Adaptive averaging methodology for handoffs in cellular systems

The purpose of this paper is to show how information in signal strength measurements can be exploited to improve the quality of handoff decisions, for both large and small cells. Averaging of signal strength fluctuations is required. This leads to the following tradeoff problem for the averaging interval for the signal strength measurements. If the interval is too short, the fading fluctuations are not sufficiently smoothed out. If the interval is too long, delay in handoff increases. With this tradeoff in mind, we present a method to adaptively change the averaging interval. The method is based on estimating the maximum Doppler frequency, f_D, as a means to obtain mobile velocity, the key to the tradeoff. A method used for estimating f_D from the squared deviations of the signal envelope is outlined. Exact analysis for the f_D estimate as a function of squared deviations of the logarithmically compressed signal envelope in Rayleigh fading is presented. An extension of the algorithm for robustness in a Rician fading environment is given. Sensitivity issues of the estimates are considered. An adaptive scheme for optimal averaging is outlined