Satellite Transmission Immunity from the Interference Using Correlation Functions Properties of PN Codes in DSSS Systems

In the satellite date telemetry transmission, controlling the power of the uplink signal, radiated away from the Earth to the spacecraft and downlink signal, radiated toward the Earth form the spacecraft is very important. The Uplink is transmitted at high power because of the unlimited power, while downlink should be controlled in power because of limited spacecraft power resources. This results in a lower Power Spectral Density (PSD) for the downlink and higher PSD for the uplink, which in many cases the uplink power due to be strong enough to reach the satellites at GEO would often also violate the PSD limits in the other orbits satellite telemetry signals like LEO. In addition due to long distance between the Earth and satellite, the received signals at the both terrestrial and transponder receivers are extremely week and strongly influenced by intentional interference (like jamming) or inadvertent interferences (such as the ASI). Spreading spectrum can solve the PSD problems for both directions but consumes a wide bandwidth. Fortunately, signals can be distinguished by using different spreading codes, allowing for CDMA. The Pseudo Noise (PN) spreading codes allow using many satellites or users (located in one satellite) the same frequency with overlapping signals simultaneously.[1] This paper specially considers to satellite data telemetry transmission immunity from the interference using Direct Sequence Spread Spectrum (DSSS) based on CDMA by the unique properties correlation functions of the Gold and M-Sequence codes

کلیدواژه ها:

Satellite data telemetry ، PSD ، CDMA ، Spread Spectrum ، DSSS ، PN Code ، M-Sequence ، Gold code ، Auto-Correlation ، Cross-Correlation