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     

Space-frequency-time turbo coded modulation

A new bandwidth and power efficient signaling scheme is proposed that achieves high data rates over wideband radio channels exploiting the bandwidth efficient OFDM modulation, multiple transmit and receive antennas and large frequency selectivity offered in typical low mobility indoor environments. Owing to its maximum transmit diversity gain and large coding gain, space-frequency-time turbo coded modulation strongly outperforms other space-frequency-time coding schemes proposed in literature. A simple way of combining space-frequency-time coding with OFDM delay diversity for cost effective exploitation of more than two transmit antennas is also proposed in this paper     

瑞利衰落信道采用组合发射机SC/接收机 MRC的MQAM性能分析

日益增长的无线业务需求要求提高衰落信道上无线通信的频谱利用率.本文研究一种使用组合发射机SC/接收机MRC(SC/MRC)的MQAM方案,推导其在平坦瑞利衰落信道上的误符号率,分析无线信道时变特性对系统性能的影响.数值计算结果表明该组合空间分集方案可以通过调整发射天线和接收天线的数目来获得比传统接收机分集接收更大的分集增益.     

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.     

Space–Time/Space–Frequency/Space–Time–Frequency Block Coded MIMO-OFDM System with Equalizers in Quasi Static Mobile Radio Channels Using Higher Tap Order

In 4G broadband wireless communications, multiple transmit and receive antennas are used to form multiple input multiple output (MIMO) channels to increase the capacity (by a factor of the minimum number of transmit and receive antennas) and data rate. In this paper, the combination of MIMO technology and orthogonal frequency division multiplexing (OFDM) systems is analyzed for wideband transmission which mitigates the intersymbol interference and hence enhances system capacity. In MIMO-OFDM systems, the coding is done over space, time, and frequency domains to provide reliable and robust transmission in harsh wireless environment. Also, the performance of space time frequency (STF) coded MIMO-OFDM is analyzed with space time and space frequency coding as special cases. The maximum achievable diversity of STF coded MIMO-OFDM is analyzed and bit error rate performance improvement is verified by simulation results. Simulations are carried out in harsh wireless environment, whose effect is mitigated by using higher tap order channels. The complexity is resolved by employing sphere decoder at the receiver.     

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)     

Combined turbo coding and unitary space-time modulation

Space-time coding is well understood for high data rate communications over wireless channels with perfect channel state information. On the other hand, channel coding for multiple transmit antennas when channel state information is unknown has only received limited attention. A new signaling scheme, named unitary space-time modulation, has been proposed for the latter case. In this paper, we consider the use of turbo coding together with unitary space-time modulation. We demonstrate that turbo coded space-time modulation systems are well suited to wireless communication systems when there is no channel state information, in the sense that the turbo coding improves the bit error rate (BER) performance of the system considerably. In particular, we observe that the turbo-coded system provides 10-15 dB coding gain at a BER of 10/sup -5/ compared to the unitary space-time modulation for various transmit and receive antenna diversity cases.     

Space-time signaling for high data rates in EDGE

Several space-time coding and processing techniques have been introduced in the literature for enhancing the capacity of wireless systems through antenna diversity or spatial multiplexing. We study the application of such techniques to an adaptive coded modulation system in multipath channels with intersymbol interference. One of the key requirements for application of these schemes is the use of appropriate training symbols for channel estimation at the receiver. We determine the training requirements for coherent receiver operation when multiple transmit antennas are used. We show that for the special case of the delay diversity scheme, transmitting the same training sequence from the two antennas is optimal. For more general schemes, we present training sequences that have good auto-correlation and cross-correlation properties that can be used in a practical system such as Enhanced Data for GSM Evolution (EDGE). We present detailed link level simulations that include channel estimation for the proposed schemes. We then determine the system throughput that is achieved for packet data with ideal link adaptation for deployment scenarios with 1/3, 3/9, 4/12, and 7/21 frequency reuse. We conclude that the gains from transmit diversity are not significant when there is frequency hopping as in an EDGE system and that a factor of 3 gain in throughput can be achieved when four transmit and four receive antennas are available using simple space-time transmission and receiver processing.     

Space–time coding and signal processing for high data rate wireless communications

The information capacity of wireless communication systems can be increased dramatically by employing multiple transmit and receive antennas [Foschini GJ, Gans MJ. On limits of wireless communications in a fading environment when using multiple antennas. Wireless Communications Magazine 1998; 6 311–335. Telatar E. Capacity of Multi‐Antenna Gaussian Channels, Technical Memorandum, AT&T Bell Laboratories, 1995.] An effective approach to increasing data rate over wireless channels is to employ coding techniques appropriate to multiple transmit antennas, that is space–time coding. Space–time codes introduce temporal and spatial correlation into signals transmitted from different antennas, in order to provide diversity at the receiver, and coding gain over an uncoded system. The spatial–temporal structure of these codes can be exploited to further increase the capacity of wireless systems with a relatively simple receiver structure. This paper provides an overview of space–time coding techniques and the associated signal processing framework. Copyright © 2001 John Wiley & Sons, Ltd.     

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.     

Diversity eigenbeamforming for coded signals

Transmit antenna diversity without feedback has been widely investigated for various wireless communication systems. Especially, space-time codes are extensively studied to exploit the spatial diversity induced by multiple transmit antennas. Apart from these approaches, there can be different methods that provide a diversity gain using multiple antennas with conventional channel coding. In this paper, diversity eigenbeamforming is studied to exploit the spatial diversity when the channel covariance matrix is available at the transmitter. Diversity eigenbeamforming is based on eigenmode (of the spatial covariance matrix) switching that converts the spatial diversity into the temporal diversity which is exploited by channel coding. Optimized diversity eigenbeamforming is considered to take into account the spatial correlation. In addition, the trade-off between diversity and multiplexing gains is addressed. It is shown that the diversity eigenbeamforming can achieve optimal trade-off for the case of one receive antenna. Although, for simplicity, binary phase shift keying (BPSK) is used to derive diversity eigenbeamforming, any higher-order modulation scheme can also be used with diversity eigenbeamforming.     

Impact of transmit antenna spacing on 2x1 Alamouti radio transmission

It is a common belief that multiple transmit antennas have to be placed far apart in order to avoid undesired effects such as mutual coupling, changing beampatterns, antenna mismatching losses, and correlation. The following radio communication setup is considered: two lambda/4-monopole ground-plane transmit antennas, a single receive antenna, 4QAM modulation, Alamouti space-time coding, uncoded single carrier transmission at 2.4 GHz, indoor scenario. By measurements, the impact of very low transmit antenna spacing on the average uncoded BER over transmit-power performance of such a radio link, therefore accounting for all losses in the transmission chain, is examined. The common belief that multiple transmit antennas have to be placed far apart cannot be confirmed     

空时码在Nakagami衰落信道下性能分析

基于Alamouti提出的BPSK调制下空时分组码在Rayleigh衰落信道中的简单分集方案。推导出多发射和多接收天线系统中正交空时分组码在Nakagami衰落信道的BPSK调制下的比特差错率的最小距离球界,并推广到在高阶调制下衰落信道中系统符号差错率的性能。仿真分析和比较了空时分组码的多天线系统中发射和接收天线分集增益,以及信道相关参数的变化对系统误比特性能的影响。     

Single-carrier space-time block-coded transmissions over frequency-selective fading channels

We study space-time block coding for single-carrier block transmissions over frequency-selective multipath fading channels. We propose novel transmission schemes that achieve a maximum diversity of order N/sub t/N/sub r/(L+1) in rich scattering environments, where N/sub t/ (N/sub r/) is the number of transmit (receive) antennas, and L is the order of the finite impulse response (FIR) channels. We show that linear receiver processing collects full antenna diversity, while the overall complexity remains comparable to that of single-antenna transmissions over frequency-selective channels. We develop transmissions enabling maximum-likelihood optimal decoding based on Viterbi's ( 1998) algorithm, as well as turbo decoding. With single receive and two transmit antennas, the proposed transmission format is capacity achieving. Simulation results demonstrate that joint exploitation of space-multipath diversity leads to significantly improved performance in the presence of frequency-selective fading channels.     

Space-time block-coded OFDMA with linear precoding for multirateservices

Relying on space-time linearly precoded orthogonal frequency-division multiple access (OFDMA) and exploiting both transmit and receive antenna diversity, we design herein multirate transceivers that guarantee deterministic symbol recovery with diversity gains regardless of the (possibly unknown) frequency-selective finite impulse response (FIR) channels and multiuser interference. Our approach is based on a three-level design of user codes: the top level (based on OFDMA) handles multiuser interference, the middle level (based on space-time block coding) results in space-time diversity gains, and the lower level (based on linear precoding) mitigates intersymbol interference (ISI). In a multiuser/multirate setting, with two transmit and a single receive antenna, our designs achieve guaranteed diversity gains, whereas the use of two receive antennas could potentially double the capacity of the system (in terms of maximum number of users or achievable transmission rates) under favorable conditions (such as no frequency offset). Simulations illustrate the merits of our approach     

Space-time coding in mobile Satellite communications using dual-polarized channels

The use of dual-orthogonal polarization (horizontal/vertical or circular right-hand/left-hand polarizations) can increase the rate of transmission of satellite communication systems by a factor of two. However, the cross polar discriminations (XPDs) of the satellite and earth station antennas may be large enough to severely interfere between the two polarizations. In this paper, we investigate the use of space-time coding techniques in satellite-land mobile systems using dual-polarized transmit and receive antennas. In particular, we show that we can achieve significant gains by using layered space-time coding concepts and iterative detection and decoding receivers in communications systems employing polarization diversity channels in the presence of line-of-sight components.     

Multiuser Interference Cancellation and Detection for Users with More Than Two Transmit Antennas

We consider J transmitter units each equipped with N transmit antennas over wireless Rayleigh fading channels. Previously in [1], it was proved that when each transmitter unit has TV transmit antennas, using (J - 1)N + r receive antennas for any r ges 1, the receiver can completely separate the signals of J users. The provided diversity to each user was shown to be Nr if the units employ space-time trellis codes even if the units transmit asynchronously. Here, we consider the case when all units are synchronized and employ quasi-orthogonal space-time block codes (N > 2). It is proved that in this case a receiver with J + r - 1 antennas with r ges 1 can separate the transmitted signals of all units and provide each unit with a diversity order of Nr. Based on our interference cancellation technique, we then offer an array processing scheme which provides trade-off between diversity and spatial multiplexing. It is shown via simulations that this array processing scheme performs better than well-known modulation schemes, e.g. space-time block codes and BLAST, for a moderate number of receive antennas.     

Equalization concepts for Alamouti's space-time block code

In this paper, we develop receiver concepts for transmission with space-time block codes (STBCs) over frequency-selective fading channels. The focus lies on Alamouti's space-time block-coding scheme, but the results may be generalized to other STBCs as well. We show that a straightforward combination of conventional equalizers and a space-time block decoder is only possible if at least as many receive antennas as transmit antennas are employed, but not for the practically interesting case of pure transmit diversity, for which space-time coding had been originally developed. This restriction is circumvented by our approach. Here, the structural properties of the transmit signal of space-time block coding, which is shown to be improper (rotationally variant), are fully used. For this, equalizers with widely linear (WL) processing are designed, such as a WL equalizer, a decision-feedback equalizer with WL feedforward and feedback filtering, and a delayed decision-feedback sequence estimator with WL prefiltering. Simulation results demonstrate that the proposed concepts may be successfully employed in an enhanced data rates for GSM evolution (EDGE) receiver, especially for pure transmit diversity. Here, significant gains can be observed, compared with a conventional single-input single-output transmission.     

Khatri-Rao space-time codes

Space-time (ST) coding techniques exploit the spatial diversity afforded by multiple transmit and receive antennas to achieve reliable transmission in scattering-rich environments. ST block codes are capable of realizing full diversity and spatial coding gains at relatively low rates; ST trellis codes can achieve better rate-diversity tradeoffs at the cost of high complexity. On the other hand, V-BLAST supports high rates but has no built-in spatial coding and does not work well with fewer receive than transmit antennas. We propose a novel linear block coding scheme based on the Khatri-Rao matrix product. The proposed scheme offers flexibility for achieving full-rate or full-diversity, or a desired rate-diversity tradeoff, and it can handle any transmit/receive antenna configuration or signal constellation. The proposed codes are shown to have numerous desirable properties, including guaranteed unique linear decodability, built-in blind channel identifiability, and efficient near-maximum likelihood decoding.     

Space-time codes for high data rate wireless communication:performance criterion and code construction

We consider the design of channel codes for improving the data rate and/or the reliability of communications over fading channels using multiple transmit antennas. Data is encoded by a channel code and the encoded data is split into n streams that are simultaneously transmitted using n transmit antennas. The received signal at each receive antenna is a linear superposition of the n transmitted signals perturbed by noise. We derive performance criteria for designing such codes under the assumption that the fading is slow and frequency nonselective. Performance is shown to be determined by matrices constructed from pairs of distinct code sequences. The minimum rank among these matrices quantifies the diversity gain, while the minimum determinant of these matrices quantifies the coding gain. The results are then extended to fast fading channels. The design criteria are used to design trellis codes for high data rate wireless communication. The encoding/decoding complexity of these codes is comparable to trellis codes employed in practice over Gaussian channels. The codes constructed here provide the best tradeoff between data rate, diversity advantage, and trellis complexity. Simulation results are provided for 4 and 8 PSK signal sets with data rates of 2 and 3 bits/symbol, demonstrating excellent performance that is within 2-3 dB of the outage capacity for these channels using only 64 state encoders