A MIMO SYSTEM EQUIPPED WITH MULTIFUNCTIONAL RECONFIGURABLE ANTENNAS Bedri A. Cetiner* (1) , Enis Akay (2) , Ersin Sengul (2) , and Ender Ayanoglu (2) (1) Morehead State University, Space Science Center, Morehead, KY, 40351 (2) Center for Pervasive Communications and Computing, University of California Irvine, Irvine, CA, 92697 Abstract A MIMO system equipped with a new class of antenna arrays, henceforth referred to as multifunction reconfigurable antenna arrays (MRAAs), is investigated. The elements of MRAA, i.e. MRAs presented in this work are capable of dynamically changing the sense of polarization of the radiated field thereby providing two reconfigurable modes of operation, i.e. polarization diversity and space diversity. The transmission signaling scheme can also be switched between transmit diversity (TD) and spatial multiplexing (SM). The results show that the reconfigurable modes of operation of an MRAA used in conjunction with adaptive space-time modulation techniques provide additional degree of freedoms to the current adaptive MIMO systems, thereby resulting in more robust system in terms of quality, capacity and reliability. A substantial performance gain is achievable with the proposed system over conventional fixed antenna MIMO systems depending on the channel conditions. Introduction and Motivation Wireless communication technology, a fundamental part of modern information infrastructure, is evolving at a frantic pace in order to meet the ever demanding performance characteristics of highly integrated mobile wireless communication devices. The true benefits of MIMO can be exploited only through a smart design that is able to respond to the channel. The goal is to maximize the resources available in multiple antenna channels by using optimal schemes at all times. In a typical adaptive MIMO system, the adjustable parameters are the modulation level, coding rate, and the transmission signaling schemes such as SM, TD and beamforming. The performance of such an adaptive MIMO system can be superior in comparison to that of a non-adaptive one. However, when an interdisciplinary analysis is performed on the interrelationships of transmission signaling schemes, antenna properties and propagation conditions it becomes clear that there is still an additional room for further exploitation of the theoretical gains of the MIMO systems [1]. In today’s adaptive MIMO systems the antenna element properties are fixed by the initial design and cannot be changed. In this work, we introduce an additional degree of freedom by treating the antenna element properties as an additional component in the joint optimization of the adaptive system parameters. We effectively integrate the antenna properties with the space-time processing techniques and the propagation environment. The goal of joint optimization of antenna array properties and the associated transmission algorithm can only be achieved if each individual element of the array can be dynamically reconfigured, i.e. MRA. In short, the adaptive MIMO system introduced in this paper will not be constrained to employ a fixed antenna design over varying channel conditions. This feature will permit the selection of the best antenna properties in conjunction with the adapted transmission