%0 Journal Article
%T Differences in User Influence on MIMO Handset Antenna Performance in Reverberation Chamber
%A Juan D. S¨¢nchez-Heredia
%A Paul Hallbj£¿rner
%A Juan F. Valenzuela-Vald¨¦s
%A Thomas Bolin
%A Antonio M. Mart¨ªnez-Gonz¨¢lez
%J International Journal of Antennas and Propagation
%D 2012
%I Hindawi Publishing Corporation
%R 10.1155/2012/826425
%X User influence on multiple-input multiple-output (MIMO) performance is studied for different dual antenna handsets specially designed to have good and bad MIMO performance. The study reveals that user influence can cause either improvement or degradation for different test objects, including a spread effect over the parameters. Differences in performance between good and bad handsets can be clear when they are measured without user influence, but become small under real person influence. This result illustrates the particular importance of user influence to characterize MIMO handsets. 1. Introduction User influence on multiple antenna device performance has been a topic for research in the last few years, since it is well known that a user in the vicinity of a wireless device affects the propagation conditions that the device is experiencing. This effect is well known for single-input single-output (SISO) communications, consisting of a degradation of radiation performance due to the losses introduced by the user. This effect is usually quantified by the changes in radiation efficiency and absorbed power [1]. In spite of this knowledge, it is still not clear what the consequences are when it comes to multiple antenna devices, since they base their enhanced capabilities on a rich field distribution in terms of signal paths. Numerous studies have been performed over the last years, agreeing to the fact that the effect of the human body is more complex in MIMO terminals than in traditional ones [1¨C5]. The presence of the user has been demonstrated to have immediate influence on radiation patterns, input impedances and therefore on the correlation matrix, yet the effects are not fully understood and contradictory findings are commonplace. In [3], the envelope correlation coefficients were significant when the user was present. These changes showed a more important dependence to antenna orientation in [1]. In contrast, an increment of the correlation coefficients is also available in the literature [6]. Contradictory findings can also be found for the effects on diversity gain [7]. In this paper, the performance of different handsets has been analyzed. All the handsets used within this study consist of two antennas, in order to implement diversity at the receiving terminal end of the link (SIMO: Single Input Multiple Output). This SIMO configuration is relevant for this study since it is one of the normal over-the-air (OTA) test cases for the new communication standards (HSDPA and LTE). 2. Measurements 2.1. Test Objects Four different handsets are used for
%U http://www.hindawi.com/journals/ijap/2012/826425/