Apparatus and method for estimating the time of arrival of a spread spectrum signal in a wireless communication system

A wireless communication device comprising a receiver for receiving a modulated spread spectrum signal, the receiver comprising a threshold tracking loop sharing circuitry with a peak tracking loop, the threshold tracking loop comprising:

• a pseudo-noise (PN) generator for generating a receive PN code for use in spread spectrum decoding;
• a series of time delay units for adjusting a phase offset of the PN code;
• a first PN despreader coupled to the time delay units and PN generator, the first PN despreader for dispreading an early pilot signal;
• a first comparison circuit coupled to the first PN despreader for comparing a signal value of the early pilot signal with a preselected threshold value that is less than a peak value of a tracked signal and, in threshold tracking mode, for advancing the PN code phase offset if the early signal value is greater than the threshold value;
• a second comparison circuit coupled to the second PN despreader for comparing a signal value of the late pilot signal with the preselected threshold value and, in threshold tracking mode, for retarding the PN code phase offset if the late signal value is less than the threshold value;
• and
• mode control circuitry coupled to the first comparison circuit and the second comparison circuit to switch the loop operation between threshold tracking mode and peak tracking mode.

A location system for calculating the distance of a mobile communication device from a base station, the mobile device comprising a transceiver for transmitting a signal to the base station and receiving a signal from the base station, the location system comprising:

• a base station comprising a transceiver for transmitting a signal to the mobile device and receiving a signal from the mobile device;
• threshold tracking loop circuitry sharing circuitry with peak tracking loop circuitry and coupled to at least one of the base station transceiver and the mobile device transceiver, the threshold tracking loop circuitry comprising:
• a pseudo-noise (PN) generator for generating a receive PN code for use in spread spectrum decoding;
• a series of time delay units for adjusting a phase offset of the PN code;
• a first PN despreader coupled to the time delay units and PN generator, the first PN despreader for dispreading an early pilot signal;
• a second despreader coupled to the time delay units and PN generator, the second PN despreader for dispreading a late pilot signal;
• a first comparison circuit coupled to the first PN despreader for comparing a signal value of the early pilot signal with a preselected threshold value that is less than a peak value of a tracked signal and, in threshold tracking mode, for advancing the PN code phase offset if the e early signal value is greater than the threshold value;
• a second comparison circuit coupled to the second PN despreader for comparing a signal value of the late pilot signal with the preselected threshold value and, in threshold tracking mode, for retarding the PN code phase offset if the late signal value is less than the threshold value;
• and
• mode control circuitry coupled to the first comparison circuit and the second comparison circuit to switch the loop operation between threshold tracking mode and peak tracking mode.

A method for estimating the time of arrival of a spread spectrum communication signal, comprising:

• (a) receiving a spread spectrum signal;
• (b) at a fractional chip of PN code phase offset of a pseudo-noise (PN) generator for generating a PN code for use in spread spectrum decoding, sampling signal values for an early pilot signal and a late pilot signal relative to a nominal phase of the signal
• (c) comparing the early signal value with a preselected threshold value;
• (d) if the early signal value is less than the threshold value, comparing the late signal value with the threshold value;
• (e) if the late signal value is less than the threshold value, retarding the PN code phase offset;
• (f) if the late signal value is less than the threshold value, retarding the PN code phase offset;
• (g) if the late signal value is greater than the threshold, comparing the early signal value and the late signal value;
• (h) if the late signal value is greater than the early signal value, repeating steps (a)-(h) to maintain threshold tracking;
• and
• (i) estimating a receive time based on the threshold tracking.

A wireless communication device for threshold directed tracking of a spread spectrum communication signal, comprising a receiver for receiving a modulated spread spectrum signal, the receiver:

• (a) receiving a spread spectrum signal;
• (b) sampling, at a fractional chip of PN code phase offset of a pseudo-noise (PN) generator for generating a PN code for use in spread spectrum decoding, signal values for an early pilot signal and a late pilot signal relative to a nominal phase of the signal;
• (c) comparing the early signal value with a preselected threshold value;
• (d) if the early signal value is less than the threshold value, comparing the 1 late signal value with the threshold value;
• (e) if the late signal value is less than the threshold value, retarding the PN code phase offset;
• (f) if the late signal value is less than the threshold value, retarding the PN code phase offset;
• (g) if the late signal value is greater than the threshold, comparing the early signal value and the late signal value;
• (h) if the late signal value is greater than the early signal value, repeating steps (a)-(h) to maintain threshold tracking.

A wireless communication system, comprising:

• a plurality of base stations in communication with a mobile device, the base stations receiving a signal from the mobile unit and transmitting a signal to the mobile unit, the signals being formed via modulation by a sequence of spreading symbols, each of the base stations comprising a threshold tracking loop sharing circuitry with a peak tracking loop for estimating the time of arrival of a signal, each of the threshold tracking loops comprising:
• a pseudo-noise (PN) generator for generating a receive PN code for use in spread spectrum decoding;
• a series of time delay units for adjusting a phase offset of the PN code;
• a first PN despreader coupled to the time delay units and PN generator, the first PN despreader for dispreading an early pilot signal;
• a first comparison circuit coupled to the first PN despreader for comparing a signal value of the early pilot signal with a preselected threshold value that is less than a peak value of a tracked signal and, in threshold tracking mode, for advancing the PN code phase offset if the early signal value is greater than the threshold value;
• a second comparison circuit coupled to the second PN despreader for comparing a signal value of the late pilot signal with the preselected threshold value and, in threshold tracking mode, for retarding the PN code phase offset if the late signal value is less than the threshold value;
• mode control circuitry coupled to the first comparison circuit and the second comparison circuit to switch the loop operation between threshold tracking mode and peak tracking mode;
• and
• a location estimate calculator coupled to each of the base stations, the location estimate calculator determining an estimated location of the mobile unite using estimated time of arrivals from each of the base stations.

A wireless communication system comprising:

• a mobile unit in communication with a plurality of base stations, the mobile unit receiving a signal from the base stations and transmitting a signal to the base stations, the signals being formed via modulation by a sequence of spreading symbols, the mobile unit comprising a threshold tracking loop for estimating the time of arrival of a signal, the threshold tracking loop comprising:
• a pseudo-noise (PN) generator for generating a receive PN code for use in spread spectrum decoding;
• a series of time delay units for adjusting a phase offset of the PN code;
• a first PN despreader coupled to the time delay units and PN generator, the first PN despreader for dispreading an early pilot signal;
• a first comparison circuit coupled to the first PN despreader for comparing a signal value of the early pilot signal with a preselected threshold value value that is less than a peak value of a tracked signal and, in threshold tracking mode, for advancing the PN code phase offset if the early signal value is greater than the threshold value;
• a second comparison circuit coupled to the second PN despreader for comparing a signal value of the late pilot signal with the preselected threshold value and, in threshold tracking mode, for retarding the PN code phase offset if the late signal value is less than the threshold value;
• and
• mode control circuitry coupled to the first comparison circuit and the second comparison circuit to switch the loop operation between threshold tracking mode and peak tracking mode;
• and
• a location estimate calculator coupled to each of the base stations, the location estimate calculator determining an estimated location of the mobile unit using estimated time of arrivals from each of the base stations.