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A Doppler Correcting Software Defined Radio Receiver Design for Satellite Communications

We present a flexible software defined radio (SDR) receiver design for the reception and demodulation of satellite signals. The proposed SDR performs an online Doppler search, as well as a code-rate and code-phase search online. The use of graphics processing units (GPUs) allows the radio to compensate Doppler offsets and achieve symbol synchronization in real time. This eliminates the need for a priori information on the satellites position and velocity to perform Doppler compensation on the downlink. To successfully utilize the enhanced computational power of graphics processing units (GPUs) and achieve real-time performance, we utilize acausal batch based signal processing, which allows for the use of fast convolution algorithms. These can efficiently be parallalized and run on GPUs. The Doppler search and demodulation is done by using matched filters. This allows one to adapt the demodulator to work for many modulation schemes by merely changing the set of filters. The demodulator itself essentially works as a batched correlation receiver. Additionally, the proposed SDR can decode signals from multiple antennas that are located at geographically spread ground stations simultaneously. The decoded bits are compared using soft decisions. This can greatly increase the rejection of local burst interference as well as polarized interference and tracking signals that rotate in polarization.