THE EFFECT OF MUTUAL COUPLING ON THE CAPACITY AND by ftj94837

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									        9th Australian Symposium on Antennas, Sydney, Australia, 16-17 Feb. 2005
         THE EFFECT OF MUTUAL COUPLING ON THE CAPACITY
             AND BER PERFORMANCE OF A MIMO SYSTEM

                       Peerapong Uthansakul and Marek E Bialkowski
                 School of Information Technology and Electrical Engineering
                 The University of Queensland, Brisbane, Qld, Australia, 4072
                              email: {ppg or meb}@itee.uq.edu.au

        With the growing expansion of wireless communication systems, there is a steady demand
for increased capacity to meet various applications involving high speed data transmission. The new
systems have to be robust against adverse effects of multipath signal propagation which become
more severe in the case of high data transmission. An application of multiple element antennas
(MEA) at transmitting and receiving sides is envisaged to solve this problem. MEA systems are
classified into three categories depending on the number of antenna elements used at
transmitter/receiver sides. These are SISO, SIMO (or MISO) and MIMO. The performance of a
particular system depends on the presence of line of sight (LOS) and non line of sight (NLOS)
components. When LOS dominates, it has been shown that smart antenna systems of SIMO/MISO
type can provide increased capacity in comparison with a conventional SISO system. However,
smart antennas fail in NLOS environments. This occurs when the communication channel is rich in
multipath signal propagation. It has been shown in [1] and [2] that under such conditions MIMO
systems can provide superior performance. The work on MIMO concerns both information theory
[1] and communication system theory [2]. It has been shown that the performance of MIMO
depends on properties of the channel matrix. An optimal performance and therefore highest capacity
is obtained when the channel matrix is given by i.i.d. (independent and identical distribution)
elements. In order to predict the MIMO system performance accurate mathematical models are
required. One important issue in these models is the effect of antenna element spacing. When the
spacing is small the MIMO system becomes compact in size, which is of practical benefit.
However, it is unclear how an increased coupling between the array elements affects MIMO
performance [3] [4].
        In this presentation we investigate this issue by revisiting foundations and formulas used for
calculating MIMO capacity in [3] and [4]. In addition, we report on single-bounce scattering and
full electromagnetic MIMO models, which are currently investigated at the University of
Queensland. Using these models the effect of mutual coupling on capacity of MIMO is assessed. In
the next part of presentation, we report on the BER performance of a MIMO system when two
approaches, one maximizing diversity (Alamouti scheme) and the other one maximizing data rate
(spatial multiplexing), are applied. The obtained results show the effect of mutual coupling on the
BER performance and indicate independence from normalization used in the definition of MIMO
capacity.

[1]   I. E. Telatar, “Capacity of multi-antenna Gaussian channels,” Eur. Trans. Tel., vol. 10, no. 6,
      pp. 585-595, Nov./Dec. 1999.
[2]   A. J. Paulraj, D. A. Gore, R. U. Nabar and H. Bolcskei, “An Overview of MIMO
      Communications-A Key to Gigabit Wireless,” Proceeding of IEEE, vol. 92, no. 2, pp. 198-
      218, Feb 2004.
[3]   P. N. Fletcher, M. Dean and A. R. Nix, “Mutual coupling in multi-element array antennas and
      its influence on MIMO channel capacity,” Electronics Letters, vol. 39, no. 4, pp. 342-344 Feb
      2003.
[4]   T. Svantesson and A. Ranheim, “Mutual coupling effects on the capacity of multi element
      antenna systems,” Proc. IEEE ICASSP 01, vol. 4, pp. 2485-2488, May 2001.

								
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