Analyzing the trade off between implementation costs and performance: PCS Channel Assignment Strategies for Hand-off and Initial Access

YI-BING LIN, SESHADRI MOHAN, AND ANTHONY NOERPEL ersonal communications is expected to provide low-power/high-quality wireless access to the public switched telephone network (PSTN) [4,5]. The service area of a network providing personal communications services (PCS) is populated with a large number of ports, with each port providing coverage in its vicinity. Each port is assigned a group of channels (time slots, frequencies, spreading codes, or a combination of these) that can be either fixed or dynamic. This article assumes a fixed or quasi-static channel assignment [9]. The results may be extensible to dynamic channel assignment schemes [lo]. When a subscriber wishes to make or receive a phone call, the portable attempts to seize an available traffic channel for the call. For some PCS radio systems, the portable launches an access request on a common signaling channel and is then directed to a traffic channel (CT-2 Plus [14]). In other PCS radio systems the access attempt can be made directly on an available traffic channel (DECT [8], or Bellcore WACS [l]’). Owing to the limited number of servers or transceivers in a port, when a port is blocked there is no idle transceiver for the signaling channel. There is usually no provision (either no channel or no protocol, or both) for a portable to signal the need for a traffic channel to a blocked port and therefore access attempts cannot be queued by the network. If there is no available traffic channel or common signaling channel, the call is blocked. (An exception to this is the WACS system, which reserves a time slot channel called the system broadcast channel.) If there is an available traffic channel it is used for the call. The channel is released eitherwhen the call iscompleted or the portable (or the PCS subscriber) moves out of the coverage area. When a user moves from one coverage area to another while a call is in progress, a hand-off to the new port is required to maintain continuity and quality of the call. If the new port does not have an idle channel, the call may be dropped o r forced terminated. The forced termination probability is an important criterion in the performance evaluation of a PCS network. Forced termination of an ongoing call is considered less desirable than blocking of a new call attempt. Radio tech-