Digital downconversion test results with a broadband L-band GPS receiver

This paper describes the architecture of a fully digital receiver designed for Global Positioning System (GPS) satellite radionavigation and other spread spectrum applications. By directly sampling L-band radio frequencies with a minimum of analog components, phase coherent measurements can be made across a broad range of frequencies, enabling a set of measurements to be optimally combined from signals of different frequencies. Band pass sampling techniques allow measurements across a 400 MHz bandwidth with signal downconversion performed by digital techniques. The receiver incorporates a unique software configurable topology for frequency selection that enables filter parameters to be loaded dynamically, achieving rapid change of tracking frequency. This allows the receiver channels to be configured for GPS navigation or spread spectrum communications simply through software commands