A Packet Data Service for CODIT UMTS

A packet data service for the CDMA-based UMTS developed in RACE-II project CODIT is described. Packet radio channels are established by the base station and time-shared by the mobile users. Mobile stations contend for uplink access using a slotted CSMA/CD protocol with exponential backoff to achieve stability. The MAC protocol has been formally specified in SDL permitting automatic generation of executable code. The performance of the CSMA/CD protocol is evaluated by analysis and simulation assuming Poisson-distributed access attempts. With 10-msec initial power ramping, a throughput of 60\% and a mean packet delay of 1 sec is achieved for a typical dialog-type packet service.