A Miniaturized Nanosatellite VHF / UHF Communications System
- Paper number
IAC-08.B2.3.12
- Author
Mr. Wouter Jan Ubbels, ISIS - Innovative Solutions In Space BV, The Netherlands
- Coauthor
Mr. Jeroen Rotteveel, ISIS - Innovative Solutions In Space BV, The Netherlands
- Coauthor
Mr. Abe Bonnema, ISIS - Innovative Solutions In Space B.V., The Netherlands
- Coauthor
Mr. Eddie van Breukelen, ISIS - Innovative Solutions In Space B.V., The Netherlands
- Year
2008
- Abstract
This paper outlines the design and development of a VHF / UHF communications system for application in small satellites in LEO orbit. In small satellites, power is often the most limited resource available. With increasing payload capabilities and associated required data rates, achieving optimum downlink throughput for a given amount of consumed power is key to mission success. Driving factors are modulation scheme Eb/N0 versus Bit Eror Rate (BER) performance, required computing power (coding) and transmitter DC to RF efficiency. Achieving high DC to RF efficiency is especially important, but this requirement can be in direct conflict with the requirement for linearity in order to allow for non-constant envelope modulation schemes to be used. Based on the VHF / UHF transceiver as used in the Delfi-C3 nanosatellite, the transceiver presented in this paper features full duplex capability by providing a VHF Binary Phased Keying (BPSK) downlink up to 9600 bit/s and a UHF Frequency Shift Keying (FSK) uplink up to 9600bit/s. Lower datarates can be accommodated as well. It is usable over a wide frequency range, allowing both the amateur radio and commercial frequency bands to be used. The entire transceiver is housed on a single Printed Circuit Board of 90 x 96mm, making it possible to apply the transceiver as a low rate telemetry / telecommand transceiver in spacecraft ranging from nanosatellites to microsatellites. The transmitter section includes a class E nonlinear power amplifier of which the supply voltage is modulated with envelope information in order to allow for processing of non-constant envelope (shaped) BPSK modulation while maintaining both high power and spectral efficiency. The transceiver uses a novel communications protocol on the downlink, instead of the AX.25 protocol which is commonly used in small satellites for low-rate applications. Although the AX.25 protocol performs satisfactorily for most applications, it was never designed to be used for space-earth links and features some shortcomings, especially when used with BPSK modulation. For example, the continuous idle stream of flags has shown to cause false lock problems in Costas-loop based BPSK demodulators. Furthermore, AX.25 has a relatively high protocol overhead. Keeping this in mind, the ISIX protocol was developed, allowing for a smaller overhead and improved acquisition performance on the ground station side. A matching groundstation software package was developed in JAVA, which incorporates software defined demodulation and automatic Doppler tuning of the BPSK downlink signal and subsequent protocol handling. The uplink receiver is based on a well-proven FM receiver design, with special emphasis on selectivity and large signal handling capability rather than sensitivity in order to optimally perform in the LEO RF space environment. It can provide for telecommand functionality with datarates up to 9600 bit/s. The use of an FM receiver allows AFSK, FSK and GMSK modulation to be used as the uplink modulation scheme. This paper discusses the design and development of the VHF / UHF transceiver, the protocol used and the accompanying ground station software defined demodulation system. Special attention is given to the design methodology used.
- Abstract document
- Manuscript document
IAC-08.B2.3.12.pdf (🔒 authorized access only).
To get the manuscript, please contact IAF Secretariat.