Optimal transmitter eigen-beamforming and space-time block coding based on channel mean feedback

Optimal transmitter designs obeying the water-filling principle are well-documented; they are widely applied when the propagation channel is deterministically known and regularly updated at the transmitter. Because channel state information is impossible to be known perfectly at the transmitter in practical wireless systems, we design, in this paper, an optimal multiantenna transmitter based on the knowledge of mean values of the underlying channels. Our optimal transmitter design turns out to be an eigen-beamformer with multiple beams pointing to orthogonal directions along the eigenvectors of the correlation matrix of the estimated channel at the transmitter and with proper power loading across beams. The optimality pertains to minimizing an upper bound on the symbol error rate, which leads to better performance than maximizing the expected signal-to-noise ratio (SNR) at the receiver. Coupled with orthogonal space-time block codes, two-directional eigen-beamforming emerges as a more attractive choice than conventional one-directional beamforming with uniformly improved performance, without rate reduction, and without essential increase in complexity. With multiple receive antennas and reasonably good feedback quality, the two-directional eigen-beamformer is also capable of achieving the best possible performance in a large range of transmit-power-to-noise ratios, without a rate penalty.     

基于相关函数的空时块编码系统的信道估计

提出了空时块编码（STBC）系统中基于相关函数的信道估计的方法。当输入符号向量的各个元素互不相关时，接收信号的相关函数有特定的结构，信道矩阵可以从接收信号的相关矩阵的特征向量中得到，信道估计结果和真实值仅相差一个常数。研究还发现当发送信号的相关函数满足特定的条件时，可以直接从接收信号的协方差得到信道参数，而不需要矩阵分解或者求逆运算。     

Distributed space-time block coding

In this paper, a new class of distributed space-time block codes (DSTBCs) is introduced. These DSTBCs are designed for wireless networks which have a large set of single-antenna relay nodes /spl Nscr/, but at any given time only a small, a priori unknown subset of nodes S/spl sube//spl Nscr/ can be active. In the proposed scheme, the signal transmitted by an active relay node is the product of an information-carrying code matrix and a unique node signature vector of length N/sub c/. It is shown that existing STBCs designed for N/sub c/2 co-located antennas are favorable choices for the code matrix, guaranteeing a diversity order of d=min{N/sub S/,N/sub c/} if N/sub S/ nodes are active. For the most interesting case, N/sub S//spl ges/N/sub c/, the performance loss entailed by the distributed implementation is analytically characterized. Furthermore, efficient methods for the optimization of the set of signature vectors are provided. Depending on the chosen design, the proposed DSTBCs allow for low-complexity coherent, differential, and noncoherent detection, respectively. Possible applications include ad hoc and sensor networks employing decode-and-forward relaying.     

On channel orthogonalization using space-time block coding with partial feedback

Orthogonal space-time block codes (OSTBCs) yield full diversity gain even while requiring only a linear receiver. Such full-rate (rate-one) orthogonal designs are available for complex symbol constellations only for N=2 transmit antennas. In this paper, we propose a new family of full-rate space-time block codes (STBCs) using a single parameter feedback for communication over Rayleigh fading channels for N=3,4 transmit antennas and M receive antennas. The proposed rate-one codes achieve full diversity, and the performance is similar to maximum receiver ratio combining. The decoding complexity of these codes are only linear even while performing maximum-likelihood decoding. The partial channel information is a real phase parameter that is a function of all the channel gains, and has a simple closed-form expression for N=3,4. This feedback information enables us to derive (channel) orthogonal designs starting from quasi-orthogonal STBCs. The feedback complexity is significantly lower than conventional closed-loop transmit beamforming. We compare the proposed codes with the open-loop OSTBCs and also with the closed-loop equal gain transmission (EGT) scheme which uses equal power loading on all antennas. Simulated error-rate performances indicate that the proposed channel orthogonalized STBCs significantly outperform the open-loop orthogonal designs, for the same spectral efficiency. Moreover, even with significantly lower feedback and computational complexity, the proposed scheme outperforms the EGT technique for M>N.     

级联信道编码的多幅值差分空时分组码方案及性能

通过引入多电平振幅调制和变换矩阵方法,提出了一种基于多幅值调制的差分正交空时分组码方案。该方案可克服通常基于PSK调制的单幅值差分空时码(DSTC,differential space-time coding)在高频带利用率下由于星座符号间的最小距离减小所带来的性能下降,而且可用于编码矩阵是非方阵情况,避免了已有方案仅适合于方阵码矩阵。与已有单幅值DSTC相比,所提方案有着高的频谱效率和编码增益,且可实现线性译码复杂度和高的码率。此外,还给出了所提方案级联信道编码时的性能。仿真结果表明所提方案与已有单幅值DSTC方案相比,有着较低的误比特率,而且信道编码后的所提多幅值DSTC也好于相应的单幅值DSTC。     

基于差分空时分组码的卡尔曼盲多用户检测

对大容量、高性能蜂窝通信系统的需求引起了人们对先进信号处理技术的极大兴趣，尤其是使用多个发射／接收天线，利用空域分集的处理技术更是受到了广泛关注。使用多个发射天线及差分空时分组码，可用一种新的适用于频率平坦信道的盲自适应多用户接收机。新方法不需要信道估计，它首先利用卡尔曼(Kalman)自适应滤波器抑制多址干扰，然后完成差分空时解码获得分集增益。计算机仿真结果表明该方法具有较强的抗衰落和抑制多址干扰的能力，并能自适应地跟踪信号环境的变化。     

基于独立分量分析的正交空时分组编码盲检测方案

通过在不同天线发射的信号之间引入时域和空域信息,正交空时分组编码(OSTBC)可以获得发射分集增益,而且可以在不牺牲带宽的情况下获得更高的编码增益。但是其译码却需要精确的信道状态信息(CSI),因此,信道信息估计的准确性严重影响系统的性能。基于独立分量分析(ICA)的盲源分离(BSS)技术可以在不进行信道估计的情况下对发射信号实现有效检测。通过利用OSTBC的正交特性,提出了2种基于ICA的盲检测方案,同时,一些基于信道估计的检测算法也被用来进行性能比较。瑞利衰落信道下的仿真结果表明,2种新方案均具有较好的系统适应性和误码率性能。     

空时分组码通信中的一类ICA盲检测方案

空时分组码（STBC）通过使用发射分集策略和空时编码方案可以明显改善系统性能。然而，其接收端必须获得准确的信道状态信息（CSI）才能进行有效的信号检测。而对于复杂的无线通信环境，这种前提条件有时却难以得到满足。独立分量分析（ICA）是一种将一个复杂的数据集合分解为多个独立子集的盲源分离（BSS）技术。通常情况下，即使没有空间信道的任何信息，ICA也可以仅凭接收信号恢复出发射信号。提出了一种利用ICA技术的STBC盲信号检测方案，在建立了适用于ICA的特定通信系统模型后，几种典型的ICA算法被用来进行性能比较。理论分析表明，ICA盲接收技术的应用可以在一定程度上替代基于信道估计的传统方法，增强系统对信道估计错误的顽健性。仿真实验结合了具体的STBC系统，比较了基于ICA的不同方案的性能，并讨论了最优的信号检测方案。     

Combining beamforming and orthogonal space-time block coding

Multiple transmit and receive antennas can be used in wireless systems to achieve high data rate communication. Efficient space-time codes have been developed that utilize a large portion of the available capacity. These codes are designed under the assumption that the transmitter has no knowledge about the channel. In this work, on the other hand, we consider the case when the transmitter has partial, but not perfect, knowledge about the channel and how to improve a predetermined code so that this fact is taken into account. A performance criterion is derived for a frequency-nonselective fading channel and then utilized to optimize a linear transformation of the predetermined code. The resulting optimization problem turns out to be convex and can thus be efficiently solved using standard methods. In addition, a particularly efficient solution method is developed for the special case of independently fading channel coefficients. The proposed transmission scheme combines the benefits of conventional beamforming with those given by orthogonal space-time block coding. Simulation results for a narrow-band system with multiple transmit antennas and one or more receive antennas demonstrate significant gains over conventional methods in a scenario with nonperfect channel knowledge     

Optimal space-time coding under iterative processing

In this paper, we deal with the design of a full-rate space-time block coding (STBC) scheme optimized for linear iterative decoding over fast fading multiple-input multiple-output (MIMO) channel. A general and simple coding scheme called diagonal threaded space-time (DTST) code is presented for an arbitrary number of transmit and receive antennas. Theoretical analysis shows that DTST code associated with linear iterative decoding tends towards full diversity performance while providing maximum MIMO multiplexing gain. Simulation results confirm the ability of DTST to outperform the state-of-the-art STBC and conventional spatial data multiplexing schemes under iterative processing.     

Optimal antenna subset selection and blind detection approach applied to orthogonal space-time block coding

An approach combining optimal antenna subset selection with blind detection scheme for Orthogonal Space-Time Block Coding （OSTBC） is proposed in this paper. The optimal antenna subset selection is taken into account at transmitter and/or receiver sides, which chooses the optimal antennas to increase the diversity order of OSTBC and improve further its performance. In order to enhance the robustness of the detection used in the conventional OSTBC scheme, a blind detection scheme based on Independent Component Analysis （ICA） is exploited which can directly extract transmitted signals without channel estimation. Performance analysis shows that the proposed approach can achieve the full diversity and the flexibility of system design by using the antenna selection and the ICA based blind detection schemes.     

波束空时分组码系统中一种基于ICA的正交检测方案

结合波束形成和空时分组编码的混合系统与传统的单波束发射以及单空时编码发射分集方案相比可以大大提高链路性能;传统的译码方案通常以接收端能够获取精确的信道状态信息为前提;但是对于某些特定的通信环境,这种前提条件通常很难满足.独立分量分析(ICA)技术可以在不进行信道估计的情况下对发射信号实现有效检测.本文针对接收端的信号结构提出了一种基于ICA的正交检测方案;并通过仿真将新方案与传统方案进行了性能比较,仿真结果表明,新方案具有较好的系统适应性和误码率特性.     

A new differential space-time block coding scheme

We present a new differential space-time block code (DSTBC). The scheme can be represented by a trellis and decoded using the Viterbi algorithm. It provides a differential coding gain of 1 dB due to redundancy introduced in the differential encoding and it is only 2 dB away from the corresponding coherent space-time block code (STBC).     

基于信道状态信息空时编码的FSOI系统设计

提出了一种新颖的基于空时编码的信道信息状态验证方法,添加训练比特序列来提高信道状态信息的精确性,确保自由空间光学互连系统的高效运行.理论分析和仿真结果表明,采用最大似然检测,利用信道信息状态进行重构,降低了系统误码率并提高了吞吐量.     

The impact of multiuser diversity on space-time block coding

In this letter, analytic performance results are derived for space-time block coding paired with multiuser diversity. We consider a scenario in which K active data users, each of which is potentially equipped with multiple antenna elements, are served by a multi-antenna element base station (BS). We focus on the downlink channel, where a space-time block coding scheme is employed and assume that channel quality information is reported to the BS by all users on a per frame basis. Using a scoring function at the BS, time resources are allocated to the user with the best instantaneous effective signal-to-noise ratio (SNR), facilitating a multiuser diversity mechanism. Using order statistics, we compute histograms and cumulative distribution functions of the effective SNR at the space-time combiner output and assess the interaction between multiuser diversity obtained via scheduling and spatial diversity obtained via the space-time code.     

频域均衡空时分组码技术研究

采用翻转矩阵定义了频域均衡空时分组码的编码方式,分析了它的系统结构和编译码过程,并且给出了信道分解的矩阵表达形式,得到了频域均衡空时分组码的一种简明的分析方法。仿真实验表明:与多载波的正交频分复用空时分组码相比,频域均衡空时分组码在频率选择性衰落信道下具有较好的性能。     

基于网络编码与空时编码的协作MAC协议

针对无线ad hoc网络中协作造成的中继效率低以及不同QoS需求难以满足等问题,提出了一种联合网络编码和空时编码的协作MAC协议(NSTCMAC)。NSTCMAC将网络编码与空时编码技术相结合,设计出区分业务类型的协作MAC协议传输机制,以满足不同业务类型的QoS需求;进一步通过马尔科夫链模型分析了区分业务类型的协作机制及性能。仿真结果表明,相比传统的DCF、COOPMAC以及CD-MAC协议,NSTCMAC协议能更好地保证不同的QoS需求,并能有效地解决协作造成的中继效率低的问题。     

Comments on "exact error performance of square orthogonal space-time block coding with channel estimation"

In a recent paper [1], Garg et al. present an expression for the exact decoding error probability (DEP) of square orthogonal space-time block codes (OSTBCs) with imperfect channel estimation. We show that their DEP expression is only asymptotically correct and point out how to obtain the exact result for arbitrary signal-to-noise ratio.     

频率选择性衰落下一种基于迭代干扰抵消的空时分组码译码算法

针对频率选择性衰落下空时分组码的正交性由于多径干扰而遭到严重破坏,提出一种基于迭代干扰抵消的最大似然序列估计(MLSE)译码方案;并结合最大比合并方法对所提方案进行改进和提高,以进一步降低计算复杂度。这些方案能很好地弥补通常空时分组码在频率选择性衰落下译码时的不足,它们不仅能抵消正交性没有破坏的在偶次项上的多径干扰,还能抵消正交性受到破坏的在奇次项上的多径干扰;有着非常好的性能。而且与直接对长序列信号进行MLSE译码相比,有着非常低的译码复杂度;从而以低复杂度实现了较好的空时分组码译码性能。     

A new high-rate differential space-time block coding scheme

A new high-rate differential space-time transmission scheme based on spatial multiplexing of Alamouti-encoded information streams is developed. At the receiver, joint space-time differential interference cancellation and decoding is performed, realizing diversity and rate gains, without requiring channel knowledge or bandwidth expansion. Our focus is on the case of two information streams with two transmit antennas per stream on flat-fading channels for simplicity. However, using previously published techniques, the development readily extends to more than two information streams, to more than two transmit antennas per stream, and to frequency-selective channels.