Space-time Coding Systems Research Articles

Performance Comparison of Detection Methods for Combined STBC and SM Systems

This paper considers detection schemes for the combined space-time block coding and spatial multiplexing (STBC-SM) transmission systems. We propose a symbol detection scheme which allows to extend the limit on the number of transmit antennas imposed by the previous group detection scheme. The proposed scheme allows to double multiplexing gain as well as provides better bit error rate (BER) performance over the group detection scheme. It is shown that the proposed QR-SIC (combined QR-decomposition and successive interference cancellation) symbol detector provides good trade-off between the BER and computational complexity performance and, thus, is the most suitable detector for the combined STBC-SM system.

Performance of Transmit and Receive Antenna Selection in the Presence of Channel Estimation Errors

This letter considers the effect of channel estimation errors on the performance of space-time coded (STC) systems with transmit and receive antenna selection over quasi-static flat fading channels. By performing pairwise error probability analysis and presenting numerical examples, we show that the diversity order achieved with perfect channel state information (CSI) is still achievable with imperfect CSI used both at the antenna selection and the space-time decoding processes. We note that our results apply to general STC systems with both transmit and/or receive antenna selection based on largest received powers which can be estimated by any channel estimator.

Performance of Transmit and Receive Antenna Selection in the Presence of Channel Estimation Errors

This letter considers the effect of channel estimation errors on the performance of space-time coded (STC) systems with transmit and receive antenna selection over quasi-static flat fading channels. By performing pairwise error probability analysis and presenting numerical examples, we show that the diversity order achieved with perfect channel state information (CSI) is still achievable with imperfect CSI used both at the antenna selection and the space-time decoding processes. We note that our results apply to general STC systems with both transmit and/or receive antenna selection based on largest received powers which can be estimated by any channel estimator.

Space-Time Coded Systems using Continuous Phase Modulation

We develop space-time trellis coded (STC) schemes using continuous-phase modulation (CPM). We employ the Rimoldi model of CPM to create a decomposed model of STC-CPM. The decomposition separates the coding from the modulation. The space-time encoding and the inherent CPM encoding is combined into a single trellis encoder on the ring of integers modulo-. This is followed by a bank of memoryless modulators. The model allows the search for good space-time codes to take into account the inherent encoding of the modulation.

Improved information outage rate in certain MIMO systems

We propose a simple class of encoding/decoding techniques that can be used to improve the information outage rate of certain multiple-input-multiple-output (MIMO) systems. Gains in outage rate can be achieved at low to moderate signal-to-noise ratios in MIMO systems that have fewer receive antennas than transmit antennas. This performance improvement is due to extra "virtual" receive antennas that are created with low-complexity signal processing. A simple space-time block code system using virtual receive antennas is also investigated

Wireless OFDM systems with multiple transmit and receive antennas with bit-interleaved coded modulation

It has recently been shown that the capacity for multi-antenna dispersive radio channels is considerably higher than single receive and transmit antenna systems. In this article we demonstrate that high data rates can be achieved at low power levels for systems where the number of transmit antennas is typically larger than the number of receive antennas. We use bitinterleaved coded modulation, iterative decoding, and OFDM system building blocks for a flexible class of space-time coding systems where it is easy to change convolutional code rate, constellation size, and the number of transmit and receive antennas for designing systems with a wide range of capabilities. The coding is typically done in the time, frequency, and space domains. The gain can be used for either high data rates and/or lower power levels. Applications can be found in future wireless LANs and/or B3G and 4G wireless cellular systems.

Interference suppressing for cellular MIMO system based on turbo receiver

Space-Time Coding (STC), which combines channel coding, modulation, and multiple transmit antennas, is a powerful scheme to achieve higher data rates and combat fading in wireless systems. In this paper, we propose a soft/cancellation turbo equalization scheme to suppress Co-Channel Interference (CCI) in STC systems. The simulation results show that the proposed method significantly improves the system’s ability of interference suppression, while preserving the space-time structure.

On the performance of distributed space-time coding systems with one and two non-regenerative relays

Spatial diversity can be induced by using wireless relay stations, which cooperate by amplifying and retransmitting the information received from a source to a destination station. In this context we propose a distributed space-time coding (DSTC) system based on the Alamouti codes. We characterize the symbol error rate of systems with one and two non-regenerative relays using bounds and high signal-to-noise ratio (SNR) approximations. The asymptotic (high SNR) symbol error probability formulas are used to optimize the power allocation in the DSTC system. Furthermore, using the asymptotic symbol error probability formulas we argue that the DSTC system has at least 1.5 times the diversity achieved by point-to-point transmissions with the same bandwidth. Simulations show not only that the DSTC outperforms the amplify-and-forward cooperative system with orthogonal transmissions, but also convolutional encoded one-hop transmissions with the same information rate as the DSTC system. Assuming full channel knowledge at the source and the relays, we find an optimum cooperative system by minimizing the bit error rate of the DSTC system with one and two non-regenerative relays subject to fixed transmit energy constraints at each radio. Numerical results show that the DSTC system with two relays performs very close to the optimum cooperative system.

TCP performance over wireless MIMO channels with ARQ and packet combining

Multiple-input multiple-output (MIMO) wireless communication systems that employ multiple transmit and receive antennas can provide very high-rate data transmissions without increase in bandwidth or transmit power. For this reason, MIMO technologies are considered as a key ingredient in the next generation wireless systems, where provision of reliable data services for TCP/IP applications such as wireless multimedia or Internet is of extreme importance. However, while the performance of TCP has been extensively studied over different wireless links, little attention has been paid to the impact of MIMO systems on TCP. This paper provides an investigation on the performance of modern TCP systems when used over wireless channels that employ MIMO technologies. In particular, we focus on two representative categories of MIMO systems, namely, the BLAST systems and the space-time block coding (STBC) systems, and how the ARQ and packet combining techniques impact on the overall TCP performance. We show that, from the TCP throughput standpoint, a more reliable channel may be preferred over a higher spectral efficient but less reliable channel, especially under low SNR conditions. We also study the effect of antenna correlation on the TCP throughput under various conditions.

FIR zero-forcing equalizer for ISI MIMO channels using space-time modulated codes

Abstract-A systematic method for designing a finite-impulse response (FIR) zero-forcing equalizer (ZFE) of the space-time modulated code (STMC) system based on nonmaximally decimated filterbank is proposed. The physical channel considered is assumed to be multiple-input-multiple-output (MIMO) with intersymbol interference (ISI) and space-time correlated noise. STMC is a space-time block code (STBC) system. Most of the STMC systems require a long guard period to avoid interblock interference (IBI), but, with the proposed equalizer, the length of the guard period is greatly reduced. This can enhance the spectral efficiency of the STMC especially when the channel dispersion is large. The existence conditions for FIR ZFE of the STMC system were derived. These include the maximal code rate STMC for a given channel and the minimal filter order of the FIR ZFE. For a given STMC precoder, the equalizability of the system was verified. The solution of FIR ZFE of STMC was parameterized, which allows the design of optimal FIR ZFE through unconstrained optimization. It is further shown that FIR ZFE could be improved by adding a simple permutation in the system. Design examples and simulation results were presented to evaluate the proposed design method.

Direct semi-blind MMSE equalization for STBC

A semi-blind method for minimum mean square square error (MMSE) equalization of space-time block coding (STBC) systems is proposed. By exploiting information from the redundancy in the structure of STBC as well as from the training symbols, MMSE equalization can be achieved without channel estimation. Simulation results demonstrate the performance of the proposed algorithm compared to existing methods.

Symbol-timing estimation in space-time coding systems based on orthogonal training sequences

Space-time coding has received considerable interest recently as a simple transmit diversity technique for improving the capacity and data rate of a channel without bandwidth expansion. Most research in space-time coding, however, assumes that the symbol timing at the receiver is perfectly known. In practice, this has to be estimated with high accuracy. In this paper, a new symbol-timing estimator for space-time coding systems is proposed. It improves the conventional algorithm of Naguib et al. such that accurate timing estimates can be obtained even if the oversampling ratio is small. Analytical mean-square error (MSE) expressions are derived for the proposed estimator. Simulation and analytical results show that for a modest oversampling ratio (such as Q equal to four), the MSE of the proposed estimator is significantly smaller than that of the conventional algorithm. The effects of the number of transmit and receive antennas, the oversampling ratio, and the length of training sequence on the MSE are also examined.

Detection schemes for space-time block code and spatial multiplexing combined system

Space-time block code is combined with spatial multiplexing technique over multiple-input multiple-output system to take advantages of both schemes. The transmit antennas are divided into groups and each group transmits space-time coded blocks in parallel. At receiver side, three types of group receivers are proposed to separate the filtered version of the multiplexed space-time coded symbol blocks followed by space-time decoder. Error rate performances of the detection schemes are evaluated in correlated channels. The diversity order of the combined system is compared with that of the SM system and the STBC system.

Detection schemes for space-time block code and spatial multiplexing combined system

Space-time block code is combined with spatial multiplexing technique over multiple-input multiple-output system to take advantages of both schemes. The transmit antennas are divided into groups and each group transmits space-time coded blocks in parallel. At receiver side, three types of group receivers are proposed to separate the filtered version of the multiplexed space-time coded symbol blocks followed by space-time decoder. Error rate performances of the detection schemes are evaluated in correlated channels. The diversity order of the combined system is compared with that of the SM system and the STBC system.

Detection schemes for space-time block code and spatial multiplexing combined system

Space-time block code is combined with spatial multiplexing technique over multiple-input multiple-output system to take advantages of both schemes. The transmit antennas are divided into groups and each group transmits space-time coded blocks in parallel. At receiver side, three types of group receivers are proposed to separate the filtered version of the multiplexed space-time coded symbol blocks followed by space-time decoder. Error rate performances of the detection schemes are evaluated in correlated channels. The diversity order of the combined system is compared with that of the SM system and the STBC system.

Performance analysis of space-time coding with imperfect channel estimation

We analyze the error performance of a space-time coding system using N transmit and M receive antennas with imperfect channel estimation in flat Rayleigh fading. A least-squares estimate of the channel matrix is obtained by using a sequence of pilot code vectors. The estimate is found to be perturbed by an M/spl times/N perturbation matrix with zero-mean circular Gaussian entries. Using the characteristic function of the decision variable, we derive a closed-form expression for the pairwise error probability (PEP). From the same expression, the PEP in case of perfect channel estimation is also obtained. Numerical results show the degradation in performance due to imperfect channel estimation that can be compensated by increasing the number of receive antennas.

Maximum Likelihood Turbo Iterative Channel Estimation for Space-Time Coded Systems and Its Application to Radio Transmission in Subway Tunnels

This paper presents a novel channel estimation technique for space-time coded (STC) systems. It is based on applying the maximum likelihood (ML) principle not only over a known pilot sequence but also over the unknown symbols in a data frame. The resulting channel estimator gathers both the deterministic information corresponding to the pilot sequence and the statistical information, in terms of a posteriori probabilities, about the unknown symbols. The method is suitable for Turbo equalization schemes where those probabilities are computed with more and more precision at each iteration. Since the ML channel estimation problem does not have a closed-form solution, we employ the expectation-maximization (EM) algorithm in order to iteratively compute the ML estimate. The proposed channel estimator is first derived for a general time-dispersive MIMO channel and then is particularized to a realistic scenario consisting of a transmission system based on the global system mobile (GSM) standard performing in a subway tunnel. In this latter case, the channel is nondispersive but there exists controlled ISI introduced by the Gaussian minimum shift keying (GMSK) modulation format used in GSM. We demonstrate, using experimentally measured channels, that the training sequence length can be reduced from 26 bits as in the GSM standard to only 5 bits, thus achieving a 14% improvement in system throughput.

On maximum-likelihood detection and decoding for space-time coding systems

Space-time coding (STC) schemes for communication systems employing multiple transmit and receive antennas have been attracting increased attention. In this paper, we address two interrelated problems: detection of space-time codes under various interference conditions and information transfer from the STC detector to an error-correcting channel decoder. By taking a systematic maximum-likelihood (ML) approach to the joint detection and decoding problem, we show how to design optimal detectors and how to integrate them with a channel decoder. We also discuss various aspects of channel modeling for STC communication receivers. In particular, while many previous works on space-time coding assume that the channel is a stochastic quantity, we find that a deterministic channel model can have some advantages for the receiver design. Finally, we illustrate our results by numerical examples. Index Terms-Interference suppression, maximum-likelihood estimation, maximum-likelihood sequence detection, MIMO systems, space-time coding, soft information.

Joint Estimation and Decoding of Space-Time Trellis Codes

We explore the possibility of using an emerging tool in statistical signal processing, sequential importance sampling (SIS), for joint estimation and decoding of space-time trellis codes (STTC). First, we provide background on SIS, and then we discuss its application to space-time trellis code (STTC) systems. It is shown through simulations that SIS is suitable for joint estimation and decoding of STTC with time-varying flat-fading channels when phase ambiguity is avoided. We used a design criterion for STTCs and temporally correlated channels that combats phase ambiguity without pilot signaling. We have shown by simulations that the design is valid.

Iterative receivers for multiuser space-time coding systems

Space-time coding (STC) techniques, which combine antenna array signal processing and channel coding techniques, are very promising approaches to substantial capacity increase in wireless channels. Multiuser detection techniques are powerful signal processing methodologies for interference suppression in CDMA systems. In this paper, by drawing analogies between a synchronous CDMA system and an STC multiuser system, we study the applications of some multiuser detection methods to STC multiuser systems. Specifically, we show that the so-called "turbo multiuser detection" technique, which performs soft interference cancellation and decoding iteratively, can be applied to STC multiuser systems in flat-fading channels. An iterative multiuser receiver and its projection-based variants are developed for both the space-time block coding (STBC) system and the space-time trellis coding (STTC) system. During iterations, extrinsic information is computed and exchanged between a soft multiuser demodulator and a bank of MAP decoders, to achieve successively refined estimates of the users' signals. Computer simulations demonstrate that the proposed iterative receiver techniques provide significant performance improvement over conventional noniterative methods in both single-user and multiuser STC systems. Furthermore, the performance of the proposed iterative multiuser receiver approaches that of the iterative single-user receiver in both STBC and STTC systems.