Installation Manual

User Reference and Installation Manual 3-9
CarrierWave Digital Radio MK-MAN-01
• Frequency
• Terrain (smooth, average, mountainous, valleys)
• Climate (dry, temperate, hot, humid)
Depending on the type of traffic carried over the link and the overall network design redundancy,
fade margin should be included to support the desired availability rate. Critical data and voice
may require a very high availability rate (99.999% or 5.3 minutes of predicted outage per year).
To improve availability, the fade margin can be increased by shortening the path length,
transmitting at a higher power level, or by using higher gain antennas.
Availability can be computed using the following formula, which is known as the Vigants Barnett
Method.
Availability = 100 × (1 – P)
P = 2.5 × 10
-9
× C × F × D
3
× 10
(-FM/10)
Where F is the frequency in MHz (5800)
D is the distance in miles
FM is the fade margin in dB
C is the climate/terrain factor as defined below:
Humid/Over Water: C = 4 (worst case channel)
Average Conditions: C = 1
Dry/Mountains: C = 0.25 (best case channel)
Example: Assume 21 dB fade margin, over 5 miles with average climate/terrain. The availability
comes out to be 99.9986. This corresponds to the link being unavailable for 7.6 minutes per
year.
3.5.3.4 Frequency Plan Determination
When configuring CarrierWave Digital Radios in a point-to-point or consecutive point
configuration, careful engineering of the CarrierWave Digital Radio frequency plans and antenna
locations should be performed in order to minimize potential interference between nearby radios.
Nearby radios should operate on different frequencies, transmitting in the same band (high side
or low side). When designing multi-radio configurations, antenna size, antenna polarization, and
antenna location are critical.
The frequency plan must be selected based on desired data rate and expected link conditions. In
a high interference environment or with lower gain antennas, higher bandwidth, more robust
modulation formats must be employed. The available frequency plans are illustrated in Figure 3-
3.