Sigtech Navigation's subATTO technology: "...for wireless location to be useful it must operate most of the time in typical environments where wireless communications are employed. These include inside houses, shopping malls, office blocks, multi-storey car parks and urban canyons." http://www.signav.com.au
GPS Receiver Algorithms & System for Weak Signal Operation, a paper by Rod Bryant, Stan Dougan and Eamonn Glennon, given at GPS 2001, describes this technology:
ABSTRACT: A key requirement for emergency call location (eg E911), for robust operation of location-based m-commerce systems and for telematics systems is that the location technology be able to operate in urban canyons and inside buildings. The primary problems associated with weak signal operation are as follows: • In conventional GPS receivers sampling at the correlator output typically occurs at a sampling interval of the order of 1ms. With weak signals, however, the signal to noise ratio of these samples is too low to support lock-in of a phaselocked or frequency-locked loop. • With weak signals the signal to noise ratio is too low to support the extraction of the 50BPS navigation message from the signal. Aiding data is therefore required from an external source. • Because the data cannot be extracted, it is not possible for the receiver to synchronize to the incoming bits, words or subframes. It is therefore not possible to construct pseudoranges without prior information. The paper describes Sigtec Navigation’s subATTO technology. This scheme is demonstrably practical with today’s technology and available communications bandwidths. It provides sensitivity down to –185dBW (19dBHz). This is 5dB below an attoWatt (10-18 Watts) and has been shown to provide reliable positioning inside buildings, multi-storey car parks and in urban canyons without any aiding aat all. Results are presented from trials of this system.
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