Method of identifying a frame for erasure in a digital data transmission system

摘要

A method of improving frame erasure performance for slow frequency hopping channels utilizing two convolutional decoding steps and two PBER thresholds in conjunction with the cyclic redundancy check. The breakdown condition in the convolutional decoding process is detected by means of a "forward backward decoding' algorithm. The breakdown condition is detected with two passes of the convolutional decoder. When the decoder breaks down an essentially random burst of erroneous decoded bits are produced, and due to the memory effect of the decoder these will be different in each decoding direction. These erroneous random errors may be detected by comparison of the two decoded sets of data.