Track quality indicator with hysteresis

A method for calculating a track quality indicator from a plurality of tracker amplitude estimates comprising the steps of:

• determining the track quality indicator at the previous time increment;
• providing a base lost track threshold before any of the steps of assigning the track quality indicator;
• providing a low SNR hysteresis constant before any of the steps of assigning the track quality indicator;
• calculating a first summed log likelihood ratio (SLLR) from the tracker amplitude estimates at the current time increment before any of the steps of assigning the track quality indicator;
• providing a base uncertain track threshold;
• providing a maximum error threshold;
• computing a second summed log likelihood ratio (SLLR) from the tracker amplitude estimates at the current time increment before any of the steps of assigning the track quality indicator;
• providing a strong track threshold;
• providing a strong SNR hysteresis constant;
• if the track quality indicator at a previous time increment indicates the track was lost then:
• adding the base lost track threshold to the low SNR hysteresis constant to give a first lost track threshold;
• comparing the calculated first SLLR with said first lost track threshold, if the calculated first SLLR is at most the first lost track threshold then indicating lost track at the track quality indicator, and if the calculated first SLLR is above the first lost track threshold then continuing determining the track quality indicator;
• if the track quality indicator at a previous time increment indicates the track was not lost at said previous time then:
• using the base lost track threshold as a second lost track threshold;
• and
• comparing the calculated first SLLR with said second lost track threshold, if the calculated first SLLR is at most the second lost track threshold then indicating lost track at the track quality indicator, and if the calculated first SLLR is above the second lost track threshold then continuing determining the track quality indicator;
• if the track quality indicator at the previous time increment indicates that the track was uncertain or lost then:
• adding the base uncertain track threshold to the low SNR hysteresis constant to give a first uncertain track threshold;
• comparing the calculated first SLLR with said first uncertain track threshold and if the calculated first SLLR is at most the first uncertain track threshold then indicating uncertain track at the track quality indicator;
• if the track quality indicator at the previous time increment indicates that the track was low SNR track then:
• using the base uncertain track threshold as the second uncertain track threshold;
• comparing the calculated first SLLR with said second uncertain track threshold and if the calculated first SLLR is at most the second uncertain track threshold then indicating uncertain track at the track quality indicator;
• if the calculated first SLLR is above the first and second uncertain track threshold then:
• calculating a tracker error residual;
• comparing the tracker error residual with the maximum error threshold, if the tracker error residual is greater than the maximum error residual then indicating uncertain track at the track quality indicator and if the tracker error residual is less than the maximum error residual then continuing determining the track quality indicator;
• if the track quality indicator at a previous time increment indicates the track was strong then:
• subtracting the high SNR hysteresis constant from the strong track threshold to give a first low SNR track threshold;
• comparing the calculated second SLLR with said first low SNR track threshold, if the calculated second SLLR is less than the first low SNR track threshold then indicating low SNR track at the track quality indicator, and if the calculated second SLLR is at least the first low SNR track threshold then indicating strong track at the track quality indicator;
• if the track quality indicator at a previous time increment indicates the track was not strong then:
• adding the high SNR hysteresis constant to the strong track threshold to give a second low SNR track threshold;
• comparing the calculated second SLLR with said second low SNR track threshold, if the calculated second SLLR is less than the second low SNR track threshold then indicating low SNR track at the track quality indicator, and if the calculated second SLLR is at least the second low SNR track threshold then indicating strong track at the track quality indicator.