Capacity analysis for parallel and sequential MIMO equalizers

Employing multiple antennas at both the transmitter and receiver ends offers a promising channel capacity. Unfortunately, equalizers that can deliver better theoretical capacity performance usually incur higher implementation cost. To facilitate the trade-off design in practice, this paper explores and compares the asymptotic capacity performance of different multiple-input-multiple-output (MIMO) equalizers for both deterministic and stochastic (in particular, Rayleigh fading) channel models, in terms of two measurements: "capacity gap" and "capacity ratio". Based on linear algebra and matrix operations, the capacity results are given in analytical form as functions of the coupling terms in the channel transfer function and the signal-to-noise ratio (SNR). The closed-form solutions enable our theoretical work serve as a reference for practical system designers. Our theoretical finding concludes that the interplay among the individual equalizers associated with each input stream plays a much more important role than the detailed filter selection, which is further verified by the Monte Carlo simulations. Although we focus on flat-fading channels in this paper, the result is naturally extendible to the inter-symbol-interference (ISI) MIMO systems.