GB/T 44086.2-2024Information interface for BDS-3 regional short message communication user terminal - Part 2: General data interface (English PDF)

3 Terms, definitions and abbreviations

The terms defined in GB/T 2312-1980 and GB/T 39267 apply together with seven terms given here. An address (3.1.1) is the unique number that identifies an interacting party in the BDS-3 short message service, a note dividing addresses into intranet and extranet addresses. An intranet address (3.1.2) is the unique number that identifies a party inside the BDS-3 system, also called the user ID and covering the point cast, broadcast and multicast IDs. An extranet address (3.1.3) is the unique number that identifies an external user interacting with the BDS-3 system by point cast communication, a note listing mobile phone numbers, WeChat user numbers and Weibo numbers.

The GB code (3.1.4) is the first Chinese character encoding standard issued by China in 1980, a note giving its full name, its short name GB 2312, its 6 763 common characters and symbols, and its representation of each character by two bytes whose most significant bits are both zero. The zone-location code (3.1.5) is a four digit decimal number used to address a Chinese character library, the high two digits being the zone code and the low two the location code, each running from 01 to 94 and together forming a 94 by 94 matrix. The compressed zone-location code (3.1.6) is the representation of the zone-location code by 14 bits in the space interface format of the BeiDou short message inbound and outbound service, the first 7 bits being the zone number and the last 7 the location number. The machine code (3.1.7) is the code of zeros and ones used inside a computer to store, process and transmit Chinese characters. The abbreviations of 3.2 are BDCS for the BeiDou coordinate system, RNSS for the radio navigation satellite service and UTC.

Clause 4 fixes the transmission protocol. The physical interface of the user terminal is the RS-232C standard interface, its electrical signal characteristics meeting Clause 2 of GB/T 6107-2000 and its serial data transmission standard meeting Clause 4 of GB/T 11014-1989; the user may choose the form of the physical connector, DB9, DB25 or another standard communication connector, according to the needs of the application. Data is sent serially and asynchronously, the first bit being the start bit, followed by the data bits and finally the stop bit, and the least significant bit is sent first. The parameters are a baud rate of 4 800 bit/s, 9 600 bit/s, 19 200 bit/s or 115 200 bit/s, settable as needed with 115 200 bit/s as the default; one start bit; eight data bits; one stop bit; and no parity.

5 Information format

5.1.1 The reserved character set is made up of the ASCII characters of Table 1, which has four columns and seven rows and gives the symbol, its hexadecimal value, its decimal value and its function: carriage return, hexadecimal 0D and decimal 13, the end of the sentence delimiter; line feed, 0A and 10; the dollar sign, 24 and 36, the start of the parameter sentence delimiter; the asterisk, 2A and 42, the checksum field delimiter; the comma, 2C and 44, the field delimiter; the backslash, 5C and 92, reserved; the tilde, 7E and 126, reserved; and the delete character, 7F and 127, reserved.

5.1.2 The valid character set comprises the ASCII characters from 0x20 to 0x7F; the upper bound of that range is the delete character, which Table 1 lists among the reserved characters, and both statements are translated here as printed. 5.1.3 ASCII characters defined neither as reserved nor as valid shall not be used at any time in any field other than the user data field. 5.1.4 Where individual characters are used to define units of measurement, to state the type of a data field or to state the type of a sentence, they shall be interpreted according to the notes in the sentence concerned.

5.2.1 A field is a string of valid characters between two appropriate delimiting characters. 5.2.2 Data fields are of character type and of numeric type. A data field in a sentence follows the delimiter comma, and its position in the sentence is determined by watching the field delimiter; at the receiving end the position is determined by counting the delimiters. A data field in a proprietary sentence contains only valid characters and the delimiter comma. Data fields may be of fixed length, of variable length, or fixed plus variable; a variable length field may be of character or of numeric type and contains one decimal point, and several zeros may stand at its beginning and at its end. In a fixed length data field, where the valid data is not long enough, enough ASCII zero characters are added in front.

5.2.3 A checksum field shall be transmitted in every sentence. It is the last field of the sentence and follows the checksum delimiter asterisk. The checksum is the result of an exclusive OR over the eight bits of every character of the sentence, excluding the start and stop bits, all the characters meaning those between the delimiters dollar sign and asterisk but not those delimiters themselves, and including the commas. On transmission the high four bits and the low four bits of the hexadecimal value are converted into two ASCII characters from 0 to 9 and A to F, the most significant being sent first. An example is given of a sentence that sends a short message to a mobile number using the Lf2 frequency, once only, with inbound acknowledgement required, with the Chinese character encoding class and a communication length of 140 bits, the hexadecimal value 1A being the checksum computed over the characters between the two delimiters.

5.3.1 A sentence starts with the sentence start delimiter dollar sign and ends with carriage return and line feed. The first field is the address field, which holds the identifier of the sending end and the sentence format character; that format character fixes the number of data fields in the sentence, the type of data they hold and the order in which the data segments are sent. The rest of the sentence may be zero or more data segments. 5.3.2 A sentence that meets the format requirements is a valid sentence; a sentence of any other form is invalid and shall not be transmitted. Every interface sentence is made up of the dollar sign, a type identifier, a series of data fields separated by commas, the asterisk, the checksum, and carriage return and line feed.

Table 2 explains the standard sentence format in two columns and seven rows. The dollar sign, ASCII 0x24, is the start marker of the sentence. The type identifier distinguishes the kind and the function of the sentence and is a fixed width of five English characters, capitals being recommended, the first two forming a common header and the last three the type. The comma, ASCII 0x2C, separates the several fields of the sentence. Each sentence may hold several data fields separated by commas, and unless otherwise stated a data field may use only printable ASCII characters other than the reserved characters of Table 1; the position of a data field in a sentence is determined only through the comma delimiters, by counting them, and never by counting the total number of characters received from the start of the sentence. The asterisk is the checksum delimiter separating the data content from the checksum field. The checksum is the byte-wise exclusive OR of all the characters between the dollar sign and the asterisk, not counting those two symbols, its high four bits and low four bits being expressed as hexadecimal digits in ASCII from 0 to 9 and A to F with the high part first. Carriage return and line feed, ASCII 0x0D and 0x0A, mark the end of the sentence.

The common header of the type identifier shows the path characteristic of the sentence: CC means that the user is using a sentence of this data interface to make the terminal carry out an operation or a setting, and BD means that the BeiDou equipment is putting out over the serial port the information it has received from the satellites, or its own status or attribute information. Data fields are of three basic types, fixed length, variable length and fixed plus variable length, and in a fixed length numeric field enough ASCII zero characters are added in front where the valid data is not long enough. Table 3 gives the data field types commonly used in the interface sentence definitions, and types not covered there are described where the sentence is described.

Table 3 has three columns and eleven rows, giving the data type, its symbol and its definition. The variable length number has both its integer and its fractional part of variable length, the decimal point and the fractional part being optional, and the field may express an integer. The fixed length number has a length equal to the number of symbol characters; where the value is negative the first character of the field is the sign, ASCII 0x2D, and the field grows by one character, while a positive value carries no sign and keeps its length. The variable length character field and the fixed length character field follow, the latter distinguishing capitals from lower case. The fixed length hexadecimal field and the variable length hexadecimal field are both written big endian. Latitude is a fixed plus variable field of degrees, minutes and a decimal fraction, the part left of the point being fixed at four digits of which the first two are degrees and the last two minutes, the digits after the point being minutes and of variable length, with leading zeros where the degrees or minutes are short and the point and fraction omitted where the value is whole; a navigation type terminal keeps four decimal places and a survey type terminal eight. Longitude follows the same scheme with five digits left of the point, three of degrees and two of minutes. Time appears in two forms, a fixed year, month and day field with leading zeros, and a fixed plus variable field of hours, minutes and seconds with six digits left of the point and a variable fraction of seconds. The status field is one character, A for affirmative, present or correct and V for negative, absent or wrong. The unit field is one capital letter, the common correspondences being M for metre, M for metre per second, K for kilometre and K for kilometre per hour, the same letters serving two units each as printed.

5.3.3 The interval between service input sentences shall meet the frequency limit set when the user registered; the time to send one complete sentence shall be not more than 1 s, and the serial communication rate should be set with the message length in mind. 5.4 The terminal shall be able to detect errors in the data transfer, namely checksum errors, invalid characters, an incorrect sending end identifier length, sentence format character or data field, and sentence transmission timeout; the terminal uses only correct sentences conforming to this document and discards erroneous ones.

6.1 List of sentences

The document defines sixteen sentences for emergency search and rescue, position reporting and message communication. By direction of the data flow the terminal data interface is divided into input and output sentences, listed in Table 4, which has four columns and sixteen numbered rows giving the number, the category, the sentence identifier, the sentence content and the clause index. The nine output sentences are EPI for emergency search and rescue and position report information, TCI for message communication information, SHZ for position query result information, SAK for communication receipt query result information, ACK for inbound acknowledgement information, TCK for communication success acknowledgement information, PWI for the outbound beam tracking status, ICZ for the subordinate user information output by a management set, and FKI for inbound feedback information. The seven input sentences are EPQ for an emergency search and rescue or position report request, TCQ for a message communication request, PSQ for a position query request, RTQ for a communication receipt query request, OFQ for a power on and off report request, KSQ for a silence request and PWS for setting the outbound beam tracking status of the user terminal.

Although Table 4 lists sixteen sentences, 6.2.3, which carries the position query result sentence SHZ, has no content of its own and states that it is merged into 6.3.1, the subclause for the emergency search and rescue and position report request EPQ; so an output result sentence is referred to the subclause of an input request sentence, and only fifteen sentences are actually described. Both statements are translated here as printed.

6.2 Output sentences

6.2.1 The EPI sentence is an output sentence by which the user terminal has received RNSS position report information; its format is shown in Figure 1 and explained in Table 5. Table 5 has five columns and thirteen numbered rows giving the serial number, the name, the value range, the unit and a description. The fields are the sending party ID and the receiving party ID, both intranet addresses running from 1 to 16 777 215; the service type or emergency identifier, 1 for emergency search and rescue and 2 for position report; the time, from 000000.00 to 235959.99, in UTC hours, minutes and seconds with two decimals, the part left of the point fixed at six digits with leading zeros; the longitude, from 00000.00 to 17959.99, as a fixed plus variable degrees and minutes field with three fixed digits of degrees, two of minutes and a variable decimal fraction of minutes; the longitude marker, E or W; the latitude, from 0000.00 to 8959.99, in the same form with two fixed digits of degrees; the latitude marker, N or S; and the altitude, in metres, as the geodetic height in the BDCS coordinate system.

Table 5 continues with the search and rescue type, 1 to 3, meaning a distress request, cancellation of a distress request and forward identity authentication; the search and rescue centre instruction type, 1 to 4, meaning a distress receipt, an inbound transmission control command, reverse identity authentication and a distress wake-up; the status data length, 0 to 468 bits, being the number of bits of the status data, that is of the search and rescue service data or of the position report status data; and the status data itself, whose range is printed as 0 to 636 bits, which is larger than the maximum the preceding length field can express, and is translated here as printed. Three footnotes state that the intranet address is 24 bits long with an address space of 1 to 16 777 215, that the search and rescue fields are present when the service type is emergency search and rescue, and that the position report fields are present when the service type is position report.

6.2.2 The TCI sentence is an output sentence by which the user terminal has received message communication information; its format is shown in Figure 2 and explained in Table 6, which has five columns and seven numbered rows. The sending party ID runs from 1 to 281 474 976 710 655 and may be an intranet or an extranet address, a footnote giving the extranet address a length of 48 bits and an address space from 16 777 216 upwards; the receiving party ID is an intranet address from 1 to 16 777 215; the time is UTC hours, minutes and seconds with two decimals and six fixed digits before the point; the encoding class is 0 for Chinese characters, 1 for code and 2 for Chinese characters mixed with ASCII; the data identifier is 0 for immediate and 1 for mailbox; the communication length runs from 4 bits to 14 000 bits and is the total number of bits of the communication data that follows, and may not be empty; and the communication data itself is described as the computer machine code with 14 bits per Chinese character, high bits first, when the encoding class is 0, as BCD code characters when it is 1, and as a mixture when it is 2, in which case the first letters of the communication data are fixed as A4 and the data is taken 4 bits at a time in order, converted into hexadecimal digits each expressed in ASCII, with high order zeros added to make the length a whole multiple of 4 bits. Calling the 14 bit per character encoding the computer machine code sits awkwardly with 3.1.6 and 3.1.7, where the 14 bit form is the compressed zone-location code and the machine code is the internal computer code; the wording is translated here as printed.

6.2.3 The position query result information sentence SHZ is merged into 6.3.1. 6.2.4 The SAK sentence outputs the receipt information a system user obtains after a receipt query; its format is shown in Figure 3 and explained in Table 7, which has three columns and eight numbered rows. The fields are the sending party ID, the intranet address of the user who started the query; the receiving party ID, the intranet address of the original communication receiver; the number of receipts, 0 to 7, zero meaning no receipt; and then pairs of communication sending date and communication sending time, each in UTC with six fixed digits, for the first through the seventh receipt, the middle rows being shown as ellipses. A footnote says that the number of sending times is set by the number of receipts, that receipts can be queried for at most the last two weeks, and that when the number of receipts is zero the following fields are empty.

6.2.5 The ACK sentence outputs the batch inbound acknowledgement that the central station makes within an agreed time for the inbound signals of some users, the acknowledgement being sent in clear over the outbound address 0xFFFFFF; the inbound types are the power on report, the silence request, emergency search and rescue, and message communication carrying the inbound acknowledgement request marker, that is immediate communication that did not succeed. The format is shown in Figure 4 and explained in Table 8, which has three columns and three rows: the inbound user ID, an intranet user from 1 to 16 777 215; the network management information class, 1 to 4, meaning power on report, silence request, emergency search and rescue and unsuccessful communication acknowledgement; and the inbound sequence number, 0 to 31, being the last five bits of the user inbound sequence number in binary.

6.2.6 The TCK sentence acknowledges a successful communication: after the terminal has sent a message communication request carrying the inbound acknowledgement privilege, it receives the communication success acknowledgement for its own ID from 0xFFFFFF. The format is shown in Figure 5 and explained in Table 9, whose two rows are the sending party ID, an intranet user from 1 to 16 777 215, and the inbound sequence number, 0 to 31, again the last five bits in binary. 6.2.7 The PWI sentence reports the current outbound beam tracking status to the user after the terminal has received the status the user set; the format is shown in Figure 6 and explained in Table 10, which has five columns and nine numbered rows: the time in UTC hours, minutes and seconds with two decimals; the number of outbound beams locked, 0 to 63; then, for the first and for the mth beam, the outbound beam number from 1 to 63 and the carrier to noise density ratios in decibel hertz of the two signal branches, each output or not according to the CCPWS input sentence. A footnote says that the number locked sets the number of branch carrier to noise ratios that follow and that when the number locked is zero the following fields are empty.

6.2.8 The ICZ sentence sets the number and the IDs of the users belonging to a management set; the format is shown in Figure 7 and explained in Table 11, which has three columns and six rows: the number of subordinate members; then, for each member, the member ID from 1 to 16 777 215 as an intranet user and a marker Y or N stating whether the member is a BDS-3 user or a BDS-2 user, the middle rows being shown as ellipses. 6.2.9 The FKI sentence feeds back the response status of a setting, query or request sentence; the format is shown in Figure 8 and explained in Table 12, which has five columns and five numbered rows. The fields are the instruction execution time in UTC hours, minutes and seconds, six fixed digits with leading zeros; the instruction name, listed as EPQ for emergency search and rescue and position report, TCQ for message communication and OFQ for the power on and off report, although the subclause says the sentence answers setting, query and request sentences generally; the transmission situation, Y for successful execution and N for failure; the failure cause, whose range is given as 0 to 9 with the meanings inbound request frequency exceeded, inbound frequency dynamic adjustment exceeded, conflict between the inbound request and the radio silence state, outbound signal not locked and no position information, the remaining values being reserved; and the remaining time in seconds, given as a waiting prompt when the terminal sends an inbound request less than the service interval after the previous one. Footnotes say that when the transmission situation is Y the failure cause is set to zero or left empty and the remaining time is zero or empty, and that for the emergency search and rescue and position report instruction transmission is allowed even when the outbound signal is not locked.

6.3 Input sentences

6.3.1 The EPQ sentence is the input sentence by which the user sends an emergency search and rescue or position report request; its format is shown in Figure 9 and explained in Table 13, which has five columns and thirteen numbered rows. The fields are the receiving party ID, an intranet user from 1 to 16 777 215; the service type or emergency identifier, 1 for emergency search and rescue and 2 for an RNSS position report; the inbound frequency point, 0 for automatic, 1 for Lf1 and 2 for Lf2; the inbound rate, in four rate steps; the frequency, 0 to 3 600 s, zero meaning a single request that then stops the continuous sending and a non-zero value meaning the sending interval; the longitude, from 00000.0000 to 17959.9999, five fixed digits before the point with leading zeros, the printed example expressing 118 degrees 6.15 minutes as 11806.15; the longitude marker, E, W or 0, the last meaning that the RNSS positioning result is used; the latitude, from 0000.0000 to 8959.9999, four fixed digits before the point, the printed example expressing 40 degrees 3.12 minutes as 4003.12; the latitude marker, N, S or 0; and the altitude in metres as the geodetic height in the BDCS coordinate system.

Table 13 ends with the search and rescue type, 1 to 3 meaning a distress request, cancellation of a distress request and forward identity authentication; the status data length, 0 to 468 bits; and the status data, whose range is again printed as 0 to 636 bits, larger than the preceding length field can express, and translated here as printed. Footnotes say that when the longitude and latitude markers are both 0 the RNSS positioning result of the terminal is used, that the search and rescue fields are present when the service type is emergency search and rescue, and that the position report fields are present when the service type is position report.

6.3.2 The TCQ sentence makes the user terminal send a message communication request; its format is shown in Figure 10 and explained in Table 14, which has five columns and seven numbered rows: the receiving party ID from 1 to 281 474 976 710 655, which may be an intranet or an extranet address; the frequency point, 0 for automatic, 1 for Lf1 and 2 for Lf2; the message communication frequency, 0 to 3 600 s, zero meaning a single request that stops the continuous sending; the inbound request acknowledgement, 1 for no acknowledgement needed and 2 for acknowledgement needed; the encoding type, 0 for Chinese characters, 1 for code and 2 for Chinese characters mixed with ASCII; the communication length from 4 bits to 14 000 bits, which may not be empty; and the communication data, described in the same terms as in Table 6, with the first letters fixed as A4 in the mixed case and high order zeros added to make the length a whole multiple of 4 bits.

6.3.3 The PSQ sentence makes the terminal send a position query request; its format is shown in Figure 11 and explained in Table 15, whose two rows are the ID number, the intranet address of the party queried, and the frequency point, 0 for automatic, 1 for Lf1 and 2 for Lf2. 6.3.4 The RTQ sentence makes the terminal send a communication receipt query request for a target user; its format is shown in Figure 12 and explained in Table 16, whose two rows carry the same two fields. 6.3.5 The OFQ sentence makes the terminal send a power on and off report to the central station; its format is shown in Figure 13 and explained in Table 17, whose two rows are the report type, 1 for power on report, 2 for power off report and 3 for status report, and the frequency point with the same three values.

6.3.6 The KSQ sentence makes the terminal request silence from the central station, a group customer or a management set being able to silence its subordinate user sets and an ordinary user set being able to silence itself; its format is shown in Figure 14 and explained in Table 18, which has three columns and six rows: the silence start and stop marker, 0 for silence and 1 for end of silence; the frequency point, 0 for automatic, 1 for Lf1 and 2 for Lf2; the number of silence addresses, 1 to 63; and then the silence addresses themselves, the middle rows being shown as ellipses.

6.3.7 The PWS sentence queries the current outbound beam tracking status from the user terminal and has it output at a stated interval; its format is shown in Figure 15 and explained in Table 19, which has three columns and three rows: the BDS-3 regional short message outbound beam number, 0 to 64, where 0 means no output, 1 to 63 name a beam and 64 means all visible beams; the signal branch, 1 to 3, where 1 and 2 name the two branches and 3 means both are supported; and the output frequency, 10 to 3 600 in units of 0.1 s, the printed example reading a value of 300 as 30 s.