|Link budget refresher:
- Received Carrier Power:
Pr = Pt + Gt – Lp + Gr (dBW)
- Received Noise Power:
Pn = 10 log (k T B) (dBW)
- Carrier to Noise Ratio:
C/N = Pt – Pn
= Pt + Gt – Lp + Gr – 10 log (T) - 10
log (B) – 10 log (k) (dB)
Carrier to Interference refresher:
- Received Wanted Carrier Power:
Pw = Pt + Gt (θ) – Lp + Gr
- Received Interfering Carrier Power
Pi = P’t + G’t(θ’) – L’p + Gr(φ’)
- So carrier to interference ratio:
C/I = Pw – Pi
= [Pt + Gt (θ) – Lp + Gr (φ)]
– [P’t + G’t(θ’) – L’p + Gr(φ’)]
Normally simplify by assuming that Lp = L’p.
Note that the Gr terms both refer to the same antenna (the receiving system
Define receive antenna discrimination, Dr = Gr (φ) - Gr
(φ’), typically –3 or –4 dB for a satellite receive antenna, generally much
higher, say +20 to +40 dB for an earth station receive antenna.
So simplify terms:
C/I = Pt + Gt (θ) + Dr – P’t – G’t(θ’)
This is a very simple equation; satellite to satellite coordination is not technically
difficult to analyse!
Some additional complications to bear in mind:
- Pt and P’t can be power spectral densities (dBW/Hz) or powers
- If Pt and P’t are densities then strictly you have calculated
Co/Io not C/I (Co/Io ~ C/I for digital carriers).
- If Pt and P’t are powers then they may have different
bandwidths - normalise C/I inside the bandwidth of the wanted carrier.