Optimal channel assignment strategies for forced channel hopping in CDPD systems

To provide an acceptable call blocking probability in circuit-switched cellular networks, such as the Advanced Mobile Phone System (AMPS) networks, a significant fraction of the channel capacity in each cell is normally unused. This “free” capacity can be effectively used for packet data transmissions that yield to voice traffic when necessary. Cellular Digital Packet Data (CDPD) is a packet-switched data service which may share radio channels with the AMPS service on a secondary basis to tap this “free” capacity. The length of time that a CDPD stream can occupy a channel is greatly influenced by the channel assignment strategies of both the AMPS and the CDPD systems. This paper investigates these channel assignment strategies and their effects on the CDPD channel holding times, in comparison with the optimal channel assignment strategy that interrupts the CDPD service only when a new AMPS call finds no other idle channels in the cell site. One such optimal strategy is the cooperative strategy in which the CDPD and AMPS networks actively communicate with each other. It is shown that other optimal strategies exist without the need of communications between the two systems. The effects of AMPS traffic levels, number of channels, and number of CDPD streams at the cell site on the CDPD channel holding time and channel utilization are also considered.