Cambium Networks PMP 450 Series, Installation Manual

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Chapter 3: System planning 180
The co-located SM receives data in one channel, and the remote AP must redistribute the data in a
different channel. The two channels need to have a frequency gap equal to at least two times the used
channel bandwidth.
Base your selection of frequency band ranges on regulatory restrictions, environmental conditions, and
throughput requirements.
Note
Each relay hop (additional daisy- chained remote AP) adds approximately 5- 7
msec round trip latency.
Rem ot e A P ( RA P) Per f or m ance
The performance of a remote AP is identical to the AP performance in cluster. Throughputs, ranges, and
antenna coverage are identical.
As with all equipment operating in the unlicensed spectrum, Cambium strongly recommends that you
perform site surveys before you add network elements. These will indicate that spectrum is available in the
area where you want to grow. Keep in mind that:
l
non-LoS ranges heavily depend on environmental conditions.
l
in most regions, not all frequencies are available.
l
your deployments must be consistent with local regulatory restrictions.
Exam p le Use Case f or RF Ob st r uct ions
A remote AP can be used to provide last-mile access to a community where RF obstructions prevent SMs
from communicating with the higher-level AP in cluster. For example, you may be able to use 900 MHz for
the last mile between a remote AP and the outlying SMs where these subscribers cannot form good links
to a higher-level 5 GHz AP. In this case, the ability of the 900-MHz wavelength to be effective around
foliage at short range solves the foliage penetration problem.
An example of this use case is shown in Example for 900-MHz remote AP behind 5 GHz SM.
In this example, the 5 GHz AP is a PMP 450i AP in the 5.8 GHz band operating on a 20 MHz channel with a
2.5 ms frame; the SMs are 5 GHz PMP 450 integrated SMs. The SM connected to the remote AP is a PMP
450i SM.
The remote AP is a PMP 450i AP in the 900 MHz band, also operating in a 20 MHz channel with a 2.5 ms
frame; the SMs are 900 MHz PMP 450 connectorized SMs using the Cambium 23 dBi gain antenna.
Figure 67 : Example for 900-MHz remote AP behind 5 GHz SM