Software-Defined Radios for Urban and Indoor Navigation

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.