Capacity analysis for parallel and sequential MIMO equalizers

Xinying Zhang, S. Y. Kung

Research output: Contribution to journalConference articlepeer-review

2 Scopus citations


It is well known that linear MMSE can outperform its zero-forcing counterpart. In combination with a successive interference canceller, MMSE can fully exploit the capacity of MIMO (Multiple-Input-Multiple-Output) channels [1, 2]. In practice, however, such an advantage is compromised due to its implementation complexity and the requirement of accurate SNR estimate. Thus other equalizers such as zero-forcing may present an attractive alternative as long as the performance gap is tolerable. This motivates a need to quantify the tradeoff between MMSE and zero-forcing in both parallel and sequential structures. In this paper, the capacity performance of different equalization schemes is investigated, with closed-form formulas provided in terms of two key measures: capacity gaps and ratios. We also conclude that the capacity gain via structural choice (between parallel and sequential) far out-weights that via filter choice (between zero-forcing and MMSE). Indeed, the latter is found to be almost negligible for most practical SNR regions. It is also shown that the sequential zero-forcing equalizers can asymptotically reach the channel capacity when SNR approaches infinity, irrelevant of the detection order. Although this paper is focused on the flat-fading channels, the result is directly extendable to the ISI case by slicing the frequency band into infinitesimal stripes, each of which can be treated as flat.

Original languageEnglish (US)
Pages (from-to)357-360
Number of pages4
JournalICASSP, IEEE International Conference on Acoustics, Speech and Signal Processing - Proceedings
StatePublished - 2003
Event2003 IEEE International Conference on Accoustics, Speech, and Signal Processing - Hong Kong, Hong Kong
Duration: Apr 6 2003Apr 10 2003

All Science Journal Classification (ASJC) codes

  • Software
  • Signal Processing
  • Electrical and Electronic Engineering


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