Capacity Performance of Adaptive Receive Antenna Subarray Formation for MIMO Systems
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Research Article Capacity Performance of Adaptive Receive Antenna Subarray Formation for MIMO Systems Panagiotis Theofilakos and Athanasios G. Kanatas Wireless Communications Laboratory, Department of Technology Education and Digital Systems, University of Piraeus, 80 Karaoli & Dimitriou Street, 18534 Piraeus, Greece Received 15 November 2006; Accepted 1 August 2007 Recommended by R. W. Heath Jr. Antenna subarray formation is a novel RF preprocessing technique that reduces the hardware complexity of MIMO systems while alleviating the performance degradations of conventional antenna selection schemes. With this method, each RF chain is not allocated to a single antenna element, but instead to the complex-weighted and combined response of a subarray of elements. In this paper, we derive tight upper bounds on the ergodic capacity of the proposed technique for Rayleigh i.i.d. channels. Furthermore, we study the capacity performance of an analytical algorithm based on a Frobenius norm criterion when applied to both Rayleigh i.i.d. and measured MIMO channels. Copyright © 2007 P. Theofilakos and A. G. Kanatas. 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.
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INTRODUCTION
The interest in multiple-input multiple-output (MIMO) antenna systems has exploded over the last years because of their potential of achieving remarkably high spectral efficiency. However, their practical application has been limited by the increased manufacture cost and energy consumption of the RF chains (performing the frequency transition between microwave and baseband) and analog-to-digital converters, the number of which is proportional to the number of antenna elements. This high degree of hardware complexity has motivated the introduction of antenna selection schemes, which judiciously choose a subset from all the available antenna elements for processing and thus decrease the number of necessary RF chains. Both analytical [1–11] and stochastic [12] algorithms for antenna selection have been proposed. However, when a limited number of frequency converters are available, antenna selection schemes suffer from severe performance degradations in most fading channels. In order to alleviate the performance degradations of conventional antenna selection, antenna subarray formation (ASF) has been recently introduced [13]. With this method, each RF chain is not allocated to a single antenna element, but instead to a combined and complex-weighted response of a subarray of antenna elements. Even though additional RF
switches (for selecting the antenna elements that participate in each subarray), variable RF phase shifters, or/and variable gain-linear amplifiers (performing the complex-weighting) are required with respect to antenna selection schemes, the proposed method achieves decreased receiver hardware complexity, since less frequency converters and analogto-digital converters are requir
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