HANDOFF WITH SIGNAL PRIORITY QUEUING IN CELLULAR SYSTEMS

Abstract

In mobile cellular systems, especially when relatively small cell sizes or microcells are used, the handoff procedure has a significant impact on the system's performance. A method of improving the quality of service in mobile cellular systems based on prioritization of handoff requests has been presented. The objective here is to improve perceived quality of cellular service by minimizing the probability of forced termination, probability of call blocking and the degradation in spectral utilization. Analysis of the method, which uses two queues one for new calls and one for handoff calls has been done. New calls, which originate within the cells at Poisson rate, are queued without giving priority to the new calls, calls are blocked if the queue is full. Handoff requests are queued such that as soon as a channel is available, it is offered to the mobile user with the measurement results based on both received signal strength (RSS) and change in received signal strength (ARSS). Handoff requests arrive with Poisson distribution and are queued if no channel is available at the time of arrival. The queue is dynamically reordered as new measurement results are substituted. The performance criteria of interest are: probability of handoff failure (Dropped call probability), probability of call blocking and number of carrier versus offered traffic. The proposed handoff policy is evaluated by simulation and compared with respect to FIFO queuing. The proposed scheme is seen to provide lower probability of forced termination and less call blocking probability.