# Communication Subsystem

## Carrier-to-Noise Density Ratio (C/N0) Explained

What is Carrier-to-Noise Density Ratio (C/N0)? Carrier-to-noise density ratio (C/N0) is the ratio of carrier power to noise power density and denotes the strength of the power of carrier wave relative to the noise. C/N0 is often used in calculating link budget, and it describes the clarity of signal. Thus, the receiver should keep the […]

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.

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