A LOCALLY OPTIMAL HANDOFF ALGORITHM FOR CELLULAR COMMUNICATIONS
V. V. Veeravalli and O. E. Kelly
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 {\em expected number of service failures} and {\em expected
number of handoffs}, 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 solution is obtained which, though impractical,
can be used as a benchmark in the comparison of suboptimal schemes. A
simple, {\em 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 is akin to the ROC curves of radar detection is presented.
Simulation results show that the locally optimal algorithm outperforms
the hysteresis 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
advantage over current approaches.