Effect of cell size reduction and access re-routing on PACS system capacity

System capacity of PACS (personal access communications system) is determined by two factors: (1) blocking due to insufficient servers at the radio port being accessed and (2) blocking due to insufficient signal quality of the radio link being accessed. The Erlang traffic capacity can be enhanced by access re-routing, i.e., a user is allowed to access other available radio ports immediately if it fails in a previous attempt. However, the signal quality would be degraded due to re-routing if the cell size is relatively large. The signal quality performance can be improved by reducing the cell size but the cell size cannot be too small for economic and technical reasons. This study is to investigate the effects of both cell size reduction and access re-routing on the overall system performance of PACS and to examine the tradeoffs between different system parameters. It is found that with cell size reduction and access re-routing together, the overall system performance is greatly improved. At a reasonably high normalized offered traffic of 60%, the overall call blocking probability is reduced from 11.5% to 3.5% by changing a port-to-port separation of 2000 ft. (i.e., a cell radius of 1000 ft.) without re-routing to 1000 ft. with re-routing. A number of 3 or 4 re-routing attempts out of a maximum of 16 is sufficient to provide a good result. In addition, more than 90% of the successful calls are admitted in the first attempt and therefore, the additional access delay and system overhead due to re-routing is insignificant