Linear diversity-embedding STBC: design issues and applications

We design a novel class of space-time codes, called linear diversity-embedding space-time block codes (LDE-STBC) where a high-rate STBC is linearly superimposed on a highdiversity STBC without requiring channel knowledge at the transmitter. In applying this scheme to multimedia wireless communications, each traffic type constitutes a transmission layer that operates at a suitable rate-diversity tradeoff point according to its quality-of-service requirements. This, in turn, provides an unequal-error-protection (UEP) capability to the different information traffic types and allows a form of wireless communications where the high-rate STBC opportunistically takes advantage of good channel realizations while the embedded high-diversity STBC ensures that at least part of the information is decoded reliably. We investigate transceiver design issues specific to LDE-STBC including reduced-complexity coherent decoding and effective schemes to vary the coding gain to further enhance UEP capabilities of the code. Furthermore, we investigate the application of LDE-STBC to wireless multicasting and demonstrate its performance advantage over conventional equal-error-protection STBC.     

一种结合空时编码的导频辅助信道估计方法

多输入多输出-正交频分复用(MIMO-OFDM)作为一种高速率无线通信的有效方式,其信道估计技术具有非常重要的位置。将OFDM技术与基于发射分集的空时格码相结合,构造了一个基于空时格码的OFDM模型。基于MIMO-OFDM系统的导频设计准则及特性,提出了一种空时编码OFDM系统中基于导频的辅助信道估计方法。仿真实验结果表明信道估计的性能接近理想信道情况下的性能。     

On the design of algebraic space-time codes for MIMO block-fading channels

The availability of multiple transmit antennas allows for two-dimensional channel codes that exploit the spatial transmit diversity. These codes were referred to as space-time codes by Tarokh et al. (see ibid., vol.44, p.744-765, Mar. 1998) Most prior works on space-time code design have considered quasi-static fading channels. We extend our earlier work on algebraic space-time coding to block-fading channels. First, we present baseband design criteria for space-time codes in multi-input multi-output (MIMO) block-fading channels that encompass as special cases the quasi-static and fast fading design rules. The diversity advantage baseband criterion is then translated into binary rank criteria for phase shift keying (PSK) modulated codes. Based on these binary criteria, we construct algebraic space-time codes that exploit the spatial and temporal diversity available in MIMO block-fading channels. We also introduce the notion of universal space-time codes as a generalization of the smart-greedy design rule. As a part of this work, we establish another result that is important in its own right: we generalize the full diversity space-time code constructions for quasi-static channels to allow for higher rate codes at the expense of minimal reductions in the diversity advantage. Finally, we present simulation results that demonstrate the excellent performance of the proposed codes.     

A rank criterion for QAM space-time codes

Space-time coding has been studied extensively as a powerful error correction coding for systems with multiple transmit antennas. An important design goal is to maximize the level of space diversity that a code can achieve. Toward this goal, the only systematic algebraic coding theory so far is binary rank theory by Hammons and El Gamal (see ibid. vol. 46, p.524-42, 2000) for binary phase-shift keying (BPSK) modulated codes defined over binary field and quaternary phase-shift keying (QPSK) modulated codes defined over modulo four finite ring. To design codes with higher bandwidth efficiency, we develop an algebraic rank theory to ensure full space diversity for 2/sup 2k/ quadrature and amplitude modulated (QAM) codes for any positive integer k. The theory provides the most general sufficient condition of full space diversity so far. It includes the BPSK binary rank theory as a special case. Since the condition is over the same domain that a code is defined, the full space diversity code design is greatly simplified. The usefulness of the theory is illustrated in examples, such as analyses of existing codes, constructions of new space-time codes with better performance, including the full diversity space-time turbo codes.     

Space-time turbo codes with full antenna diversity

In attempting to find a spectrally and power efficient channel code which is able to exploit maximum diversity from a wireless channel whenever available, we investigate the possibility of constructing a full antenna diversity space-time turbo code. As a result, both three-antenna and two-antenna (punctured) constructions are shown to be possible and very easy to find. To check the decodability and performance of the proposed codes, we derive non-binary soft-decoding algorithms. The performance of these codes are then simulated and compared with two existing space-time convolutional codes (one has minimum worst-case symbol-error probability; the other has maximal minimum free distance) having similar decoding complexity. As the simulation results show, the proposed space-time turbo codes give similar or slightly better performance than the convolutional codes under extremely slow fading. When fading is fast, the better distance spectra of the turbo codes help seize the temporal diversity. Thus, the performance advantage of the turbo codes becomes evident. In particular, 10^-5 bit-error rate and 10^-3 frame-error rate can be achieved at less than 6-dB E_b/N₀ with 1 b/s/Hz and binary phase-shift keying modulation. The practical issue of obtaining the critical channel state information (CSI) is also considered by applying an iteratively filtered pilot symbol-assisted modulation technique. The penalty when the CSI is not given a priori is about 2-3 dB     

一种基于STTC变形码的MIMO跨层安全研究方案

用于高速无线通信的空时网格码,能够达到频谱利用率、分集增益与编码复杂度之间的最佳折中,是一种最佳空时码。文中提出在STTC系统中设计一种STTC变形码并将其与上层密码技术结合,充分利用信道的有噪特性,可以实现增强的无线通讯加密方式,防止信息泄露。     

On the theory of space-time codes for PSK modulation

The design of space-time codes to achieve full spatial diversity over fading channels has largely been addressed by handcrafting example codes using computer search methods and only for small numbers of antennas. The lack of more general designs is in part due to the fact that the diversity advantage of a code is the minimum rank among the complex baseband differences between modulated codewords, which is difficult to relate to traditional code designs over finite fields and rings. We present general binary design criteria for PSK-modulated space-time codes. For linear BPSK/QPSK codes, the rank of (binary projections of) the unmodulated codewords, as binary matrices over the binary field, is a sufficient design criterion: full binary rank guarantees full spatial diversity. This criterion accounts for much of what is currently known about PSK-modulated space-time codes. We develop new fundamental code constructions for both quasi-static and time-varying channels. These are perhaps the first general constructions-other than delay diversity schemes-that guarantee full spatial diversity for an arbitrary number of transmit antennas     

Using Orthogonal and Quasi-Orthogonal Designs in Wireless Relay Networks

Distributed space-time coding was proposed to achieve cooperative diversity in wireless relay networks without channel information at the relays. Using this scheme, antennas of the distributive relays work as transmit antennas of the sender and generate a space-time code at the receiver. It achieves the maximal diversity when the transmit power is infinitely large. This paper is on the design of practical distributed space-time codes (DSTCs). We use orthogonal and quasi-orthogonal designs which are originally used in the design of space-time codes for multiple-antenna systems. It is well known that orthogonal space-time codes have full diversity and linear decoding complexity. They are particularly suitable for transmissions in the network setting using distributed space-time coding since their ldquoscale-freerdquo property leads to good performance. Our simulations show that they achieve lower error rates than the random code. We also compare distributed space-time coding to selection decode-and-forward using the same orthogonal designs. Simulations show that distributed space-time coding achieves higher diversity than selection decode-and-forward (DF) when there is more than one relay. We also generalize the distributed space-time coding scheme to wireless relay networks with channel information at the relays. Although our analysis and simulations show that there is no improvement in the diversity, in some networks, having channel information at the relays saves both the transmission power and the transmission time.     

Existence and construction of noncoherent unitary space-time codes

We consider transmission using N transmit and reception using M receive antennas in a wireless environment assuming that neither the transmitter nor the receiver knows the channel coefficients. For the scenario that the transmission employs noncoherent T /spl times/ N unitary space-time codes and for a block-fading channel model where the channel is static during T channel uses and varies from T channel uses to the other, we establish the bound r /spl les/ min(T-N, N) on the diversity advantage rM provided by the code. In order to show that the requirement r /spl les/ min(T-N, N) cannot be relaxed, for any given R, N, T, and r /spl les/ min(T-N, N), we then construct unitary T /spl times/ N space-time codes of rate R that guarantee diversity advantage rM. Two constructions are given that are also amenable to simple encoding and noncoherent maximum-likelihood (ML) decoding algorithms.     

Space-Time Cooperation Diversity Using High-Rate Codes

In a multi-user communication system, cooperative diversity allows single-antenna mobile sets to achieve transmit diversity. Cooperative diversity improves the communication capacity and enhances the robustness of a wireless link when a single channel alone is not reliable. In this paper, a novel cooperative diversity scheme is introduced that enables simultaneous transmission of non-redundant data from all cooperative terminals. By taking advantages of both high-rate full-diversity space-time codes and the cooperative diversity, the proposed method provides high diversity gain beyond the number of physical transmit antennas without compromising the data rates. In essence, the proposed system aims at higher data rates over the non-cooperative counterpart, while maintaining the full diversity gain.     

无线光通信中的空时编码研究进展（二）

无线光MIMO技术结合了天线发射分集、接收分集与信道编码分集,可以显著提高信道容量。介绍了笔者在分层空时编码方面的若干研究进展,分析了误码率特性与发射/接收天线数目、检测算法之间的关系,比较了水平分层空时码、螺旋分层空时码、对角分层空时码和垂直分层空时码不同的编码方案,以及不同检测算法对不同的湍流强度的抑制作用。经分析得出:三种分层空时编码性能最好的是对角分层空时编码,其次是螺旋分层空时编码,最后是水平分层空时编码。     

High-rate orthogonal space-time block code for four transmit antennas

A high-rate (rate 1.5) nonlinear orthogonal space-time block code for four transmit antennas is presented. It outperforms previous space- time block codes where there are more than two receive antennas. This high-rate code improves on the performance of a recently proposed nonlinear orthogonal space-time block code of the same rate and without any extra constellation expansion.     

空时格码和OFDM系统联合建模及性能分析

发射端分集、编码和调制结合空时格码，可以有效地提高信号在无线衰落信道中传输的有效性和可靠性；在正交频分复用调制OFDM(Omiogonal Frequency Division Multiplexing)系统中应用空时格码可以有效地对抗多径干扰，提高系统容量，适合于在高速无线数据通信中采用。本文详细地说明了它们结合的基础，进而构造了一个基于空时格码的OFDM系统模型，并分析了在高斯信道下的系统性能。     

Some analytical tools for the design of space-time convolutional codes

Space-time convolutional codes have shown considerable promise for providing improved performance for wireless communication through combined diversity and coding gain. An efficient design procedure is presented for optimizing the coding and diversity gain measures proposed in the first papers on space-time codes. The procedure is based on some simple lower and upper bounds on coding gain. The same calculations needed to compute these bounds can be used to check either necessary or sufficient conditions on space-time codes which achieve maximum diversity gain. A new simple, but useful, measure of code performance is also suggested which augments existing measures. The use of the design procedure is illustrated and new codes are provided. These codes are shown to outperform the space-time convolutional codes provided in the initial papers introducing space-time codes.     

无线通信系统中的MIMO空时编码技术

在无线通信系统中,对优质、高效宽带服务的要求不断增加。空时编码（STC）的目的是利用多输入多输出（MIMO）天线系统,提高传输质量,降低误码率,并获得较高的编码增益和分集增益,提高系统容量和频谱利用率。较详细地介绍了MIMO无线通信中的三种空时编码方案：分层空时码、空时格形码、空时分组码,对这三种方案进行了性能分析以及比较。     

空时编码在单天线UWB通信系统中的应用

超宽带(UWB)适用于基带多用户通信、战场无线通信和高数据率多媒体业务等通信系统,其数据传输速率高、功耗低、多径分辨能力强。但超宽带脉冲信号时域支撑区极窄,信道为密集多径,将空时编码技术引入超宽带通信系统,能够提升无线通信系统的信道容量与抗误比特率性能。在对UWB空时分组编码系统模型性能理论分析的基础上,对空时分组码在单天线UWB系统应用方案与UWB空时分层码方案进进行了简要介绍,利用Matlab对IEEEUWB信道模型进行仿真,提出了空时编码在UWB通讯技术中应用后提升短距高速率无线通信的性能的结论 。     

Concatenation of trellis coded modulation and space-time block codes for high data rate on wireless systems using multiple antenna elements

Performance results using concatenation of high-rate pragmatic TCM (trellis coded modulation) codes with a simple high-rate space-time block code operating on a multiple input/multiple output (MIMO) channel with 4 transmit and 4 receive antennas are presented. Four TCM encoders feed 4 data streams consisting of 32-QAM symbols into a simple Alamouti — like space-time code, spreading the data over 4 transmit antennas. In this way an overall data rate of 8 information bits per channel use is obtained. Perfect channel state information (CSI) at the receiver is assumed for all investigations. Using 4 receive antennas with a low complexity zero-forcing (ZF) receiver we get diversity order of approximately 6. Compared with coded V-BLAST (Foschini, 1996) operating on the same information bit rate and decoder complexity, our system performs much better for all types of spatially correlated and uncorrelated MIMO channels under investigation.     

LOW RATE SPACE-TIME TRELLIS CODES INPOWER LIMITED WIRELESSCOMMUNICATION SYSTEMS

Space-time trellis codes can achieve the best tradeoff among bandwidth efficiency, diversity gain, constellation size and trellis complexity. In this paper, some optimum low rate space-time trellis codes are proposed. Performance analysis and simulation show that the low rate space-time trellis codes outperform space-time block codes concatenated with convolutional code at the same bandwidth efficiency, and are more suitable for the power limited wireless communication system.     

Maximal diversity algebraic space-time codes with low peak-to-mean power ratio

The design requirements for space-time coding typically involves achieving the goals of good performance, high rates, and low decoding complexity. In this paper, we introduce a further constraint on space-time code design in that the code should also lead to low values of the peak-to-mean envelope power ratio (PMEPR) for each antenna. Towards that end, we propose a new class of space-time codes called the "low PMEPR space-time" (LPST) codes. The LPST codes are obtained using the properties of certain cyclotomic number fields. The LPST codes achieve a performance identical to that of the threaded algebraic space-time (TAST) codes but at a much smaller PMEPR. With M antennas and a rate of one symbol per channel use, the LPST codes lead to a decrease in PMEPR by at least a factor of M relative to a Hadamard spread version of the TAST code. For rates beyond one symbol per channel use and up to a guaranteed amount, the LPST codes have provably smaller PMEPR than the corresponding TAST codes. Additionally, with the concept of punctured LPST codes proposed in this paper, significant performance improvement is obtained over the full diversity TAST schemes of comparable complexity. Numerical examples are provided to illustrate the advantage of the proposed codes in terms of PMEPR reduction and performance improvement for very high rate wireless communications.     

无线通信系统中的低码率空时网格码

空时网格编码能在频带利用率、分集增益、调制方式与编码网络图复杂度之间达到最佳的折衷。本文给出了几种低码率空时网格码的好码。理论分析和系统仿真表明,在相同的频带利用率下,该空时网格码可具有比空时块码级联卷积码具有更好的误码率性能,更适合于对频带利用率要求不高的功率受限无线通信系统。