Digital L-band receiver architecture with direct RF sampling

This paper describes the architecture of a fully digital receiver well suited for Global Positioning System (GPS) satellite radio-navigation and other spread-spectrum applications. The unique design of this receiver allows phase coherent measurements to be made across a broad range of frequencies, enabling optimal combination of a set of measurements from signals on different frequencies, for example GPS L1, L2, and L3, GLONASS or ground-based pseudolites. The receiver methodology provides precise absolute positioning measurements by maintaining phase coherency between frequencies of interest by direct L-band digital sampling. A one-bit sampler head is discussed that is suitable for navigation and digital communications applications. Surveillance applications can be accommodated with an expanded, multi-bit sampler. The design is particularly suited for chip set integration leading to a miniaturized and low cost receiver. Design of the receiver´s digital front-end provides coherency between the code and carrier phase of the measurements across a 400 MHz bandwidth with down-conversion effected by digital techniques. In addition, it features a software configurable topology that enables filter parameters to be loaded dynamically, allowing rapid change of tracking frequency. The flexible “software receiver” architecture has been developed to allow the receiver to be dynamically reconfigured for different applications. This allows the receiver channels to be used for GPS navigation, ionospheric calibration, attitude determination, or even GLONASS navigation simply through software commands. Sampler performance criteria are discussed as well as test data demonstrating the effect of sampler performance on the receiver correlation loss