1、 Rec. ITU-R M.1477 1 RECOMMENDATION ITU-R M.1477 TECHNICAL AND PERFORMANCE CHARACTERISTICS OF CURRENT AND PLANNED RADIONAVIGATION-SATELLITE SERVICE (SPACE-TO-EARTH) AND AERONAUTICAL RADIONAVIGATION SERVICE RECEIVERS TO BE CONSIDERED IN INTERFERENCE STUDIES IN THE BAND 1 559-1 610 MHz (Questions ITU-
2、R 91/8 and ITU-R 217/8) (2000) Rec. ITU-R M.1477 The ITU Radiocommunication Assembly, considering a) that Resolution 220 (WRC-97) calls for studying the technical criteria and operational and safety requirements to determine if sharing between aeronautical radionavigation/radionavigation satellite s
3、ervices (ARNS/RNSS) and MSS in the space-to-Earth direction is feasible in a portion of the band 1 559-1 567 MHz; b) that the band 1 559-1 610 MHz is allocated on a primary basis to RNSS (space-to-Earth) and ARNS; c) that Recommendations ITU-R M.1088 and ITU-R M.1317 provide characteristics and desc
4、riptions of several types of receivers that are used with the radionavigation-satellite systems, known as the GPS and the GLONASS; d) that there is an essential need to protect systems operating in the ARNS and RNSS in the band 1 559-1 610 MHz; e) that GPS and GLONASS navigation safety services exis
5、t for a variety of applications including aeronautical, land and marine applications, and that the use of these services will expand in the future; f) that any properly equipped earth station may receive navigation information from the GPS, GLONASS and other RNSS systems on a worldwide basis; g) tha
6、t the International Civil Aviation Organization (ICAO) is developing standards for the GNSS, whose elements include GPS and GLONASS; h) that the International Maritime Organization (IMO) requires ships to equip with RNSS for navigation in narrow waterways and for docking; j) that RR No. S4.10 states
7、 that the safety-of-life aspects of radionavigation and other safety services require special measures to ensure their freedom from harmful interference (see also RR No. S1.169), recognizing a) that there are a number of receivers of GPS and its augmentations used in safety-of-life applications that
8、 process the GPS signals in different ways as described in Annex 1, within the RNSS/ARNS band; b) that there are a number of receivers of GLONASS used in safety-of-life applications that process the GLONASS signals in different ways, as described in Annex 2, within the RNSS/ARNS band; c) that at the
9、 current time, the Standards and Recommended Practices (SARPs) of ICAO do not recognize, for use in aircraft, the use of the wideband signals of GPS or GLONASS, nor their use of carrier frequencies above 1 604.25 MHz, on a worldwide basis, after 2005; d) that there are a number of different existing
10、 and planned augmentations of GPS and GLONASS which support safety-of-life services in aeronautical and other environments; e) that there are a large number of non-aeronautical GNSS applications used in support of both safety-of-life and non-safety-of-life services; f) that Recommendation ITU-R M.13
11、43 defines the essential technical requirements of mobile earth stations (MESs) for global non-GSO MSS systems in the bands 1-3 GHz, 2 Rec. ITU-R M.1477 recommends 1 that the characteristics of the receivers described in Annexes 1 to 4 be used in performing interference analyses that include ARNS an
12、d RNSS in the band 1 559-1 610 MHz (see Note 1); 2 that a safety margin, as discussed in Annex 5, be applied for the protection of the safety-of-life aspects and applications of RNSS and ARNS, when performing interference analyses. NOTE 1 This Recommendation is not intended to be used to form the ba
13、sis for future modifications to maximum unwanted emission levels for the band 1 559-1 610 MHz that are stated in the Annexes to Recommen-dation ITU-R M.1343. The maximum unwanted emission levels for the band 1 559-1 610 MHz stated in Recommendation ITU-R M.1343 have been developed pursuant to a spec
14、ific interference scenario, and are not intended to be applied to any service other than MSS MESs operating in the 1-3 GHz range without further study. ANNEX 1 GPS receiver and signal characteristics 1 GPS receiver characteristics Several GPS receiver types are described in this Annex. There are thr
15、ee aeronautical receivers for which the requirements are relatively well developed. Each has its counterpart for land and/or marine applications, and it is intended that the characteristics stated in this Annex would apply to GPS receivers that are used in such applications. At this time it is not k
16、nown whether the non-aviation applications are more susceptible to interference or less, nor is it known how susceptible future applications will be, considering both the current GPS with its augmentations and evolutions of GPS. The first aeronautical receiver is a civil navigation receiver designed
17、 to provide category I precision approach guidance. It must meet the requirements of a satellite-based augmentation system (SBAS) specification. It must track both GPS satellites and SBAS satellites, which have GPS-like codes and transmit at the same centre frequency of 1 575.42 MHz. The SBAS signal
18、 is modulated with data using a symbol rate of 500 bit/s, which is then decoded with a convolutional decoding scheme to output information at a rate of 250 bit/s. The second aeronautical receiver is an air navigation receiver designed to provide Category II/III precision approach guidance. It must m
19、eet the requirements of a ground-based augmentation system (GBAS). It must track GPS satellites and pseudolites. Pseudolites are ground-based transmitters which emit a signal having the characteristics of GPS, but utilizing different spreading codes. There are wideband and narrow-band pseudolites cu
20、rrently under consideration. Wideband pseudolites emit a code similar to the Y code (see Note 1), thus the signal has the spectral characteristics of the Y code. The pseudolites are pulsed with a duty cycle of less than 4%. The narrow-band pseudolites emit a signal having C/A code characteristics, o
21、ffset from the L1 (L1 band is at 1 559-1 610 MHz) centre frequency by 10.23 MHz. They are pulsed, with a duty cycle of about 9%. NOTE 1 Y code is a modified P code, having the same chipping rate and spectral characteristics as that of the P code. The third receiver is a ground-based receiver which i
22、s used in SBAS operations to determine ionospheric delays. It is also used in non-SBAS ground applications. This receiver uses a semi-codeless technique that exploits a unique feature of the GPS architecture whereby the L1 and L2 (L2 band is at 1 215-1 260 MHz) Y code signals are cross-correlated to
23、 provide a measurement of signal delay at L2, thus making it possible to determine the signal delay due to the ionosphere. The cross-correlation scheme is made possible by the fact that the GPS L1 and L2 signals have identical codes. This receiver must acquire and track both GPS and SBAS satellites
24、at L1. Semi-codeless receivers are more sensitive to interference because they operate without benefit of knowing the Y code. In the following descriptions power levels at the antenna input refer to the power that would be received by an isotropic, circularly polarized antenna of the proper polarity
25、, while power levels at the antenna output refer to the power levels that account for the antenna gain in the direction of the specific signal or interference source. The specification of interference levels and bandwidths is shown in Fig. 1. Rec. ITU-R M.1477 3 1477-01101251022512510251022510325104
26、25105150160140130120110Interference bandwidth (kHz)Interference power(antenna port) (dBW)TrackingAcquisitionFIGURE 1Aggregate interference threshold for SBAS and GBAS air navigation receiversFIGURE 1/M.1477.D01 = 3 CM The maximum interference levels in Tables 1 to 10 do not refer to the allowable le
27、vel of interference but rather to the interference level that manufacturers must design equipment to withstand, while still meeting performance requirements. The total allowable level of interference from known sources must be significantly below this value, namely by the safety margin (see Annex 5)
28、. This is to allow for variations in GNSS receiver performance and unknown sources of interference. 1.1 Land vehicle and marine navigation receiver Land vehicle and marine navigation receivers are designed to provide metre-level guidance, using differential corrections obtained from any of a number
29、of GPS augmentation systems, including SBASs, radiobeacon networks, or other local area broadcasts that use one of several frequencies from HF to UHF. Their characteristics are similar to those of the first aeronautical receiver described above. 1.2 Semi-codeless receivers Semi-codeless GPS receiver
30、s use a technique unique to GPS whereby the L1 and L2 Y code signals are cross-correlated to provide an estimate of the ionospheric delay or an independent set of carrier phase measurements that support rapid removal of wavelength ambiguities, even when the receiver is in motion. This process provid
31、es improved position accuracy. The cross-correlation scheme is made possible by the fact that L1 and L2 have identical, synchronized Y codes. This receiver will have characteristics similar to the third aeronautical receiver described above, but may differ in its susceptibility to interference. 4 Re
32、c. ITU-R M.1477 TABLE 1 SBAS air navigation receiver, Category I precision approach operations 1.3 Commercial ground network receiver Some commercial ground network receivers operate at a single frequency, in which case their characteristics will be similar to the first aeronautical receiver describ
33、ed. Two frequency receivers may also be used in commercial networks. If so, their characteristics are similar to the third aeronautical receiver, except that instead of performing relative carrier phase computations, the cross-correlated L1 and L2 signals are processed to determine the ionospheric d
34、elay in the signals. This information is used by the network to improve accuracy over a large region. 2 Analysis methodology An analysis methodology is presented that shows that for worst-case conditions, full availability of GPS service, in the presence of additional external interference, may not
35、be met due to the effects of C/A-code co-channel self-interference. A model for predicting these location and time specific events is developed in this Annex. Preliminary experimental validation of the results (not shown) has been conducted; additional tests are in progress. L1 carrier centre freque
36、ncy 1 575.42 MHz C/A code chip rate 1.023 Mbit/s Navigation data rate, GPS 50 bit/s Navigation data rate, SBAS, with FEC, rate 1/2 500 symbols/s Word error rate (1 word = 250 information bits) 103per s Minimum received power level at antenna input, SBAS 161 dBW Minimum antenna gain towards satellite
37、 at 5 elevation 4.5 dBic Maximum antenna gain in upper hemisphere +7 dBic Assumed antenna gain in lower hemisphere 10 dBic Maximum pre-correlation filter 3 dB bandwidth(1)16.5 MHz Receiver noise figure 4.4 dB RF pulse overload recovery time25 10 6s Receiver aggregate wideband interference threshold
38、in track mode(2), (3)140.5 dB(W/MHz) Receiver aggregate wideband interference threshold in acquisition mode(2), (3)146.5 dB(W/MHz)Receiver aggregate narrow-band interference threshold in track mode(2), (3)150.5 dBW Receiver aggregate narrow-band interference threshold in acquisition mode(2), (3)156.
39、5 dBW(1)A more stringent pre-correlator filter may be needed to protect receiver operations from adjacent band RF emissions. (2)The interference threshold already takes into account the effects of GPS intra-system interference-based on random code analysis. See 2. The threshold must account for all
40、other aggregate interference. The applicability of a safety margin is discussed in Annex 5. (3)Wideband interference has a bandwidth in the range 100 kHz to 1 MHz; narrow-band interference has a bandwidth less than or equal to 700 Hz. For other bandwidths, refer to Fig. 1. Rec. ITU-R M.1477 5 TABLE
41、2 GBAS air navigation receiver, Category II/III precision approach operations 2.1 Same service interference In an analysis to determine the effect of external interference to GPS, the effects of thermal noise as well as the interference caused by the GPS signals must first be accurately analysed. In
42、 this way, a baseline is established for GPS, which produces same-service or intra-system interference, to which the signals from other systems seeking allocation can be added. It is recognized that different criteria apply to same-service interference than to external interference from other servic
43、es. GPS as well as planned augmentations, due to the constant monitoring and control, will avoid harmful levels of self-interference. Such assurances cannot be made for other services. 2.2 Random noise versus short code In analysing same-service interference, this Annex presents results that recogni
44、ze the distinct co-channel self-interference that GPS signals experience. GPS is a single-frequency CDMA system that uses a family of short pseudo-random-noise codes known as Gold codes. The result is a system with a limited CDMA capacity, due in part to the short (1 ms) length of the Gold code. Whi
45、le earlier studies assumed Gaussian noise models for co-channel self-interference from GPS, the mutual interference of the codes is much greater than that from random noise. Therefore, when analysing the performance of GPS in the presence of external sources of interference, an accurate model of co-
46、channel self-interference from the GPS must be used as well. In order to analyse the co-channel self-interference, the non-linear behaviour of the GPS receiver needs to be taken into account. L1 carrier, wideband pseudolite frequency 1 575.42 MHz Narrow-band pseudolite carrier frequency L1 10.23 MHz
47、 C/A code, narrow-band pseudolite chip rate 1.023 Mbit/s Wideband pseudolite code chip rate 10.23 Mbit/s Navigation data rate, GPS 50 bit/s Minimum received C/A code power level at antenna input 161 dBW Minimum average wideband pseudolite power level at antenna input 140 dBW Minimum average narrow-b
48、and pseudolite power level at antenna input 140 dBW Minimum antenna gain towards pseudolite 21 dBic Minimum antenna gain towards GPS satellite at 5 elevation 4.5 dBic Maximum antenna gain in upper hemisphere +7 dBic Maximum pre-correlation filter, 3 dB bandwidth(1)16.5 MHz Receiver noise figure 4.4
49、dB RF pulse overload recovery time 25 106s Receiver aggregate wideband interference threshold in track mode(2), (3)140.5 dB(W/MHz) Receiver aggregate wideband interference threshold in acquisition mode(2), (3)146.5 dB(W/MHz)Receiver aggregate narrow-band interference threshold in track mode(2), (3)150.5 dBW Receiver aggregate narrow-band interference threshold in acquisition mode(2), (3)156.5 dBW(1)A more stringent pre-correlator filter may be needed to protect receiver operations from adjacent band RF emissions. (2)The interference threshold alr
