The effect of multipath fading on automatic link transfer for a random walk trajectory

Abstract

This paper considers the performance of automatic link transfer(ALT) in a frequency-reuse portable radio system using time-division multiple-access (TDMA) for portable-to-base transmission. It is assumed that customers undergo small-scale movement that would be typical of an office environment, where customers may be walking around in their office, changing posture, etc. Without line-of-sight transmission paths from the bases to the portable radio, signals undergo multipath fading. In this environment, the decision by the portable to initiate an ALT is sensitive to wavelength, customer speed, measurement acquisition time, number of signal samples averaged, hysteresis, and average signal power. Results pertaining to these factors are presented, including the effect of delay of the call switch and intentional blind ALT limiting. Implications to system design and equipment topology are discussed. It is shown that ALT in a narrow-band frequency channelized portable radio system could be a significant contributing factor to overhead in the fixed radio infrastructure when the customer does not have line-of-sight to nearby base stations. The radio measurement process, trigger conditions, and channel selection method depend on whether a local, fast, dedicated controller is used, or whether the call transfer is made in the fabric of a remote general purpose switch, such as those used in the local exchange. This paper is targeted towards understanding the implications to local exchange networks of wireless system alternatives that could provide access to those networks. >