Bandwidth-efficient trellis coded modulation schemes

The author proposes a scheme that shapes the power density spectrum of the transmitted signal to reduce its bandwidth. The encoder is modeled as a finite-state machine consisting of a shift register and a mapper. A pulse-shaping filter generates time-limited or Nyquist pulses. The whole system is optimized with respect to bandwidth and power efficiency, where average-power and peak-power criteria are considered. The author presents the achievable data rates of systems with quaternary input symbols and an out-of-band power of -20 dB for the various mappers and pulse-shaping filters considered. It can be seen that bandlimited pulses allow roughly a doubling of the data rate with respect to time-limited pulses. The bandwidth gain that can be reached with proper coding is remarkable. The drawback is the increased receiver complexity needed to resolve the intersymbol interference