High-resolution channel parameter estimation for MIMO applications using the SAGE algorithm

This contribution presents an extension of the SAGE (space-alternating generalized expectation-maximization) algorithm originally published in Fleury et al. (1999) that allows for joint estimation of the complex weight, the relative delay, the direction (i.e. azimuths and co-elevations) of departure and of incidence, as well as the Doppler frequency of waves propagating from the transmitter to the receiver in mobile radio environments. The scheme is particularly well suited for MIMO (multiple-input multiple-output) channel investigations. Its performance, in terms of convergence rate and asymptotic behaviour of the root-mean-square estimation errors, is assessed by means of Monte-Carlo simulations in synthetic time-invariant channels. The results demonstrate rapid convergence (six SAGE iteration cycles) of the root-mean-square estimation errors towards values close to the root of the corresponding Cramer-Rao lower bounds for the "one-wave" scenario, even when the waves only slightly differ either in delay, in direction of departure, or in direction of incidence. The SAGE algorithm is also applied to measurement data to assess the propagation constellation in a non-line-of-sight and an obstructed line-of-sight situation. Most of the estimated waves can be easily related to the propagation environments. Finally, the computational expense of the scheme is shortly discussed.