Efficient Power Allocation in Turbo Decoded OFDM Systems Using Logarithmic Maximum A-Posteriori Algorithm and Soft Output Viterbi Algorithm Under Various Fading Environments

Abstract

Orthogonal frequency division multiplexing (OFDM) is a multicarrier modulation technique which is gaining wide popularity in Wireless cellular networks as it is used to mitigate the multipath effects and to achieve high data rate. The Coded Orthogonal Frequency Division Multiplex (COFDM) technique is an extension of the conventional OFDM systems as they provide reliable reception of signals affected by strong distortions. The increase spectral efficiency in turn increases power. Therefore power optimization has to be considered, when coding is incorporated into the existing system. In this paper, the conventional Viterbi decoder is used along with soft coding technique which provides better convergence property. These results are compared to the Soft Output Viterbi Algorithm (SOVA) and Logarithmic Maximum A-posteriori Decoder (Log-Map) which give better performance than conventional Viterbi algorithm. The power optimization is done in all the cases and the advantages of multicarrier modulation are thus reassured without much channel information feedback from receiver to transmitter.