AMCP - WG/F WP/38
GNSSP SPECTRUM SUBGROUP ACTION ITEM RESPONSES
SG1/7
Document the SARPS GBAS unwanted emission requirements, compare to ITU regulations.
Prepared by T. Jacob
Introduction:
Within the GNSSP Spectrum Sub-group the question was raised whether the unwanted emission limits defined in the current Draft ICAO GNSS SARPs for GBAS ground stations comply with ITU regulations.
From the definitions given in the Radio Regulations (RR), it can be seen that unwanted emissions consist of spurious and out-of-band emissions.
Appendix S3 to the Radio Regulations indicate the maximum permitted levels of spurious emissions of any spurious component supplied by a transmitter to the antenna transmission line.
It has to be considered that there are no general guidelines available in ITU Recommendations covering unwanted emissions in the out-of-band domain from a transmission at the edge of one allocation into the adjacent allocation.
Note: The ITU-R is currently developing material to consider issues related to unwanted emissions. WRC-2003 will have to review under its Agenda Item 1.8.1 the results of studies regarding the boundary between spurious and out-of-band emissions, with a view to modify Appendix S3 of ITU Radio Regulations.
ITU provisions relevant to unwanted emission limits:
When reviewing unwanted emission limits the following ITU RR provisions have to be recognised:
Unwanted emissions (RR Article S1.146)
Consist of spurious emissions and out-of-band emissions.
Spurious emission (RR Article S1.145)
Emission on a frequency or frequencies which are outside the necessary bandwidth and the level of which may be reduced without affecting the corresponding transmission of information. Spurious emissions include harmonic emissions, parasitic emissions, intermodulation products and frequency conversion products, but exclude out-of-band emissions.
Spurious domain emissions:
All emissions, including intermodulation products, conversion products and parasitic emissions, which fall at frequencies separated from the centre frequency of the emission by 250% or more of the necessary bandwidth of the emission will generally be considered as emissions in the spurious domain. However, this frequency separation may be dependent on the type of modulation, the maximum symbol rate in the case of digital modulation, the type of transmitter, and frequency coordination factors. For example, in the case of some digital, broadband, or pulse-modulated systems, the frequency separation may need to differ from the 250% factor.
Out-of-band emission (RR Article S1.144)
Emission on a frequency or frequencies immediately outside the necessary bandwidth which results from the modulation process, but excluding spurious emissions.
Out-of-band domain emissions
Any emission outside the necessary bandwidth which occurs in the frequency range separated from the assigned frequency of the emission by less than250% of the necessary bandwidth of the emission will generally be considered an emission in the out-of-band domain. However, this frequency separation may be dependent on the type of modulation, the maximum symbol rate in the case of digital modulation, the type of transmitter, and frequency coordination factors. For example, in the case of some digital, broadband, or pulse modulated systems, the frequency separation may need to differ from the 250% factor.
Occupied bandwidth (RR Article S1.153)
The width of the frequency band which is just sufficient such that, below the lower and above the upper frequency limits, the mean powers emitted are each equal to a specified percentage b/2 of the total mean power of a given emission.
Unless otherwise specified in an ITU-R Recommendation for the appropriate class of emission, the value of b/2 should be taken as 0.5%.
Necessary bandwidth (RR Article S1.152)
For a given class of emission, the width of the frequency band which is just sufficient to ensure the transmission of information at the rate and with the quality required under specified conditions.
Assigned frequency band (RR Article S1.147)
The frequency band within which the emission of a station is authorized; the width of the band equals the necessary bandwidth plus twice the absolute value of the frequency tolerance. Where space stations are concerned, the assigned frequency band includes twice the maximum Doppler shift that may occur in relation to any point of the Earth's surface.
Assigned frequency (RR Article S1.148)
The centre of the frequency band assigned to a station.
Figure 1 gives a generic example of evaluation of the unwanted emissions in the out-of-band domain falling into the adjacent allocated band, where the boundary between the out-of-band and spurious domains is 250% of the necessary bandwidth Bn.
(1) Actual out-of-band mask for the system under consideration
(2) Spurious limit defined by Appendix S3 or Recommendation ITU-R SM.329
(3) Unwanted emissions in the out-of-band domain falling in the adjacent allocated frequency band
Figure 1
Maximum permitted spurious emission power levels:
The Appendix S3 to the RR indicate the maximum permitted levels of spurious emissions, in terms of power as indicated in the tables below, of any spurious component supplied by a transmitter to the antenna transmission line.
For the purpose of setting limits, all emissions, including harmonic emissions, intermodulation products, frequency conversion products and parasitic emissions, which fall at frequencies separated from the centre frequency of the emission by ± 250%, or more, of the necessary bandwidth of the emission will generally be considered as spurious emissions.
Section I of Appendix S3 is applicable until 1 January 2012 to transmitters installed on or before 1 January 2003; Section II is applicable to transmitters installed after 1 January 2003 and to all transmitters after 1 January 2012. This Appendix does not cover out-of-band emissions (see Section below).
Section I – Spurious emission limits for transmitters installed on or before 1 January 2003 (valid until 1 January 2012)
Frequency band containing the assignment(lower limit exclusive,
upper limit inclusive) / For any spurious component, the attenuation
(mean power within the necessary bandwidth
relative to the mean power of the spurious
component concerned) shall be at least that
specified below and the absolute mean power
levels given shall not be exceeded 1
30 MHz to 235 MHz
– mean power above 25 W
– mean power 25 W or less / 60 dB
1 mW
40 dB
25 mW
Note: Only the GBAS related material has been quoted.
Section II – Spurious emission limits for transmitters installed after 1 January 2003 and for all transmitters after 1 January 2012
Attenuation values used to calculate maximum permitted spurious emission power levels for use with radio equipment
Service category inaccordance with Article S1 / Attenuation (dB) below the power
supplied to the antenna transmission line
All services except those services
quoted below / 43 + 10 log (P), or 70 dBc, whichever is less stringent
Note: Only the GBAS related material has been quoted.
The spurious emission levels given in Appendix S3 are specified in the following reference bandwidths:
– 1 kHz between 9 kHz and 150 kHz
– 10 kHz between 150 kHz and 30 MHz
– 100 kHz between 30 MHz and 1 GHz
– 1 MHz above 1 GHz.
Maximum permitted out-of-band emission power levels:
It was stated in the introduction that there are no general guidelines available in ITU Recommendations covering unwanted emissions in the out-of-band domain from a transmission at the edge of one allocation into the adjacent allocation. Therefore, ITU-R Study Group 1 established Task Group 1/5 to study all unwanted emissions. The final Task Group 1/5 meeting (Geneva, 23 – 30 October 2000) completed a number of draft new ITU-R Recommendations. WRC-2003 will have to review under its Agenda Item 1.8.1 the results of studies regarding the boundary between spurious and out-of-band emissions, with a view to modify Appendix S3 of ITU Radio Regulations (RR).
In order to conduct the comparison between the GBAS SARPs and the ITU unwanted emission levels the material of Draft New Recommendation ITU-R SM.[OOB] developed by TG 1/5 [2] has been used. This Draft New Recommendation provides no limits for aeronautical radio navigation services however, in its Annex 11 out-of-band limits for the aeronautical mobile service are given.
For aeronautical-mobile and maritime-mobile transmitters other than aeronautical telemetry and exempted systems, the required attenuation of the mean power of any emission in the out-of-band domain, relative to the mean power of the transmitter, is:
50-150% / 25 dBc150-250% / 35dBc
Figure 2
Out-of-band mask for aeronautical and maritime mobile
GBAS SARPs unwanted emission requirements:
The current Draft ICAO GBAS SARPs define in Section A.3.5.4.6 the following maximal allowable power limits for unwanted emissions produced by GBAS ground stations (see Table below).
In order to be able to compare the maximum unwanted emission limits given in Appendix S3 to the RR and the limits defined in GBAS SARPs the power levels are provided in addition with a 100kHz reference bandwidth.
Frequency / Relative Unwanted Emission Level [2] / Maximum Unwanted Emission Level [1] / Maximum Unwanted Emission Level with 100kHz reference bandwidth9kHz to 150 kHz / -93 dBc [3] / -55 dBm/1 kHz [3] / -35 dBm
150 kHz to 30 MHz / -103 dBc [3] / -55 dBm/10 kHz [3] / -45 dBm
30 MHz to 106.125 MHz / -115 dBc / -57 dBm/100 kHz / -57 dBm
106.425 MHz / -113 dBc / -55 dBm/100 kHz / -55 dBm
107.225 MHz / -105 dBc / -47 dBm/100 kHz / -47 dBm
107.625 MHz / -101.5 dBc / -53.5 dBm/10 kHz / -43.5 dBm
107.825 MHz / -88.5 dBc / -40.5 dBm/10 kHz / -30.5 dBm
107.925 MHz / -74 dBc / -36 dBm/1 kHz / -16 dBm
107.975 MHz / -65 dBc / -27 dBm/1 kHz / -7 dBm
118.000 MHz / -65 dBc / -27 dBm/ 1 kHz / -7 dBm
118.050 MHz / -74 dBc / -36 dBm/1 kHz / -16 dBm
118.150 MHz / -88.5 dBc / -40.5 dBm/10 kHz / -30.5 dBm
118.350 MHz / -101.5 dBc / -53.5 dBm/10 kHz / -43.5 dBm
118.750 MHz / -105 dBc / -47 dBm/100 kHz / -47 dBm
119.550 MHz / -113 dBc / -55 dBm/100 kHz / -55 dBm
119.850 MHz to 1 GHz / -115 dBc / -57 dBm/100 kHz / -57 dBm
1 GHz to 1.7 GHz / -115 dBc / -47 dBm/1 MHz / -57 dBm
Note 1.- The maximum unwanted emission level (absolute power) applies if the authorized transmitter power exceeds 150 W.
Note 2. – The relative unwanted emission level is to be computed using the same bandwidth for desired and unwanted signals. This may require conversion of the measurement for unwanted signals done using the bandwidth indicated in the maximum unwanted emission level column of Table 2.
Note 3.- This value is driven by measurement limitations. Actual performance is expected to be better.
Note 4.- The relationship is linear between single adjacent points designated by the adjacent channels identified above.
Comparison of the maximum permitted unwanted emission power limits:
According to Appendix S3 the spurious domain generally consists of frequencies separated from the centre frequency of the emission by 250% of the necessary bandwidth of the emission. In this analysis it has been assumed that 25kHz is the appropriate value for the necessary bandwidth of GBAS transmissions. The boundary between spurious and out-of-band emissions is set to 2.5 * 25kHz = 62.5kHz. The lowest assignable GBAS channel is 25kHz from the band edge, the boundary is set at 107.9625MHz.
Spurious Emissions Limits:
For any spurious component of a GBAS transmitter installed before 1 January 2003 (valid until 1 January 2012) the attenuation (mean power within the necessary bandwidth relative to the mean power of the spurious component concerned) shall be at least 60dB below and the absolute mean power levels given shall not exceed 1mW. Assuming a mean power of a GBAS transmitter of 150W equals 21.76dBW within 25kHz reference bandwidth minus an attenuation of 60dB gives a maximum spurious emission power level of –38.24dBW or 8.24dBm. In order to make the different power levels comparable a conversion of the reference bandwidth from 25kHz to 100kHz is necessary. This leads to a bandwidth conversion factor of 6dB. And so, the maximum spurious emission power level is –2.24dBm within a 100kHz reference bandwidth.
A GBAS transmitter installed after 1 January 2003 must meet a spurious domain emission attenuation of 43 + 10log (P), or 70dBc, whichever is less stringent. To measure spurious domain emissions in the frequency range between 30MHz and 1000MHz, Appendix S3 indicates use of a reference bandwidth of 100kHz.
With a maximum total mean power of 150W for GBAS ground stations the attenuation relative to the total mean power equals 43 + 10log (150) = 64.76dB. The 64.76dB is less stringent than 70dBc, so the 64.76dB value is used. Therefore, spurious domain emissions of GBAS transmitters must not exceed 64.76dBc in a 100kHz reference bandwidth, or converting to an absolute power level, the spurious emission must not exceed 21.76dBW – 64.76dBc = 43dBW or –13dBm in a 100kHz reference bandwidth.
Out-of-band Emission Limits:
For aeronautical-mobile transmitters the required attenuation of the mean power of any emission in the out-of-band domain, relative to the mean power of the transmitter, is:
50-150% / 25 dBc150-250% / 35dBc
With a maximum total mean power of 150W in a 25kHz (and also 100kHz) reference bandwidth of a GBAS transmitter the out-of-band emissions must not exceed 21.76dBW – 25dBc = 3.24dBW (26.76dBm) in the frequency range separated from the assigned frequency between 50 and 150% of the necessary bandwidth and 13.24dBW (16.76dBm) for frequencies between 150 and 250% of the necessary bandwidth.
The table below provides the different emission limits with a 100kHz reference bandwidth.
Frequency(MHz) / GBAS SARPs Unwanted emission levels
(dBm/100kHz) / ITU RR Appendix S3 Spurious emission levels for Tx installed before 1.1.2003
(dBm/100kHz) / ITU RR Appendix S3 Spurious emission levels for Tx installed after 1.1.2003
(dBm/100kHz) / ITU-R Doc 1/33 Rev.1 Out-of-band emission levels
(dBm/100kHz)
107.8250 / -30,5 / -2,24 / -13
107.9250 / -16 / -2,24 / -13
107.9625 / -2,24 / -13
107.9750 / -7 / 16,76
107.9875 / 16,76
108.0000 / -7 / 26,76