Cambium Networks PMP 450 Series, Руководство по установке

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Chapter 3: System planning 162
Rx signal level is calculated as follows:
Rx signal level dB = Tx power
−
Tx cable loss + Tx antenna gain
−
free space path loss + Rx antenna gain
−
Rx cable loss
Note
This Rx signal level calculation presumes that a clear line of sight is established
between the transmitter and receiver and that no objects encroach in the Fresnel
zone.
Calculat ing Fad e Mar g in
Free space path loss is a major determinant in Rx (received) signal level. Rx signal level, in turn, is a major
factor in the system operating margin (fade margin), which is calculated as follows:
System operating margin (fade margin) dB = Rx signal level dB
−
Rx sensitivity dB
Thus, fade margin is the difference between strength of the received signal and the strength that the
receiver requires for maintaining a reliable link. A higher fade margin is characteristic of a more reliable link.
A d ap t ive m od ulat ion
Adaptive modulation ensures that the highest throughput that can be achieved instantaneously will be
obtained, taking account of propagation and interference. When the link has been installed, web pages
provide information about the link loss currently measured by the equipment, both instantaneously and
averaged. The averaged value will require maximum seasonal fading to be added, and then the radio
reliability of the link can be computed.
For details of the system throughput, link loss and maximum distance for each frequency band in all
modulation modes, see Configuration Guide.
Planning f o r co nnect o rized unit s
This section describes factors to be considered when planning to use connectorized ODUs with external
antennas in 450 Platform Family links.