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Hindawi Publishing Corporation EURASIP Journal on Advances in Signal Processing Volume 2011, Article ID 137541, 10 pages doi:10.1155/2011/137541 Research Article Experimental Investigation of TDD Reciprocity-Based Zero-Forcing Transmit Precoding Per Zetterberg ACCESS Linnaeus Center, KTH Royal Institute of Technology, Osquldasv¨ g 10, 100 44 Stockholm, Sweden a Correspondence should be addressed to Per Zetterberg, per.zetterberg@ee.kth.se Received 2 June 2010; Revised 16 November 2010; Accepted 14 December 2010 Academic Editor: Dragan Samardzija Copyright © 2011 Per Zetterberg. 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. | Hindawi Publishing Corporation EURASIP Journal on Advances in Signal Processing Volume 2011 Article ID 137541 10 pages doi 10.1155 2011 137541 Research Article Experimental Investigation of TDD Reciprocity-Based Zero-Forcing Transmit Precoding Per Zetterberg ACCESS Linnaeus Center KTH Royal Institute of Technology Osquldasvag 10 100 44 Stockholm Sweden Correspondence should be addressed to Per Zetterberg per.zetterberg@ee.kth.se Received 2 June 2010 Revised 16 November 2010 Accepted 14 December 2010 Academic Editor Dragan Samardzija Copyright 2011 Per Zetterberg. 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. We describe an implementation of TDD reciprocity based zero-forcing linear precoding on a wireless testbed. A calibration technique which self-calibrates the base-station without the need for help from other nodes is described. Performance results in terms of downlink channel estimation error as well as bit error rate BER and signal to interference noise and distortion ratio SINDR are presented for a scenario with two base-stations and two mobile stations with two antennas at the base-stations and a single antenna at the mobile-station. The results show considerable performance improvements over reference schemes such as maximum ratio transmission . However our analysis also reveals that the hardware impairments significantly limit the performance achieved. We further investigate how to model these impairments and attempt to predict the SINDR such as what would be needed in a coordinated multipoint CoMP scenario where scheduling is performed jointly over the two cells. Although the results are obtained for a MISO scenario the general conclusions are relevant also for MIMO scenarios. 1. Introduction Multiple antenna systems MASs are widely employed to enhance the performance of wireless communication
