# Preparations for Galileo PRS in Poland
## 4 Coexistence with RNSS Systems and Other Services  
All global GNSS systems occupy the same frequency resources, which are allocated to all RNSS services. Over the course of a few recent years, an issue of harmful interference affecting the RNSS receivers and caused by an amateur service (the so-called 23 cm band) has become a source of significant controversy in Europe. Those interference incidents, formally reported by at least two European countries, occurred in the E6 band (1260-1300 MHz), triggering questions on possible actions to protect the RNSS from this undesirable effect. As specified in the latest, 2020 edition of the ITU-R's Radio Regulations (RR), the frequency band 1240-1300 MHz is allocated on a primary basis to the radio navigation satellite service RNSS (space-to-Earth and space-to-space). Other services that have co-primary allocations in that band are radiolocation, Earth-exploration (active) and space research (active), but these three are unrelated to the topic of this article. On the other hand, the segments of this band are also allocated--but on a secondary basis--to the amateur service (1240-1300 MHz) and to the amateur satellite service (1260-1270 MHz, via RR footnote 5.282). All frequency allocations mentioned above are worldwide, which means they apply to all three ITU-R Regions [4]. When analyzing the current utilization of the 1240-1300 MHz frequency band by the RNSS, we can conclude it is heavily used by various GNSS systems occupying specific spectrum blocks, including [5]: the European Galileo (1260-1300 MHz), Russian GLONASS (1240-1260 MHz), Chinese Compass (1250-1280 MHz), Japanese QZSS (1260-1300 MHz) and American GPS (some transmissions in the 1215-1240 MHz band may extend above 1240 MHz). In the context of Galileo, it should be noted that the E6 band is essential for the operation of several important services planned in the system, including the HAS and, primarily, the PRS. Consequently, the interference with the RNSS in that band can be a very serious threat for the future development, and operation, of the European GNSS system. At the same time, the utilization of this band by radio amateurs is also significant [5]. The IARU (International Amateur Radio Union) band plan for Region 1 (Europe, Middle East, Africa and northern Asia) divides the 1240-1300 MHz range into portions to be used by numerous wideband and narrowband amateur applications, including: digital voice, telegraphy, amateur TV (digital or analogue), satellite services and machine-generated modes (MGM). Various applications relevant to that frequency range translate into different types of possible stations, different transmitted power values and/or different sizes/parameters  
Figure 2: PRS keying procedure. of the utilized antennas. As a whole, it generates a lot of requirements to be fulfilled in order to ensure the smooth coexistence of these two service categories. The number of radio amateurs obviously varies among countries, but it is generally noticeable, e.g., in Poland, there are approximately 13,000 private persons and almost 450 clubs registered with a Category 1 license (maximum allowed output power of 500 W). This is also the factor that needs to be considered when analyzing the compatibility between the amateur services and RNSS. As mentioned before, the amateur and amateur satellite services have worldwide secondary allocations in the 1240-1300 MHz band. According to the Radio Regulation's terminology, the secondary status of a service means that the stations of such service [4]:  
* shall not cause harmful interference to stations of primary services to which frequencies are already assigned or to which frequencies may be assigned at a later date;
* cannot claim protection from harmful interference from stations of a primary service to which frequencies are already assigned or may be assigned at a later date;
* can claim protection, however, from harmful interference from stations of the same or other secondary service(s) to which frequencies may be assigned at a later date.