基于空时分组码及空频分组码的OFDM系统性能分析

讨论了正交频分复用系统中空时分组码与空频分组码的基本原理,并对信道条件为快变或慢变的多径信道下的两种系统误码性能进行分析与比较,指出在慢变信道条件下采用空时分组码的系统可取得较空频分组码系统更佳的性能。     

频率选择性衰落信道中的空时分组编码系统性能研究

空时分组码（STBC）由于具有较高的分集增益和简单的编译方法，从而得到普遍关注。但是它只适于频率平坦信道，而实际的信道多为频率选择性信道。丈中将考虑两种适用于频率选择性信道的空时分组码系统方案：OFDM-STBC和SC／FDE-STBC方案，即考虑空时分组码与正交频分复用或单载波频域均衡结合。通过对OFDM-STBC和SC／FDE-STBC系统性能仿真结果的比较和分析，表明SC／FDE-STBC方案要优于OFDM-STBC方案。此外，文中也给出一些细致的仿真性能的观察。     

空时分组码OFDM系统的上行多用户检测

针对目前空时编码结构大多只研究单用户检测这一现状，研究了空时分组码OFDM系统的多用户结构，并提出了一种性能次优的基于均值的软判决多用户检测（SDMUD）算法。仿真表明，该检测算法性能要比MMSE线性检测算法提高约4dB，可获得较为满意的干扰消除效果，满足系统对多用户检测性能的现实期望。     

短波单载波空时分组码的频域均衡研究

短波通信受多径衰落、干扰复杂等影响严重。空时分组码(Space Time Block Code,STBC)技术在无需增加频谱资源和天线发射功率的前提下,可以利用多输入多输出(Multiple-Input Multiple-Output,MIMO)信道提供的分集增益提升传输可靠性。分析短波MIMO研究现状,提出短波单载波STBC频域均衡(Frequency-Domain Equalization,FDE)系统架构,针对短波信道引入的码间干扰研究MIMO MMSE-FDE均衡技术,并将单载波STBC频域均衡与时域均衡及短波现有波形进行仿真对比。仿真结果表明,相较于短波现有波形,单载波STBC频域均衡系统的可靠性有较大幅度提升,且性能与STBC时域均衡接近,但计算复杂度远低于STBC时域均衡。     

正交空时分组码在OFDM系统中的性能估计

在宽带OFDM系统中对正交空时分组码方案进行了研究,根据Almouti方案的译码原理给出了在正交空时分组码传输的频率选择性衰落信道条件下接收机输出瞬时信噪比的一般表达式,同时分两种情况进一步分析了其最小距离球界的符号差错性能。结果表明,在系统发送天线数、接收天线数及多径数目乘积较小的情形下,系统可以达到最大的分集增益。     

空时编码在瑞利衰落信道下的性能分析

以正交空时分组码为例讨论了空时编码技术的性能特征。给出了各种STC-OFDM系统的BER性能。理论分析和仿真结果表明,STBC-OFDM系统在频率选择性的瑞利衰落信道下,性能优于其它STC-OFDM系统。     

MIMO-OFDM系统关键技术空时编码的研究

分集技术在无线信道上的应用,适应了有限带宽和功率资源。基于多输入多输出(Multipe Input Multiple Output,MIMO)的多天线系统的空时编码技术(Space Time Code,STC)可以充分利用无线通信信道中的多径,提高了无线链路的质量和谱效率,从而降低误码率、提高系统的可靠性。本文在空时编码技术的基础上,基于OFDM(正交频分复用)的多载波调制技术,提出一种STBC-OFDM(空时分组码)的编码改进方案,以期更高效利用频谱资源。     

MIMO-OFDM系统中的空频编码技术的研究

基于多输入多输出（MIMO）的空时编码技术可以充分利用无线通信信道中的多径,从而降低误码率、提高系统的可靠性。本文在空时编码技术的基础上,基于OFDM（正交频分复用）系统提出了一种空频分组码的编码改进方案。经仿真证明：编码后的系统相对于STBC-OFDM（空时分组编码）系统的性能更优越,提高了系统的可靠性。     

一种降低空时分组码OFDM信号峰均功率比的方法

正交频分复用(OFDM)信号包含许多独立调制的子载波,当子载波相干地叠加时会产生一个很大的峰均功率比。空时分组码OFDM系统是在OFDM系统中引入空时分组编码,通过选择映射的方法来降低空时分组码OFDM信号的峰值功率,从而降低峰均功率比(PAPR),并通过仿真对系统性能进行比较。     

正交空时分组编码系统的信号检测技术

正交空时分担编码（OSTBC）技术可以提高信道容量和误码性能,准静态平坦衰落信道和时变平坦衰落信道下正交空时分组编码率的信号检测技术得到广泛研究。利用正交频分复用技术（OFDM）,研究了时变多径衰落信道下OSTBC-OFDM的信号检测方法,提出了一种能够有效利用无线信道的多径传播效应的发射天线数目等于4的OSTBC信号检测算法,仿真结果表明,发射天线书等于4,接收天线数等于2时,与已有信号检测算法相比,提出的算法有4.5dB性能增益。     

Frequency domain decision feedback equalizer for time-reversal space-time block coding

In this paper,a frequency domain decision feedback equalizer is proposed for single carrier transmission with time-reversal space-time block coding (TR-STBC).It is shown that the diagonal decision feed...     

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.     

Bit-interleaved space-time trellis coding for frequency selective block fading channels

In this paper, the performance of a bit-interleaved space-time trellis coding (BISTTC) scheme is investigated for orthogonal frequency division multiplexing (OFDM) systems utilizing multiple antennas. The BISTTC scheme considered here concatenates the outer code with the well-known spacetime trellis code (STTC) through a bit interleaver. Compared to existing concatenation of BICM with space-time block code (STBC), BISTTC has significant performance advantage in applications with low spectral efficiency and simple outer code, due to its ability to exploit available diversity resources more efficiently.     

Block channel equalization in the frequency domain

In this paper, channel equalization algorithms processing two samples of the received signal per channel symbol and operating in the frequency domain are described in a unifying framework. First, minimum mean-square error linear and decision-feedback equalizers are derived, and a synthesis technique based on the well-known Levinson-Durbin algorithm is proposed for the latter. Then, iterative linear and decision-feedback equalization algorithms for turbo processing are devised. Performance results for both uncoded and coded phase-shift keying transmissions show the efficacy of the proposed equalization techniques and their superiority over other existing frequency-domain equalization strategies.     

Blind and semi-blind equalization for generalized space-time block codes

This paper presents a general framework for space-time codes (STCs) that encompasses a number of previously proposed STC schemes as special cases. The STCs considered are block codes that employ arbitrary redundant linear precoding of a given data sequence together with embedded training symbols, if any. The redundancy introduced by the linear precoding imposes structure on the received data that under certain conditions can be exploited for blind or semi-blind estimation of the transmitted sequence, a linear receiver that recovers the sequence, or both simultaneously. Algorithms based on this observation are developed for the single-user flat-fading case and then extended to handle multiple users, frequency-selective fading, as well as situations where the channel is rank deficient, or there are fewer receive than transmit antennas.     

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).     

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     

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.     

Double differential space-time block coding for time-selectivefading channels

Most existing space-time coding schemes assume time-invariant fading channels and offer antenna diversity gains relying on accurate channel estimates at the receiver. Other single differential space-time block coding schemes forego channel estimation but are less effective in rapidly fading environments. Based on a diagonal unitary matrix group, a novel double differential space-time block coding approach is derived in this paper for time-selective fading channels. Without estimating the channels at the receiver, information symbols are recovered with antenna diversity gains regardless of frequency offsets. The resulting transceiver has very low complexity and is applicable to an arbitrary number of transmit and receive antennas. Approximately optimal space-time codes are also designed to minimize bit error rate. System performance is evaluated both analytically and with simulations