1、 Rec. ITU-R M.589-3 1 RECOMMENDATION ITU-R M.589-3*Technical characteristics of methods of data transmission and interference protection for radionavigation services in the frequency bands between 70 and 130 kHz (1982-1986-1992-2001) The ITU Radiocommunication Assembly, considering a) that radionavi
2、gation systems exist or are being implemented in the three Regions of the ITU; b) that various services, including radionavigation systems, operate in frequency bands between 70 and 130 kHz; c) that the operating characteristics of these radionavigation systems are well established and sufficiently
3、documented by the appropriate service providers; d) that radionavigation being a safety service, all practical means consistent with the Radio Regulations (RR) should be taken to prevent harmful interference to any radionavigation system; e) that users of phased pulsed radionavigation systems in the
4、 band 90-110 kHz receive no protection outside that band, yet may receive benefit from their signals outside the occupied bandwidth; f) that in the band 90-110 kHz, different phased pulsed radionavigation systems may operate in adjacent areas, on the same assigned frequency and within the same occup
5、ied bandwidth; g) that Loran-C and Chayka systems are characterized by ground waves that follow the Earths contours with ranges that exceed comparably powered medium frequency systems, and by sky waves that may be received at considerably greater distances; h) that Loran-C or Chayka systems provide
6、an independent radionavigation system to complement the global navigation satellite system (GNSS); j) that GNSS components exist or are being implemented and the accuracy may not be enough for some specialized navigation, or for the position sensor in electronic chart systems; k) that safety applica
7、tions require integrity information for position fixes derived from GNSS; l) that the accuracy and integrity of GNSS can be improved considerably by the transmission of differential corrections or other data; *This Recommendation should be brought to the attention of the International Maritime Organ
8、ization (IMO), the International Civil Aviation Organization (ICAO), the International Association of Marine Aids to Navigation and Lighthouse Authorities (IALA) and Radiocommunication Study Group 7. 2 Rec. ITU-R M.589-3 m) that appropriate modulation of Loran-C and Chayka transmissions enables thes
9、e systems to transmit differential GNSS corrections, integrity messages and other data without interfering with the Loran-C or Chayka navigation function; n) that the transmission of differential GNSS corrections, integrity messages and other data may benefit from the long-range transmission charact
10、eristics of Loran-C or Chayka; o) that appropriate modulation of Loran-C and Chayka transmissions increases the efficiency of the use of the available bandwidth; p) that a number of administrations currently provide Loran-C or Chayka coverage of coastal waters and land areas enabling a worldwide sta
11、ndard for the transmission of differential GNSS corrections, integrity messages and other data to be introduced efficiently and economically; q) that other methods of data transmission using Loran-C or Chayka signals may be introduced, recommends 1 that information be exchanged between the authoriti
12、es operating radionavigation systems in the band 90-110 kHz with those operating other systems in the band 70-130 kHz employing stable transmissions; 2 that administrations operating radionavigation systems in the band 90-110 kHz in adjacent areas coordinate the technical characteristics of their in
13、dividual systems in accordance with the RR; 3 that within the allocated band 90-110 kHz, the protection criteria for pulsed radionavigation systems (e.g. Loran-C and Chayka) should be in terms of unwanted to wanted emissions and in accordance with Annex 1; 4 that determination of Loran-C signal leve
14、ls should be in accordance with the guidelines given in Annex 1; 5 that any method of data transmission using Loran-C and Chayka signals should preserve the utility of the existing radionavigation services; 6 that a data service using tri-state pulse position modulation of Loran-C or Chayka signals
15、should be designed in accordance with the technical characteristics given in Annex 2. ANNEX 1 Loran-C/Chayka protection criteria and signal level determination guidelines 1 Protection criteria 1.1 The protection criteria for Loran-C/CW interference as a function of frequency offset are given in Fig.
16、 1. 1.2 Near-synchronous interference at frequency, f, should satisfy the following relationship: GefGefGefGefGefGeff n2 GRI1 and 4 10 (2) 4 and 8 11 (3) Reference station not useable Rec. ITU-R M.589-3 13 4.4.4 Satellite identification Standard format (1-32, 32 is indicated with all zeros). 4.4.5 P
17、seudorange correction (PRC) The PRC describes the estimated correction at the time of measurement in the reference receiver. The relationship between PRC, RRC and reference time is defined by the following equation: )()()(referencemeasuredcorrectedttRRCPRCtPRtPR += The PRC is given as a 2s complemen
18、t value. The resolution depends on the scale factor. 4.4.6 Range-rate correction (RRC) The RRC describes the estimate of the rate of change of the PRC at the time of measurement in the reference receiver. The use of the RRC is described by the previous equation. The resolution depends on the scale f
19、actor. 4.4.7 Issue of data (IOD) The IOD as broadcast by the reference station is the value in the GPS navigational messages which corresponds to the GPS ephemeris data used to compute corrections. This is a key to ensure that the user equipment calculations and reference station corrections are bas
20、ed on the same set of broadcast orbital and clock parameters. 4.4.8 Tbof navigation data (TOD) The time within the current 24-h period by UTC(SU), which includes the operational information transmitted in the frame. 4.4.9 Sequence number The message number should be equal for all portions of one tex
21、t message. The message number should increase with unit step for subsequent text messages, restarting at “000” after “111”. 4.4.10 End of message (End) The end of message indicates the last portion of a text message. A value of “0” should indicate that more portions are required to complete the text
22、 message. A value of “1” should indicate completion of the text message. 4.4.11 Text characters Up to six (6) characters of eight (8) bits each are accommodated in each portion of a text message. Codes from 0-127 should correspond to standard ASCII codes. Cyrillic characters should be represented by
23、 codes greater than 127. 14 Rec. ITU-R M.589-3 4.5 Cyclic redundancy check (CRC) The CRC should be generated using the following polynomial: G(x) = x14+ x13+ x7+ x5+ x4+ 1 The following steps should be used in the calculation of the CRC: Step 1: translation of the data, including the message type fi
24、eld to a polynomial following the convention defined in Table 11. The resulting polynomial will not contain higher orders of x than x55; Step 2: multiplication of the polynomial obtained in Step 1 with x14; Step 3: division of the polynomial obtained in Step 2 by the generator polynomial; Step 4: translation of the remainder of the division in Step 3 to a binary representation is the CRC. TABLE 11 Relation between binary and polynomial representation Position Bit number Multiply with Least significant symbol I1x0I2x1 Most significant symbol Inxn1
