Link Budget

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   Satellite communication is radio communication with RF waves traveling through the air from the earth station to the satellite (uplink) and some information received from the satellite to the earth station (downlink).

•  Link budget is the calculation of various factors such as transmitted power, received power, power loss & gain.

•  To receive data without adding noise, digital modulation is needed.

• Link budget calculation is the determination of power required to transmit and receive data. It is also known as equivalent isotropic radiated power. The link budget calculation is done by decibel & decilog calculation.

•  Some Factors are affecting to the link budget calculation—

• Transmitted power Pt—The power density is defined as the amount of power an antenna receives in a spherical area.

Power Density = Pt/4πr² and its unit is w/m².

2. Antenna gain—an isotropic transmitting antenna that radiates power uniformly in all directions. The transmit antenna is directional in nature with gain Gt. Then the power density = Pt*Gt/4ㅠr²

Here Pt & Gt are equivalent isotropic radiated power along the direction of the directional antenna.

[EIRP]=[Pt] +[Gt] dB W

If the antenna has effective Aperture Ae at the receiver end then the total received power is Pr= Pt*Gt*Ae/4πr2 watts

Since, Ae=nA

Ae = Effective Aperture

A = physical area of the mouth of antenna

So, Gr= 4πAe/λ²

Gr=receiver gain & λ is the wavelength

Ae=Grλ²/4π

Pr=Pt*Gt*Gr/(4πr/λ)²

3. Frequency of Operations f -The frequency at which data transmission and reception occurs without adding noise. 

             λ=c/f, where λ is wavelength

•             C = velocity of light travels in a second = 3*10 to the power 8

• Feeder loss – Feeder loss occurs at the receiver end due to the presence of couplers, filters and waveguides.

• Absorption or atmospheric loss – Absorption loss occurs due to environmental situations that are not good.

• Carrier to noise ratio (C/N): It is the ratio of carrier power to noise power at the input terminal of the receiver & is a measure of the performance of the satellite link. 

• Antenna Noise – Noise is introduced by the satellite & antenna present at the ground station.

• Antenna Misalignment Losses – This alignment of the earth station and satellite link antenna must provide maximum gain value. There is some kind of mismatching of misalignment

  

  nown as antenna misalignment losses.

  
  

  Importance of Link Budgets

  Link budgets are essential for several reasons:

  1. System Design: Link budgets guide the design and dimensioning of communication systems, ensuring that the transmitted power, antenna gains, and receiver sensitivity are appropriately chosen for reliable communication.

  2. Performance Evaluation: By accounting for all gains and losses, link budgets provide a quantitative assessment of the system’s performance, helping engineers estimate the achievable data rates, coverage range, and signal quality.

  3. Regulatory Compliance: Link budgets help ensure compliance with regulatory standards, such as maximum permissible transmit power levels, interference limits, and signal quality requirements.