The performance of the PACS radio link and its improvements at vehicular speeds

The personal access communication system (PACS) radio interface is the leading low-tier candidate for standardization in North America. This radio interface was originally conceived to serve pedestrian and fixed-distribution applications; there has been significant recent interest in extending this technology into high-mobility environments. In such environments, rapid channel variations significantly degrade the performance of the preselection diversity scheme proposed for use in PACS handsets. The effects of time-delay spread on the PACS radio link was also included in our investigation. It is found that a received signal strength indicator (RSSI) with a short measurement length can better cope with high fading rates than can a quality measure in a preselection diversity system, although a quality measure has better performance than RSSI at low speeds in the presence of time-delay spread. In the preselection diversity scheme, using short-measurement RSSI provides relatively good performance in both low- and high-mobility environments. However, its performance degrades rapidly for RMS delay spreads larger than about 9% of a symbol time. Postselection diversity using two complete receiver chains is more robust than preselection diversity, both to high fading rates and to delay spread. Postselection diversity is relatively insensitive to changes in the fading rate and can tolerate an RMS delay spread up to 12.5% of a symbol time.