Coded overlapped quadrature modulation

A coding method using sequence coding and overlapping quadrature pulses to improve error performance and spectral efficiency is presented. It is introduced as an extension of trellis coded modulation (TCM) and achieves its bandwidth efficiency not by signal space coding in an expanded signal set, but by increasing signaling speed via pulse overlapping. Results are presented for overlapped coded quadrature phase shift keying (QPSK) signaling, and it is shown that for time-raised cosine quadrature pulses, power and spectral efficiencies rivaling those attainable by coded Nyquist signalling are achieved. The new codes are easily generated using tables of optimum convolutional codes