On the impact of noise power estimation for soft information generation in OFDM-based PLC systems

In this paper, a sub-optimal log probability ratio is proposed as soft decision information for the Viterbi decoding in OFDM based PLC system with differentially modulated QPSK, which requires average noise power on each subcarrier. A simple method to determine average noise power is described. Potential narrow band interferer, which may negatively affect the quality of the soft decision information, is detected and erased. Performance evaluation by using a simulated channel model and by using real field data shows that a proper consideration of frequency dependent noise power in the soft decision information can lead to a significant reduction of erroneous received packet compared to the case where a constant noise power over all subcarrier is assumed.