Radio Frequency (RF) Local Area Network (LAN) for satellites (Funded by Naval Research Board, Govt. of India)
Bulky wired harness is used in satellites for data communication viz., routing the command signals, from telecommand receivers to various packages for necessary operations and telemetry signals for monitoring the health of the satellite and for data transfer from payloads and satellite positioning receivers to transmitters. In a satellite, all subsystems are connected often with communication standards like RS-232, CAN-bus, 1553 data bus etc., are adopted for signal transfer among the systems.
The physical connection in a satellite increases the risk of system malfunctioning due to EMI and total failure due to any short circuit. Furthermore, in case of a failure, it is difficult to isolate the faulty system. Wired signal harness accounts up to 20% of total dry mass of the satellite and has been the most important criterion. Furthermore, they lead to formation of ground loops and often pose a problem by generating Electromagnetic Interference (EMI) requiring special care. Unwired applications are highly sought after in many networks that are characterized by numerous nodes designed to enable two-way communications
A transceiver operating at a suitable frequency, like ISM S-band, is embedded into each package for sending and/or receiving information/data. CDMA technique, an optimum multiple access scheme in performance in multipath environment, is considered for communication within the satellite. The transceiver consists of a transmitter, receiver and a common conformal antenna. Spread spectrum technique is used to transmit data between subsystems. The data to be transferred is spread with a code of higher rate and BPSK modulated on an S-band carrier. Each receiver is assigned a separate Walsh or Gold code and a system uses the code of the intended receiver for transmitting the data. A conventional low profile microstrip patch antenna is used for transmitting and receiving signals.