Collision resolution in packet radio networks using rotationalinvariance techniques

This paper deals with the multiuser medium access problem in the packet radio environment. Under the framework of network diversity multiple access (NDMA), a previously proposed medium access method, a blind collision resolution scheme is proposed employing rotational invariance and factor analysis techniques. The proposed approach (dubbed B-NDMA for blind NDMA) overcomes the difficulty of orthogonal identification codes required by the original protocol, thereby improving channel utilization and system capacity, while being insensitive to multipath effects and synchronization errors. Performance issues of the proposed technique are addressed both analytically and numerically     

Decentralized multiuser diversity with opportunistic packet transmission in MIMO wireless sensor networks

In this study, we consider a single-hop wireless sensor network where both the sensor nodes and the controller node have multiple antennas. We focus on single beam opportunistic communication and propose a threshold-based medium access control (MAC) scheme for uplink packet transmission which exploits multiuser diversity gain without feedback in a decentralized manner. Packet transfer from sensor nodes to the controller node is initiated when the channel quality of any node exceeds the predefined threshold based on the effective signal-to-noise ratio (ESNR) measurements at the sensor nodes through linear combining techniques. The optimum threshold is determined to maximize the probability of successful packet transmission where only one sensor node transmits its packet in one time-slot. The proposed scheme trades the successful packet rate to increase the SNR of the successful packets assuming Rayleigh fading and collision-based reception model. Computer simulations confirm that proposed scheme has higher successful packet SNR compared to the simple time division multiple access (TDMA)-based MAC scheme with round-robin fashion. The use of multiple antennas at the sensor nodes can also improve the throughput of proposed scheme compared with our previous scheme without implementing the spatial diversity at the SNs.     

Network-assisted diversity multiple access in dispersive channels

Network-assisted diversity multiple access (NDMA) is a novel random medium access method, which provides impressive throughput efficiency for multiplexing variable-bit-rate data sources. We study the implementation of the NDMA scheme in the presence of multipath channels. A transceiver architecture and random access strategies are proposed, which are able to detect and resolve collisions in the presence of unknown propagation channels. The performance issues are studied both analytically and numerically     

Combined array processing and space-time coding

The information capacity of wireless communication systems may be increased dramatically by employing multiple transmit and receive antennas. The goal of system design is to exploit this capacity in a practical way. An effective approach to increasing data rate over wireless channels is to employ space-time coding techniques appropriate to multiple transmit antennas. These space-time codes introduce temporal and spatial correlation into signals transmitted from different antennas, so as to provide diversity at the receiver, and coding gain over an uncoded system. For large number of transmit antennas and at high bandwidth efficiencies, the receiver may become too complex whenever correlation across transmit antennas is introduced. This paper dramatically reduces encoding and decoding complexity by partitioning antennas at the transmitter into small groups, and using individual space-time codes, called the component codes, to transmit information from each group of antennas. At the receiver, an individual space-time code is decoded by a novel linear processing technique that suppresses signals transmitted by other groups of antennas by treating them as interference. A simple receiver structure is derived that provides diversity and coding gain over uncoded systems. This combination of array processing at the receiver and coding techniques for multiple transmit antennas can provide reliable and very high data rate communication over narrowband wireless channels. A refinement of this basic structure gives rise to a multilayered space-time architecture that both generalizes and improves upon the layered space-time architecture proposed by Foschini (see Bell Labs Tech. J., vol.1, no.2, 1996)     

Space-time overlays for convolutionally coded systems

We consider the design of space-time overlays to upgrade single-antenna wireless communication systems to accommodate multiple transmit antennas efficiently. We define the overlay constraint such that the signal transmitted from the first antenna in the upgraded system is the same as that in the single-antenna system. The signals transmitted from the remaining antennas are designed according to space-time coding principles to achieve full spatial diversity in quasi-static flat fading channels. For both binary phase-shift keying (BPSK) and quaternary phase-shift keying modulation systems, we develop an algebraic design framework that exploits the structure of existing single-dimensional convolutional codes in designing overlays that achieve full spatial diversity with minimum additional decoding complexity at the receiver. We also investigate a concatenated coding approach for a BPSK overlay design in which the inner code is an orthogonal block code. This approach is shown to yield near optimal asymptotic performance for quasi-static fading channels. We conclude by offering a brief discussion outlining the extension of the proposed techniques to time-varying block fading channels.     

A practical transmit beamforming strategy for closed‐loop MIMO communication

A new beamforming strategy is proposed for multiuser systems with N transmit antennas at the transmitter and M ? N single antenna receivers. The proposed scheme remarkably improves on the classical spatial division multiple access, and achieves the same data rates as spatial multiplexing for all users but with significantly superior performance/diversity gain. When compared with the Bell labs layered space–time system, the symbol rate is the same and the performance is much superior because of the presence of diversity gain. In addition, unlike the Bell labs layered space–time system, the receivers do not need to know each other's vector channels. Finally, the proposed algorithm is based on dirty‐paper coding, but does not require much complexity and is implementable. Copyright © 2011 John Wiley & Sons, Ltd.     

现代移动通信中发射分集技术研究

基于发送端多天线系统的发射分集技术是现代移动通信系统中抗信道衰落影响的一项关键技术。全面介绍发射分集技术的概念和实现方式,利用频率、时间、空间、极化、角度、调制等各种无线资源均可实现有效的发射分集方案,并且详细分析了各类典型的发射分集技术的特点和性能,理论分析有助于推广多天线发射分集系统在实际通信系统中的进一步应用。