US Patent 7515658 Method to adaptively scale the input to a channel decoder

The range R of effective bits (those containing information) within the N bit output(s) from an inner modem is determined and employed to select the M soft bits passed to a channel decoder, thereby avoiding underflow or overflow degrading the channel decoder performance. The average and standard deviation of 1P values for a base-two logarithm of the N bit output are used to determine the range R of effective bits, with the N bits shifted and clipped based on the computed value of R so that the M most significant bits from that range R are passed to the channel decoder.