We present multiuser space-time receiver algorithms for synchronization, channel estimation, and data detection in the downlink of a universal mobile telecommunications system (UMTS)/time-division duplex (TDD) cellular communication system with multiple receive antennas. These algorithms were designed for use in a network monitoring device that analyzes the interference situation present, thereby allowing the operators to improve their networks. For interference analysis, we decode the broadcast channels (BCHs) of surrounding base stations. To cope with the widely differing power levels of signals received from different base stations, we combine multiuser space-time signal processing techniques with reestimation and successive cancellation schemes. Simulation results demonstrate that our algorithms enable reliable BCH data detection even at low SINR.

A space-time detection algorithm for a UMTS/TDD downlink scenario with strong interference is proposed. Conventional space-time detection schemes based on MMSE equalization require accurate estimation of the correlation matrix of the received signal vector, which is difficult because of the time variation of the mobile radio channel. We thus develop a decision feedback detection scheme in which the correlation matrix is "detected" rather than estimated. For detection of the active data channels, a maximal invariant detection statistic is presented. Simulation results demonstrate that the proposed space-time detection algorithm features good performance for various realistic propagation scenarios even at low SINR.

We present space-time methods for channel estimation in the downlink of a UMTS/TDD system. The channels associated to all base stations near the mobile receiver are estimated by a multiuser, multi-antenna technique. We develop a minimum mean-square error (MMSE) channel estimator that incorporates midamble detections/estimation and least-squares channel estimation as preparatory stages. Combination of this MMSE channel estimator with a successive interference cancellation scheme allows to cope with strong co-channel interference. Simulation results indicate the good performance of our space-time channel estimator for various realistic propagation scenarios.

This paper presents methods for synchronization In the downlink of a UMTS/TDD system. Space-time processing based on multiple receive antennas is used to suppress potentially strong co-channel interference caused by other base stations. We develop a detection-based synchronization procedure exploiting the structure of UMTS/TDD, and we present three alternative detection algorithms. Simulation results using various propagation scenarios indicate the good performance of our synchronization methods in the presence of strong co-channel interference.

We investigate various array combining algorithms considering the special requirements of the UTRA/FDD uplink. After formulating the algorithms, we assess their performance in a modified vehicular B channel that is spatially inhomogeneous. The bit error ratios in different situations are presented together with some considerations about the computational complexity of the used methods. From bit error performance and required effort, we conclude that the minimum mean squared error (MMSE) algorithm with reduced complexity is the most suitable method for a real operating system.

We propose a semi-blind algorithm for smart antennas that, in addition to some structural signal properties, utilises user identifiers that are available in existing cellular systems. Our algorithm estimates, first, the row span of the adequately composed data matrix and then projects the obtained basis vectors iteratively to the finite alphabet (FA) constellation. We call the projection part of our algorithm DILSF (decoupled iterative least-squares with subspace fitting). Assuming two co-channel users in a GSM-like TDMA system and a Rayleigh fading channel with finite angular spread, we obtained a BER<10/sup -3/ with only 3 antennas, spaced 10/spl lambda/ apart. We also demonstrate that co-channel signals are resolvable even if they are not separable in angle. We gain a factor of up to 70 in computational complexity by employing subspace tracking algorithms and demonstrate the robustness of the method against array imperfections.