In traditional navigation, position is determined, and utilized, locally aboard the vehicle. By contrast, in many emerging applications the objective is remote tracking. Examples include tracking of security personnel within (and external to) structures, monitoring and supervision of children and the elderly, theft alarm location, E911 response systems, and electronic home incarceration systems.
Industry is currently evolving two differing approaches to achieve these location-based commercial, and mandated, services: a) Assisted GPS (AGPS), and b) Network based Time Difference of Arrival (TDOA) and/or Angle of Arrival (AOA). PointTrack™ enhances performance for both.
In civilian embedded GPS applications such as cell phones and PDA’s, severe GPS signal attenuation is experienced while operating from within buildings. Very much like the military scenarios previously discussed, the ratio of signal-to-noise power is impaired. In this case, not by hostile noise jamming, but by weakening of the signal as it passes through a building’s structure. One industry thrust is to utilize aiding information from a central station to the mobile handset’s GPS receiver in order to speed acquisition. Even with this assistance, the signal levels may be too low to meet accuracy requirements. As greater demands are placed upon GPS signal tracking in these AGPS systems, TISI’s underlying IDN core technology will become more valuable.
A major objective of the network tracking approach is compatibility with current and future cell phone handsets. In these terrestrial-based systems Angle of Arrival (AOA), Time Difference of Arrival (TDOA), and combined AOA/TDOA architectures are being deployed. By contrast with GPS based approaches that require new cellular handsets, the network approach utilizes cellular transmissions from unmodified handsets to estimate positions. In network based tracking, the battle shifts back to signal processing issues at the wireless receiving stations (i.e. cell sites).
Fundamentally, these systems require precise tracking of received phase and delay at multiple terrestrial receiving sites. Economic viability is driven by the number of stations needed to populate the coverage area. Reception coverage on the back-link from handset to multiple network towers must contend simultaneously with interference from other signals sharing the same frequency and with signal fading and attenuation. The need for enhancement of signal tracking in such systems was anticipated in TISI’s development of IDN processing as well as in TISI’s patents.
PointTrack™ supports improvements in both TDOA and AOA estimation. Because of these improvements, with all air interface formats, the number of receiving stations needed to cover a given region with acceptable accuracy is reduced.