User Guide
Table Of Contents
- Cambium
- PMP 450 Planning Guide
- Accuracy
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- Contents
- List of Figures
- List of Tables
- About This Planning Guide
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- Address:
- Chapter 1: Planning considerations
- Regulatory planning
- Network migration planning
- Site planning
- Link planning
- Analyzing the RF Environment
- Selecting Sites for Network Elements
- Diagramming Network Layouts
- Grounding and lightning protection
- Configuration options for TDD synchronization
- Data network planning
- Security planning
- Isolating APs from the Internet
- Managing module access by passwords
- Filtering protocols and ports
- Port Lockdown
- Isolating SMs
- Filtering management through Ethernet
- Allowing management from only specified IP addresses
- Configuring management IP by DHCP
- Planning for airlink security
- Planning for RF Telnet Access Control
- Forwarding Downlink PPPoE PADI packets
- Planning for RADIUS integration
- Planning for SNMP security
- Ordering components
- Chapter 2: Legal information
- Cambium Networks end user license agreement
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- Survival of provisions
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- Cambium Networks end user license agreement
- Chapter 3: Reference information
PMP 450 Planning Guide
Diagramming Network Layouts
Avoiding Self Interference
The following section includes information maximizing tower performance by minimizing self-interference.
Physical Proximity
Two AP clusters co-located on the same tower require a CMM. The CMM properly synchronizes the transmit
start times of all modules to prevent interference and de-sensing of the modules. At closer distances without
GPS synchronization, the frame structures cause self-interference. Non-synchronized deployments are highly
discouraged.
Furthermore, non-synchronized APs on the same tower require that the effects of their differing receive start
times be mitigated by either
• 100 vertical feet (30 meters) or more and as much spectral separation as possible within the same frequency
band range
• the use of the frame calculator to tune the Downlink Data parameter in each, so that the receive start time
in each is the same
The constraints for collocated modules in the same frequency band range are to avoid self-interference that
would occur between them. Specifically, unless the uplink and downlink data percentages match, intervals
exist when one is transmitting while the other is receiving, such that the receiving module cannot receive the
signal from the far end.
The interference is less a problem during low throughput periods and intolerable during high. Typically, during
low throughput periods, sufficient time exists for the far end to retransmit packets lost because of interference
from the collocated module.
Spectrum Analysis
You can use an SM as a spectrum analyzer. See Mapping RF Neighbor Frequencies on Page 1-95. Through a
toggle of the Device Type parameter, you can temporarily transform an AP into an SM to use it as a spectrum
analyzer.
SM Automatic Transmit Power Control
The PMP 450 AP automatically sets the transmitter output power in its SMs through a feature named Auto-
TPC (Transmit Power Control). The conceptual reason for this feature is OFDM reception in the AP is sensitive
to large differences in power levels received from its SMs, and by limiting power levels of close-in SMs the
overall RF noise floor is lowered.
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pmp-0047 (March 2014)