Applicability of polarization diversity to indoor propagation at 900 MHz

Abstract

This paper repats the results of propagaticn measurements and simulation made in a large room and a long carridor by transmitting a 900 MHz (cw) s i g d from a fixed emitter to a mobile receiver. The receiver is equipped with a two branch diversity system. which makes possible the application of polarization diversity in order to redux the deep fades that affect the signal envelopeThe increasing demand for mobile and pefional communication systems and the fast moving electronic technology constitute a major incentive towards the d e v e l o p " d indoor microadlular systems 111. First of all, we explore the features affecting propagation between transmitter and receiver. There is rarely a line of sight between the transmitter and receiver in indoor radio wmmunication. but multiple si& propagation paths are present. The signals fiom these paths combine both constructively and destructively at the receiver to produce multipath fading. In addition to multipath fading. there is also shadowing caused by blockage and attenuation of the signals by walls. doors. etc.. The deep fades that affect the indoor transmitted signals constitute a serious impediment toperfamance.It is well know that diversity reception is effective for reducing excessive deep fades that affect the slgnal envelope [21[31. In practice. diversity branches with small correlation coefficients and prOvidmg received signal levels as close as possible are required. An adequate combination of the signals transmitted Over independently fading paths reduces considerably the effect of fading. since deep fades seldom occur simultaneously during the same intervals on two or more paths. In indoor propagation environments. polarization diversity has showed a good performance. It offers a very compact diversity arrangement. it does not q u i r e extra bandwidth. and high isolation (of the order of 20 dl3) is available.In this paper we describe the appiicabiliry of polarization diversity technique to indoor communication systems. including selection combining and switch and stay combining. We show how diversity can be used to overwme the problem generated by the propagation environment. The polarization diversity antenna is composed of two branches making a specific angle (polarization angle) relative to a known direction, w i t h a wrrelaticm coefficient between the diversity branches less than 0.7.Tbe propagation measurements. reported and analyzed have been performed by transmitting a 900 MHz signal from a fixed emitter to a mobile receiver. and recording the received signal envelope as a function of receiver location.For a good simulation of the received @, we have established a system of equations. based on the rays of optical geometry (i.e.: direct ray and reflected rays) and on the rays diffracted by the Merent obstacle shapes. as given by the d o r m theory of diffraction iUTD).In our simulation model, we have considered not only the complex reflection coefficients and the scattering coefficients by intmiucing a diffraction ma& (signal depolarization by the...