Alamouti proposed a very attractive transmit diversity technique which ensures orthogonality across two transmit antennas. This technique alone, however, offers no coding gain. In this work, powerful binary turbo codes are combined with Alamouti's diversity technique to achieve a coding gain on top of the diversity gain. Performance analysis on the combined scheme is presented and optimum turbo codes with transmit diversity on fading channels are proposed. Simulation results are shown to illustrate the improvement this scheme can offer.

This letter proposes recursive space-time TCM with two transmit antennas. A recursive component code is crucial in a serial or parallel concatenation scheme. These codes were obtained through computer search and their performance was simulated and compared with previously known codes.

We propose a method to represent non-binary error patterns for Reed-Solomon codes using a trellis. All error patterns are sorted according to their Euclidean distances from the received vector. The decoder searches through the trellis until it finds a codeword. This results in a soft-decision maximum likelihood algorithm with lower complexity compared to other known MLD methods. The proposed MLD algorithm is subsequently modified to further simplify complexity, reflecting in a slight reduction in the error performance.

A generalized algorithm for designing an optimum VQ source codec in systems with channel coding is presented. Based on an AWGN channel model, the algorithm derives the distribution of the channel decoder soft-output and substitutes it in the expression for the system end-to-end distortion. The VQ encoder/decoder pair is then optimized by minimizing this end-to-end distortion. For a Gauss-Markov source, the proposed algorithm outperforms the conventional SOVQ source coding scheme by 5.0 dB in the decoded source SNR. Application of this algorithm for designing optimum low-bit-rate speech codec is given. A 4.0 kbps VQ based CELP codec is designed for performance evaluations, where all the CELP parameter encoder/decoder pairs are optimized by minimizing their end-to-end distortions, respectively. As a result, the speech distortion over the noisy channel is minimized. Subjective tests show that the proposed algorithm improves the decoded speech quality by 2.5 MOS relative to a regular SOVQ CELP speech coding system. The performances of the algorithm under channel mismatch conditions are also shown and discussed.

This paper gives an overview of Turbo codes principles, performance, and design issues for practical application. As fundamentals of Turbo codes, encoder structure, interleaver, and iterative decoding are explained. The performance is analyzed through their weight distribution, and the analysis gives code design rules for component codes. Practical decoding algorithms are presented in addition to MAP algorithm. Design issues are discussed for mobile communications as an example of practical application. Finally, research trends are briefly mentioned.

Channel estimation is one of the key technologies in mobile communications. Channel estimation is critical in providing high data rate services and to overcome fast fading in very high-speed mobile communications. This paper presents a novel channel estimation based on hybrid spreading of I and Q signals (CEHS). Simulation results show that it can effectively mitigate the influence of fast fading and enable to provide high data rates for very high speed mobile systems.