Hello all, This is my first post here. :) I am currently working on a 802.16d receiver where I have to combine signals from 4 antennas and then pass on soft decisions values to the Viterbi decoder for the final output. I have managed to figure out how to combine the 4 signals and figure out which point was transmitted. I used a method described by a user on this very forum named James Sungjin Kim. He recommended that you multiply each of the received subcarriers by the channel estimate at that subcarrier. The method is described in the following thread: http://www.dsprelated.com/showmessage/48861/1.php The only problem I am having now is how to determine how good this point is. I have read in papers which says that for a channel with only AWGN, using the signal power itself is good enough. But when we combine a rayleigh fading channel or any kind of frequency selective fading, this method falls apart. Since fading only happens at specific frequencies, the SNR is no longer uniform across all of the sub-carriers. We don't know if the power at that specific subcarrier is all noise power or actual signal power. Does anyone know of a method to properly estimate the SNR using the pilot tones?? One paper I read recommended that the SNR can be estimated as: imag(ek)^2 Where ek is the equalized signal at the pilot tones. This does not make much sense in simulation since the signal at the pilot tone locations are used as starting points for linear interpolation for the channel estimate. In my simulation, equalizing the pilot tones with the channel estimate will always result in zero for the imaginary part. Anyone have any clues? I would greatly appreciate any help. Thanks in advance.. Sam

# Soft Decision for Viterbi Decoding..

Started by ●October 5, 2008