LT-AF Codes: LT Codes with Alternating Feedback

LT codes are capacity achieving and flexible rateless that need a single-bit feedback to inform the encoder of the successful decoding. However, this weak feedback channel remains unused when the transmission is in progress. In addition, although LT codes are asymptotically capacity achieving, their performance significantly degrades for short block lengths. Consequently, we propose LT Codes with Alternating Feedback (LT-AF Codes) that considerably improve the performance of LT codes for short-block lengths when belief propagation decoder is in use. In our proposed scheme, the decoder alternatively issues two types of feedbacks based on the dependencies of the still undecoded received output symbols and the number of decoded input symbols. We propose two methods to form the latter type of feedback with a trade-off in their complexity and performance.