Dynamic Frequency Selection (DFS) for 5 GHz RLANs

Report
Dynamic Frequency
Selection (DFS) for 5 GHz
RLANs
Johnny Dixon
Overview

Available channels in the 5 GHz band
 Who is currently using the 5 GHz band?
 Why do we need DFS?
 What does DFS do?
 How will DFS operate?
 Why is it all so important?
 Can the UK ignore all this?
 What about the Interim Arrangements?
 What happens if we don’t implement DFS?
 What about the 5725 - 5875 MHz band?
 Conclusion
© British Telecommunications plc, 2002
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Available channels in 5 GHz band

5150 - 5350 MHz;
5470 - 5725 MHz;

What is the problem?

According to the ITU Radio Regulations,
these bands are (currently) primarily for
other users, not for RLANs

© British Telecommunications plc, 2002
8 channels available
11 channels available
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Who is currently using the 5 GHz
band?

5150 - 5250 MHz used for MSS feeder links
-

Need to ensure even distribution of RLAN channel
occupancy
5300 - 5900 MHz used for radars
Meteorological radars
- Instrumentation radars (mostly military)
- Maritime surveillance
- (Aeronautical Radionavigation)
-
© British Telecommunications plc, 2002
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Why do we need DFS?

To enable usage of the 5 GHz band for
RLANs, we need to:
Ensure that the RLANs operate evenly across the
channels
- Ensure that an RLAN does not interfere with an
existing radar system
-

Therefore 5 GHz RLANs need a Dynamic
Frequency Selection (DFS) mechanism
© British Telecommunications plc, 2002
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What does DFS do?
Before operation
 Chooses an operating channel at random
 Checks whether it is currently being used
During operation
 Continues to “listen” for other users
© British Telecommunications plc, 2002
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How will DFS operate ?




Choose an operating channel at random
“Listen” to that channel for Channel
Availability Check Time, for any signals
greater than Detection threshold
If the channel is clear, then it can be used by
the RLAN, however…
… the RLAN must continue to listen to the
channel for any signals which are greater
than Detection threshold (“In Service
monitoring”)
© British Telecommunications plc, 2002
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How will DFS operate ?
(continued)



If the In Service Monitoring detects a radar,
the RLAN must leave the channel within
Channel Move Time
The RLAN then needs to identify a new
operating channel (i.e. perform a Channel
Availability Check)
Studies are currently underway to identify
agreed values for the various parameters
© British Telecommunications plc, 2002
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Why is it all so important?
The ITU Radio Regulations are an International
Treaty on the global use of the radio spectrum
 Currently no allocation for RLANs in the (body
of the) Radio Regulations
 For global adoption of RLANs
 We need a (Primary) Mobile Service allocation
 We need ability to share with existing users
 We need DFS

© British Telecommunications plc, 2002
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Why is it all so important?
(continued)

A European Decision (ERC DEC(99)23)
identified 5 GHz band for RLANs, providing
Indoor operation only in 5150 - 5350 MHz
- Power limits (EIRP)
- Transmitter Power Control (TPC)
- Dynamic Frequency Selection (DFS)
-

That has the basis for all work over the last 3
years
© British Telecommunications plc, 2002
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Can the UK ignore all this?




The UK does have obligations to protect
MSS & radars
The UK has signed up to the ERC Decision,
as the best solution for the 5 GHz band
The UK is always keen to promote a
responsible and equitable attitude towards
frequency sharing matters
We want a consistent policy for all countries,
to enable a global market for products
© British Telecommunications plc, 2002
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What about the “Interim
arrangements”?





There is already demand to allow RLAN
devices in the 5 GHz band
There is not (yet) an agreed DFS
mechanism which can be implemented
The IR allows the deployment of 5 GHz
RLAN devices in the short term, without DFS
“Interim Arrangements” are only for the
Interim
DFS will be essential in the long term
© British Telecommunications plc, 2002
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What happens if we don’t
implement DFS?




The World Radio Conference 2003 is
reviewing spectrum allocations at 5 GHz
A lot of work has been done to demonstrate
sharing between RLANs & other services
A pre-requisite is that an effective DFS
mechanism will be available
If we don’t accept DFS, then the 5 GHz band
will NOT be identified for RLANs
© British Telecommunications plc, 2002
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What about the 5725 - 5875 MHz
band?



Some of the radars operate in the 5725 5875 MHz band
An agreed DFS mechanism would enable
frequency sharing in the band (for FWA)
DFS “modules” designed for the 5150 - 5350
& 5470 - 5725 MHz band could be easily
implemented in 5725 - 5875 MHz band
© British Telecommunications plc, 2002
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Conclusion



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We need a Primary allocation for RLANs in
the ITU Radio Regulations
We need to demonstrate that RLANs can
share the 5 GHz band
DFS is an a pre-requisite for those sharing
studies
Devices without DFS are permitted on a
limited basis for an interim period, but not in
the long term
© British Telecommunications plc, 2002
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