Doppler frequency estimation for channel sounding using switched multiple-element transmit and receive antennas

We proposed (Fleury, B.H. et al., Proc. XXVII Gen. Assy of Int. Union of Radio Scientists, p.2127, 2002; Proc. IEEE Veh. Tech. Conf., VTC 2002, p.522-6, 2002) the ISI-SAGE (improved-search-and-initialization space-alternating generalized expectation-maximization) algorithm for joint estimation of the relative delay, the directions of departure and of incidence, the Doppler frequency (DF) and the complex weight (or attenuation) of waves propagating from the transmitter (Tx) site to the receiver (Rx) site in mobile radio environments. We now present theoretical and simulation results describing the performance of the scheme for DF estimation applied in combination with channel sounding using switched multiple-element Tx and Rx antennas. The maximum absolute DF that can be estimated is shown to be half the switching rate rather than half the measurement cycle rate as commonly believed. The switching rate is the rate with which the pairs of Tx and Rx elements are switched, while the measurement cycle rate is the rate with which any fixed pair of Tx and Rx elements is switched. The ratio of the former rate by the latter is larger than or equal to the product of the numbers of Tx and Rx elements. Hence, the scheme allows for DF estimation in a range much larger than commonly believed. Monte-Carlo simulations also show that above a certain signal-to-noise-ratio (SNR) threshold, depending on the characteristics of the TDM mode, the estimator performs close to optimum. The results make it possible to link the parameter setting of the TDM mode to the operational SNR range for individual waves to be estimated.