Protocol Design for Content Transfer in Deep Space Network

Space communications feature large round-trip time (RTT) delays and highly variable data error rates. In this paper, we propose a new content transfer protocol based on RaptorQ codes and turbo codes, incorporated with a real-time channel prediction model, to maximize file transfer from space vehicles to Earth stations. While turbo codes are used to correct channel errors, RaptorQ codes are applied to eliminate the need for negative-acknowledgment (NAK) of the loss of any specific packet. To reduce the effect of channel variation, a practical signal-to-noise ratio (SNR) prediction model that is used to periodically adjust the turbo encoder in distant source spacecraft is developed. This new protocol, termed as the dynamic code selection method (DCSM), is compared with two other methods: a turbo codes based genie method (upper bound of DCSM performance) assuming that the channel condition is perfectly known in advance and a static method in which a fixed turbo encoder is used throughout each communication pass. Simulation results demonstrate that the genie and the new DCSM methods can increase telemetry channel throughput by about 47% and 46%, respectively, compared to the static method. In addition, throughput performance using the DCSM is about 99% of the upper bound achieved with the genie method.