Bad frame indicator for radio-telephone receivers in GSM mobile systems

A method for bad frame indication of a current speech frame in a GSM mobile station, comprising steps of:

• estimating a signal-to-noise ratio of the speech frame;
• checking a cyclic redundancy code value that indicates whether the speech frame passes or fails a cyclic redundancy code error detection;
• setting a current BFI flag to indicate bad frame when the speech frame fails said cyclic redundancy code error detection;
• setting said current BFI flag to indicate bad frame when said signal-to-noise ratio is below a pre-specified value of said signal-to-noise ratio;
• checking a current receive signal quality metric of the speech frame when the speech frame passes said cyclic redundancy code error detection and said signal-to-noise ratio is above said pre-specified value;
• setting said current BFI flag to indicate good frame when said current receive signal quality metric is above a high-threshold;
• setting said current BFI flag to indicate bad frame when said current receive signal quality metric is not above a low-threshold;
• and
• varying a calculation of the current frame conditionally on an outcome of a calculation for a previous frame, when said current receive signal quality metric is not above said high-threshold and is above said low-threshold, by adding the steps of:
• checking a previous BFI flag and a previous receive signal quality metric;
• setting said current BFI flag to indicate good frame when either or both occur that said previous BFI flag indicates good frame or said previous receive signal quality metric is above said high-threshold;
• and
• setting said current BFI flag to indicate bad frame when said previous BFI flag indicates bad frame and said previous receive signal quality metric is not above said high-threshold.

A method for bad frame indication of a speech frame in a GSM mobile station, comprising:

• a step for providing a signal-to-noise ratio of the speech frame;
• a step for evaluating a cyclic redundancy code error detection for the speech frame and providing a cyclic redundancy code value that indicates whether the speech frame passes or fails said cyclic redundancy code error detection;
• a step for decoding the speech frame into a decoded frame;
• a step for re-encoding said decoded frame into a re-encoded frame;
• a step for correlating the speech frame with said re-encoded frame to provide a correlation;
• a step for using said correlation to provide a current receive signal quality metric;
• a step for storing a previous BFI flag and a previous receive signal quality metric;
• a step for providing a comparison of said signal-to-noise ratio to a pre-specified value;
• a step for comparing said current receive signal quality metric to a high-threshold when the speech frame passes said cyclic redundancy code error detection and said signal-to-noise ratio is above said pre-specified value;
• a step for comparing said current receive signal quality metric to a low-threshold when said current receive signal quality metric is not above said high-threshold;
• a step for varying a frame calculation for the speech frame using an outcome of a previous speech frame calculation of said previous BFI flag and said previous receive signal quality metric, including:
• when said current receive signal quality metric either is above said high-threshold or is not above said low-threshold,
• a step for setting a current BFI flag indicate whether the speech frame is a bad frame or a good frame according to said comparison of said signal-to-noise ratio, said cyclic redundancy code value, said current receive signal quality metric, and
• when said current receive signal quality metric is not above said high-threshold and is above said low-threshold,
• a step for checking said previous BFI flag and said previous receive signal quality metric;
• and
• a step for setting said current BFI flag to indicate whether the speech frame is a bad frame or a good frame according to said previous receive signal quality metric,and said previous BFI flag.

A GSM mobile station that receives a current speech frame, comprising:

• means for estimating a signal-to-noise ratio of the current speech frame;
• means for checking a cyclic redundancy code value that indicates whether the current speech frame passes or fails a cyclic redundancy code error detection;
• means for checking a current receive signal quality metric of the current speech frame when the current speech frame passes said cyclic redundancy code error detection and said signal-to-noise ratio is above a pre-specified value;
• means for setting a current BFI flag to indicate whether the current speech frame is a bad frame according to said signal-to-noise ratio, said cyclic redundancy code value, and said current receive signal quality metric when said current receive signal quality metric either is above a high-threshold or is not above a low-threshold;
• means for conditionally using an outcome of a calculation for a previous speech frame, said outcome including a previous BFI flag and a previous receive signal quality metric, by checking said previous BFI flag and said previous receive signal quality metric when said current receive signal quality metric is not above a high-threshold and is above a low-threshold and setting said current BFI flag to indicate whether the current speech frame is a bad frame according to said previous receive signal quality metric, and said previous BFI flag.

A mobile station that receives a speech frame, comprising:

• a DSP module that provides a signal-to-noise ratio of the speech frame, evaluates a cyclic redundancy code error detection for the speech frame, provides a cyclic redundancy code value that indicates whether the speech frame passes or fails said cyclic redundancy code error detection, and decodes the speech frame into a decoded frame;
• an encoder, connected to said DSP module, that receives said decoded frame and re-encodes said decoded frame into a re-encoded frame;
• a correlator, connected to said encoder, that correlates the speech frame with said re-encoded frame to provide a correlation, and that uses said correlation to provide a current receive signal quality metric;
• and a BFI module, connected to said DSP module and to said correlator, wherein said BFI module:
• stores a previous BFI flag and a previous receive signal quality metric;
• receives said signal-to-noise ratio and provides a comparison of said signal-to-noise ratio to a pre-specified value;
• receives said cyclic redundancy code value;
• receives said current receive signal quality metric and compares said current receive signal quality metric to a high-threshold when the speech frame passes said cyclic redundancy code error detection and said signal-to-noise ratio is above said pre-specified value;
• compares said current receive signal quality metric to a low-threshold when said current receive signal quality metric is not above said high-threshold;
• performs a frame calculation, when said current receive signal quality metric either is above said high-threshold or is not above said low-threshold, wherein said BFI module:
• sets a current BFI flag to indicate whether the speech frame is a bad frame or good frame according to said comparison of said signal-to-noise ratio, said cyclic redundancy code value, and said current receive signal quality metric;
• varies said frame calculation, when said current receive signal quality metric is not above said high-threshold and is above said low-threshold, for the speech frame using an outcome of a previous frame calculation of said previous BFI flag and said previous receive signal quality metric, wherein said BFI module:
• checks said previous BFI flag and said previous receive signal quality metric;
• and
• sets said current BFI flag to indicate whether the speech frame is a bad frame or good frame according to said previous receive signal quality metric, and said previous BFI flag.

A GSM system including a mobile station that receives a speech frame, said mobile station comprising:

• a receiver that demodulates a radio frequency signal to provide the speech frame received by said mobile station;
• a DSP module that provides a signal-to-noise ratio of the speech frame, evaluates a cyclic redundancy code error detection for the speech frame and provides a cyclic redundancy code value that indicates whether the speech frame passes or fails said cyclic redundancy code error detection, and decodes the speech frame into a decoded frame using a Viterbi decoder;
• an encoder, connected to said DSP module, that receives said decoded frame and re-encodes said decoded frame into a re-encoded frame;
• a correlator, connected to said encoder, that correlates the speech frame with said re-encoded frame to provide a correlation, and that uses said correlation to provide a current receive signal quality metric;
• a BFI module, connected to said DSP module and to said correlator, wherein said BFI module:
• stores a previous BFI flag and a previous receive signal quality metric;
• receives said signal-to-noise ratio and provides a comparison of said signal-to-noise ratio to a pre-specified value;
• receives said cyclic redundancy code value;
• sets a current BFI flag to indicate bad frame when said cyclic redundancy code value indicates the speech frame fails said cyclic redundancy code error detection;
• sets said current BFI flag to indicate bad frame when said signal-to-noise ratio is below said pre-specified value;
• receives said current receive signal quality metric and, when the speech frame passes said cyclic redundancy code error detection and said signal-to-noise ratio is above said pre-specified value, compares said current receive signal quality metric to a high-threshold corresponding to a first pre-determined value of said correlation;
• sets said current BFI flag to indicate good frame when said current receive signal quality metric is above said high-threshold;
• compares, when said current receive signal quality metric is not above said high-threshold, said current receive signal quality metric to a low-threshold corresponding to a second pre-determined value of said correlation;
• sets said current BFI flag to indicate bad frame when said current receive signal quality metric is not above said low-threshold;
• varies, when said current receive signal quality metric is not above said high-threshold and is above said low-threshold, a calculation for said speech frame of said current BFI flag conditionally on an outcome of a calculation for a previous speech frame of a previous BFI flag and a previous receive signal quality metric, wherein said BFI module:
• checks said previous BFI flag and said previous receive signal quality metric;
• sets said current BFI flag to indicate good frame when either, or both, occur that said previous BFI flag indicates good frame or said previous receive signal quality metric is above said high-threshold;
• sets said current BFI flag to indicate bad frame when said previous BFI flag indicates bad frame and said previous receive signal quality metric is not above said high-threshold.