Browsing by Author "Mkhaliphi, Sandile"
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- ItemAn FPGA-based adaptive forward error correction protocol for cubeSats(Stellenbosch : Stellenbosch University, 2017-03) Mkhaliphi, Sandile; Barnard, Arno; Stellenbosch University. Faculty of Engineering. Dept. of Electrical and Electronic Engineering.ENGLISH ABSTRACT: CubeSats have become popular due to their simplified model that reduces development time and costs. The standard, however, suffers from limitations imposed by the small form factor. Research is undertaken at different levels to improve the performance of CubeSats, of which one is on the communication subsystem. The question is how the throughput per satellite-to-ground communication session can be improved using modified error correction methods. Previous work at the ESL proposed a hybrid protocol design of the AX.25 and the FX.25, known as the AFX.25, whose simulation results suggested improved performance over pure protocol implementations. The AX.25 protocol has an error checking functionality but without error correction, so the FX.25 was introduced as a wrapper to the AX.25 to provide for error correction. Inasmuch as the AX.25 is popular among university CubeSat designs, it was necessary that an investigation be done to evaluate if it was the best choice of implementation. The CCSDS Telecommand protocol was chosen for performance evaluation against the AFX.25 due to its functionality which is closer to the FX.25. The evaluation was based on simulation and hardware complexity analysis. SatSim was used as a satellite network simulation environment. The results showed that the AFX.25 is a better choice over the CCSDS TC. The AFX.25 hardware design and implementation was therefore considered on a Field Programmable Gate Array (FPGA). The FPGAs’ parallel processing capability makes them an attractive choice of implementation for error encoding and decoding. The adaptive protocol was designed to switch between no error correction (AX.25) and error correction (FX.25) where the number of correctable errors is 8 using the Reed Solomon code (255, 239). The switching from AX.25 to FX.25 is determined by the packet loss rate while switching from FX.25 to AX.25 is influenced by the packet success rate. The system was implemented on a FusionM1AFS1500 development board interfaced with a half duplex RF board. Tests were carried out successfully on a terrestrial testbench which modelled a typical satellite pass.