GMDSSChapter 3.4

1、GMDSSCommunication Equipment and ServicesCommunication office, Navigation College2022年年5月月27日日Chapter 3 Marine MF/HF communication equipmentCommunication office, Navigation College2022年年5月月27日日Outlines 3.1 SSB communication principle 3.2 Marine MF/HF SSB transmitter 3.3 Marine MF/HF SSB receiver 3.4

2、 MF/HF NBDP terminal equipment 3.5 MF/HF DSC terminal devices 3.6 Ships antennasGMDSS Communication Equipment and Services3.4 NBDP terminal equipment 3.4.1 NBDP terminal composition 3.4.2 Main technology involved in the terminal 3.4.3 Error Detecting and correcting methods 3.4.4 NBDP communication w

3、ork patterns 3.4.5 ARQ and FEC communication procedures3.4 NBDP terminal equipmentHF NBDP is compulsory equipment for sea area A4overview Narrow-Band Direct-Printing (NBDP), means of communication to exchange text messages It can achieve the automatic telex operations between ship-shore, ship-ship,

4、ship station through shore station to connect with international telex network users. At the same time it can also transmit telex messages to a group of ships or all ships. 3.4 NBDP terminal equipment Primarily used as a means of subsequent communication for exchanging messages after initial contact

5、 has been established by the use of MF/HF DSC. An optional means of long range communication in an A3 area & a required means of long range communications in an A4 area.overview3.4 NBDP terminal equipment 3.4.1 NBDP terminal composition 3.4.2 Main technology involved in the terminal 3.4.3 Error

6、Detecting and correcting methods 3.4.4 NBDP communication work patterns 3.4.5 ARQ and FEC communication procedures3.4 NBDP terminal equipmentATUPowerprinterNBDPMF/HF TransceiverDSC/NBDP MODEMAC/DC3.4.1 NBDP terminal composition3.4 NBDP terminal equipment3.4 NBDP terminal equipment 3.4.1 NBDP termina

7、l composition 3.4.2 Main technology involved in the terminal 3.4.3 Error Detecting and correcting methods 3.4.4 NBDP communication work patterns 3.4.5 ARQ and FEC communication procedures3.4 NBDP terminal equipment3.4.2 Main technology involved in the terminal Calling identification number is 9 digi

8、t Maritime Mobile Service identification number (MMSI). Before MMSI introduction, NBDP communication uses Selective Calling Number, the ship station is represented with 5 digits, and coast radio station is represented with 4 digits. At present, both of two (MMSI and Selcall) are compatible. MMSI: sh

9、ip station：MID ship group station：0MID coast station：00MID 004122100/004121300MID (maritime identification digits) 海上移动业务识别码，China-412,4133.4 NBDP terminal equipment NBDP emission type is F1B or J2B, RF channel information speed is 100 baud (waveform/second). NBDP communication modulation is frequen

10、cy shift keying (FSK) or called digital frequency modulation.3.4 NBDP terminal equipment3.4.2 Main technology involved in the terminalFSK， F1B/J2B“1”1615 Hz（ mark signal 传号传号 ）“0”1785 Hz（ space signal 空号空号 ）1700 85 Hz100 bps/ baud /波特波特 0.01 s = 10 ms / bit4B/3Y = 70 ms NBDP communication uses 4B/3Y

11、 constant ratio code (恒比码恒比码) to detect errors, uses Automatic Repetition reQuest (自动请求重自动请求重复复) and dual time diversity (二重时间分集二重时间分集) to correct errors. There are 2 work mode for NBDP communication: ARQ (自动自动请求重复请求重复) and FEC (前向纠错前向纠错). ARQ works with automatic repeat request error correction met

12、hod; FEC works with dual time diversity error correction methods.3.4 NBDP terminal equipment3.4.2 Main technology involved in the terminalCoding technology involve in NBDPASCII The American Standard Code for Information Interchange (ASCII, pronunciation: ass-kee) is a character-encoding scheme based

13、 on the ordering of the English alphabet, it includes definitions for 128 characters: 33 are non-printing control characters that affect how text and space is processed; 94 are printable characters, and the space is considered an invisible graphic. ASCII codes represent characters in computers, comm

14、unications equipment, and other devices. Most modern character-encoding schemes are based on ASCII.3.4 NBDP terminal equipment4B/3Y 4B/3Y seven unit constant ratio code consists of seven 0“ and 1 symbol, the 0 and 1 proportion is constant at 4:3. In practical use, 0 or B stands for space signal, 1 o

15、r Y stands for mark signal. Seven-unit code has total of 128 different encoding, but of which meet 4B/3Y constant ratio is only 35. 3.4 NBDP terminal equipmentExample：01010014 B / 3Y code（7-bit constant ratio in order to detect error）0（space）1（mark）Coding technology involve in NBDPITA No.2国际电传国际电传2号

16、码号码 It is used in international user telex network to exchanges information. It is a five-unit codes, shore station NBDP device must convert 4B/3Y seven unit constant ratio to ITA No.2 codes and vice versa. In ITA No.2 codes, space signal is represented by letter A or digital 0, Mark letter Z or dig

17、ital 1.3.4 NBDP terminal equipmentCoding technology involve in NBDPHow to use ITA No.2?3.4 NBDP terminal equipmentCoastal radio stationTelex userInternational user telex networkITA No.2 codeITA No.2 To ensure strict synchronization, prior each five unit code adds a special 1 bit as starting bit and

18、adds 1.5 bit behind as the terminating bit. Starting bit transmits 1 bit space, and terminating bit transmits 1.5 bit mark, In the actual communications we can see that in a five-unit codes characters actually transmits 7.5 bit, as formulated in terrestrial telex network speeds is 50 Baud, so each b

19、it takes 20ms, 7.5 bit takes total of 150ms.3.4 NBDP terminal equipment011100 010.5150msSSBTransceiverMODEMCPUperipheralsRadiostationTelex subscriber4B/3YARQ UnitASCII码码FSKFSKITA NO.2Coding technology involve in NBDP3.4 NBDP terminal equipment 3.4.1 NBDP terminal composition 3.4.2 Main technology in

20、volved in the terminal 3.4.3 Error Detecting and correcting methods 3.4.4 NBDP communication work patterns 3.4.5 ARQ and FEC communication procedures3.4 NBDP terminal equipment3.4.3 Error Detecting and correcting methods3.4 NBDP terminal equipment 4B/3Y seven unit constant ratio code consists of sev

21、en 0“ and 1 symbol, the 0 and 1 proportion is constant at 4:3.Example：01010014 B / 3Y code（7-bit constant ratio in order to detect error）0（space）1（mark） Error Detecting3.4.3 Error Detecting and correcting methods Automatic Repetition reQuest (ARQ) is an error-control method for data transmission tha

22、t uses acknowledgements and timeouts to achieve reliable data transmission over an unreliable service. If the sender does not receive an acknowledgment before the timeout, it usually re-transmits the frame/packet until the sender receives an acknowledgment or exceeds a predefined number of re-transm

23、issions.3.4 NBDP terminal equipment Error CorrectingError checking and correcting technology Dual time diversity (280ms) twice the characters received are in line with the 4B/3Y, and the same; Correct Receive twice the characters received are in line with the 4B/3Y rule, but not identical; * two of

24、the characters received only one subjects to 4B/3Y; Correct Receive twice received the characters do not meet 4B/3Y rule; 3.4 NBDP terminal equipment Error Correcting3.4 NBDP terminal equipment 3.4.1 NBDP terminal composition 3.4.2 Main technology involved in the terminal 3.4.3 Error Detecting and c

25、orrecting methods 3.4.4 NBDP communication work patterns 3.4.5 ARQ and FEC communication procedures3.4 NBDP terminal equipment3.4.4 NBDP communication work patterns A Mode: Automatic Repetition reQuest (ARQ) B Mode: Forward Error Correction (FEC) Collective FEC（集群性前向纠错）（集群性前向纠错） Selective FEC (选择性前向

26、纠错选择性前向纠错)3.4 NBDP terminal equipmentARQ modeABABmessageShip A transmitter Ship B transmitter Ship A receiver Ship B receiver Error detection codeIf no error, ship A will send next message, otherwise the existing message will re-sent.FEC modeAmessageShip A transmitter Many ships receiver Ship A send

27、s each message twice onlyARQ ModePoint to point two-way communications, the information is exchanged between two stations only. Error Detection and CorrectionDetection：4B/3Y codeCorrection：ARQ TermsThe roles changes at a given timeBISS : Information sending stationIRS: Information receiving stationA

28、 Master : the station which initiate the callingSlave: the station called at the beginning of communicationThe roles not change in the communications Transmission ProceduresI.Data is packed in blocks of 3 characters by ISSII. Each block of data transfer to 4B/3Y code.III.The data is transmitted by I

29、SS.IV.If the IRS indicates correct reception, the next block is sent.If the IRS indicates that an error in reception, a request is transmitted to send the block again.Noticed: Each block can be retransmitted up to 32 times.ARQ Mode ARQ communication period one period of ARQ equals to 450ms In each p

30、eriod, three 4B/3Y codes information characters will be sent. (21 bits=210 ms) In each period, 1 control character will be sent. (7 bits=70 ms) The time spent by signal propagation is 170ms(round trip) and single trip costs 85ms. 3105 8510-3 = 2.55104 Km, The circumference of the earth is 4104 Kmhen

31、ce could get anywhere in the world. 1 period = 450ms Each period transmit 3 informationCharacters = 210 ms The time for signal propagation = 170 ms largest propagation distance= 2.55104 Km Each period transmit 1 controlCharacter = 70 msARQ mode basic work procedure Phasing process Identification procedure Communication process Rephrasing process Terminate communication process3.4 NBDP terminal equipmentARQ Work ProcedureThe line is brokenTerminate the communication Only performed by ISS“BRK+” or “KKKK”“OVER” or “ + ”ISS and IRS exchangetheir roles via“WRU”“DE”Phasing processIdentificationComm