A bandwidth-efficient binary turbo coded waveform using QAM signaling

Although a significant amount of coding gain can be achieved, the binary turbo code does not have good bandwidth efficiency unless it is heavily punctured. Turbo trellis coded modulation (TTCM) can provide good turbo code performance without bandwidth expansion. However, it requires unique code design. The simplest way to attain both power and bandwidth efficiency is to adopt high-order modulation schemes with a commonly studied binary turbo code. This approach requires a conversion of demodulator output, which is associated with the nonbinary channel symbol, into bit metrics to input to the binary turbo decoder. This paper investigates various conversion functions for 16QAM and 64QAM constellations. The turbo coded bit error rate performances are compared using these metrics.