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23cm band and Sat-Nav Coexistence: Studies maturing in ITU‑R WP4C

Dur­ing the peri­od 4–10 May 2022, the IARU con­tin­ued to engage in the prepara­to­ry work for WRC-23 agen­da item 9.1b in ITU‑R Work­ing Par­ty 4C (WP4C).

Work con­tin­ued to devel­op the coex­is­tence stud­ies between the ama­teur ser­vices in the 23cm band and the radio-nav­i­ga­tion satel­lite ser­vices (RNSS) oper­at­ing across the band. New stud­ies were sub­mit­ted by France, Chi­na and the Russ­ian Federation.

The scale of the prob­lem for the ama­teur ser­vices is becom­ing clear. For exam­ple, the stud­ies pre­dict that even a 10W 23cm band sta­tion could cause inter­fer­ence to RNSS receivers at up to 30km on the anten­na main beam head­ing. Although the lev­el of ama­teur activ­i­ty and the den­si­ty of users is quite low (com­pared to oth­er more pop­u­lar bands) the issue remains that from a reg­u­la­to­ry per­spec­tive the ama­teur ser­vices are required to not cause harm­ful inter­fer­ence to RNSS services.

The fig­ure below is a sam­ple of one result from one study sub­mit­ted into ITU‑R and fur­ther illus­trates the scale of the prob­lem. In this exam­ple a sta­tion using an 18dBi gain anten­na is used for both nar­row band and wide­band (ATV) trans­mis­sions and a range of pow­er lev­els. The pro­tec­tion cri­te­ria for the RNSS receivers dif­fers for nar­row­band and wide­band inter­fer­ing sig­nals. The fig­ure shows the dis­tances out from the ama­teur sta­tion where the RNSS pro­tec­tion cri­te­ria could be exceed­ed along the anten­na main beam heading.

These results have been devel­oped based the ITU‑R defined receiv­er pro­tec­tion lev­el for the GALILEO RNSS. For the nar­row band modes this is ‑134.5dBW and for the wide­band modes is ‑140dBW/MHz. In addi­tion, mea­sure­ment cam­paigns have shown that an improve­ment in the com­pat­i­bil­i­ty poten­tial can be seen if the ama­teur sig­nals avoid the cen­tre por­tion of the GALILEO receiv­er passband.

Of course the stud­ies can­not take into account every pos­si­bil­i­ty that might mit­i­gate the prob­lem (e.g clut­ter, ter­rain block­ing etc.) but it is clear that the poten­tial for inter­fer­ence is considerable.

The IARU is work­ing hard to ensure that the ama­teur ser­vice can con­tin­ue to devel­op in this band and allow all the ama­teur appli­ca­tions in use today to con­tin­ue. How­ev­er, giv­en the heavy spec­trum occu­pan­cy of the band by the var­i­ous RNSS sys­tems it is evi­dent that pro­pos­als will come call­ing to restrict our abil­i­ty to oper­ate in cer­tain parts of the band and at the pow­er lev­els pos­si­ble today. IARU is total­ly engaged in the dis­cus­sion of these con­sid­er­a­tions and these will con­tin­ue with­in ITU‑R (and oth­er region­al bodies).

The IARU sum­ma­ry report on the WP4C meet­ing can be found here which in turn includes a link to the full draft stu

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Statement from IARU

In response to recent world events, the Inter­na­tion­al Ama­teur Radio Union has issued the fol­low­ing statement:

“IARU is an apo­lit­i­cal orga­ni­za­tion focused on pro­mot­ing and defend­ing ama­teur radio and the ama­teur radio ser­vices. The ama­teur radio ser­vice is about self-instruc­tion in com­mu­ni­ca­tions and friend­ship between people.”

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23cm Band and RNSS – Compromises need to be found

As we head into 2022 the ITU‑R and CEPT work con­sid­er­ing the 23cm band and coex­is­tence with the RNSS sys­tems (GALILEO, COMPASS, GLONASS, GPS…) will con­tin­ue so where have we got to and where is it heading?

The IARU has pro­vid­ed exten­sive infor­ma­tion regard­ing the ama­teur and ama­teur satel­lite ser­vice appli­ca­tions in the band 1240–1300MHz as well as oper­a­tional char­ac­ter­is­tics and data indi­cat­ing the den­si­ty of active trans­mit­ting sta­tions and the busiest peri­ods when these are most like­ly to be oper­a­tional. Using this data, one CEPT admin­is­tra­tion has pro­vid­ed an exten­sive set of prop­a­ga­tion mod­el pre­dic­tions for a num­ber of ama­teur oper­at­ing sce­nario assump­tions (includ­ing satel­lite work­ing and EME oper­a­tion) that pre­dict an “inter­fered area” over which an ama­teur trans­mis­sions may be received by a RNSS receiv­er at lev­els exceed­ing a defined pro­tec­tion lev­el. Anoth­er ITU‑R mem­ber admin­is­tra­tion con­tributed a small­er set of pre­dic­tions using the same mod­el. The received RNSS inter­fer­ence lev­el that the RNSS can tol­er­ate (receiv­er pro­tec­tion lev­el) is based on ITU‑R rec­om­mend­ed cri­te­ria and depends on whether nar­row­band or wide­band inter­fer­ing sig­nals are being transmitted.

The prop­a­ga­tion mod­el pre­dicts that an inter­fered area can extend out to sev­er­al tens of km (depend­ing on the sce­nario) but at the extremes of the area, the time prob­a­bil­i­ty of exceed­ing the pro­tec­tion lev­el is very low (1%) and for only 50% of loca­tions. The mod­el can only assume a full pow­er con­tin­u­ous transmission.

In addi­tion much atten­tion has been paid to doc­u­ment­ing an inter­fer­ence case record­ed in Italy between an Ital­ian 23cm band repeater and GALILEO receivers at the near­by Euro­pean Com­mis­sion Joint Research Cen­tre in Ispra where work is under­tak­en to devel­op and test GALILEO sys­tem appli­ca­tions. The impact of traf­fic through this very local repeater (12.5km dis­tant) on three dif­fer­ent GALILEO receivers has been doc­u­ment­ed. This work sug­gests that whilst RNSS receiv­er band­width can have a part to play in enabling coex­is­tence, beyond that noth­ing has been report­ed that could help devel­op any coex­is­tence cri­te­ria. Noth­ing is report­ed about the mode of fail­ure in the receivers beyond degra­da­tion on C/N.

This one case is often cit­ed as the “proof” that inter­fer­ence can occur.

At present the con­clu­sions from this work are being devel­oped (in ITU‑R and CEPT) and IARU work con­tin­ues to ensure these results are put into a real world con­text to under­stand what they imply with respect to suc­cess­ful coexistence.

Ama­teur trans­mis­sions vir­tu­al­ly any­where in the band will be co-fre­quen­cy with the RNSS receivers from one sys­tem or anoth­er. It is there­fore obvi­ous that any RNSS receiv­er will be open to any co-fre­quen­cy ama­teur trans­mis­sion and ama­teur oper­a­tors have no way of know­ing where or when a RNSS ser­vice user is active. There­fore IARU has expressed a view that for suc­cess­ful coex­is­tence guid­ance to be devel­oped, some com­pro­mis­es will need be necessary.

As we move through the work in 2022 we need these com­pro­mis­es will become appar­ent so that the ama­teur com­mu­ni­ty can know how to respond appro­pri­ate­ly in a way that can allow our diverse set of appli­ca­tions to con­tin­ue to devel­op whilst min­imis­ing any poten­tial dis­rup­tion to RNSS ser­vices. It is antic­i­pat­ed that the inter­na­tion­al views on the ITU‑R stud­ies will need to sta­bilise by the mid­dle of this this year in order to meet the timetable for the WRC-23 prepara­to­ry work. These views will like­ly pro­pose tech­ni­cal and oper­a­tional mea­sures to be applied to the ama­teur and ama­teur satel­lite ser­vices that could be for­malised in the Radio Regulations.

As the study activ­i­ties work towards con­clu­sions it is vital that the nation­al soci­eties engage with their nation­al ama­teur radio reg­u­la­tors to ensure they under­stand and hear about the impor­tance of this band for the ama­teur radio community.

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23cm Band Studies progressing in ITU‑R towards WRC-23

Prepara­to­ry activ­i­ties and stud­ies relat­ing to WRC23 AI9.1b have con­tin­ued in the ITU‑R work­ing par­ties 4C and 5A dur­ing Octo­ber and Novem­ber 2021. Although Region 1 admin­is­tra­tions have been most active­ly engaged, the stud­ies con­tin­ue to evolve and RNSS oper­a­tors from all regions have been par­tic­i­pat­ing in the discussions. 

In ITU‑R WP5A a first draft ITU‑R Rec­om­men­da­tion was pro­posed which may form the basis for rec­om­mend­ing guid­ance for con­cerned admin­is­tra­tions regard­ing ama­teur ser­vice coex­is­tence with the RNSS. Work on all these ele­ments will con­tin­ue into 2022. 

Click here for the WP4C sum­ma­ry report.

Click here for the WP5A sum­ma­ry report.

This post from the Region 1 web site pro­vides fur­ther detailed infor­ma­tion on developments.

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23cm band and Sat-Nav Coexistence: Preliminary Studies considered in ITU‑R WP4C

Dur­ing the peri­od 5–13 July 2021, the prepara­to­ry work for WRC-23 agen­da item 9.1b con­tin­ued in ITU‑R Work­ing Par­ty 4C (WP4C). (See Region 1 Feb 23rd news item for fur­ther back­ground). The IARU mem­ber rep­re­sen­ta­tives from Aus­tralia, Brazil, Cana­da, Ger­many, Japan, Nor­way, UK and USA, par­tic­i­pat­ed in the meet­ing and deliv­ered addi­tion­al infor­ma­tion on ama­teur activ­i­ties in this key microwave band. 

Pre­lim­i­nary stud­ies came from France based on the ongo­ing CEPT work to pro­vide ini­tial esti­mates of sep­a­ra­tion dis­tances required between RNSS GALILEO receivers and a sam­ple of ama­teur emis­sions. The Euro­pean Com­mis­sion GALILEO team pro­vid­ed a set of obser­va­tions per­tain­ing to a RNSS inter­fer­ence event in north­ern Italy.

Glob­al IARU Band Plans and RNSS sys­tem fre­quen­cy band overlaps

The work con­tributed by France, although need­ing refine­ment, is going in a good direc­tion, using ITU‑R rec­om­mend­ed prop­a­ga­tion mod­els and assump­tions based on oper­at­ing sce­nar­ios pro­vid­ed by the ama­teur com­mu­ni­ty. Fur­ther work is need­ed to take account of the large dis­par­i­ty between the RNSS ser­vice receiv­er band­widths and the fre­quen­cy band off­sets of the ama­teur appli­ca­tions based on the mea­sure­ments car­ried out by Germany.

One exam­ple result from a pre­lim­i­nary sim­u­la­tion run

The RNSS com­mu­ni­ty have updat­ed their RNSS receiv­er pro­tec­tion cri­te­ria with an update to ITU‑R Rec­om­men­da­tion M.1902 that now includes para­me­ters rel­e­vant to the GALILEO E6 sig­nal block. How­ev­er these cri­te­ria only dis­tin­guish between a nar­row band and wide band inter­fer­er lev­el at the receiv­er and take no account of off­set fre­quen­cy in the receiv­er band­width or any time variance.

The IARU is work­ing to ensure the ama­teur ser­vices are real­is­ti­cal­ly rep­re­sent­ed in the stud­ies as they move for­ward. It remains vital that nation­al ama­teur com­mu­ni­ties present their views on the impor­tance of this band to their nation­al reg­u­la­tors in a con­sol­i­dat­ed and con­sis­tent man­ner. The work will con­tin­ue through­out the year and beyond both in ITU‑R and in the region­al telecom­mu­ni­ca­tions organ­i­sa­tions and the IARU is com­mit­ted to ensure every group hears the ama­teur posi­tion on this impor­tant microwave band.

Click for the sum­ma­ry report from the WP4C meet­ing.

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