Abstract: A method for estimating a communication channel comprising one or more sub-channels between at least a first transceiver and at least a second transceiver is provided. The method comprises transmitting a first set of training data from the first transceiver to the second transceiver, receiving observed signals at the second transceiver, re-transmitting said observed signal back to the first transceiver, and calculating a roundtrip channel estimate at the first transceiver. The method further comprises transmitting a second set of training data from the second transceiver to the first transceiver, receiving observed signals at the first transceiver, and calculating a reverse link channel estimate. From the roundtrip channel estimate and the reverse link channel estimate, a forward link channel estimate is computed at the first transceiver.

Abstract: A system and method for estimating the number of emitters having wavefronts impinging on an array of m sensors may be used in the presence of correlated, unequal-level, as well as uncorrelated, equal-level noise. In the invention, the m eigenvalues of the sensor correlation matrix are evaluated to determine whether they are related to noise or to signals. Each eigenvalue, scaled by the estimated noise power level, is compared to the arithmetic mean of the preceding noise eigenvalues to determine whether the difference is enough to indicate the presence of a signal. Similarly, the successive slopes (differences between each scaled eigenvalue and its predecessor) may be compared to the arithmetic mean of the preceding slopes to make the determination. In an alternative embodiment, the eigenvalues are desensitized by increasing each by an amount not much larger than the first noise eigenvalue.