On Interference Rejection in Wireless Multichannel Systems

To meet the growing demands for service provisioning using wireless access, efficient utilization of the available radio spectrum is a key issue of great importance. To achieve high spectrum efficiency, use of spectral efficient modulation methods in combination with tight physical channel reuse are anticipated in future cellular communication systems. As a consequence, the link performance and hence the capacity of these systems will to a large extent be limited by the robustness against interference provided by the receiving terminals operating within the systems. Thus, in all future system aiming at serving mass markets, interference rejection algorithms—both transmitter and receiver oriented—will be natural components along with other capacity increasing means such as adaptive resource allocation etc. In this thesis, interference rejection and parameter estimation methods suitable for multichannel systems are developed and investigated, i.e., methods suitable for receivers exploiting different diversity techniques to recover the data from a desired user. In particular, statistical methods to reject cochannel interference originating from transmitters supporting transmit diversity based on space-time block codes and methods to retrieve information about unknown interferers needed to accomplish interference suppression are studied. To handle the presence of transmit diversity interference, a spacetime processing based extension of the conventional interference rejection combining algorithm is proposed. For single antenna receivers, it is shown that noise whitening techniques are effective for interference rejection purposes if the rate of the space-time block code is smaller than one. It is further shown that for receivers with more than one antenna, alternatively if space-time block codes with rate smaller than one are used, taking into account the inherent structure of the transmit diversity interference is of major importance as interference rejection by means of conventional