Trunked radio network development for data transmission using OPNET

Abstract

Tetrapol is a modern digital, cellular trunked radio system for voice and data communication that offers faster call set-up, group calls, priority calls, end-to-end encryption and the possibility of direct calls from mobile station to mobile station without the intervention of the base station. The primary users of trunked radio systems include closed user groups such as transport and logistical services, airports, energy companies and government agencies. Performance of telecommunication networks may be characterized by Grade of Service (GoS), defined as the probability of a call being blocked or delayed for more than a specific interval. The Tetrapol systemts performance is limited by the number of radio channels and the traffic load. In addition to the contention for limited radio resources, the channel access delay is also affected by collisions on the shared Control Channel, when mobile stations request for call setup. In this project a measure of the Tetrapol networkts GoS was estimated in terms of system utilization, probability of blocked voice calls and the channel access characteristics for data communications. A Tetrapol network offering basic voice and data services was modeled using OPNET. Each base station serves 10 mobile stations, using 2 traffic channels. A number of scenarios were defined, in which mobile stations offer increasing traffic load to the base station. The results show that as traffic load increases, the average system utilization increases. The probability of voice call being blocked also increases to the point where the GoS may be unacceptable to the user, as data call requests in the queue are always served first. The channel access delay for data calls also increases, within acceptable limits. As the offered traffic increases, the impact of collisions on the Control Channel during call set-up is relatively small; it is the queuing delay that makes up the bulk of the overall channel access delay.