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Open Access Research Article

Design of FIR Precoders and Equalizers for Broadband MIMO Wireless Channels with Power Constraints

Yongfang Guo* and Bernard C Levy

Author Affiliations

Department of Electrical and Computer Engineering, University of California, Davis, CA 95616-5294, USA

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EURASIP Journal on Wireless Communications and Networking 2004, 2004:249123  doi:10.1155/S1687147204406185

The electronic version of this article is the complete one and can be found online at: http://jwcn.eurasipjournals.com/content/2004/2/249123

Received:20 June 2003
Revisions received:13 July 2004
Published:22 December 2004

© 2004 Guo and Levy

This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

This paper examines the optimum design of FIR precoders or equalizers for multiple-input multiple-output (MIMO) frequency-selective wireless channels. For the case of a left-coprime FIR channel, which arises generically when the number of transmit antennas is larger than the number of receive antennas, the Bezout matrix identity can be employed to design an FIR MIMO precoder that equalizes exactly the channel at the transmitter. Similarly, for a right-coprime FIR channel, the Bezout identity yields an FIR zero-forcing MIMO equalizer. Unfortunately, Bezout precoders usually increase the transmit power, and Bezout equalizers tend to amplify the noise power. To overcome this problem, we describe in this paper a convex optimization technique for the optimal synthesis of MIMO FIR precoders subject to transmit power constraints, and of MIMO FIR equalizers with output noise power constraints. The synthesis problem reduces to the minimization of a quadratic objective function under convex quadratic inequality constraints, so it can be solved by employing Lagrangian duality. Instead of solving the primal problem, we solve the lower-dimensional dual problem for the Lagrange multipliers. When an FIR MIMO precoder has already been selected, we also describe a technique for adding a vector shaping sequence to the transmitted signal in order to reduce the transmit power. The selection of effective shaping sequences requires a search over a trellis of large dimensionality, which can be accomplished suboptimally by employing reduced-complexity search techniques.

precoder; equalizer; Bezout identity; quadratic optimization; Lagrangian duality; shaping sequence

Research Article