M-QAM modem verification

The objective of this program was to verify the technical feasibility of the variable mode M-ary Quadrature Amplitude Modulation (M-QAM) concepts. Specifically, the adaptive predistortion and baseband equalizer techniques were to be breadboarded and evaluated for M-QAM modes for M = 4, 16, and 64. The breadboard was to operate within the constraints of FCC docket 19311 and achieve spectral efficiencies of 1.5, 3.0, and 4.5 bits/sec/Hz for M = 4, 16, and 64. The breadboard was constructed and tested and the adaptive predistortion and baseband equalizer techniques proven feasible. Performance curves are presented for the various modes (M = 4, 16, and 64) for back-to-back operation as well as through a simulated microwave link. Performance for various levels of TWT power backoff when predistortion is enabled or disabled and when the baseband equalizer is enabled or disabled are presented.