# Communication Subsystem

ITU Radio Regulations define feeder link as follows: A radio link from an earth station at a given location to a space station, or vice versa, conveying information for a space radiocommunication service other than for the fixed-satellite service. The given location may be at a specified fixed point, or at any fixed point within …

## Communication Subsystem

Communication Subsystem handles communication in satellite bus systems. Communcation Subsystem:

Very Low Frquency（VLF） 3 kHz-30 kHz Low Frequency（LF） 30 kHz-300 kHz Medium Frequency（MF） 300 kHz-3 MHz High Frequency（HF） 3 MHz-30 MHz Very High Frequency（VHF） 30 MHz-300 MHz Ultra High Frequency（UHF） 300 MHz-3 GHz Super High Frequency（SHF） 3 GHz-30 GHz Extremely High Frequency（EHF） 30 GHz-300 GHz

## Satellite Frequency

S band : 2 GHz C band : 4~5 GHz X band : 7~9 GHz Ku band : 10~15 GHz Ka band : 17~30 GHz

## Frequency Coordination

International frequency coordination is required to use the frequency in satellite communication.

## Parabola Antenna

Parabola antenna is commonly used in satellite communication. The gain of parabola antenna $$G$$ can be written as: $G = \eta\left(\frac{\pi D}{\lambda}\right)^2$ where $$D$$ is the diameter of the antenna, $$\lambda$$ is the wavelength, and $$\eta$$ is the aperture efficiency ($$0<\eta<1$$)

## Digital Modulation

To transmit the ditgital signal by radio wave, it is required to modulate the carrier wave. Digital modulation method can be categorized into 3 types: FSK and PSK are generally used in satellite communications.

## Antenna Noise

Receiver antenna detects not only radio waves but alo various noises. The examples of the noise are: Noise temperature received by the antenna $$T_a$$ is: $T_a = T_s + (1-\eta)T_0$ where $$T_s$$ is the noise temperature, $$T_0$$ is the ambient temperature, and $$\eta$$ is the radiation efficiency of the antenna.

## Coherent Detection

Coherent detection is one of the method to demodulate the signal modulated by PSK. Coherent detection multiplies the signal by the carrier wave. The signal modulated by PSK can be written as: $s(t) = A\cos{(2\pi ft+\phi)}$ where $$A$$ is amplitutde, $$f$$ is frequency, and $$\phi$$ is the phase difference. Multiplying this signal by the carrier …