Space-time modulation and coding over transmit correlated fading channels

Multi-dimensional space-time modulation schemes can be classified by the manner in which signal dimensions are shared among transmit antennas. In aggregate transmit antenna (ATA) systems, a generalization of Tarokh, Seshadri, Calderbank's (TSC) approach, there is total sharing of dimensions. In orthogonal transmit antenna (OTA) systems, a generalization of many traditional diversity schemes, there is no sharing of dimensions. In partially orthogonal transmit antennas (POTA), a combination of ATA with OTA, subsets of available dimensions are shared by subsets of transmit antennas. This letter considers such coded schemes for spatially correlated fading channels. Over strongly transmit correlated channels, in addition to coding and diversity gains, ATA and POTA can harvest a transmit beamforming-like gain. This letter presents a scheme, POTARep, designed to provide beamforming-like gain as well as diversity and coding gains, yielding improved performance over a highly transmit correlated channel.     

Transmit antennae space-time block coding for generalized OFDM inthe presence of unknown multipath

Transmit antenna diversity has been exploited to develop high-performance space-time coders and simple maximum-likelihood decoders for transmissions over flat fading channels. Relying on block precoding, this paper develops generalized space-time coded multicarrier transceivers appropriate for wireless propagation over frequency-selective multipath channels. Multicarrier precoding maps the frequency-selective channel into a set of flat fading subchannels, whereas space-time encoding/decoding facilitates equalization and achieves performance gains by exploiting the diversity available with multiple transmit antennas. When channel state information is unknown at the receiver, it is acquired blindly based on a deterministic variant of the constant-modulus algorithm that exploits the structure of space-time block codes. To benchmark performance, the Cramer-Rao bound of the channel estimates is also derived. System performance is evaluated both analytically and with simulations     

Nakagami衰落信道中差分空时分组码误比特率分析

研究差分空时分组码在Nakagami衰落信道下的性能.在介绍2发1收差分空时分组码编译码方案的基础上,得出Nakagami信道下差分空时分组码的误比特率.仿真结果与理论计算值一致,证明了所推导误比特率计算表达式的正确性.     

Achievable Performance of Orthogonal STBC Over Spatially Correlated Rician Channels

The effect of spatial correlation on the performance of orthogonal space-time block codes (OSTBCs) over multiple-input-multiple-output (MIMO) Rician fading channels is studied. Asymptotic error-rate formulas for OSTBC with high average signal-to-noise ratios (ASNRs) over arbitrarily correlated Rician MIMO channels are derived in terms of the diversity and coding gains. Our results show that, in correlated fading, the phase vector phi of the channel line-of-sight (LOS) components affects the effective Rice K-factor at the OSTBC receiver output and, hence, may result in a coding gain that is significantly higher than that for independent Rician MIMO channels. Furthermore, when the channel covariance matrix is rank deficient and under some additional mild conditions, the error and outage probabilities of OSTBC achieve those in a nonfading additive-white-Gaussian-noise channel. For both cases of full-rank and rank-deficient channel covariance matrices, analytical expressions of optimal and worst case phase vectors phi, and exact upper and lower bounds of OSTBC performance are derived. These results provide new insights into the achievable performance of OSTBC over correlated Rician MIMO channels and, if incorporated into future multiple antenna systems design, will bring about significant performance enhancement     

Diagonal block space-time code design for diversity and coding advantage over flat fading channels

The potential promised by multiple transmit antennas has raised considerable interest in space-time coding for wireless communications. In this paper, we propose a systematic approach for designing space-time trellis codes over flat fading channels with full antenna diversity and good coding advantage. It is suitable for an arbitrary number of transmit antennas with arbitrary signal constellations. The key to this approach is to separate the traditional space-time trellis code design into two parts. It first encodes the information symbols using a one-dimensional (M,1) nonbinary block code, with M being the number of transmit antennas, and then transmits the coded symbols diagonally across the space-time grid. We show that regardless of channel time-selectivity, this new class of space-time codes always achieves a transmit diversity of order M with a minimum number of trellis states and a coding advantage equal to the minimum product distance of the employed block code. Traditional delay diversity codes can be viewed as a special case of this coding scheme in which the repetition block code is employed. To maximize the coding advantage, we introduce an optimal construction of the nonbinary block code for a given modulation scheme. In particular, an efficient suboptimal solution for multilevel phase-shift-keying (PSK) modulation is proposed. Some code examples with 2-6 bits/s/Hz and two to six transmit antennas are provided, and they demonstrate excellent performance via computer simulations. Although it is proposed for flat fading channels, this coding scheme can be easily extended to frequency-selective fading channels.     

满速率串行级联空时分组MTCM编码方法研究

该文研究了级联空时编码系统在编码增益,分集增益和传输能量效率的限定下最大化传输速率的问题,提出了一种在保留TCM编码方法校验位冗余的同时,还可获得满速率串行级联空时分组TCM编码方法。新方法通过引入具有不同功率分集因子的正交发射码字矩阵,并给出新的译码算法,从而使得新的编码方法在获得满速率的同时还可以获得满分集增益。分析和MATLAB仿真结果表明,在相同的编码状态数下,新方法在编码增益上比现有的满速率超正交空时分组编码方法提高1dB左右。     

On Trellis Coded Noncoherent Space-Time Modulation

Unitary space-time modulation (USTM) is well-tailored for noncoherent space-time modulation. Trellis coded USTM (TC-USTM) can obtain significant coding gains over uncoded USTM for the noncoherent block fading channel. Conventional TC-USTM schemes expand the signal set of uncoded USTM by a factor of two. In this letter, we propose a new TC-USTM scheme in which the size of USTM set is not limited to be just double for uncoded USTM. However, in TC-USTM schemes, because signals of the same trellis branch are transmitted over the same fading coefficients, one trellis branch can only obtain one temporal diversity. In this letter, we also propose a new trellis coded noncoherent space-time modulation scheme by interleaving space-time signals. The proposed scheme can enlarge temporal diversity at the price of increased complexity and delay. Simulation results demonstrate the excellent error performances of codes found by computer searches for both schemes.     

Best antenna selection for coded SIMO–OFDM

Multiple receive antennas with optimal combining have been known to improve error performance over fading multipath channels by providing spatial diversity. This benefit is obtained at the cost of greatly increased system complexity due to the need for multiple RF chains and signal combiners. Best antenna selection is a technique that can provide multiple antenna gains with only a single RF chain and no combiners. Best antenna selection is complicated by frequency selectivity in orthogonal frequency division multiplexing (OFDM) as the signal at any one antenna may not be the best at all subcarriers. In this paper, we propose a novel technique for best antenna selection in coded OFDM. To simplify the receiver, we assume a block fading model for the underlying frequency selective channel. The best antenna will then determined based on coding theorems known for block fading channels. Our simulations show significant improvement in coded OFDM performance over existing techniques.     

基于天线子集选择算法的DSTBC优化

为进一步提高空时码性能,在信道模型为瑞丽和莱斯慢衰落信道的情况下,文中提出了一种优化差分空时分组码的＂天线子集选择算法＂——假设发射信号为特定的Alamouti正交空时分组码,通过最大化信道参数矩阵F范数的方法,优化了MIMO系统的天线集。仿真结果表明：此方法可降低码元的比特错误率,并且可获得相当客观的分集增益和能量增益。此外,还讨论了该优化方法的适用范围。     

频率选择性衰落信道下一种空时分组码的直接解码

该文针对 3个发射天线,1个接收天线的空时分组码系统,提出了频率选择性衰落信道下,无需信道估计,直接对空时分组码进行解码的方法,把子空间方法应用于空时编码当中,从信号处理和空时编码两个方面考虑空时分组码的直接解码问题,利用空时分组码所特有的正交设计,较为方便地从子空间中解出信号信息,从单载波的角度,解决了频率选择性衰落下空时分组码的解码问题。Monte-Carlo仿真给出了直接解码算法的性能,并与使用准确信道信息的解码算法做了性能比较。     

Space-time bit-interleaved coded modulation for OFDM systems

Space-time coding techniques significantly improve transmission efficiency in radio channels by using multiple transmit and/or receive antennas and coordination of the signaling over these antennas. Bit-interleaved coded modulation gives good diversity gains with higher order modulation schemes using well-known binary convolutional codes on a single transmit and receive antenna link. By using orthogonal frequency division multiplexing (OFDM), wideband transmission can be achieved over frequency-selective fading radio channels without adaptive equalizers. In this correspondence, we combine these three ideas into a family of flexible space-time coding methods. The pairwise error probability is analyzed based on the correlated fading assumption. Near-optimum iterative decoders are evaluated by means of simulations for slowly varying wireless channels. Theoretical evaluation of the achievable degree of diversity is also presented. Significant performance gains over the wireless local area network (LAN) 802.11a standard system are reported.     

Analysis of Differential Orthogonal Space–Time Block Codes Over Semi-Identical MIMO Fading Channels

We study the performance of differential orthogonal space-time block codes (OSTBC) over independent and semi-identically distributed block Rayleigh fading channels. In this semiidentical fading model, the channel gains from different transmit antennas to a common receive antenna are identically distributed, but the gains associated with different receive antennas are nonidentically distributed. Arbitrary fluctuation rates of the fading processes from one transmission block to another are considered. We first derive the optimal symbol-by-symbol differential detector, and show that the conventional differential detector is suboptimal. We then derive expressions of exact bit-error probabilities (BEPs) for both the optimal and suboptimal detectors. The results are applicable for any number of receive antennas, and any number of transmit antennas for which OSTBCs exist. For two transmit antennas, explicit and closed-form BEP expressions are obtained. For an arbitrary number of transmit antennas, a Chernoff bound on the BEP for the optimal detector is also derived. Our results show that the semi-identical channel statistics degrade the error performance of differential OSTBC, compared with the identical case. Also, the proposed optimal detector substantially outperforms the conventional detector when the channel fluctuates rapidly. But in near-static fading channels, the two detectors have similar performances     

用于快时变MIMO衰落信道的一种差分空时调制技术

针对快时变多输入多输出(MIMO)平坦衰落信道,利用时变信道的基扩展模型(BEM),提出了一种差分空时调制方案。差分编码按块进行,发射信号矩阵为对角酉矩阵。通过设计发射端的交织及接收端的解交织,判决反馈差分检测不需要信道状态信息。理论分析和仿真表明,该方案能同时实现最大的天线分集和信道时变性所提供的Doppler分集。     

基于空时分组编码的MC-CDMA下行链路合并方案

基于空时分组编码的发射分集技术利用空间和时间分集 ,能有效抗多径 ,增强信道可靠性。将空时分组编码应用到MC -CDMA下行链路中 ,构建了一种新的多载波CDMA系统 (ST -MC -CD MA) ,通过在每个子载波信道中获得空间分集增益来提高系统性能。具体实现时 ,依据传统MC -CDMA信号合并方案 ,提出了ST -MC -CDMA空时译码后相应的四种合并方案。仿真结果验证了这 4种合并方案的优、缺点 ;并进一步证明 :在频率选择性瑞利衰落信道中 ,该系统比采用相同合并方案的传统MC -CDMA有明显的性能改善。     

Feedback gain in multiple antenna systems

Multiple antenna transmission and reception have been shown to significantly increase the achievable data rates of wireless systems. However, most of the existing analysis assumes perfect or no channel information at the receiver and transmitter. The performance gap between these extreme channel assumptions is large and most practical systems lie in between. Therefore, it is important to analyze multiple antenna systems in the presence of partial channel information. We upper bound the outage probability performance of multiple antenna systems with preamble-based channel estimation and quantized feedback. We design causal feedback and power control schemes to minimize this upper bound on outage probability. We consider the following practical issues in our analysis and design: (1) the channel information is imperfect both at the receiver and at the transmitter and (2) part of the total available resources for the system need to be used for estimation and feedback. Our results demonstrate that for block fading channels, sending a periodic preamble and causally receiving channel state information via a feedback channel can lead to substantial gains in the outage performance over any nonfeedback scheme. Most of the gains achieved by perfect feedback can be achieved by very few bits of feedback. Furthermore, it is demonstrated that these outage probability gains can be translated into improvements in frame error rate performance of systems using space-time codes. Thus, implementing a power control, even at the cost of reduced spectral resources for the forward channel is beneficial for block fading channels     

Reduced-Complexity Receiver Structures for Space–Time Bit-Interleaved Coded Modulation Systems

Transmission efficiency in radio channels can be considerably improved by using multiple transmit and receive antennas and employing a family of schemes called space-time (ST) coding. Both extended range and/or improved bandwidth efficiency can be achieved, compared with a radio link with a single transmit and receive antenna. Bit-interleaved coded modulation schemes give diversity gains on fading channels with higher order modulation constellations combined with conventional binary convolutional codes also for the case of a single transmit and receive antenna radio link. In this paper, we study a family of flexible bandwidth-efficient ST coding schemes which combine these two ideas in a narrowband flat-fading channel and single-carrier modems. We address receiver complexity for the case of a large number of transmit antennas and higher order modulation constellations. Especially, we focus on practical configurations, where the number of transmit antennas is greater than that of receive antennas. Simplified receivers using tentative decisions are proposed and evaluated by means of simulations. Tradeoffs between complexity reduction and performance loss are presented. We emphasize systems that are of particular interest in applications where the number of transmit antennas exceeds the number of receive antennas. A system with four transmit antennas with an eight-fold complexity reduction and a performance loss of about 1 dB is demonstrated     

Cooperative Protocols Design for Wireless Ad-Hoc Networks with Multi-hop Routing

Wireless ad-hoc networks can experience significant performance degradation under fading channels. Spatial diversity has been shown to be an effective way of combating wireless fading with the multiple-input multiple-output (MIMO) technique by transmitting correlated information through multiple antennas. The virtual MIMO technique, which allows multiple wireless stations with single antenna to form a virtual transmission array, is shown to be a viable solution from several recent studies. In this paper, we propose a complete system framework for wireless ad-hoc networks utilizing two different cooperative relaying techniques at the physical layer: the repetition coding and the space-time coding. In the data link layer, two medium access control protocols are proposed to accommodate the corresponding physical layer cooperative diversity schemes. In the network layer, diversity-aware routing protocols are proposed to determine the routing path and the relaying topology. Simulations with both constant bit rate and TCP (transmission control protocol) traffic show significant performance gains of the proposed cooperative relaying schemes.     

Approximately universal codes over slow-fading channels

Performance of reliable communication over a coherent slow-fading multiple-input multiple-output (MIMO) channel at high signal-to-noise ratio (SNR) is succinctly captured as a fundamental tradeoff between diversity and multiplexing gains. This paper studies the problem of designing codes that optimally tradeoff the diversity and multiplexing gains. The main contribution is a precise characterization of codes that are universally tradeoff-optimal, i.e., they optimally tradeoff the diversity and multiplexing gains for every statistical characterization of the fading channel. This characterization is referred to as approximate universality; the approximation is in the connection between error probability and outage capacity with diversity and multiplexing gains, respectively. The characterization of approximate universality is then used to construct new coding schemes as well as to show optimality of several schemes proposed in the space-time coding literature.     

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.     

On the design of space-time and space-frequency codes for MIMO frequency-selective fading channels

The authors introduced an algebraic design framework for space-time coding in flat-fading channels . We extend this framework to design algebraic codes for multiple-input multiple-output (MIMO) frequency-selective fading channels. The proposed codes strive to optimally exploit both the spatial and frequency diversity available in the channel. We consider two design approaches: The first uses space-time coding and maximum likelihood decoding to exploit the multi-path nature of the channel at the expense of increased receiver complexity. Within this time domain framework, we also propose a serially concatenated coding construction which is shown to offer a performance gain with a reasonable complexity iterative receiver in some scenarios. The second approach utilizes the orthogonal frequency division multiplexing technique to transform the MIMO multipath channel into a MIMO flat block fading channel. The algebraic framework is then used to construct space-frequency codes (SFC) that optimally exploit the diversity available in the resulting flat block fading channel. Finally, the two approaches are compared in terms of decoder complexity, maximum achievable diversity advantage, and simulated frame error rate performance in certain representative scenarios.