A High Bandwidth Efficiency Adaptive Turbo Trellis Coded OFDM over A Wideband Fading Channel

摘要

This paper is concerned with the employment of Turbo Trellis Code Modulation (TTCM) technique in an adaptive OFDM system over a frequency selective fading channel to increase the power efficiency and data rate. The structure of TTCM modulator provides the separation of coding and modulation design but a method is proposed in this paper to combine TTCM and adaptive modulation. In this method the number of coded bits is kept constant and the number of uncoded bits is adapted according to the state of the channel. With this approach the coding part and the modulation part are separated and can be designed independently. This system can be called "adaptive TTCM-OFDM" or A-TTCM-OFDM. The presented simulation results are compared with the bit error rate (BER) performance of a non adaptive system. This system shows an approximately 25 dB improvement in comparison with a non-adaptive system over a frequency selective fading channel.