Trellis Coding of Nonlinearly Amplified Quadrature Amplitude Modulation (NLA-QAM)

Generation of quadrature amplitude modulation (QAM) by superposition of quadrature phase shift keying (QPSK) components enables the use of nonlinear amplifiers. QAM generated using nonlinear amplifiers in this way is referred to as nonlinearly amplified QAM, or NLA-QAM. In this thesis, trellis coding of NLA-QAM is studied. Convolutional codes are determined which provide the best normalized free distances. The best codes are those whose performance is best for variations which may occur in the amplifier ratio and phase offset of the amplifiers used. These convolutional codes are determined for constraint lengths of two through seven. Code searches are conducted for all of the unique codes with these constraint lengths, except where the number of codes to search becomes too large. The amplifier ratio and phase offset are varied for all codes in the searches to determine the values which provide the peak performance. After determination of the parameters corresponding to peak performance, the amplifier ratio and phase offset are varied to determine the codes which are most resistant to variations in the amplifier ratio and phase offset which may occur in a practical system using QAM generated by superposition