Design of irregular repeat accumulate codes for OFDM systems with partial channel state information

Irregular repeat accumulate (IRA) codes perform very close to capacity on some memory-less channels with coherent detection. Further, they can be encoded and decoded in linear time. This paper considers the design of IRA codes for intersymbol interference (ISI) channels when only partial channel state information (CSI) is available at the receiver and orthogonal frequency-division multiplexing (OFDM) is used as the modulation format. The authors use a simple receiver structure that performs iterative channel estimation and decoding and use nonsystematic IRA codes that are optimized for this receiver. This combination is shown to perform within a few tenths of a decibel from the capacity of a receiver with perfect CSI and is also shown to be robust to change in the number of channel taps and Doppler.