A Mark5B Formatter and a 10G Network Transmission System Applied to VLBI

Radio signals from distant radio sources are extremely weak and have very low signal-to-noise ratios when observed with current radio telescopes. In order for VLBI data to reach high measurement accuracies, large measurement bandwidths and sampling bits need to be adopted, resulting in huge amounts of observation data produced by the VLBI terminals (such as Digital Base-Band Converters). Traditional data transmission systems of VLBI terminals use VSI interfaces, which cannot meet the requirements of broadband VLBI observation. The limitation of VSI interfaces is due to two factors: First, their data transmission speeds do not exceed 2Gbps, and second, their data-recording equipments are conformed to the rather rigid Mark5B format. We have designed a 10G network system for a new Digital Base-Band Converter (which is developed by the Shanghai Astronomical Observatory based on polyphase-filter banks and the FFT) to enhance its flexibility and transmission speed. The data-transmission method of this system is the packet switching, so a data arrival time at the data receiver is not accurate and reliable. This requires that data must be of a standard VLBI format before being processed by the 10G system. To achieve this we have also designed a Mark5B data formatter to convert data before being sent to the 10G system. This paper describes the principles of the Mark5B formatter and the 10G network system, which are both based on FPGA. The final part of the paper describes three sets of experiments verifying the accurateness and stableness of our designs.