Two related cancellation techniques based on "tentative" decisions are proposed for removing intersymbol interference, due to channel nonlinearities, for voiceband data transmission. Cancellation of intersymbol interference avoids the need for equalizing or "inverting" analog nonlinear operations as in the decision-feedback method previously proposed by Falconer. The nonlinear cancellation approach removes nonlinear interference terms without excessive noise enhancement and allows effective implementation with ROM's to generate the needed nonlinear signal variables that are to be weighted and summed. The first technique can be incorporated as an "add-on" unit to a present-day modem; the second technique requires a different receiver architecture but offers somewhat enhanced improvement. Simulation results for 9.6 kbit/s data transmission over nonlinear channel models show that both techniques can offer substantial performance improvements for 16-point QAM systems.

A phase modulator with good phase linearity over an extended range of inputs is described. Performance results in terms of signal-to-distortion ratio are given.

Matched and Wiener filters are considered for two-dimensional signal processing applications when the a priori information about signal and noise characteristics are not completely specified. This work is an extension of previous work on robust filters for one-dimensional processing. The approach is to design filters which are saddle-point or mini-max solutions for the criterion functional (mean-squared-error or signal-to-noise ratio) over the classes of allowable signal shapes and signal and noise spectral densities.

Finite-bit representation of the coefficients and quantization of input data are studied in digital matched filters for weak-signal detection. An algorithm for optimum coefficients and equations for the optimum input quantizer are obtained for the known signal in additive noise problem. Some numerical performance results are given.

A study of non-coherent digital matched filters (DMF's) with multibit quantizers, matched to phase-shift-keyed signals, is presented. Results relating output and input signal-to-noise ratios are given for three types of additive channel interference and mixtures thereof: white Gaussian noise and incoherent and coherent constantamplitude sine-wave jamming. These results are compared with both analog filter results and computer simulation runs obtained previously.