The invention relates to compounds of the general formulawherein Ar1, Ar2, R4, R5, R6, R7, R8, W, X, a and b have the significances given in the specification, and optionally the enantiomers thereof. System includes an advanced digital signal processing method provides spatial and temporal interference cancellation, super-resolution direction-finding, and high resolution spectrum analysis techniques. The resulting weight is identified as the weight of each attribute of the identified user.