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A number of decoding schemes have recently been proposed to perform maximum-likelihood (ML) detection for multi-input-multi-output (MIMO) systems. In this paper, employing a 'breadth-first' search algorithm for closet points in a lattice, we propose a novel ML decoding scheme called the breadth-first signal decoder (BSIDE). Through analysis and computer simulations, it is shown that the BSIDE has the same bit-error-rate performance as the conventional ML decoders while allowing significantly lower computational complexity. In addition, we introduce a simple tuning scheme that allows the BSIDE to have a performance--complexity tradeoff capability as necessary. Index Terms--Breadth-first searching, maximum-likelihood (ML) detection, multi-input-multi-output (MIMO) systems, sphere decoder (SD).

In this paper, the detection of weak signals in additive noise described by the first-order moving average (FOMA) of an impulsive process is considered. Specifically, decision regions of the maximum likelihood (ML) and suboptimum ML (S-ML) detectors are derived in the FOMA noise model, and specific examples of the ML and S-ML decision regions are obtained. The ML and S-ML detectors are employed in the antipodal signaling system and compared in terms of bit error rate in an impulsive noise environment. Numerical results show that the S-ML detector, despite its reduced complexity and simpler structure, exhibits practically the same performance as the optimum ML detector. It is also observed that the performance gap between detectors for FOMA and independent and identically distributed noise becomes larger as the degree of noise impulsiveness increases. Index Terms--Dependent noise, detection, first-order moving average (FOMA), impulsive noise, suboptimum scheme, weak signal.

A truncated adaptive transmission scheme for the hybrid multicarrier CDMA/FDM system is considered in forward link. In the proposed scheme, a data substream is transmitted over the subchannels of which the channel gains are greater than a given threshold, based on the feedback information from the mobile station. We analyze the performance of the proposed system when orthogonal and random signature sequences are used in single- and multiple-cell environment. In the single-cell environment, when orthogonal signature sequences are used, the proposed scheme outperforms the adaptive FH/DS system as well as the conventional MC DS/CDMA system, and accommodates more users than the adaptive FH/DS system while maintaining the orthogonality between users. In the multiple-cell environment also, the proposed scheme has better performance characteristics than the adaptive FH/DS system when orthogonal or random codes are used as spreading sequences. Index Terms--Adaptive transmission, code division multiple access (CDMA), FDM, multicarrier, truncation.

In this paper, a fast acquisition scheme of pseudonoise (PN) sequences for direct-sequence spread-spectrum systems is proposed. The scheme exploits a new decision logic not only to estimate chip values, but also to check the reliability of the chip estimates. As a result, the internal state of a PN sequence generator is estimated more accurately. We derive the probability of finding a correct state estimate and show that the proposed scheme can reduce the average number of chips for acquisition when compared with the conventional scheme. It is also shown that the performance improvement is more noticeable in the moderate signal-to-noise-ratio range. Index Terms--Direct-sequence spread spectrum (DS/SS), pseudonoise (PN) sequence, code acquisition, sequential estimation.

In this paper, analysis of an adaptive rate convolutionally coded multicarrier direct sequence code division multiple-access (DS/CDMA) system is considered. In order to accommodate a number of coding rates easily and make the encoder and decoder structure simple, we use the rate-compatible punctured convolutional (RCPC) code. We obtain data throughputs at several coding rates, and choose the coding rate that has the highest data throughput in the signal-to-interference and noise ratio (SINR) sense. To achieve maximum data throughput, a rate adaptive system is proposed based on the channel state information (the SINR estimate). The SINR estimate is obtained by the soft decision Viterbi decoding metric. We show that the proposed rate adaptive convolutionally coded multicarrier DS/CDMA system can enhance spectral efficiency and provide frequency diversity. Index Terms--Multicarrier direct sequence code division multiple-access (DS/CDMA), rate adaptive system.