User's Manual

Exalt Installation and Management Guide
ExtendAir (TDD) Series Digital Microwave Radios
108 203591-010
2012-09-04
Dynamic Frequency Selection
Dynamic Frequency Selection (DFS) may be required by regional regulation in some frequency bands
to avoid causing interference to radar systems. Prior to the start of any transmission, devices equipped
with DFS monitor the spectrum and are not permitted to transmit on any frequency in use for radar
transmissions for a period of 30 minutes, during which time the frequency will not be available and the
link will be dropped.
During operation of the device, the spectrum is continually monitored by DFS to detect radar
transmissions on the operating frequency. If radar transmissions are detected, the device must drop the
channel within a specified time period so as not to cause interference with the radar transmission.
Devices equipped with DFS are required to stay off that part of the spectrum for a minimum of 30
minutes, after which time the device may then re-check the spectrum for radar transmissions and begin
transmitting if no radar is detected.
Enable Automatic Channel Switching to automate a search for frequencies without radar interference.
Note that DFS adds a one-minute wait time per channel switch. See Automatic Channel Selection
(ACS) Page.
The FCC (the Commission), NTIA, FAA, and industry are working to resolve interference to Terminal
Doppler Weather Radar (TDWR) systems used near airports that occurs from some outdoor wireless
systems operating in the 5470–5725 MHz band. These wireless devices are subject to Section 15.407
of FCC rules: When operating as a master device they must implement radar detection and DFS
functions. The Commission is continuing to develop long-term equipment authorization test
procedures to ensure that the devices comply, including protecting TDWR operations. In the interim,
the Commission now allows wireless master-device certification with radar detection function and
with DFS capability when meeting the following conditions:
• Devices must not transmit on channels overlapping the 5600–5650 MHz band.
1
• Devices intended for outdoor use must be further restricted, as follows:
– Must be professionally installed when operating in the 5470–5725 MHz band.
2
– Grantees must provide owners, operators, and all such installers with specific instructions in
their user’s manual on requirements to avoid interference to TDWRs, and information that
meets the following instructions:
– Any installation of either a master or a client device within 35km of a TDWR location
shall be separated by at least 30 MHz (center-to-center) from the TDWR operating
frequency (a table of locations can be obtained from the FCC on page 3 of document
443999)
3, 4, 5
, and
– Procedures for installers and operators on how to register the devices in the industry-
sponsored database with the appropriate information regarding the location and operation
of the device and installer information is included.
6
Note: When DFS is enabled, the radio temporarily stops transmitting for at least 60 seconds to
ensure that no radar interference is present. This is called Channel Availability Check (CAC).
The DFS status displays on the Alarms Page
. Once CAC passes, the radio resumes normal
operation. If at any time during CAC or regular operation a qualifying radar signature is
detected, the radio shuts down communications for a minimum of 30 minutes. This is the
Non-Occupancy Period (NOP). Transmission only resumes after the NOP completes and then
only after a successful CAC.