Realization of a Spatially Multiplexed MIMO System
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Realization of a Spatially Multiplexed MIMO System ´ Per Zetterberg, and Bjorn ¨ Ottersten David Samuelsson, Joakim Jalden, Department of Signals, Sensors, and Systems, Royal Institute of Technology (KTH), 100 44 Stockholm, Sweden Received 14 December 2004; Revised 1 April 2005; Accepted 5 April 2005 Multi-antenna systems can provide improvements in wireless systems increasing spectral efficiency, reliability, range, and system capacity. Herein we show how some of the potentials of MIMO systems can be realized on a simple radio hardware platform by utilizing advanced real-time signal processing and coding. We present a real-time implementation of a 2 by 2 MIMO system employing spatial multiplexing to achieve high spectral efficiency in an indoor non-line-of-sight environment operating in the 1800 MHz range. Well-known processing and coding techniques are employed and our contributions lie in: discussing implementational aspects and solutions often overlooked but critical for high-performance operation; demonstrating the degree to which the simple baseband AWGN model can be used to accurately model/predict the MIMO system on the current hardware; and demonstrating the feasibility of real-time spatial multiplexing achieving up to 15 bps/Hz on a 2 by 2 system in a realistic indoor environment with off-the-shelf radio hardware. Copyright © 2006 David Samuelsson et al. 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
Multiple antennas at the transmitter and receiver have emerged as one of the key technologies for increasing the spectral efficiency of future wireless communication systems. At this stage, many of the theoretical aspects of the multiple-antenna channel are well understood [1, 2]. Similarly, a wealth of techniques exists for the exploitation of the potential gain offered by the multiple-antenna channel, both when the channel is assumed known to the transmitter and when it is not. Traditionally, space-time techniques have been designed either to maximize throughput or to increase robustness. However, recent theoretical results exist on the tradeoff between the two competing objectives [3]. Spatial multiplexing, which is employed in this project, is an example of a technique which aims at increasing the overall data rate. It does so by creating several virtual data paths across the wireless interface [4]. Most of these transmission techniques are based on simple linear discrete-time models of the multiple-antenna channel. While the signal processing required by many of these techniques is readily implemented in DSP software, it is essential that the model accurately reflects the underlying hardware as well as the actual wireless channel. Most common models of wireless channels implicitly assume accurate synchronization and carrier frequency offset compensation. It is thus important that such practical issues are dealt with in
a fashion wh
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