Subspace-Based SIR Estimation for CDMA Cellular Systems

The signal-to-interference ratio (SIR) has been highlighted in the literature to be an efficient criterion for several radio resource management algorithms such as power control and handoff. In this paper we address the problem on how to obtain fast and accurate measurements of this quantity in a practical context. We develop a general SIR estimation technique for code division multiple access (CDMA) cellular systems, that is based on a signal subspace approach using the sample covariance matrix of the received signal. Analysis and simulation results for an IS-95 like system show that the SIR can be estimated to within 80% of the actual SIR after less than seven frames, or within 90% of the actual SIR after less than 15 frames. We also study a computationally less expensive SIR tracking algorithm based on updating the signal subspace. We show that the algorithm works well in the context of a rapidly time varying channel. Index Terms--code division multiple access (CDMA), signal-to-interference ratio (SIR), subspace algorithms.