Uppsala universitet

Reduced-rank Channel Estimation and Tracking in Time-slotted CDMA Systems.

Monica Nicoli, Politecnico di Milano, Mikael Sternad, UU
Umberto Spagnolini, Politecnico di Milano, and Anders Ahlén , UU

IEEE International Conference on Communications, ICC 2002 New York, USA, April 28-May 2, 2002, pp. 533-537.   © IEEE

Multiuser detectors that combine signals from multiple antennas or radio access points are powerful tools in CDMA systems. Since the number of parameters to be estimated grows with the number of antennas, we need to make best use of the limited amount of training data available.

We propose a method that reduces the number of parameters required to estimate the channel and also extends the training set by using detected symbols. These two tools are combined in a method of reasonable computational complexity, that also allows the tracking of the temporal variability within time slots caused by rapidly moving mobiles.

This paper investigates the estimation and tracking of time varying propagation channels in the uplink of a time slotted CDMA system. An antenna array is present at the base station. Both the channel estimation and tracking are performed by exploiting the low-rank nature of the channel matrix. The accuracy of the estimate is improved by using a multi-slot approach: the slowly varying component of the low-rank channel is estimated from the observation of successive midambles (inter-slot tracking), while the fast varying component is updated over the burst interval in decision-direced mode (intra-slot tracking).

Related publications:
Tracking algorithms of low complexity,
Reduced-rank channel estimation, method by Erik Lindskog and Claes Tidestav, IEEE VTC'99.

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