A Software GPS Receiver Application for Embedding in Software Definable Radios

The Software Defined Radio (SDR) is an enabling technology that is being leveraged across a wide range of areas within the wireless industry to provide efficient and comparatively inexpensive solutions to several constraints posed in current systems. Since SDR-enabled user devices and network equipment can be dynamically programmed in software, this allows them to be adapted to provide richer feature sets and introduce advanced new services that provide more choices to the end-user and new revenue streams for the service provider. In this paper, the principle of operation of a Software GPS Receiver, designed for embedding within a Software Defined Radio, is described and test results are presented showing the operation of an SDR test-bed in generating the modernized GPS signals. INTRODUCTION The Global Positioning System (GPS) provides positioning and navigation capabilities through processing the L-band, CDMA signals broadcast by the GPS satellite constellation. Currently, GPS chip sets can be purchased for embedding in mobile radios. These are being used to provide position and location-based services to mobile radio users. NAVSYS has developed a Software GPS Receiver (SGR) application that will allow a Software Defined Radio (SDR) to provide GPS positioning information without requiring the use of a separate embedded GPS chip-set. This not only has the advantages of providing a cost effective method for embedding GPS functionality within an SDR, but also allows a forward upgrade path for the next generation GPS signals that are being introduced in the GPS satellite constellation. NEXT GENERATION GPS WAVEFORMS In addition to the current C/A and P(Y) GPS signals, the next generation GPS satellites (Block IIR and IIF) will include new waveforms to improve the GPS performance for both military and civil users. For military users, a new M-code signal is planned to be added to the L1 and L2 frequencies that will improve the robustness of GPS to jamming. This is a Binary Offset Carrier (BOC) code which will also use an encrypted code generation sequence. The spectral characteristics of the 1.023 Mbps C/A code the 10.23 Mbps P(Y) code and the BOC M-code are shown in Figure 1.