A Locally Optimal Handoff Algorithm for Cellular Communications

Abstract

£ —The design of handoff algorithms for cellular communication systems based on mobile signal-strength measurements ¤ is considered. The design problem is posed as an optimization to obtain the best tradeoff between the expected ¥ number ¦ of service failures and expected number of handoffs, § where a ¨ service failure is defined to be the event that the signal str © ength falls below a level required for satisfactory service to the subscriber. Based on dynamic programming arguments, an optimal solution is obtained, which, though impractical, can be used as a benchmark in the comparison of suboptimal schemes. A simple locally optimal handoff algorithm is derived from the optimal solution. Like the standard hysteresis algorithm, the locally optimal algorithm is characterized by a single threshold. A systematic method for the comparison of various handoff algorithms¨that are akin to the receiver operating characteristic (ROC) curves of radar detection is presented. Simulation results show © that the locally optimal algorithm outperforms the hystere-sis © algorithm, especially in situations where accurate prediction of signal strength is possible. A straightforward technique for adapting¨the locally optimal algorithm to changing environments is suggested. That natural adaptability is the algorithm's principle advantagë over current approaches.

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