Exploiting macrodiversity based decoder feedback for cochannel interference suppression in narrowband cellular mobile systems

An iterative minimum mean square error (MMSE) cochannel interference suppressor is proposed for coded narrowband time division multiple access (TDMA) uplink channels. This scheme discriminates the desired user from interferers, and the latter from each other, based on the differences in their propagation channel responses which serve as their spatial signatures. Assuming a protocol that provides for synchronisation between cochannel base stations, each receiver decodes its desired user and interferers (that are served by neighbouring cochannel receivers) whose channel responses can be estimated. It feeds these soft-decoded values back to aid (in the next iteration) a channel state estimator and a multiuser demodulator in MMSE suppression and subtractive cancellation of these interferers. The fact that this scheme displays the successive cancellation property across iterations, enables it to exploit the near-far nature of cochannel interferers in a narrowband cellular system. Practical realisations of this technique depend on the accuracy of the channel estimation procedure; with sufficiently diverse and accurately estimated channel responses, almost universal frequency reuse seems possible