An FPGA-Based MIMO and Space-Time Processing Platform
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An FPGA-Based MIMO and Space-Time Processing Platform J. Dowle,1 S. H. Kuo,2 K. Mehrotra,1 and I. V. McLoughlin1 1 Group 2 School
Research, Tait Electronics Ltd, 535 Wairakei Road, P.O. Box 1645, Christchurch, New Zealand of Engineering Science, Simon Fraser University, Burnaby, BC, Canada V5A 1S6
Received 29 November 2004; Revised 23 June 2005; Accepted 30 June 2005 Faced with the need to develop a research unit capable of up to twelve 20 MHz bandwidth channels of real-time, space-time, and MIMO processing, the authors developed the STAR (space-time array research) platform. Analysis indicated that the possible degree of processing complexity required in the platform was beyond that available from contemporary digital signal processors, and thus a novel approach was required toward the provision of baseband signal processing. This paper follows the analysis and the consequential development of a flexible FPGA-based processing system. It describes the STAR platform and its use through several novel implementations performed with it. Various pitfalls associated with the implementation of MIMO algorithms in real time are highlighted, and finally, the development requirements for this FPGA-based solution are given to aid comparison with traditional DSP development. Copyright © 2006 Hindawi Publishing Corporation. All rights reserved.
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INTRODUCTION
Most papers describing a MIMO-related subject are prefaced by the words “in a richly-scattering environment.” Other phrases that can be found include “in the absence of noise” or “assuming perfect synchronization.” Still more papers do not even acknowledge such caveats, and yet these phrases have been found to collectively describe some of the major challenges faced when designing a practical working MIMO system. One particular example is the assumption of AWG noise only when performing channel estimation from training data. Generally BER against SNR simulation curves are plotted for data decoded by the channel estimates. In reality, time averaging in a practical implementation is unlikely to be sufficient for the noise power to smooth out, and thus local noise excursions will have an impact on channel estimation accuracy, and that impact is proportional to the noise power. The widely shown BER against SNR curves for such systems (which collectively describe almost any implemented system) therefore ignore an important SNR-dependent factor which can skew performance results. This paper is primarily concerned with the challenges of MIMO and ST implementation within a baseband signal processing context. A more immediate challenge than the realism of academic MIMO research models is in the very nature of MIMO algorithms themselves; that they comprise some of the more computationally complex problems that face contemporary wireless system designers.
The STAR (space-time array research) platform was designed by Tait Electronics to allow it and its international research partners to explore novel MIMO algorithms, not just through simulation and theory, but through practical wor
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