Space-time Turbo Codes Research Articles

An Expurgated Union Bound of Punctured Space-Time Turbo Codes

This paper presents a new technique to obtain an expurgated union bound on the frame error rate of punctured space-time turbo codes (STTuC) in quasi-static Rayleigh fading channels. The STTuC scheme is composed of two component space-time trellis encoders connected in parallel via an interleaver. An adjacent matrix of an augmented state diagram is defined which allows the enumeration of each punctured component encoder. The distance spectrum of the STTuC is then obtained using the concept of uniform interleaver. A method to identify the dominant error events is proposed and an expurgated union bound on the frame error rate of STTuC schemes is computed using these dominant error events. Comparisons with simulated results reveal that the expurgated union bound is tight for codes with different construction criteria for a wide range of signal to noise ratio.

Implementation of Space-Time Turbo Coded MC-CDMA Systems

In this paper, the performances of space-time turbo-code (STTuC) and space-time trellis code (STTC) in conjunction with multi-carrier code-division multiple-access (MC-CDMA) systems are evaluated. The minimum mean-square error (MMSE) detection technique is used with multiple input multiple output (MIMO) antenna diversity in quasi static fading channel. The symbol error rate (SER) is obtained using simulation by employing maximum a posteriori (MAP) decoding technique for turbo code and Viterbi algorithm for trellis code system. It is observed that the STTuC-MC-CDMA system performs better then STTC-MC-CDMA system. It is also noted that by increasing the number of iterations the performance gain can be increased up to a certain limit. On the other hand, this improvement in performance comes at the cost of increased computational complexity.

Performance Analysis of MIMOOFDM System using Spacetime Turbo Codes and Adaptive Beamforming

paper aims at performance analysis of the system which uses space-time turbo codes combined with adaptive beamforming for multiple transmits and receives antennas based orthogonal frequency division multiplexing (OFDM) system. The performance of the proposed technique is tested for two adaptive beamforming algorithms LMS & LLMS. Simulation results demonstrate that the proposed system not only has good ability of suppressing interference, but also significantly improves the bit-error rate (BER) performance of the system. Experimental results show that an adaptive beamforming gives the optimum performance on AWGN channels. This system will also be optimum on fading channels when combined with space-time turbo codes.

Efficient High-Performance Decoding for Overloaded MIMO Antenna Systems

The practical challenge of capacity-achieving forward error-correcting codes (e.g., space-time turbo codes) is overcoming the tremendous complexity associated by their optimal joint maximum-likelihood (ML) decoding. For this reason, iterative soft decoding has been studied to approach the optimal ML decoding performance at affordable complexity. In multiple-input multiple-output (MIMO) channels, a judicious decoding strategy consists of two stages: 1) estimate the soft bits using list version of sphere decoding or its variants, and 2) update the soft bits through iterative soft decoding. A promising MIMO decoder is required to produce reliable soft-bit estimates at the first stage before iterative soft decoding is performed. In this paper, we focus on the overloaded (or fat) MIMO antenna systems where the number of receive antennas is less than the number of signals multiplexed in the spatial domain. In this scenario, the original form of sphere decoding is inherently not applicable and our aim is to generalize sphere decoding geometrically to cope with overloaded detection. The so-called slab-sphere decoding (SSD) proposed guarantees to obtain exact-ML hard detection while reducing complexity greatly. With the list-version of SSD, (his paper proposes an efficient MIMO soft decoder, which can generate reliable soft-bit estimates at affordable complexity as inputs for iterative soft decoding for promising performance. A case study in the IEEE 802.16 settings is carried out for performance evaluation

Transmit Delay Structure Design for Blind Channel Estimation over Multipath Channels

Wireless communications often exploit guard intervals between data blocks to reduce interblock interference in frequency-selective fading channels. Here we propose a dual-branch transmission scheme that utilizes guard intervals for blind channel estimation and equalization. Unlike existing transmit diversity schemes, in which different antennas transmit delayed, zero-padded, or time-reversed versions of the same signal, in the proposed transmission scheme, each antenna transmits an independent data stream. It is shown that for systems with two transmit antennas and one receive antenna, as in the case of one transmit antenna and two receive antennas, blind channel estimation and equalization can be carried out based only on the second-order statistics of symbol-rate sampled channel output. The proposed approach involves no preequalization and has no limitations on channel-zero locations. Moreover, extension of the proposed scheme to systems with multiple receive antennas and/or more than two transmit antennas is discussed. It is also shown that in combination with the threaded layered space-time (TST) architecture and turbo coding, significant improvement can be achieved in the overall system performance.

Low-density parity-check codes for space-time wireless transmission

Irregular low-density parity-check (LDPC) codes have shown exceptionally good performance for single antenna systems over a wide class of channels. In this paper, we investigate their application to multiple antenna systems in flat Rayleigh fading channels. For small transmit arrays, we focus mainly on space-time coding with 2/sup p/-ary LDPC codes, where p equals the number of encoded bits transmitted by the transmit antenna array during each signaling interval. For large transmit arrays, we study a layered space-time architecture using binary LDPC codes as component codes of each layer: We show through simulation that, when applied to multiple antenna systems with high diversity order, LDPC codes of quasi-regular construction are able to achieve higher coding gain and/or diversity gain than previously proposed space-time trellis codes, space-time turbo codes, and convolutional codes in a number of fading conditions. Extending the work of density evolution with Gaussian approximation, we study 2/sup p/-ary LDPC codes on multiple antenna fading channels, and search for the optimum 2/sup p/-ary quasi-regular codes in quasi-static fading. We also show that on fast fading channels, 2/sup p/-ary irregular LDPC codes, though designed for static channels, have superior performance to nonbinary quasiregular codes and binary irregular codes specifically designed for fast fading channels.

Study of energy and performance of space-time decoding systems in concatenation with turbo decoding

Recent studies have shown that using space-time code is an effective approach to increase the data rate over wireless channels. Space-time turbo (ST-Turbo) codes formed by concatenating space-time codes with turbo codes, take advantage of both the high diversity order of space-time systems and the randomness of the turbo codes. In this paper, we compare two ST-Turbo codes, i.e., simple space-time turbo codes (SiSTT) and turbo trellis-coded modulation space-time block codes (TTCM-STBCs), and their approximate versions with respect to performance and energy consumption for both general-purpose processor and synthesized implementations. The approximations are aimed at reducing the computational complexity and include reduction in the number of paths, number of iterations, and datapath computations. Analysis of the simulation results show that SiSTT-based versions should be used for higher SNR applications where low energy consumption is the primary design objective, and TTCM-STBC-based versions should be used where performance is the primary design objective. Finally, four ST-Turbo algorithms (i.e., baseline SiSTT and its energy-efficient approximate version and the baseline TTCM-STBC and its energy-efficient approximate version) have been synthesized in 0.18-/spl mu/m CMOS technology and the implementations compared with respect to area, power, and latency.

Doubly Iterative Decoding of Space–Time Turbo Codes With a Large Number of Antennas

We examine the performance of a reduced-complexity doubly iterative decoder for space-time turbo codes on a quasi-static fading channel. The decoder works by using preliminary soft values of the coded symbols, obtained after a limited number of turbo iterations, to reduce the spatial interference from the received signal. Then, new turbo iterations are performed to improve on the quality of the soft values, and so on. Using a number of approximations, we obtain a receiver interface that achieves a good tradeoff between performance and complexity, and allows the use of turbo space-time codes for a large number of transmit and receive antennas.

Space-time codes with full antenna diversity using weighted nonbinary repeat-accumulate codes

Like turbo codes, repeat-accumulate codes have remarkably good performance when r/spl ges/3, where r is the number of repetition times. We present space-time codes with full antenna diversity using weighted nonbinary repeat-accumulate codes. Compared with the space-time turbo codes of Y. Liu et al. (see IEEE J. Select. Areas Commun., vol.19, p.969-80, 2001) and of H. Su and E. Geraniotis (see ibid., vol.49, p.47-57, 2001), the main advantage of this new scheme is to construct space-time codes with full diversity for any m/spl les/r and any length of frame without searching for interleavers, where m is the number of transmit antennas. These space-time codes have rate m/r and, so, have full rate when m=r. Furthermore, they have an efficient decoding based on the message passing algorithm.

Enhanced Multi-Antenna Technologies on OFDM for Future Mobile Communication Systems

Various types of multi-antenna techniques have been discussed to realize high speed data transmission in mobile communication systems. Those multiple antenna systems obtain space diversity gain by utilizing multi-paths as independent channels from transmitter and receiver. One important issue to utilize the powerful diversity gains of those multi-antenna technologies is how to create independent channels between transmitter and receiver. Almost all of conventional multi-antenna technologies have been discussed with assuming that there is not any correlation among channels between transmitter and receiver. However in realistic world this assumption is not always true and the correlation among channels becomes very high. This high correlation drastically degrades the performance of those multi-antenna technologies. In this paper we present an enhanced transmission diversity method to solve the problem of high correlation among channels. The following contents of this paper mainly focus on the Space Time Turbo Coding in OFDM systems, however the concept of the presented method can be adopted in various types of multi-antenna systems.

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: code design and decoding

Turbo-codes are by now well-known as a computationally-feasible coding scheme able to attain capacities very close to the Shannon bound for the scalar (single-input, single-output) channel. Recently it has been shown that much greater capacities are possible on wireless MIMO (multiple-input, multiple-output) channels, attained by means of space-time codes. The proposed paper will review the application of turbo-codes to these channels, proposing an encoding scheme, together with criteria for optimum performance and decoding techniques based on the iterative decoding algorithm used conventionally for turbo-codes. Performance competitive with other published schemes is attained.

Space-Time Turbo Coded Modulation: Design and Applications

A design method for recursive space-time trellis codes and parallel-concatenated space-time turbo coded modulation is proposed that can be applied to an arbitrary existing space-time trellis code. The method enables a large, systematic increase in coding gain while preserving the maximum transmit diversity gain and bandwidth efficiency property of the considered space-time trellis code. Applying the above method to Tarokh et al. space-time trellis codes, significant performance improvements can be obtained even with extremely short input information frames. The application of space-time turbo coded modulation to the space-frequency domain is also proposed in this paper. Exploiting the bandwidth efficient orthogonal frequency division modulation (OFDM), multiple transmit antennas and large frequency selectivity offered by typical low mobility indoor environments, the proposed space-frequency turbo coded modulation performs within 2.5 dB of the outage capacity for a variety of practical wideband multiple-input multiple-output (MIMO) radio channels.

Full rate space-time turbo codes

This paper proposes a class of full space diversity full rate space-time turbo codes. Both parallel concatenated and serially concatenated codes are designed. A rank theory proposed by the authors earlier is employed to check the full space diversity of the codes. The simulations show that the space-time turbo codes can take full advantage of space diversity and time diversity if they are available in the channels. We also study the robustness of performance of both turbo codes and trellis codes in space-time correlated fading channels.

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/sup -5/ bit-error rate and 10/sup -3/ frame-error rate can be achieved at less than 6-dB E/sub b//N/sub 0/ 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.