Performance analysis of velocity (Doppler) estimators in mobile communications

The knowledge of the maximum Doppler spread, or equivalently the vehicle velocity is of paramount importance in such diverse applications as adaptive modulation and handoff. In this paper we derive the Cramer-Rao bound for all Doppler estimators that utilize the I/Q components of the channel coefficients, which is also shown to be a bound for all estimators that utilize the envelope or the logarithm of the envelope. Furthermore, by exploiting the method of stationary phase, we show that the sample covariances of the small scale fading converge at a rate of O(log(N)/N), regardless of the angle of arrival distribution. This is used to conclude that the covariance-based estimators in the literature converge to their true values at that same rate. We compare the CRB with the variance of covariance-based Doppler estimators by Monte Carlo simulation.