Radiosonde Spectrum Issues

Radiosonde Spectrum Issues

Presented by David FrancU.S. National Weather Service

October 8, 2002

Outline

• General Technical Information (D. Franc)– Definitions– Interference Protection Criteria– Radiosonde Technology

• 400.15-406 MHz (J.Nash)– Discussion of operations– Proposed changes to band

• 1668.4-1700 MHz (D. Franc)– Discussion of Operations– Proposed changes to band

Definitions

• Radiosondes fall under the ITU radio service of meteorological aids (metaids)– Meteorological aids service: a

radiocommunication service used for meteorological , including hydrological, observations and exploration

• Dropsondes and rocketsondes are also part of the metaids service

Metaids Frequency Bands

• Two common bands are used for metaids– 400.15-406 MHz (primary allocation)– 1668.4-1700 MHz (primary allocation)

• Other bands identified in ITU Radio Regulations (not covered in this workshop)– 2.025-2.045 MHz (secondary allocation, ITU Region 1)– 27.5-28 MHz (primary allocation)– 153-154 MHz (secondary allocation, ITU Region 1)– 35.2-36 GHz (primary allocation)

Metaids Bands – Additional Information

• The Handbook on Use of Radio Spectrum for Meteorology has additional information– Section 3.1: Discussion of bands that are

allocated for metaids operations– Sections 3.6.4 – 3.6.6: Discussion of why

multiple bands are required

Working Party 7C

• Working Party 7C is the ITU-R working Party responsible for development of metaids protection criteria and conducting studies regarding metaids systems

• Working Party 7C also is responsible for passive and active remote sensing and meteorological satellite data links

Metaids Interference Protection Criteria

• ITU-R Recommendation SA.1263 specifies the maximum interference level that allows radiosonde systems to still meet performance objectives

• Level based on margin in radio link at maximum range– Margin is excess receive power above minimum

receive threshold– A small percentage of the margin is taken by

interference

Metaids Interference Protection Criteria (cont)

• Criteria are different for the two bands, 400.15-406 MHz and 1668.4-1700 MHz

• Criteria value is assumed to apply at receiver input connector

• Criteria are specified as two types:– Short term: less restrictive value that can only be

exceeded for a very small percentage of time– Long term: More restrictive value that can be exceeded

for up to 20% of time – still allows reliable operation of system

Summary of Metaids Interference Protection Criteria (SA.1263)

400.15-406 MHzOmni

Antenna

400.15-406 MHz

Directional Antenna

1668.4-1700 MHz

Directional Antenna

Short Term Criteria- no more than 0.2 % time

-141.9 dBW -140.6 dBW -135.3 dBW

Short Term Crietria- no more than 1.25% time

-154.4 dBW -149.6 dBW -148.4 dBW

Long Term Criteria- no more tha 20% time

-156.1 dBW -154.9 dBW -149.4 dBW

Metaids Transmitter Characteristics

• Metaids transmitters typically exhibit poor characteristics for several reasons– Expendable device - costly technology to stabilize the

transmitter is avoided– Extreme operating conditions

• Temperature: +50 to –90 ºC• Pressure: Surface to 36 km

• Transmitter standards of normal communications systems should not be applied to radiosonde transmitters

Metaids Receiver Characteristics

• Metaids users should strive for the best receiver system design possible– Receivers are a long term investment where

advanced technology is more applicable– Good receiver design helps reduce the potential

for interference problems– Good receiver design also increases link

reliability and increases data availability

Metaids Receiver Characteristics (cont)

• Some receiver characteristics necessary to operate with poor radiosonde transmitters result in greater interference susceptibility– Large receive bandwidth to receive signals that

jump quickly in frequency– Automatic tracking loops that track strongest

signal in band

Metaids Equipment – Additional Information

• Handbook on Use of Radio Spectrum for Meteorology:– Section 3.4.1- Ground based receiving equipment– Section 3.4.2- Ground-based signal processing systems– Section 3.4.3- Expendable sensing packages

(radiosondes)– Section 3.6 – Discussion of national selection of

metaids technology

The Band 400.15-406 MHz

The Band 1668.4 - 1700 MHz

Operations in 1668.4-1700 MHz

• In general, metaids systems operated in this band use radio direction finding for wind measurement– Winds calculated from balloon movement– Movement determined by change in signal

azimuth and elevation, and balloon height• GPS radiosondes have also been developed

for operation in this band

Sharing Issues in 1668.4-1700 MHz with the Metsat Service

• The band 1670-1700 MHz is currently shared with the Metsat service

• Radiosondes cause interference to Metsat earth stations if they are operated in close proximity

• The WMO SG-RFC recommends the band be segmented to prevent interference– Metsat operations: 1670-1675 MHz and 1683-1700

MHz– Metaids operations: 1675-1683 MHz

Interference to Metsat Service

Radiosonde Receiver

Radiosonde Link

MetSat

MetSat Earth Station

MetSat Data Link (GVAR or S-VISSR)

Interference

Sharing Issues in 1668.4-1700 MHz with the Radio Astronomy

• The Radio Astronomy service has an allocation below 1670 MHz.

• Metaids users should ensure transmitters do not operate below or drift in frequency to below 1668.4 MHz– Keep in mind the WMO recommends Metaids

operations should be conducted within 1675-1683 MHz.

Interference to Radioastronomy

Radiosonde Receiver

Radiosonde Link

RadioAstronomyStation

Signals from Stars

Interference

Mobile-Satellite Service Proposals for 1670-1700 MHz

• WARC-92 allocated the band 1675-1710 MHz to the MSS in ITU Region 2 (N. and S. America)

• Proposals were made to WRC-95, WRC-97, and WRC-2000 to extend the allocation, in at least part of the band, to worldwide

• Past WRCs made no additional allocations• WRC-03 Agenda Item 1.31 calls for considering

proposals for an MSS allocation in 1683-1690 MHz or some other band (if identified)

Sharing Issues with MSS- Pre WRC-2000 Studies

• The ITU-R concluded that metaids and MSS can not share spectrum on a co-frequency, co-location basis– Metaids typically operate in 1675-1683 MHz

making that band infeasible for MSS use– Metsat operations exist in 1670-1675 and 1683-

1700 MHz - metaids can not be moved

MSS and MetAids Incompatibility

Radiosonde Receiver

Radiosonde Link

Interference

Interference

MSS Service Links

Radiosonde

Sharing Issues with MSS- Pre WRC-2000 Studies (cont)

• The conclusion that MSS cannot share with metaids in 1675-1683 MHz combined with the conclusion that sharing is not possible in 1690-1700 MHz due to metsat, concentrated post-WRC-2000 efforts on the band 1683-1690 MHz and an alternative band of 1670-1675 MHz

Preparations for WRC-03Agenda Item 1.31 (Res 227)

• WRC-03 agenda item 1.31 calls for additional studies in accordance with Resolution 227

• Resolution 227 contains a large volume of information, but the are two key points– Conduct studies for the band 1683-1690 MHz– If necessary, conduct studies on alternative

bands (bands not specified)

Studies: 1683-1690 MHz

• WMO recommends metaids operate in 1675-1683 MHz to avoid interference to metsat stations

• The ITU has concluded, with WMO concurrence, that an MSS allocation at 1683-1690 MHz will have little impact on worldwide metaids operations.

• The sharing issue in 1683-1690 MHz centers on the significant sharing problems with the metsat service. (Covered in Workshop Session B - 3.1)


• Resolution 227, referenced in WRC-03 Agenda Item 1.31 requests the ITU-R study alternative bands if the band 1683-1690 proves to be infeasible

• In response, the ITU-R has conducted studies on the band 1670-1675 MHz, even though the MSS has not fully agreed 1683-1690 MHz is not feasible


• ITU-R studies conclude that MSS operations in 1670-1675 MHz will have little impact on worldwide metaids operations– Several countries will continue to require 1670-

1675 MHz into the future– MSS operations in those countries will not be

feasible

ITU-R Recommendation SA.1264

• Recommendation SA.1264 addresses sharing between the MSS and metaids in 1670-1700 MHz– Sharing not feasible in 1675-1683 MHz – primary sub-

band for radiosonde operations– MSS operations in 1670-1675 MHz will have little

impact on metaids operations except for several countries

– Radiosondes can not moved elsewhere in 1683-1700 MHz due to incompatibility with metsat downlinks

CPM Report Text on Agenda Item 1.31

• Section 2.8.2 addresses sharing between MSS and metaids

• CPM Report Text is consistent with conclusions stated in Recommendation SA.1264.

• CPM Text will be reviewed and possibly edited one last time at the CPM Meeting, November 18-29

Summary of Band 1670-1700 MHz

Metaids Metsat

1670-1675 MHz

Band used in several countries.MSS operations will have minimal impact on worldwide metaids operations.

Band used only for main metsat earth stations. MSS operations possible if main metsat earth stations are protected.

1675-1683 MHz

Primary sub-band for metaids operations (WMO recommended). MSS operations not feasible due to interference to metaids.

Not used for metsat operations due to incompatibility with metaids operations.

1683-1690 MHz

Generally not used for metaids operations due to incompatibility with metsat operations.

Used for metsat operations in ITU Regions 2 and 3. MSS use not feasible due to incompatibility with metsat operations.

1690-1700 MHz

Not used for metaids operations. metaids operations incompatible with metsat operations.

Used for metsat operations. MSS not feasible due to incompatibility with metsat operations.

Recommended Strategy for Agenda Item 1.31

• From the metaids perspective, the CPM text is well balanced, so it should not be modified at the CPM– Text is not perfect, but also is not damaging to

metaids operations– Opening text to modifications could lead to

introduction of unacceptable text from the MSS• Recommend to your CPM delegation “no

change” to CPM text relating to Res 227.

Recommended Strategy for Agenda Item 1.31 (cont)

• An allocation to the MSS in 1683-1690 MHz should be opposed, it will have a significant impact on meteorological operations– ITU Regions 2 and 3: Protection of metsat

earth stations not feasible– ITU-Region 1: Limits availability of spectrum

for future metsat growth


• An allocation to the MSS in 1670-1675 MHz should not be opposed– Not the optimum solution since some metaids

stations in several countries could be impacted– Since there is great pressure to provide the

MSS some spectrum, the band 1670-1675 MHz offers a solution that the worldwide meteorological community can live with


• Discussions of the sub-bands 1675-1683 or 1690-1700 MHz should be opposed - Resolution 227 considers work on them completed and MSS use infeasible – The sub-band 1675-1683 is the only available

spectrum in this area of spectrum that can be used to meet metaids operations requirements


• Resolution 227 should be suppressed or modified to remove any part of 1675-1700 MHz from future consideration– All studies have been completed - if WRC-03

cannot make a decision, no new work can occur to help a future WRC make a decision

– Unresolved questions on protecting meteorological services in 1670-1675 MHz could be addressed in a resolution if necessary

Documents

Radiosonde Spectrum Issues