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We present an algorithm and real time implementation for rapid code phase synchronization to direct sequence spread spectrum signals.The synchronization algorithm utilizes a complex matched filter to achieve code synchronization without sequential search over code phases, significantly reducing synchronization time. The algorithm is implemented on a Xilinx Spartan FPGA and is highly tailored to exploit the integrated signal processing resources on that device. Real time performance was demonstrated using less than one fourth of the device resources. Synchronization can be achieved with a latency of one code cycle and zero synchronization overhead in the signal.

Southwest Research Institute ® (SwRI ® ) has developed a radio frequency (RF) receiver that is agile in frequency and waveform over the ultra high frequency (UHF) band. The software defined receiver is CubeSat-scale in size and power consumption, and it provides a flexible, adaptable solution for a number of RF application areas including communications, tracking and locating, and signals intelligence. Based on SwRI internal funding and previous developments for the U.S. Government, the receiver, which is currently at a technology readiness level of five, enables premission and on-orbit reconfiguration plus RF agility from 300 to 3,000 MHz with a bandwidth of up to 30 MHz. This paper describes the hardware architecture of the agile receiver and provides an application example of the geographical location of a terrestrial RF transmitter. In this example, geolocation performance is simulated using performance parameters of the receiver modeled on two or three low Earth orbit spacecraft to estimate the location of the transmitter. A number of spatial separations of the three spacecraft configuration are considered. Further, two RF frequencies are simulated, one for an RF transmitter in the lower portion of the UHF band and another for an RF transmitter in a higher portion of the UHF band. Results show that this small, low power technology, which is suitable for a CubeSat payload, provides a capability for geolocating terrestrial transmitters.

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