Method for the determination of coexistence of digital signals on the same frequency band

The frequency spectrum is a natural resource. For decades the International Telecommunication Union (ITU) and consequently its individual member countries have been regulating and assigning this spectrum to ensure its optimal usage. The analogue systems that dominated the frequency bands until a few decades ago had known radiation properties and thus the conditions for coexistence were also known. A certain part of the frequency band was assigned to an exactly known service, with no other service being allowed to operate on the same frequency. Yet with the development of digital systems and digital signal processing this situation has changed. It is no longer the case that some part of the frequency band is dedicated exclusively to one service. In certain conditions, the ITU allows the coexistence of several systems on the same frequency band. The main reason for this thesis is the current condition established by the ITU for the coexistence of satellite systems (Broadcasting Satellite Systems) and MMDS (Multi-channel Multipoint Distribution Systems) on the same frequency band. The thesis primarily focuses on the parameters that have a major impact on the coexistence of the MMDS and satellite systems working on the same frequency band and with the same geographical coverage. Another issue is how the parameters of terrestrial systems should be set so as to enable their coexistence with satellite systems without limiting the terrestrial systems. One must be cautious with restrictions because the potentially excessive restrictions on MMDS systems would limit their economic viability or even completely stop their deployment. This doctoral thesis contains the results of comprehensive research into these matters. All parameters that could potentially have some impact on the coexistence of digital systems have been included in the research work and appropriately processed. Calculations have been made in compliance with the ITU’s recommendations and regulations. Those calculations have been confirmed with extensive measurements of professional commercial systems (MMDS and BSS). In addition, a special transmitting/receiving system was constructed for the worst-case simulation – having a BSS transmitter, MMDS transmitter and BSS/MMDS receiver on the same line. The motivation for this work was the general concern of the EU and US electronic communications administrations regarding the coexistence of local MMDS and BSS according to the ITU’s regulations. The measurements and calculations show that, due to the latest technological developments, modern systems coexisting on the same frequency band (according to the ITU) are much less sensitive to mutual interference. It is therefore necessary to change the ITU regulation. This doctoral thesis proposes which changes should be made. As stated in the conclusion, the study concentrates on a single parameter R – the protection ratio between the desired and interfering signals. According to the results of our calculations and measurements, parameter R in the equation for the allowed power flux density of an interfering signal is critical. This figure is set by ITU-RR Appendix 30 Annex 3 to 30 dB for digital receivers. Yet in this thesis we propose the following value for parameter R: 11 dB (8 dB + 3 dB in the event of locally extremely bad weather). In this case, the power flux density would be -84 dBW/m2 which is an adequate power flux-density for the interferer (in our case for MMDS), and its coexistence with BSS