User Manual
Table Of Contents
- Cambium
- PMP 450 Planning Guide
- Accuracy
- Copyrights
- Restrictions
- License Agreements
- High Risk Materials
- Safety and regulatory information
- Contents
- List of Figures
- List of Tables
- About This Planning Guide
- PMP support website: http://www.cambiumnetworks.com/support
- Cambium main website: http://www.cambiumnetworks.com/
- Sales enquiries: solutions@cambiumnetworks.com
- Email support: support@cambiumnetworks.com
- Cambium Networks
- 3800 Golf Road, Suite 360
- Rolling Meadows, IL 60008
- Chapter 1: Product description
- Chapter 2: 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
- Planning for RADIUS integration
- Planning for SNMP security
- Ordering components
- Chapter 3: Legal information
- Cambium Networks end user license agreement
- Acceptance of this agreement
- Definitions
- Grant of license
- Conditions of use
- Title and restrictions
- Confidentiality
- Right to use Cambium’s name
- Transfer
- Updates
- Maintenance
- Disclaimer
- Limitation of liability
- U.S. government
- Term of license
- Governing law
- Assignment
- Survival of provisions
- Entire agreement
- Third party software
- Hardware warranty
- Limit of liability
- Cambium Networks end user license agreement
- Chapter 4: Reference information
PMP 450 Planning Guide Diagramming Network Layouts
pmp-0047 (December 2012)
2-29
Diagramming Network Layouts
Avoiding Self Interference
The following section includes information maximizing tower performance by minimizing self-interference.
Physical Proximity
An AP cluster on the same tower requires a CMM. The CMM properly synchronizes the transmit start times of all
modules to prevent interference and desensing of the modules. At closer distances without sync from a CMM, the
frame structures cause self interference.
Furthermore, 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 2-18. 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.