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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