Design of a reduced complexity rateless spinal decoder

Taş, Murat
Wireless communication systems utilize several forward error correcting techniques to cope with changing channel conditions efficiently. One way is selecting from a list of coding/modulation schemes by considering the actual channel state. When this approach of choosing a fixed rate code is not applicable, one can use rateless codes whose rates are dynamically changing with respect to the changing channel conditions. A rateless encoder continues to send its codeword/packet to the destination unless the receiver sends an acknowledgement. In this thesis, after investigating and evaluating the effects of the main parameters on the performance of the rateless spinal codes; our work focuses on making the spinal decoder algorithm more efficient in terms of the number of computations, while achieving the same rate values. We propose a modification that uses the initial information extracted from path metric distributions to decrease the computational burden at the initial steps of the ‘bubble decoder’ of Perry et al. The reduction offered by our modified algorithm is up to 70% of the original computational complexity at the cost of negligible rate losses.