Performance of a semi-blind receiver for the uplink of the UMTS TDD mode

The most classical UMTS TDD Mode receivers use a training sequence channel estimation followed by a Joint Detection algorithm (e.g. MMSE BL or ZF DFE). However, it seems quite relevant to take benefit of the observations generated by unknown symbols in order to improve the performance of the channel estimate. This approach is classically called semi-blind channel estimation. Several semi-blind techniques have been recently proposed in the context of TDMA systems. The purpose of this paper is to evaluate the performance (in terms of bit error rate) of the statistically optimal semi-blind estimate, which is based on a maximum likelihood method implemented via the classical Expectation Maximization (EM) algorithm. This algorithm provides a high performance channel estimate but also an optimal Joint Detection of the transmitted symbols. The corresponding results represent lower bounds to which we compare classical sub-optimal procedures.