THE INFLUENCE OF MIMO TERMINAL USER’S HAND ON CHANNEL CAPACITY T. Zervos 1,2 , A. Alexandridis 1 , K. Peppas 1 , F. Lazarakis 1 , K. Dangakis 1 , C. Soras 2 , B. Lindmark 3 1 Institute of Informatics & Telecommunications, National Centre for Scientific Research “Demokritos”, Athens, Greece 2 Department of Electrical & Computer Engineering, University of Patras, Patras, Greece 3 Department of Signals, Sensors, and Systems, Royal Institute of Technology, Stockholm Sweden ABSTRACT In this paper the impact of user’s hand holding a Multiple-Input-Multiple-Output (MIMO) terminal on the system performance is investigated. A 4x4 MIMO system is considered with a Personal Digital Assistant (PDA) terminal equipped with a compact array of 4 patch elements. The radiation patterns of the antenna elements are simulated in the presence of the other elements and in the presence of a user’s hand. The obtained patterns are used to evaluate the covariance matrix of the receive antenna which is incorporated in a correlation-based MIMO channel model. MIMO channel capacity is calculated to demonstrate the capacity degradation caused by the user’s hand. 1. INTRODUCTION During last years many research activities have been carried out to investigate the interaction between electromagnetic fields emitted by wireless terminals and biological tissues. These studies generally deal with two aspects. The first aspect is the deposition of the microwave energy in the user’s body, significant from the safety standards point of view. The second aspect is the influence of the user’s body on the radiation properties of the mobile terminal, significant from the antenna design point of view. Antenna characteristics that are mostly affected by the presence of the human body are radiation pattern, input impedance and radiation efficiency. Previous studies clearly showed that the presence of biological tissue alters the radiation patterns and reduce the antenna gain [1],[2]. Most of those studies [3] investigate the effect of human’s head which is in close proximity to the user’s terminal as it is the case in voice-centric systems. Some of them they have also studied the effect of the hand holding the mobile terminal and they have found that it has small influence in antenna properties comparing to that connected to head’s presence [4]. However, it has been found that for some terminal antenna types like side-mounted PIFA, the position of the hand holding the handset has significant role in the variation of the antenna frequency matching and impedance. A higher impedance mismatch occurs when the hand begins to mask the antenna [5]. As data communications become more and more important in present and future wireless systems, new test cases scenarios should be studied e.g. the “multimedia viewing position” where the user is holding the terminal while the rest of his/her body does not influence the terminal’s operation. Besides, Multiple-Input-Multiple-Output (MIMO) systems have proven their ability to offer significant increase in system performance with improved link quality, extremely high data rates and increased channel capacity. MIMO techniques are expected to play major role in future wireless networks. Within that frame, the effect of user’s hand becomes very interesting for the case of MIMO terminals. In this paper we focus on the impact of user’s hand on system performance and especially on MIMO channel capacity. Firstly, we evaluate the influence of user’s hand on antenna radiation patterns. Then, the radiation patterns are incorporated into a correlation- based MIMO channel model which is used for channel capacity evaluation. Our studies refer to a 4x4 MIMO system where a mobile terminal with limited size is included. At one end, a standard linear array is assumed playing the role of the base station. At the other end, a Personal Digital Assistant (PDA) terminal is considered with a compact array of 4 patch elements. The user’s hand has been modelled by means of a 3D electromagnetic simulator and antenna radiation patterns were obtained through simulations. The paper is organized as follows. In section 2 the antenna configuration of the PDA is given and s-parameters as well as antenna patterns are simulated to demonstrate the effect of user’s hand. Section 3 explains how the obtained antenna patterns are incorporated into MIMO channel modelling. Section 4 investigates channel capacity in the presence of user’s hand for the specific antenna array design. Finally, section 5 summarizes the conclusions of the paper. 2. THE IMPACT OF USER’S HAND ON ANTENNA RADIATION PATTERNS The antenna configuration in this paper is based on the design of the planar inverted-F antenna (PIFA) model for dual band mobile terminal application. The antenna elements of the PDA are folded PIFA patches designed for operation at 1800 and 2450 MHz frequency bands. The geometry of an antenna element is shown in Fig. 1. A rectangular patch was folded on both sides of a dielectric layer with low permittivity ( r =2.33) and dimensions 77.5 x 75 mm. The dielectric layer is supported by a layer of foam with dimensions (length, width, thickness) 125 x 75 x 10 mm made from Rohacell ( r =1.03) which is propped on a finite ground plane of same dimensions but thinner (3mm). The upper side patch is fed using a cylindrical feed pin of 0.2 mm _____________________________________________________ Proc. ‘EuCAP 2006’, Nice, France 6–10 November 2006 (ESA SP-626, October 2006)