Adaptive hard handoff algorithms

摘要

The design of hard handoff algorithms based on optimizing thentradeoff between link quality and rate of handoffs is considered. Fornhandoff algorithms based on this criterion, adaptation is preciselyndefined in terms of remaining on a locus of desirable operating pointsnas system parameters (such as mobile velocity) change. A rule based on anlinear cost criterion is used to select desirable operating points. Fornthis rule, it is shown that the optimal handoff algorithm, which isnimpractical, is easily adapted by fixing a single tradeoff parameter atnan appropriate value. The same adaptation property is shown to hold fornan easily implementable approximation to the optimal algorithm, thenlocally optimal (LO) handoff algorithm. This is in contrast to the poornadaptation of hysteresis based approaches which require lookup tablesnfor adaptation. Practical estimators for all relevant system parametersnbased on a short window of pilot signal strength measurements are alsondiscussed. It is shown that the LO algorithm adapts well when thesensimple estimators are used. A hysteresis-threshold approximation to thenadaptive LO algorithm is also developed