Abstract:The channel noise variance information is required by the soft decision for a channel decoder. However, such information is usually unknown and/or time varying. In this paper, the effects of channel noise variance on soft decision metric are analyzed. Then, a new channel noise variance estimation method applied to the multipath fading channel is presented to generate exact soft-decision metric for a channel decoder. Applying the proposed method to the outer receiver of Digital Terrestrial Multimedia Broadcasting(DTMB) system, simulation results indicate that the proposed method converges rapidly and the generated soft decision metric is very close to the optimal one.