Uppsala universitet

Spatio-Temporal Equalization for Multipath Environments in Mobile Radio Applications

Erik Lindskog, Anders Ahlén and Mikael Sternad

IEEE Vehicular Technology Conference,
Chicago, IL, July 26-28, 1995. © 1995 IEEE.

When digital data are transmitted over multipath radio channels, the use of base station receivers with multiple antenna elements can improve the performance significantly, if the measurements are combined in an appropriate way. The paper studies ways to perform this combination in TDMA systems. A key problem is that a large number of filter coefficients may have to be adjusted based on short training sequences.

Combined spatial and temporal equalization using an antenna array combined with a decision feedback equalization scheme is investigated. In particular a TDMA type system, with a relatively short training sequence, is considered.

Three algorithms are introduced. The first two algorithms are based on indirect schemes, where the channels to each receiver antenna element are identified. The identified channels and the correlations of the residuals are then used for the tuning of the beamformer/equalizer coefficients. The spatio-temporal correlations of the residuals are used in the first algorithm while in the second algorithm only the spatial correlations of the residuals are considered.

The third algorithm forms a number of beams by using mixtures of different delayed versions of the training sequence as reference signals. It then performs temporal equalization by combining the outputs from the different beamformers, with appropriate delays. This latter algorithm requires less computations for the tuning of the equalizer, at the expense of a performance degradation in general.

The algorithms are evaluated with simulations of multipath scenarios involving co-channel interference.

Related publications:
PhD Thesis by Erik Lindskog.
Licentiate Thesis by E Lindskog 1995, which includes the paper.
Conference paper in IEEE ICASSP'95, which investigates related algorithms.

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