Performance of turbo-coded OFDM

We consider the performance of coded OFDM using turbo-codes, for application in digital broadcasting systems. We consider in particular the effect of excess multipath delay, greater than the OFDM guard period. We show that turbo-codes of length 8192 can give performance improvements of some 8 dB on a Rayleigh fading channel (such as may be expected), over the conventional convolutional codes in the existing standards. We show that this makes the system much more robust to excess multipath delay, and may allow the reduction of the guard period. We also consider the use of higher order modulation (e.g. 16-QAM) within a turbo-coded modulation scheme, and show that turbo-codes should allow an increase in order which in some circumstances may double the capacity