1、STD*ITU-R RECMN M.B2L-L-ENGL 1997 4855212 0527405 375 Rec. ITU-R M.821-1 371 RECOMMENDATION ITU-R M.821-1* OPTIONAL EXPANSION OF THE DIGITAL SELECTIVE-CALLING SYSTEM FOR USE IN THE MARITIME MOBILE SERVICE (Question ITU-R 9/8) (1992-1997) Summary The Recommendation provides in Annex 1 optional expans
2、ion sequences to calls in the digital selective-calling (DSC) system described in Recommendations IT-R M.493 and ZTU-R M.541. These expansion sequences enable DSC equipment to transmit optional messages of more precise geographic coordinates, the navigation equipment used to derive the position, the
3、 datum used for its calculation and the resolution of the fix, ships speed, course or alternative ship identification. The ITU Radiocommunication Assembly, considering a) that the digital selective-calling (DSC) system described in Recommendation ITU-R M.493 currently provides an efficient method of
4、 geographic calling and transmitting a ships position in geographic coordinates in degrees and minutes, and that Recommendation IT-R M.825 also uses DSC sequences; b) that the addition of a brief optional message to a DSC sequence providing more precise information for geographic calling and concern
5、ing a ships position, the type of navigation equipment used to derive the position, the resolution of the fix and the datum used, speed, course or identification would serve useful safety and operational purposes; c) that new navigation systems can routinely provide position resolution to an accurac
6、y significantly better than 1 min of the geographic coordinates of a ships location as well as accurate data concerning the ships current speed and course; d) that providing additional ships identification (ships name or registratiordocumentation information, for example) could speed the process of
7、retrieving pertinent vessel parameters and eliminate unnecessary audio traffk in some basic calling situations; e) that an automated maritime VHF vessel position reporting system of sufficient precision would increase the efficient surveillance and management of ship movement and operations; f) that
8、 the optional capability in 0 b) may be implemented only in those DSC equipments where it is desired; g) that the optional capability in 8 b) can be implemented in a manner that will not derogate the normal functioning of other DSC operations where this capability is not employed, recommends 1 that
9、where there is a need for DSC equipment capable of transmitting optional messages of more precise geographic coordinates, the navigation equipment used to derive the position, the datum used for its calculation and the resolution of the fix, ships speed, course or alternative ship identification, it
10、 should be designed in accordance with characteristics given in Annex 1; 2 that when VHF channel 70 and other DSC distress, safety and calling frequencies are used for this purpose care should be taken not to load these channels above 0.1 E on MF or HF or 0.15 E on VHF. * This Recommendation should
11、be brought to the attention of the International Maritime Organization (IMO). COPYRIGHT International Telecommunications Union/ITU RadiocommunicationsLicensed by Information Handling ServicesSTD-ITU-R RECMN M*BZL-L-ENGL 1797 m 4855212 0527LiOb 201 m 312 Rec. ITU-R M.821-1 ANNEX 1 Technical character
12、istics of an expansion of the digital selective-calling system for use in the maritime mobile service 1 General 1.1 All expansion sequences must utilize all the technical characteristics outlined in Recommenda- tion ITU-R M.493 except as otherwise noted in this Annex. 1.2 The expansion sequence dire
13、ctly follows the end of the call sequence and error-check character of the transmission sequences defined in Recommendations ITU-R M.493 and ITU-R M.541. The expansion sequence consists of one or more message fields as defined in the technical characteristics section of this Annex followed by a seco
14、nd end of call sequence with error-check character. The sequence is implicitly addressed to the same station with the same category as the transmission sequence to which it is appended. 1.3 implementation of the expansion sequences is optional. The content of the message fields varies with the conte
15、nt of the standard transmission sequence. Some expansion data may be automatically included with DSC calls of certain types, however, the expansion sequence should normally only be transmitted upon request from another station so as to minimize the effect that the additional data has on DSC channel
16、loading. 1.4 When processing a received sequence, a character should be searched for following the error-check character of the standard transmission. If a symbol pertaining to a data specifier character is detected, additional characters should be received until the second error-check character is
17、received. 2 Technical format of added data 2.1 Expansion message fields The expansion message fields allow more explicit data pertaining to the transmitting station to be passed to receiving stations than is defined in Recommendation ITU-R M.493. The data passed allows for increased resolution in po
18、sitioning; information on navigation equipment, fix resolution and datum used; reporting of station current speed and course; and a means of tendering a secondary method of station identification. Each message field is preceded by an expansion data specifier character followed by one or more data ch
19、aracters representing the value of the message field. 2.1.1 The expansion data specifiers for the message fields are found in Table 1. Each specifier must have a value in the range 10-127. This distinguishes the specifiers from messages which cannot fall within this range with the exception of the c
20、ommand characters of Table 3. TABLE 1 Symbols used for expansion data specifiers SymbolNo. I Expansion data specifier 100 101 102 i03 104 1 05 106 Enhanced position resolution Source and datum of position Current speed of the vessel Current course of the vessel Additional station identification Enha
21、nced geographic area Number of persons on board 2.1.2 The data content and length for each message field varies with the type of message. COPYRIGHT International Telecommunications Union/ITU RadiocommunicationsLicensed by Information Handling ServicesSTD-ITU-R RECMN M-dZL-L-ENGL 1777 q8552L2 0529i07
22、 LiB Rec. ITU-R M.821-1 373 2.1.2.1 The data for the enhanced position resolution message field consist of either a command character taken from Table 3 or four characters (eight digits). These digits represent the tenths, hundredths, thousandths and ten thousandths of minutes for both latitude and
23、longitude. The first two characters are the extra resolution for latitude and the second two for longitude. Unused digits are filled with zeros. 2.1.2.2 The data for the navigation equipment, fix resolution and datum used message field consist of either a single command character taken from Table 3
24、or three characters (six digits). The first and second digits indicate the type of navigation receiver the position data was derived from and the status of that fix. This character is obtained from Table 4. The third and fourth digits indicate the current fix resolution (GDOP for LORAN-C. HDOP for G
25、PS fixes). The third digit indicates units and the fourth digit indicates tenths. Any GDOP or HDOP equal to or exceeding 9.9 should be indicated by 99. The fifth and sixth digits indicate the datum used in calculating the position fix. This character is obtained from Table 5. 2.1.2.3 The data for th
26、e vessel speed message field consist of either a single command character taken from Table 3 or two characters (four digits). These digits represent the hundreds, tens, units and tenths of units of the speed of the ship in knots. Unused positions are filled with zeros. 2.1.2.4 The data for the vesse
27、l course message field consist of either a single command character taken from Table 3 or two data characters (four digits). These digits represent true course in hundreds, tens, units and tenths of degrees. Unused positions are filled with zeros. 2.1.2.5 The data for the additional station identifi
28、cation message field consist of either a single command character taken from Table 3 or up to ten characters taken from Table 2 representing the name or other identification of the transmitting station. 2.1.2.6 The data for the enhanced geographic area message field consists of twelve data character
29、s (twenty-four digits). The first sixteen digits represent tens, units, tenths and hundredths of minutes for the latitude, longitude, vertical and horizontal extension of the rectangle. Unused digits are filled with zeros. The first two characters (four digits) are the extra resolution for latitude
30、and the second two characters (four digits) are the extra resolution for longitude. The fifth and sixth characters (four digits) are the extra resolution in the vertical extension of the rectangle and the seventh and eighth characters (four digits) are the extra resolution in the horizontal extensio
31、n of the rectangle. The last eight digits represent hundreds, tens, units and tenths of units for the speed and course of the vessel. Unused digits are filled with zeros. The ninth and tenth characters (four digits) are the estimated speed of the vessel, or two symbols No. 126 if no speed estimation
32、 is available. The eleventh and twelfth characters (four digits) are the estimated course of the vessel, or two symbols No. 126 if no course estimation is available. 2.1.2.7 The data for the number of persons on board message field consists of either a command character taken from Table 3 or two dat
33、a characters (four digits). These digits represent thousands, hundreds, tens and units of persons on board. Unused positions are filled with zeros. 2.2 Start and end of transmission of expansion sequence 2.2.1 The symbols used in the first two RX positions should be 126. 2.2.2 tion ITU-R M.493. The
34、sequence consists of end of sequence characters and error-check characters. The end of transmission sequence is formulated in a manner identical to that defined in Recommenda- 2.2.2.1 character used is the same as that used to terminate the standard portion of the entire DSC formatted call. The end
35、of sequence character is transmitted three times in the DX position and once in the RX position. The 2.2.2.2 The error-check character is generated by taking the modulo-2 sums of all the characters in the message fields including the data specifiers and one end of sequence character. This character
36、is transmitted once in the RX and once in the DX position. 2.2.3 Figure 1 illustrates the technical format and transmission sequence of the expansion. COPYRIGHT International Telecommunications Union/ITU RadiocommunicationsLicensed by Information Handling Services374 Symbol No. 110 126 STD-ITU-R REC
37、MN M*BZL-L-ENGL 1797 4855232 0527408 OB4 Rec. ITU-R M.821-1 - _ Command characters Data request No data available Symbol No. 00 o1 02 03 o4 05 06 07 08 o9 10 11 12 13 14 15 TABLE 2 Symbols used to denote alphanumeric characters Character _ O 1 2 3 4 5 6 7 8 9 Not used A B C D E Symbol No. 16 17 18 1
38、9 20 21 22 23 24 25 26 27 28 29 30 31 Character F G H I J K L M N O P Q R S T U Symbol No. 32 33 34 35 36 37 38 39 40 41 TABLE 3 Symbols used for command characters TABLE 4 Symbols used in describing the type of positioning device used for VTS positioning Symbol No. o0 o1 02 03 o4 o5 06 07 08 Charac
39、ter V W X Y Z II “ “ I “ I “ Space Position information source Current position data invalid Position data from differential GPS Position data from uncorrected GPS Position data from differential LORAN-C Position data from uncorrected LORAN-C Position data from GLONASS Position data from radar fix P
40、osition data from Decca Position data from other source COPYRIGHT International Telecommunications Union/ITU RadiocommunicationsLicensed by Information Handling ServicesSTDmITU-R RECMN M-823-3-ENGL 3777 M 4855232 0529409 T30 o0 I O1 Rec. ITU-R M.821-1 WGS-84 WGS-72 TABLE 5 02 Symbols used in describ
41、ing the datum for calculating position with the VTS area Other I Svml NT -Datum indicated for coordinate calculations Standard DSC cai1 Rec. ITU-R M.493 Message 1 Expansion data specifier EDS 1 data specifier EDS 2 FIGURE 1 Technical format and transmission sequence of expansion 375 b) Transmission
42、sequence A,: first expansion data specifier A,: second expansion data specifier B,-B,: characters of message 1 CI-C,: characters of message 2 D: EOS end of sequence E: ECC error-check character X: symbol No. 126 no information a) Technical format 3 Operational characteristics of expanded transmissio
43、n 3.1 Enhanced position resolution The expansion message field with enhanced position resolution may be appended to any standard DSC transmission sequences which include position information, provided the data is available. Transmission with other types of sequences is meaningless. COPYRIGHT Interna
44、tional Telecommunications Union/ITU RadiocommunicationsLicensed by Information Handling ServicesSTD-ITU-R RECMN M*BZL-L-ENGL 1997 q855212 0529YLO 732 376 Rec. ITU-R M.821-1 As an example of an enhanced position resolution message field, if the position 27O, 54.0572 N and 82”, 42.5933 W was to be tra
45、nsmitted, the extra position message field (consisting of the tenths, hundredths, thousandths and ten thousandths of minutes) would consist of five characters total, as follows: 10005725933. To request this information from a vessel, the expansion data specifier 100 would be followed by the command
46、character 110. 3.2 generally be transmitted together and upon request from another station. The type of navigation equipment, the fix resolution and the datum used for calculating the position should As an example, for a vessel using differential GPS to report the position without specified HDOP usi
47、ng WGS-84 datum, the message field would consist of four characters total, as follows: 101 O1 0000. To request this information from a vessel, the expansion data specifier 101 would be followed by the command character 110. 3.3 Ship speed and course Ship speed and course data should generally be tra
48、nsmitted together. This expansion sequence can be appended to any standard DSC call, however, normally the speed and position data should only be transmitted upon request from another station. A ships speed or course may be requested by another station utilizing the data request command from Table 3
49、. As an example of a transmitted speed and course field, if a vessels speed is 12.4 knots and the true course is 298” the speed data field would consist of three characters 102 O1 24 and the course data field would consist of three characters 1030298. To request the speed of another vessel, the speed expansion data specifier character 102 would be followed by the command character 110. To request the course of another vessel, the course data specifier character 103 would be followed by the command character 110. 3.4 Additional station identification The ad
