Adaptive Nonlinear Canceller (ANLC)

This study was directed at the analysis and characterization of nonlinearities associated with the AFSATCOM/ALT-32H interference problem and the development of an automatic nonlinear cancellation system. Analysis included the use of power series, volterra series, and perturbation analysis to predict the generation of intermodulation products. Characterization studies included the use of variable power input two-tone or notch noise to measure IMP generation by various nonlinear devices. Manual and automatic nonlinear interference cancellation systems were designed and implemented. Experimental studies are conducted using different nonlinearities, a wide range of input powers, a wide range of frequency spectra exciting the nonlinearities, various delays and multipath before and after the nonlinearities, and a number of modulation formats. To achieve a good automatic nonlinear cancellation, the following conditions must be met: (1) A good nonlinear must be generated. (2) Amplitude versus frequency shape of the signal impinging on the interfering and reference nonlinearities are critically important for good nonlinear cancellation. (3) Interfering and reference nonlinearity types must be matched. (4) Multipath before the interfering and reference nonlinearities is critically important. A multipath difference on the order of a few feet will cause complete loss of cancellation. (5) The total power input to the interfering nonlinearity for good cancellation.