A LOCALLY OPTIMAL HANDOFF ALGORITHM FOR CELLULAR COMMUNICATIONS

The design of handoff algorithms for cellular communication systems ba sed on mobile signal-strength measurements is considered. The design p roblem is posed as an optimization to obtain the best tradeoff between the expected number of service failures and expected number of handof fs, where a service failure is defined to be the event that the signal strength falls below a level required for satisfactory service to the subscriber. Based on dynamic programming arguments, an optimal soluti on is obtained, which, though impractical, can be used as a benchmark in the comparison of suboptimal schemes, A simple locally optimal hand off algorithm is derived from the optimal solution. Like the standard hysteresis algorithm, the locally optimal algorithm is characterized b y a single threshold. A systematic method for the comparison of variou s handoff algorithms that are akin to the receiver operating character istic (ROC) curves of radar detection is presented. Simulation results show that the locally optimal algorithm outperforms the hysteresis al gorithm, especially in situations where accurate prediction of signal strength is possible. A straightforward technique for adapting the loc ally optimal algorithm to changing environments is suggested. That nat ural adaptability is the algorithm's principle advantage over current approaches.