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The problem of pilot and data channel mismatch in a steered space-time spreading (SSTS) system is addressed by means of advanced signal processing at the mobile receiver. The main idea is to apply the SSTS antenna array architecture and transmission algorithm and involve both the pilot and traffic signals in channel estimation at the receiver. Two semiblind algorithms are compared with the conventional pilot-based receiver in a CDMA2000-1X RC3 environment by means of simulations with variable speed and spatial angular spread, taking into account main imperfections such as estimation error for the correlation coefficient at the reverse link, calibration error, and different pilot powers for diversity antennas. It is demonstrated that the semiblind algorithms outperform the conventional receiver in the low- and medium-speed area. Index Terms--Alamouti coding, beamforming, semiblind channel estimation, space-time coding, steered space-time spreading, transmit diversity.

Various advances in multiple input, multiple output (MIMO) networks are presented that are designed to make reconfigurable operation possible in the context of a Universal Mobile Telecommunications System (UMTS) network environment. The problem of robust/reconfigurable operation with respect to channel correlation having a significant effect on the performance of MIMO links is mainly focused.

The problem of unsupervised (blind) space-time equalization of frequency-selective multiple-input multiple-output (MIMO) channels are discussed. A family of globally convergent blind space-time equalization techniques developed from multi-user kurtosis output-based criteria is given and explained.

Multiple-access interference is one of the major impediments in the reverse link of code-division multiple-access (CDMA) systems, due to the synergy of the users' spreading codes, transmission delays, and the channel characteristics. A space--time dynamic signature-assignment (DSA) algorithm was briefly described by the authors in a previous paper. In this paper, we further elaborate on the space-time DSA approach and its receiver structure for the reverse link of direct-sequence (DS)-CDMA systems using multiple antennas at the receiver. The space-time DSA dynamically assigns the users' spreading codes and transmission delays, i.e., to assign the user signatures, in order to minimize mutual crosscorrelations. In assigning the signatures, the DSA adopts a low-complexity iterative algorithm which utilizes channel information and aims to maximize the signal-to-interference-plus-noise ratio of the poorest performing user at the base station. Analytic results as well as further simulation results are provided to support our arguments. Index Terms--Direct-sequence code-division multiple access (DS-CDMA), interference avoidance, multiple-input/multiple-output (MIMO) systems.

In this letter, we show that the performance of recently proposed quasi-orthogonal space--time codes can be improved by phase-shifting the constellations of the symbols constituting the code. The optimal rotation of the symbols increases the minimum distance of the corresponding space-time codewords, leading to substantially improved performance. Index Terms--Diversity, multiple antennas, space--time codes, wireless communications.

The design of space--time codes that are capable of approaching the capacity of multiple-input-single-output (MISO) antenna systems is a challenging problem, yet one of high practical importance. While a remarkably simple scheme of Alamouti is capable of attaining the channel capacity in the case of two-transmitter and one-receiver antennas (2, 1), no such schemes are known for the case of more than two transmitter antennas. In this correspondence, we propose a family of space-time codes that are especially designed for the case of four-transmitter antennas (1) and that are shown to allow the attainment of a significant fraction of the open-loop Shannon capacity of the (4, 1) channel. Index Terms--Capacity of wireless links, multiple-input-multiple-output (MIMO) systems, smart antennas, space-time codes, space-time processing, transmit diversity.

Recent results in information theory have demonstrated the enormous potential of wireless communication systems with antenna arrays at both the transmitter and receiver. To exploit this potential, a number of layered space-time architectures have been proposed. These layered space-time systems transmit parallel data streams, simultaneously and on the same frequency, in a multiple-input multiple-output fashion. With rich multipath propagation, these different streams can be separated at the receiver because of their distinct spatial signatures. However, the analysis of these techniques presented thus far had mostly been strictly narrowband. In order to enable high-data-rate applications, it might be necessary to utilize signals whose bandwidth exceeds the coherence bandwidth of the channel, which brings in the issue of frequency selectivity. In this paper, we present a class of layered space--time receivers devised for frequency-selective channels. These new receivers, which offer various performance and complexity tradeoffs, are compared and evaluated in the context of a typical urban channel with excellent results. Index Terms--Adaptive antennas, BLAST, equalization, frequency selectivity, interference cancellation, layered architectures, MIMO, space-time processing.

The normalized stochastic gradient algorithms for blind linear equalization (BE) of quadrature amplitude modulation systems help in the formulation of the constant modulus (CM) and the decision-directed (DD) separation principles. These CM and DD principles, with the help of the classical adaptive filtering algorithms, lead to a family of CM or DD BE algorithms. These algorithms offer high convergence speed and ability to avoid convergence problems. Algorithms obtained with the help of the affine projection adaptive filtering algorithm are presented.

An algorithm for blind source separation is introduced, that is free of undesired stationary points in arbitrary number of user signals, is proposed.

The problem of linear equalization of polyphase channels and its blind implementation were examined. The channels may result from oversampling the single output of a transmission circuit and/or by receiving multiple outputs of an antenna array. Optimal settings of different well-known types of linear equalization structures were derived blindly using only the output's second-order statistics via multichannel linear prediction or related methods.