Analysis of signal-to-interference ratio estimation methods for wireless communication systems

The signal-to-interference ratio (SIR) is an important metric of communication link quality. For wireless data systems SIR estimates are used in several control actions and for optimal allocation of radio resources. This paper first develops SIR estimators based on pilot symbols and then extends the results to estimators based on data symbols. It is shown that long-term smoothing of the interference variance estimates improves the overall estimation accuracy. Since both pilot and data symbols are available, estimators that optimally combine estimates from both types of symbols are also considered. In all cases, approximate analytic results are provided and validated using simulations. The analytic expressions serve two purposes. Firstly, improved estimators based on bias correction become apparent from the expressions and secondly, optimal weights for combining pilot and data based estimators can be evaluated. Results show that modest to substantial improvement in estimation accuracy is possible through optimal combining