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System and method for warning of and providing greater immunity from an impeding call drop in a digital wireless system

  • US 6,381,455 B1
  • Filed: 10/15/1998
  • Issued: 04/30/2002
  • Est. Priority Date: 10/15/1998
  • Status: Expired due to Term
First Claim
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1. In a wireless telecommunications system including a Mobile Switching Center (MSC) connected to at least one radio base station that services at least one mobile radio unit, said base station and said mobile unit communicating with each other in a digital transmission mode wherein voice data is digitally encoded by voice encoders located in said MSC (or said base station) and said mobile unit as a sequence of variable rate information frames, said information frames being packaged by physical layers located in said MSC (or said base station) and said mobile unit into a sequence of physical transmission frames that include said information frames with appended control and error checking bits, a method for warning a user of, and providing greater immunity from, an impending call drop, comprising the steps of:

  • monitoring transmissions between said base station and said mobile unit for frame errors while said voice encoders are encoding voice data at an initial information frame rate and said physical layers are receiving initial rate information frames from said voice encoders and transmitting physical transmission frames at an initial physical frame rate corresponding to said initial information frame rate;

    upon the number of said frame errors reaching a predetermined threshold, controlling said voice encoders to reduce the information frame rate from said initial information frame rate to a reduced information frame rate such that reduced rate information frames are provided to said physical layers;

    controlling said physical layers to add error correction bits to said reduced rate information frames to transmit error correction enhanced physical transmission frames at said initial physical frame rate; and

    whereby said error correction enhanced physical transmission frames provide increased error correction robustness for greater immunity from call dropping, and result in a characteristic change in speech quality due to said reduced rate information frame being incorporated therein to serve as an impending call drop warning.

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