User's Manual

MP-622 Installation Guide
6 - 2
Radio Path Planning
Although the MP-622 uses IEEE 802.11a radio technology, which is capable of reducing the effect
of multipath signals due to obstructions, the wireless bridge link requires a “radio line-of-sight”
between the two antennas for optimum performance.
The concept of radio line-of-sight involves the area along a radio link path through which the bulk
of the radio signal power travels. This area is known as the first Fresnel Zone of the radio link.
For a radio link not to be affected by obstacles along its path, no object, including the ground, must
intrude within 60% of the first Fresnel Zone.
The following figure illustrates the concept of a good radio line-of-sight.
Figure 6–1. Radio Line-of-Sight
If there are obstacles in the radio path, there may still be a radio link but the quality and strength
of the signal will be affected. Calculating the maximum clearance from objects on a path is
important as it directly affects the decision on antenna placement and height. It is especially
critical for long-distance links, where the radio signal could easily be lost.
When planning the radio path for a wireless bridge link, consider these factors:
Avoid any partial line-of-sight between the antennas.
Be cautious of trees or other foliage that may be near the path, or may grow and obstruct the
path.
Be sure there is enough clearance from buildings and that no building construction may
eventually block the path.
Check the topology of the land between the antennas using topographical maps, aerial photos,
or even satellite image data (software packages are available that may include this information
for your area)
Avoid a path that may incur temporary blockage due to the movement of cars, trains, or aircraft.
Note:
For wireless links less than 500 m, the IEEE 802.11a radio signal will tolerate some
obstacles in the path and may not even require a visual line of sight between the
antennas.
Visual Line of Sight
Radio Line of Sight