Microwave Link Design
Microwave link design is to be done very carefully , taking the various following issues into consideration :
Microwave Link Design :-
A Path Profile is a graphical representation of the path traveled by the radio waves between the two ends of a link. The Path Profile determines the location and
height of the antenna at each end of the link, and it insures that the link is free of obstructions, such as hills (Microwave radio link must be on Line-of-sight (LOS), and not subject to propagation losses from radio phenomena, such as multipath reflections.
1.Calculate Free Space Loss (FSL) :-
Before determine if a link is feasible, at first the Free Space Loss must be calculated. Free Space Loss is the expected attenuation of a signal as it travels away from the transmitting device. When a signal radiates from the antenna, it spreads out over an increasingly larger distance. As the area covered increases, the power density (or the amount of power per unit area) decreases. This effectively weakens the radio signal.
FSL=32.44 20 log F 20 log D
F= frequency, MHz
D= distance between link endpoints, km
2. Calculate Link Budget :-
Receiver Sensitivity (Rx)
The minimum RF signal power level required at the input of a receiver for certain performance (e.g. BER). EIRP (Effective Isotropic Radiated Power) The antenna transmitted power. Equal to the transmitted output power minus cable loss plus the transmitting antenna gain.
Pout = Output power of transmitted in dBm
Ct =Transmitter cable attenuation in dB
Gt =Transmitting antenna gain in dBi
Gr= Receiving antenna gain in dBi
FSL =Path loss in dB
Cr =Receiver cable attenuation is dB
Si =Received power level at receiver input in dBm
Ps =Receiver sensitivity is dBm
Si = Pout - Ct Gt - FSL Gr - Cr
EIRP = Pout - Ct Gt
3. Calculate Fade Margin and Link Availability :-
Fade Margin is the difference between the unfaded Receive Signal Level and the Receiver Sensitivity Threshold. Fade Margin is directly related to Link Availability, which is the percentage of time that the link is functional. The percentage of time that the link is available increases as the Fade Margin increases. A link will experience fewer system outages with a greater Fade Margin. A link with little or no Fade Margin may experience periodic outages due to path fading phenomena.
4 .Rain Zone Map :-
Rain zone map is to be taken into consideration while designing microwave link in order to estimate the attenuation and losses due to rain in various regions of propagation of microwaves.