Turbo equalization and channel re-estimation in OFDM over doubly-selective channel

We study the application of turbo equalization in orthogonal frequency division multiplexing (OFDM) system over doubly-selective channel. Maximum A Posteriori (MAP) equalization that exploits characteristics of the banded channel structure in OFDM is used in our turbo equalization. In settings similar to Japan´s ISDB-T standards, we find that banded channel structure that accounts for only 1 neighboring subcarrier (on one side) is sufficient to ensure a good equalization performance. At moderate Doppler frequency, turbo equalization does not enhance the system performance significantly. Furthermore, the effects of 1) initial channel estimation with turbo equalization; 2) channel re-estimation with turbo equalization are investigated, with the latter conferring greater bit error-rate (BER) enhancement than the former. Channel estimation has a more prominent effect on performance than turbo equalization, as verified by numerical simulations.