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A novel channel estimation method is proposed for the uplink of a combined space-time UMTS system. The method is based on the periodic transmission of very short sequences of pilot bits on the DPCCH channels of each transmitter element of the MIMO system. The key feature is that the pilot bit sequence used for each transmitter element is orthogonal to those used by the other transmitter elements in order to provide the necessary information about each path. In the receiver, a dedicated channel estimator is used to descramble and despread the signals from the DPCCH channel of each receiver element of the MIMO receiver to recover the pilot signals. This information is then used to estimate the channel matrix under Rayleigh flat fading conditions. The BER performance of the space-time/UMTS system with the new channel estimator is provided and compared with the performance of the system when perfect channel estimation is assumed.