Space-time equalization and interference cancellation for MIMO OFDM

The paper develops equalization techniques that facilitate aggressive frequency reuse in cellular OFDM systems. The initial focus is on the case of a single strong interfering base at the mobile. The interfering base is asynchronous in that its cyclic prefix is not time-aligned with the desired base´s cyclic prefix. Various methods for combating the asynchronous, interfering base are developed, based on channel shortening ideas. The most promising method works to align the cyclic prefixes while holding all channel lengths equal to the cyclic prefix length or less. For the case of two receive antennas at the mobile, two sets of space-time filters are designed so that the respective channels at either output for either base are time-aligned with length no greater than the cyclic prefix length. As a result, standard frequency-domain equalization/interference suppression techniques (e.g., MMSE combining) can be applied to the outputs of the space-time filters on a per frequency bin basis to obtain symbol estimates for the desired base. Simulations are presented comparing the BER performance of the candidate techniques.