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Space-time alignment for asynchronous interference suppression in MIMO OFDM cellular communications

Future broadband cellular wireless communication systems will be characterized by high delay spread and the need to maximize the system capacity. One method of increasing capacity, aggressive frequency reuse, subjects mobiles to high levels of interference from neighboring basestations. Receiver interference suppression algorithms that work well for conventional MIMO systems may not be appropriate for suppressing interference in multiple-input-multiple-output (MIMO) orthogonal frequency division multiplexing (OFDM) cellular systems, since differing propagation delays and channel lengths can destroy the alignment of the cyclic prefixes, making the interference asynchronous. This work presents MIMO algorithms for cyclic prefix based systems that are suitable for scenarios where the interferer's cyclic prefix is not time-aligned with the desired signal's cyclic prefix. Specifically, we present several space-time partial equalization techniques for the alignment of cyclic prefixes for aiding in interference suppression. We use a two-stage architecture with partial equalization for cyclic-prefix alignment in the time domain followed by simple channel equalization in the frequency domain. We consider interference suppression in both domains and demonstrate the efficacy of the two-stage architecture over both zero-forcing (ZF) and per frequency bin minimum mean squared error (MMSE) equalization. Copyright © 2004 John Wiley & Sons, Ltd.