Signal processing is performed by a field-programmable gate array (FPGA) card and a Pentium-class central processing unit. Received GPS and/or TOA radio signals are converted to digital signals by use of digital antenna elements (DAEs), which are compact and can be easily modified to operate at alternative signal frequencies and sampling rates. Each DAE is responsible for radio-frequency down-conversion and up-conversion as well as high-speed analog-to-digital and digital-to-analog conversion. Each DAE uses a common sample clock and phase-locked reference local oscillator, thereby maintaining a coherent sampling environment for all transmitted and received signals.

In a test of an early prototype POSCOMM SDR system, four master units were set up around a building, and slave units were operated at various inside and outside positions. Distances between slave positions as determined by TOA and those determined by GPS were found to be no more than about 5 m in most cases.

This work was done by Alison K. Brown, Yan Lu, and Janet Nordlie of NAVSYS Corp.
NAVSYS-0001

This Brief includes a Technical Support Package (TSP).

Software-Defined Radios for Urban and Indoor Navigation (reference NAVSYS-0001) is currently available for download from the TSP library.

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