Theoretical limits on time-of-arrival (equivalently,range) estimation are derived for multicarrier systems in thepresence of interference. Specifically, closed-form expressions areobtained for Cramer-Rao bounds (CRBs) in various scenarios.In addition, based on CRB expressions, an optimal power allocation(or, spectrum shaping) strategy is proposed. This strategyconsiders the constraints not only from the sensed interferencelevel but also from the regulatory emission mask. Numericalresults are presented to illustrate the improvements achievablewith the optimal power allocation scheme, and a maximumlikelihood time-of-arrival estimation algorithm is studied to assessthe effects of the proposed approach in practical estimators.
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