Apparatus for preventing use of erroneous speech encoding parameters for decoding digital speech transmissions

A cellular radio system, comprising:

• a plurality of base stations;
• a speech decoder located further uplink and remote from said base stations and arranged to serve said base stations;
• a mobile station arranged for transmitting a signal containing information decodable as speech, to one of said base stations;
• a corresponding one of said base stations which has received said signal being arranged to communicate to said remote speech decoder information frames carrying speech encoding parameters, a synchronization word in a first portion of each said information frame, and a synchronization check bit recurring at predetermined intervals within a remaining portion of each said information frame;
• said remote speech decoder further comprising:
• means for receiving said information frames from said corresponding one of said base stations;
• means for synchronizing said remote speech decoder with a received one of said received information frames only by use of a corresponding said synchronizing word in the first portion of the frame;
• means for extracting said speech encoding parameters from said received information frame in order to provide extracted speech encoding parameters;
• means for detecting errors in the remaining portion of the frame by monitoring for errors only in the recurring synchronization check bit, errors in the recurring synchronization check bit being indicative of an errors in the remaining portion of the frame;
• and
• means for storing said extracted speech encoding parameters in said remote speech decoder in order to update speech parameters presently used in speech decoding, when no error is detected in said recurring synchronization check bit in said received information frames, and for preventing storing of said extracted speed encoding parameters in said remote speech decoder and for preventing the updating of speech parameters presently used in said speech decoding when an error is detected in said recurring synchronization check bit in said received information frames.