Cambium PMP 450 AP, User Manual

Page: 156 / 301

Chapter 3: System planning Radio Frequency planning
Page 3-23
Figure 48 Reflection
Reflection likelihood guidance
As shown in the previous section, reflection can cause a decrease in throughput in an ABAB base site.
This section provides guidance on whether a reflection is likely to cause interference. The first condition
for whether a reflection can cause the data rate to reduce is that the reflecting object must be in view of
the AP and the SM in order to re-transmit the signal. If this is not the case, then the object cannot cause
interference.
Given that the potential reflecting object is seen by the AP and the SM, there are a range of object sizes
and a range of zones where we can predict that interference will occur which may reduce the throughput
when both sector 1 and sector 3 are carrying traffic.
Figure 49 and Figure 50 show regions enumerated A, B, C, and D. We also need to consider objects of
size 1, 2, 3 and 4 and define the areas where the objects may interfere.

object size 1: a flat building face with a clear reflecting property from sector to AP

object size 2: random metalwork such as a wireless tower

object size 3: a 0.5 X 0.5m flat metallic face or tree

object size 4: a 0.2 X 0.2m random metal structure or 0.5 X 0.5m foliage.
The conditions for no interference are:

size 2 outside zone B

size 3 outside zone C

size 4 outside zone D
The size 1 object can interfere at large distances. It is necessary to look at the geometry by which
reflection could occur and cause interference. Typically, this will occur at a restricted range of azimuths
and ranges.