"When widely deployed, wireless terminal location techniques based on signal signatures will provide location information over a wider service area and more accurately than other location techniques based on Time Difference of Arrival (TDOA), Angle of Arrival (AOA) or Augmented GPS (A-GPS). Both TDOA and AOA require reliable signals for at least three base stations to provide location information, but these are not available for many user locations. Also, heavy multipath severely degrades the accuracy of both time difference and angle measurements. A-GPS degrades or does not work at all when too many satellites are blocked from view in city streets and within buildings where the augmentation cannot overcome the losses for enough satellite paths. Signal signature location techniques do not suffer from these problems. Often the 'richness' of signatures in heavy multipath improves the accuracy of this technique. Signature techniques can provide some location information from fewer than three base stations (although with degraded accuracy)."

Donald C. Cox, Professor of Electrical Engineering and Harald Trap Friis Chair Professor Stanford University, CA

• about polaris
• facts at a glance
• management
• careers
• contact