Effect of handoff delay on the system performance of TDMA cellular systems

Handoff delay is one of the major criteria to evaluate a handoff algorithm. A good handoff algorithm is expected to minimize both the handoff delay and the mean number of handoffs. But it is generally very difficult to minimize both, if not impossible. We would like to find out the amount of increase in the outage probability when we try to minimize the mean number of handoffs by introducing some handoff delay, which, in turn, may make it possible to identify an optimum operating point from a system design perspective. We assumed that the underlying handoff algorithm is either received signal strength or signal-to-interference ratio based. Furthermore, a probabilistic model for the handoff delay was introduced. Since the handoff delay can introduce increased co-channel interference only in the uplink because of the penetration of mobile stations into the neighboring cells, the outage probability was calculated in the uplink as function of the mobile station´s position on straight path from one base station to another for different cluster sizes and handoff delays. We concluded that the handoff delays up to 10 % do not change the outage probability significantly and can be used to decrease the mean number of handoffs while keeping the outage probability at an acceptable level.