Separate Turbo Code and Single Turbo Code Adaptive OFDM Transmissions

This paper discusses the application of adaptive modulation and adaptive rate turbo coding to orthogonal frequency-division multiplexing (OFDM), to increase throughput on the time and frequency selective channel. The adaptive turbo code scheme is based on a subband adaptive method, and compares two adaptive systems: a conventional approach where a separate turbo code is used for each subband, and a single turbo code adaptive system which uses a single turbo code over all subbands. Five modulation schemes (BPSK, QPSK, 8AMPM, 16QAM, and 64QAM) are employed and turbo code rates considered are 1/2 and 1/3. The performances of both systems with high (10−2) and low (10−4) BER targets are compared. Simulation results for throughput and BER show that the single turbo code adaptive system provides a significant improvement.