User guide

March 2005 Designing Your Canopy Network
Through Software Release 6.1
Page 96 of 425 Issue 1
Canopy System User Guide
12 ENGINEERING YOUR RF COMMUNICATIONS
Before diagramming network layouts, the wise course is to
◦ anticipate the correct amount of signal loss for your fade margin calculation.
◦ recognize all significant RF conditions.
◦ evaluate potential sites by their fitness to address fade margin and ambient RF
conditions.
12.1 ANTICIPATING RF SIGNAL LOSS
The C/I (Carrier-to-Interference) ratio defines the strength of the intended signal relative
to the collective strength of all other signals. Canopy modules typically have an especially
low C/I ratio of
◦ 3 dB or less at 10-Mbps modulation.
◦ 10 dB or less at 20-Mbps modulation.
The C/I ratio is alternatively known as jitter. The C/I ratio is typically a design feature of
the radio.
12.1.1 Understanding Attenuation
An RF signal in space is attenuated by atmospheric and other effects as a function of the
distance from the initial transmission point. The further a reception point is placed from
the transmission point, the weaker is the received RF signal.
12.1.2 Calculating Free Space Path Loss
The attenuation that distance imposes on a signal is the free space path loss.
PathLossCalcPage.xls calculates free space path loss.
12.1.3 Calculating Rx Signal Level
The Rx sensitivity of each module is stated under Specifications and Limitations on
Page 52. The determinants in Rx signal level are illustrated in Figure 37.