Coding Applications in Satellite Communication Systems

摘要

This paper provides a brief insight in satellite communication systems from the perspective of coding applications. CDMA based systems for use in Low Earth Orbit (LEO) satellite systems is the focus of the paper. The code-division-multiple-access (CDMA) format is emerging as a dominant air interface technology for cellular, personal-communications-services (PCS) as well as satellite installations. This transmission technology relies on a combination of spread-spectrum modulation, Walsh coding, and sophisticated power-control techniques. In a typical CDMA transmitter, a data signal is encoded using a Walsh code and then mixed with the RF carrier, which has been spread using a pseudorandom-noise (PN) source. In a base-station transmitter, multiple data signals are assigned unique Walsh codes and combined. In the CDMA receiver, the signal is filtered and fed to a correlator, where it is despread and digitally filtered to extract the Walsh code. The paper examines some weaknesses of such systems.