TIME-DELAY AND SPATIAL SIGNATURE ESTIMATION USING KNOWN ASYNCHRONOUS SIGNALS

This paper considers the problem of estimating the parameters of known signals received asynchronously by an array of antennas, The paramete rs of primary interest are the time delays of the signals and their sp atial signatures at the array, Estimates of the signal directions of a rrival are also considered but are of secondary importance in this wor k, Maximum likelihood algorithms and more computationally efficient ap proximations are developed for both the case where all received signal s are identical (the channel estimation/overlapping echo problem) and where they are all distinct, Conditions are also derived under which t he standard matched filter approach yields consistent and statisticall y efficient parameter estimates, The issue of solution uniqueness is a ddressed, and in particular, an upper bound on the number of signals w hose parameters may be uniquely identified is derived for a number of different cases, Typically, the bound is far greater than the number o f sensors and is limited only by the number of data samples collected, Some representative simulation examples are also included to illustra te the algorithms' performance relative to the Cramer-Rao bound.