Software defined radios as cognitive relays for satellite ground stations incurring terrestrial interference

摘要

Satellite to ground links are extremely vulnerable to any type of terrestrial interference due to the relatively weak satellite signal at the ground stations. This can cause connection failures or degradation in performance at the ground station, which could in some cases be significant or even catastrophic. The great flexibility of software defined radio (SDR) systems facilitates the implementation of cognitive relays as a complementary entity that can help reduce the effects of interference. In this paper, we describe a cognitive SDR testbed that has been developed based on the Universal Software Radio Peripheral (USRP) and the GNU radio software platform. One of our testbed's aims is to evaluate error performance improvements of satellite signal relays in the presence of interference. We report on performance evaluation in terms of bit error ratio (BER) as a function of carrier-to-noise ratio (CNR) and in the presence of interference, for our detect and relay algorithms in an example frequency band, using an emulated desired (satellite-relay-ground station) signal. Our testbed contains four separate segments: satellite (emulated), relay, interferer, and ground receiver. At each segment, we transmit and/or receive signals via SDRs or standard communication laboratory equipment. We consider two relaying protocols in our work, amplify-and-forward (AF), and decode-and-forward (DF). Initial experiments were indoors, although outdoor testing with small unmanned aircraft systems is planned for future work. Our experiments explore the effects of different relaying techniques, and provide some quantitative results on performance improvements via our software defined radio approach.