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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