Some Issues on Compatibility and Interoperability TAN Shusen May 2011,Shanghai 中国卫星导航定位应用管理中心 China National Administration of GNSS and Applications (CNAGA)

Outline: 1 Concept of Radio Frequency Compatibility 2 Frequency sharing’s content and its status quo 3 Analysis method of RFC 4 Interference estimation method 2 中国卫星导航定位应用管理中心 China National Administration of GNSS and Applications (CNAGA)

5 Basis for interference threshold 6 Concept of Interoperability 7 Importance of Interoperability 8 Cooperation in Interoperability 3 中国卫星导航定位应用管理中心 China National Administration of GNSS and Applications (CNAGA)

RF interference by signals within multi-navigation systems shall not affect its own navigation performance, nor other systems’, which is the demand of GNSS operation as well as the demands of other radio navigation system. 4 1 Concept of Radio Frequency Compatibility 中国卫星导航定位应用管理中心 China National Administration of GNSS and Applications (CNAGA)

The related Rules made by the ITU, including the efforts of Res. 609 meeting, are for solving the RF interference among signals of different navigation systems. ITU has done a lot in compatibility, such as its definition, estimation method and common standard. Especially, pursuant to the Resolution 609, in order to protect ARNS systems, the epfd level produced by all space stations of all RNSS systems does not exceed the level –121.5 dB(W/ ) in any 1 MHz band. 5 中国卫星导航定位应用管理中心 China National Administration of GNSS and Applications (CNAGA) 1 Concept of Radio Frequency Compatibility

Frequency sharing implies Sharing Resources, Sharing Responsibilities. Relevant frequency bands: L1: 1559MHz ～ 1610MHz 51MHz L2: 1215MHz ～ 1300MHz 85MHz L3 ： 1164MHz ～ 1215MHz 51MHz Bands in pool/total navigation frequency resources:187MHz. 6 2 Frequency sharing’s content and its status quo 中国卫星导航定位应用管理中心 China National Administration of GNSS and Applications (CNAGA)

Demands ： 7 Signals Systems Authorized signalsOpen signals Bands Band width (MHz) RatingBands Band width (MHz) Rating GPS L 1M +L 2 M L 1C +L 2C +L GLONASS L 1 +L L 1C +L 2C 3 GALILEO PRS1+ PRS2+C S E1+E COMPASSB1+B (24.6) 3 (4) B1C+B 中国卫星导航定位应用管理中心 China National Administration of GNSS and Applications (CNAGA) 2 Frequency sharing’s content and its status quo

If spectrum separation was for authorized signals (AS) and frequency sharing for open signals (OS), frequency demands for the current four GNSSs would be MHz. So, demands>frequency resources, frequency overlapping is inevitable. Spectrum used by COMPASS authorized signals is the lowest, with the rating No 4. 8 中国卫星导航定位应用管理中心 China National Administration of GNSS and Applications (CNAGA) 2 Frequency sharing’s content and its status quo

It is reasonable for the spectrum separation between AS and OS as well as a system’s bandwidth demands. But it is unrealistic in frequency resources for “full” spectrum separation. The rationales for COMPASS’ AS design are ITU Rules and equal sharing, as well as the possibility of spectrum separation, which leaves some space for spectrum separation. The rationale for COMPASS’ OS design is to do its utmost to satisfy the needs for interoperability of four GNSS. 中国卫星导航定位应用管理中心 China National Administration of GNSS and Applications (CNAGA) 2 Frequency sharing’s content and its status quo

Some thoughts on improving AS spectrum separation: Rational use of frequency resources and equally take other stakeholders’ interests into account; “Crossing” spectrum separation for AS is not necessarily better than partly frequency overlapping; 10 中国卫星导航定位应用管理中心 China National Administration of GNSS and Applications (CNAGA) 2 Frequency sharing’s content and its status quo

Whether a radio system is compatible is determined by interference evaluation, including inter- and intra-electronic compatibility of different avionics within a system. On the one hand, even those signals are physically separated, they may not be compatible. Harmonic suppression and thermal noise suppression have to be evaluated before jumping to a conclusion. On the other hand, even if there is a frequency overlap between systems, but will not affect their performance, it can be defined as compatible Analysis method of RFC

The effective carrier-to-noise ratios degradation effected by : 12 4 Interference estimation method Is receiver pre-correlator thermal noise power spectral density post-correlator effective receiver thermal noise power spectral density post-correlator equivalent white-noise power spectral-density (W/Hz) due to the intrasystem inteference

Interference estimation threshold reflects its effects on navigation performance, which shall be determined by bilateral coordination. Navigation performance includes: positioning velocity accuracy, availability, continuity and integrity. Factors on positioning velocity accuracy include signal acquisition ability, pseudo-range accuracy, velocity accuracy and bite error rate Basis for interference threshold

14 For instance: Variance appropriate formula proposed by Dr.John Betz 5 Basis for interference threshold

15 —— noise variance generalized by chip width —— signal bandwidth —— correlator interval —— Code tracking loop bandwidth, Hz —— correlation integration time, s —— carrier-to-noise ratio, dB/Hz When calculating the interference from another navigation signal, becomes 5 Basis for interference threshold

The effects on navigation performance can be evaluated in both AS and OS services. The thresholds for AS and OS services can be different,which can be determined by the coordination of related sides. To take spectrum separation as the only way of RFC is inconformity with the principles claimed in the Preamble of ITU Radio Regulation of making “equal, rational, economic and efficient ” use of frequency. Over claimed “spectrum separation” is blind on the reality of satellite navigation frequency as limited natural resources, which will worsen the situation of the frequency shortage Basis for interference threshold

The objective of interoperability is to maximize the benefits of open services of multi-GNSS, which is the common vision of system operators or service providers. The system operators have the willing of achieving consensus on interoperability to realize the best navigation performance (accuracy, availability, continuity and availability). The consensus shall be achieved first in bilateral coordination, followed by multi- lateral coordination. Interoperability shall not exclude the diversity of signals and navigation data on the condition of frequency compatibility, which offers better services for users at different levels Concept of Interoperability

The importance of interoperability of multi-system’s open services is to satisfy to the largest extent the navigation and positioning needs of civil users, which will make use of all satellite navigation systems and augmentation systems, largely improve the accuracy, availability, continuity and integrity. Interoperability will improve the efficiency in using frequency, lessen the conflict between the shortage and the great demands of navigation frequency. In the current available bands, roughly 400MHz, if the two center frequencies （ 1176MHz,1575MHz ） with the largest interval can be chosen, the ionosphere correction will be the best. If other interoperability signals are added between the above two frequencies, its efficiency will be reduced Importance of Interoperability

The third possible frequency for tri-frequency positioning is S- band in 2500MHz, whose global primary allocation in RDSS is worthy of efforts from all the sides. The highest objective of interoperability is to achieve the satisfactory service accuracy of the combination of any four GNSS satellites, no matter they are from GPS, GLONASS, GALILEO or COMPASS. So, it is quite necessary to strength the cooperation of time and coordinate systems Importance of Interoperability

Three factors for interoperability in the bands of 1575MHz and 1176MHz: Economic and efficient use of frequency resources and satellite/signal power; Optimization/configuration of Efficient payload; Navigation performance; Keeping the current civil signals outside the above frequency bands is beneficial Cooperation in Interoperability

Support the action of opening copyrights for interoperability; Support the adoption of open copyrights for offering users cheaper and more convenient receivers; Support the performance commitment of any single satellite, and the efforts of real time monitoring of signal quality of civil service and broadcasting the data of satellite health and integrity Cooperation in Interoperability

By monitoring satellites in view by ground system, and broadcast the data of selective satellites, reduce the difficulty of RAIM for users. It is reasonable for the same maximum and minimum EIRP broadcasted by the interoperability satellites. It is reasonable for the same maximum and minimum EIRP broadcasted by the interoperability satellites. It is necessary to evaluate the correlation of spreading code for interoperability satellites. Under the condition of no copyright disputes, it is beneficial to choose the same code family. It is necessary to evaluate the correlation of spreading code for interoperability satellites. Under the condition of no copyright disputes, it is beneficial to choose the same code family Cooperation in Interoperability

Thanks ！ 23 中国卫星导航定位应用管理中心 China National Administration of GNSS and Applications (CNAGA)