Joint source-channel coding over frequency selective fading channels with feedback using OFDM

We investigate joint source-channel coding for frequency selective fading channels with feedback. We use multicarrier modulation (also called OFDM-orthogonal frequency division multiplexing) as modulation procedure to reduce the effects of ISI. We model the time variation of a stationary and ergodic frequency selective fading channel as a finite state Markov chain and we perform optimal power allocation for channel states and subchannels. In the case when the number of subcarriers is small, equalization is required; we use a recursive block MAP receiver that provides soft decisions and accounts for the residual redundancy at the vector quantizer output. This decoder is used in conjunction with a channel optimized vector quantization (COVQ) or channel matched tree structured vector quantization (CM-TSVQ) in which the VQ design is performed with respect to channel error matrices computed by simulation. When using TSVQ, the indices of the first stages of the TSVQ are transmitted on the subchannels with higher power. Results are presented for codebooks designed by using COVQ and CM-TSVQ for a Markov source; we consider a two subchannel case with equalization, and a fading channel with two equiprobable states and flat fading.