Meteorological Radar Radio Spectrum Issues

Presented by: David Franc

U.S. National Weather Service

October 8, 2002

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Meteorological Radars

• This section of the workshop covers ground-based radars used or monitoring the atmosphere with the exception of wind profiler radars

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Outline

• Bands for meteorological radar operations• Interference protection criteria• Effects of interference• Proposed changes to bands used by

meteorological radars– IMT-2000 in 2700-2900 MHz– New allocations to multiple services in 5600-5650

MHz

• Strategy to defend meteorological radar spectrum requirements

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Purpose of Briefing

• The information contained in this briefing is intended to prepare workshop participants with necessary information on meteorological radar issues to interact with their representatives to ITU meetings and conferences

• The information presented is consistent with WMO views of the subject matter and promotes protecting meteorological operations

• The information does not necessarily reflect the positions of the United States

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Meteorological Radar Bands

• Three allocations exist in the Radio Regulations specifically for meteorological radars– 2700-2900 MHz- ground based radars– 5600-5650 MHz- ground based radars– 9300-9500 MHz- ground based and airborne radars

• Allocation by footnote• Depending on type of use, aeronautical

radionaviagtion and radiolocation bands can also be used

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Meteorological Radar Bands2700-2900 MHz

• Radio Regulations Footnote 5.423- In the band 2700-2900 MHz, ground based radars used for meteorological purposes are authorized to operate on a basis of equality with stations of the aeronautical radionavigation service

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Meteorological Radar Bands5600-5650 MHz

• Radio Regulations Footnote 5.452- Between 5600 and 5650 MHz, ground based radars used for meteorological purposes are authorized to operate on a basis of equality with stations of the maritime radionavigation service

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Meteorological Radar Bands9300-9500 MHz

• Radio Regulations Footnote 5.475- The use of the band 9300-9500 MHz by the aeronautical radionavigation service is limited to airborne weather radars and ground-based radars. … In the band 9300-9500 MHz, ground-based radars used for meteorological purposes have priority over other radiolocation services.

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Comparison of The Bands

System Cost: Highest- 2700-2900 MHzLowest- 9300-9500 MHz

System Complexity: Highest-2700-2900 MHzLowest- 9300-9500 MHz

Operating Distance: ~450 km- 2700-2900 MHz<200 km- 5600-5650 MHz<75 km- 9300-9500 MHz

Severe Weather Highest- 2700-2900 MHzPerformance: Lowest- 9300-9500 MHz

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Comparison of The Bands (con’t)

• System cost, complexity and operating range are all limitations that can be addressed through additional engineering and funding

• Severe weather performance is a physical limitation that can not be addressed through additional engineering or funding

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Comparison of the Bands Severe Weather Performance

• The ability of a meteorological radar to measure high wind speeds at its outer operational range is limited by the frequency of operation.

v * r 1/f

Therefore, as frequency increases, the maximum range or maximum observable velocity, or both must decrease.

Maximum velocity Maximum range Frequency

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Meteorological Radar Interference Protection Criteria

• Interference Protection Criteria: The highest interference level that does not degrade the system performance beyond performance requirements

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Interference-to-Noise Ratio

• I/N is specified as a interference signal level relative to the radar noise floor

• Interference is added to receiver noise to produce a higher noise + interference level

• Higher noise + interference level masks and corrupts weak but vital returns

Example of Effect of Interference on Receiver Noise

-105

-104

-103

-102

-101

-100

-99

-98

-97

-96

-95

1

Noise

Interference

Noise +Interference

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Meteorological Radar Interference Protection Criteria

• The ITU-R has historically used I/N= -6 dB for meteorological radars

• Discussions have been held in the ITU during the last year on making the criteria more stringent– Proposals for I/N = -10 dB… no technical basis

provided– U.S. has proposed a value of –14 dB should be used for

2700-2900 MHz radars… based on testing– Testing is still required for 5600-5650 MHz and 9300-

9500 MHz

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Meteorological Radar Base Products

• Modern meteorological radars measure reflectivity, velocity and spectrum width– Reflectivity: return signal level used to measure

total water in sample volume– Velocity: measure of speed and direction of

movement of the atmosphere– Spectrum Width: measurement used to

determine turbulence and wind shear

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Effects of Interference on Radar Performance

• Presence of interference:– Raises the radar noise floor making it less

sensitive to very weak return signals– Increases intensity of reflectivity measurement

resulting in overestimation of atmosphere moisture content and rainfall

– Corrupts base data products used for measuring wind velocity, turbulence, wind shear and detection tornadoes

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Example of Interference on Radar Operations

No Interference Interference

Proposed Changes to Frequency Bands Used for Meteorological

Radar Operations

2700 - 2900 MHz

5600 - 5650 MHz

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2700-2900 MHz and IMT-2000

• In 1999 the ITU-R identified the band 2700-2900 MHz as a candidate expansion band for IMT-2000– WRC-2000 considered proposals to create a mobile

service allocation in the band for use by IMT-2000– WRC-2000 concluded insufficient technical studies had

been complete to support the proposed allocation– WRC-2000 created a preliminary agenda item for

WRC-05/06– Studies have been ongoing in the ITU-R to evaluate

compatibility between meteorological radars and IMT-2000

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WRC-05/06 Agenda Item

• Agenda Item 3.1: to consider results of ITU-R studies on the feasibility of sharing in the band 2 700‑2 900 MHz between the aeronautical radionavigation service, meteorological radars and the mobile service, and to take appropriate action on this subject;

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What is IMT-2000?

• Also known as “3G”: Third Generation Mobile Telecommunications

• Intended to provide seamless worldwide mobile telecommunications (voice and high speed data)– Use one band plan worldwide– Use a common radio standard for worldwide mobility

• Worldwide compatibility standards development being led by ITU

• Seeking spectrum in the 1-3 GHz range

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Background: 2700-2900 MHz and IMT-2000

• Two ITU Working Parties involved– Working Party 8B: Represents radar interests

– Working Party 8F: Represents IMT-2000 interests

• Preliminary studies showed the two systems are not compatible– Co frequency operation would result in harmful

interference

– Radars would have to be removed from the band if it were to be used for IMT-2000

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Current Work: 2700-2900 MHz and IMT-2000

• More in-depth studies are underway for evaluating compatibility– Some studies show separation distances as great as

several hundred km are required to prevent interference– Other studies show some IMT-2000 systems can

withstand radar interference but do not address interference into the radars

• Support of this proposed use is decreasing• The CPM Report (Ch. 7) to WRC-03 states that

studies show incompatibility and WRC-03 may consider deleting the WRC-05/06 agenda item

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Last Working Party 8F Meeting:September 25 - October 2

• At the last Working Party 8F meting a decision was made to suspend any further studies in WP 8F until WRC-03 confirms or suppresses the WRC-05/06 agenda item on 2700-2900 MHz– If agenda item is suppressed WP 8F will

discontinue work indefinitely– If agenda item confirmed, WP 8F will restart

work on the compatibility studies

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Working Party 8B Work on 2700-2900 MHz

• Independent of the final decision taken by WRC-03 on the agenda item for WRC-05/06, Working Party 8B will continue general compatibility work between meteorological radars and other radio services– Finalize radar protection criteria– Improve methodology for evaluating

compatibility with radars

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Working Party 8B Work on Protection Criteria

• Working Party 8B approved a revision of ITU-R Recommendation M.1464 at its most recent meeting– Revision changes the meteorological radar

protection criteria from a I/N = -6 dB to I/N = -14 dB based on testing

– Revision of M.1464 will be on agenda for approval at February 2003 Study Group 8 Meeting

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Near Future: 2700-2900 MHz and IMT-2000

• The Conference Preparatory Meeting (CPM) will review and possibly modify or delete the text in Chapter 7 of the CPM Report.

• WRC-03 will evaluate the need for the current agenda item on the WRC-05/06 agenda.

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New Allocations in 5600-5650 MHz

• WRC-2000 created a WRC-03 Agenda Item for possible allocation changes in the range 5150-5725 MHz– Agenda Item 1.5: to consider, in accordance with

Resolution 736 (WRC-2000) regulatory provisions and spectrum requirements for new and additional allocations to the mobile, fixed, Earth exploration-satellite and space research services, and to review the status of the radiolocation service in the frequency range 5150-5725 MHz, with a view to upgrading it, taking into account the results of ITU-R studies.

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What does Agenda Item 1.5 mean?

• ITU to conduct studies determining the effect of:– New and expanded allocations to mobile, fixed, Earth

exploration-satellite and space research services– Upgrade of radiolocation service from secondary to

primary status

• WRC-03 to consider creating new and additional allocations in the frequency range 5150-5725 MHz

• WRC-03 to consider upgrading the radiolocation service to primary status

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Potential Impact to Meteorological Radar Operations• The radiolocation upgrade will probably have

minimal impact since radiolocation systems already exist in the band on a secondary basis

• Introduction of fixed and mobile services could result in harmful interference to meteorological radars

• Introduction of Earth exploration satellite service and space research service will most likely have no impact on meteorological radar operations

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Radiolocation Upgrade

• Radiolocation means “radars”… radars can generally share well with other radars

• The only potential problem is meteorological radars losing equal status with all other services in the band 5600-5650 MHz per footnote 5.452. – If radiolocation is upgraded to primary status,

the words “and radiolocation” should be inserted in footnote 5.452

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Introduction of Fixed and Mobile Services

• To be used for wireless access systems (WAS) such as wireless local area network (LAN) devices

• The level of interference to meteorological radars is dependent on WAS deployment and distance from radar– As density of WAS increases, interference levels

increase

– Devices close to radar will result in higher interference levels than devices at a large distance

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Introduction of Fixed and Mobile Services (con’t)

• There are proposals to use technology for the WAS to detect radar signals and avoid those frequencies… called DFAS.

• The ability of DFAS to reliably detect a radar is questioned by many– Radar signals are pulsed and the antenna is

rotating making detection very difficult– Radars are not always in operation… DFAS

could miss a radar going into operational mode

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Introduction of Fixed and Mobile Services (con’t)

• There is no way to control WAS deployment to prevent operation near a radar or at a high density

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EESS and SRS Allocation

• The Earth Exploration Satellite Service and Space Research Service are seeking a primary allocation up to 5570 MHz

• The allocation for meteorological radars is 5600-5650 MHz- does not overlap

• EESS and SRS proposals should not impact meteorological radar operations

Strategies for WRC-03 to Promote Protection of

Meteorological Operations

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Recommended Strategy for 2700-2900 MHz

• IMT-2000 operation in 2700-2900 MHz will place unacceptable operational restrictions on meteorological radar operations and result in harmful interference to the radars

• Encourage your CPM delegation to support retaining text in section 7.2 of the CPM Report

• Encourage your WRC-03 delegation to propose/support deleting the WRC-05/06 agenda item

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Recommended Strategy for 2700-2900 MHz (con’t)

• The revision to ITU-R Recommendation M.1464 will be considered for adoption at the February Study Group 8 Meeting

• The revision tightens the protection criteria of meteorological radars in the band

• Encourage your Study Group 8 delegation to support adoption of Revised recommendation M.1464

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Recommended Strategy for Agenda Item 1.15 (5600-5650 MHz)

• Radiolocation upgrade should have little impact on meteorological radar operations with exception that footnote 5.452 needs to now include a reference to the radiolocation service– 5.452 Between 5600-5650 MHz, ground based radars

used for meteorological purposes are authorized to operate on a basis of equality with stations of the maritime radionavigation and radiolocation services

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Recommended Strategy for Agenda Item 1.15 (5600-5650 MHz) (cont)

• The EESS and SRS allocations should present no problems for meteorological radar operations

• EESS allocations often benefit meteorological operations

• Encourage your CPM delegation to support text in the CPM report favorable to creating the EESS and SRS allocations

• Encourage your WRC-03 delegation to support creation of the EESS and SRS allocations

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Recommended Strategy for Agenda Item 1.15 (5600-5650 MHz) (cont)

• WAS devices pose a significant risk to meteorological operations

• Encourage your CPM delegation to support CPM text that protects meteorological radar operations

• Encourage your WRC-03 delegation to only support allocation changes if meteorological radar operations are protected– No allocation to fixed and mobile services is best solution– Regulatory text ensuring protection of radars is an

alternative

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Recommended Strategy for Agenda Item 1.15 (5600-5650 MHz) (cont)

• The necessary protection criteria for radars operated in this band should be studied and the ITU-R Recommendation should be modified– Current recommendation on met radars

operated in 5600-5650 MHz specifies an I/N = -6 dB

– The value of -6 dB randomly selected based on other radars and not based on testing or analysis

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Future Protection of Meteorological Radar Operations• The ITU-R defines certain systems and

radio services to perform safety-of-life functions

• The users of meteorological radars may wish to consider having meteorological radars classified as safety-of-life– Provides meteorological radars special

consideration in cases where interference may occur