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 2

Available channels in 5 GHz band

 5150 - 5350 MHz;  5470 - 5725 MHz; 8 channels available 11 channels available  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 3

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 4

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 5

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 6

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 monitoring”

) (“

In Service

© British Telecommunications plc, 2002 7

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 8

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 9

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 10

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 11

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 12

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 13

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 14

Conclusion

 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 15