Signal-to-noise ratio measurement employing trellis decoders

In many practical applications (eg. time varying channels, adaptive communication systems), it is useful to measure the signal-to-noise ratio (SNR) of the channel. The known algorithms require a sufficient amount of computer calculations and a very large number of received symbols must be examined before a statistically reliable SNR estimate can be made. The authors introduce two new techniques for SNR measurement using trellis structure. To do this, two metric values at the output of the trellis decoder are defined. These metrics are derived from the original decoding processes by subtracting the confidence of the greatest likelihood path from that of the next greatest likelihood path, and/or the one with minimum likelihood path