22-02-2013, 04:04 PM
ANALOG COMMUNICATION SYSTEM
ANALOG COMMUNICATION.pdf (Size: 172.41 KB / Downloads: 23)
ABSTRACT
Most optical crosslinks between satellites have been developed for digital signal transmission between digital (regenerative) payloads using a dedicated digital data format. Target applications were LEO, MEO and GEO constellations consisting of several more or less identical satellites which used the same optical terminals to communicate between them and a few inter orbit link applications. It was common to all these systems that their architecture was closed and no ISL traffic had to be routed outside the constellation. As there was no demand for interoperability between different satellite systems no standardization of the crosslinks was necessary and each system used its own (optical) communications technique. In earlier time the coherent Sync bit data transmission technology for high performance digital data transmission was introduced. Sync bit BPSK modulation provides the best receiver sensitivity which in turn allows to keep the optical output power of the transmitter to an minimum. As a consequence, DC power consumption from the host spacecraft-a precious resource - can be kept to a minimum. The communication system is designed such, that for analog transmission the same electro-optical signal chain (transmitter- laser, modulator, booster amplifier and optical receiver frontend) as for digital transmission can be used.