1、 Recommendation ITU-R M.2010(03/2012)Characteristics of a digital system, named Navigational Data for broadcastingmaritime safety and securityrelated information from shore-to-shipin the 500 kHz bandM SeriesMobile, radiodetermination, amateurand related satellite servicesii Rec. ITU-R M.2010 Forewor
2、d The role of the Radiocommunication Sector is to ensure the rational, equitable, efficient and economical use of the radio-frequency spectrum by all radiocommunication services, including satellite services, and carry out studies without limit of frequency range on the basis of which Recommendation
3、s are adopted. The regulatory and policy functions of the Radiocommunication Sector are performed by World and Regional Radiocommunication Conferences and Radiocommunication Assemblies supported by Study Groups. Policy on Intellectual Property Right (IPR) ITU-R policy on IPR is described in the Comm
4、on Patent Policy for ITU-T/ITU-R/ISO/IEC referenced in Annex 1 of Resolution ITU-R 1. Forms to be used for the submission of patent statements and licensing declarations by patent holders are available from http:/www.itu.int/ITU-R/go/patents/en where the Guidelines for Implementation of the Common P
5、atent Policy for ITU-T/ITU-R/ISO/IEC and the ITU-R patent information database can also be found. Series of ITU-R Recommendations (Also available online at http:/www.itu.int/publ/R-REC/en) Series Title BO Satellite delivery BR Recording for production, archival and play-out; film for television BS B
6、roadcasting service (sound) BT Broadcasting service (television) F Fixed service M Mobile, radiodetermination, amateur and related satellite services P Radiowave propagation RA Radio astronomy RS Remote sensing systems S Fixed-satellite service SA Space applications and meteorology SF Frequency shar
7、ing and coordination between fixed-satellite and fixed service systems SM Spectrum management SNG Satellite news gathering TF Time signals and frequency standards emissions V Vocabulary and related subjects Note: This ITU-R Recommendation was approved in English under the procedure detailed in Resol
8、ution ITU-R 1. Electronic Publication Geneva, 2012 ITU 2012 All rights reserved. No part of this publication may be reproduced, by any means whatsoever, without written permission of ITU. Rec. ITU-R M.2010 1 RECOMMENDATION ITU-R M.2010 Characteristics of a digital system, named Navigational Data for
9、 broadcasting maritime safety and security related information from shore-to-ship in the 500 kHz band (2012) Scope The Recommendation describes an MF radio system, named Navigational Data (NAVDAT), for use in the maritime mobile service, operating in the 500 kHz band for digital broadcasting of mari
10、time safety and security related information from shore-to-ship. The operational characteristics and system architecture of this radio system are included in Annexes 1 and 2. The two different modes of broadcasting data are detailed in Annexes 3 and 4 The ITU Radiocommunication Assembly, considering
11、 a) that high speed data broadcast from shore-to-ships enhances operational efficiency and maritime safety; b) that the existing MF Maritime Safety Information system (NAVTEX) has limited capacity; c) that the e-Navigation system of the International Maritime Organization (IMO) increases the demand
12、for data transmission from shore-to-ship; d) that the 500 kHz band provides good coverage for digital systems, recognizing that the Digital Radio Mondiale (DRM) system referenced in Annex 4 has been incorporated in Recommendation ITU-R BS.1514-2, noting that Report ITU-R M.2201 provides the basis fo
13、r NAVDAT system, recommends 1 that the operational characteristics for the broadcasting of maritime safety and security related information should be in accordance with Annex 1; 2 that the system architecture of the broadcasting system for maritime safety and security related information should be i
14、n accordance with Annex 2; 3 that the technical characteristics and modem protocols for digital data transmission from shore-to-ships in the 500 kHz band should be in accordance with Annex 3 or Annex 4. 2 Rec. ITU-R M.2010 Annex 1 Operational characteristics The NAVDAT system uses a time-slot alloca
15、tion similar to the NAVTEX system which could be coordinated by IMO in the same manner. That NAVDAT system can also work on Single Frequency Network (SFN) as described in Annex 4. In this case transmitters are frequency synchronized and the transmit data must be the same for all transmitter. The NAV
16、DAT 500 kHz digital system offers a broadcast transmission of any kind of message from shore-to-ships with possibility of encryption. 1 Type of messages Any broadcasting message should be provided by a secure and controlled source. Message types broadcast can include, but are not limited to, the fol
17、lowing: safety of navigation; security; piracy; search and rescue; meteorological messages; piloting or harbour messages; vessel traffic system files transfer. 2 Broadcast modes 2.1 General broadcast These messages are broadcasted for the attention of all ships. 2.2 Selective broadcast These message
18、s are broadcasted for the attention of a group of ships or in a specific navigation area. 2.3 Dedicated message These messages are addressed to one ship, using the maritime mobile service identity. Rec. ITU-R M.2010 3 Annex 2 System architecture 1 The broadcast chain The NAVDAT system is organized u
19、pon five vectors performing the following functions: System of information and management (SIM): collects and controls all kinds of information; creates message files to be transmitted; creates transmitting programme according to message files priority and need of repetition. Shore network: assures
20、the transportation of the message files from sources to the transmitters. Shore transmitter: receives the message files from SIM; translates message files to orthogonal frequency division multiplexing (OFDM) signal; transmits RF signal to the antenna for broadcast to ships. Transmission channel: Tra
21、nsports the 500 kHz RF signal. Ship receiver: demodulates the RF OFDM signal; reconstructs the message files; sorts and makes the message files available for the dedicated equipment according to the message files applications. Figure 1 shows the diagram of the broadcast chain. 4 Rec. ITU-R M.2010 FI
22、GURE 1 NAVDAT 500 kHz broadcast chain block diagram M.2010-01ShoretransmitterShipreceiverTransmission channel 500 kHzShorenetworkSystem of information and management(SIM)Controls/signalisationsMessage filesMessagesTypes No. 1MessagesTypes No. n1.1 System of information and management The SIM term in
23、cludes: all the sources that deliver file messages (e.g. meteorological office, safety and security organizations, etc.); the file multiplexer which is an application running on a server; the file multiplexer manager; the shore transmitter manager. All the sources are connected to the file multiplex
24、er through a network. Figure 2 shows the general diagram of the SIM. Rec. ITU-R M.2010 5 FIGURE 2 NAVDAT system of information and management block diagram M.2010-02ShorenetworkFile multiplexerFile multiplexermanagerShore transmittermanagerMessage filesControls/signalisationsMessagesTypes No.1Messag
25、esTypes No.n1.1.1 File multiplexer The file multiplexer: takes delivery of the message files from the data sources; encrypts the message files if asked; formats the file messages with recipient information, priority status and time validity; sends the message files to the transmitter. 1.1.2 File mul
26、tiplexer manager The file multiplexer manager is a man machine interface that enables the user to, among other tasks: have a look at the message files coming from any source; specify the priority and periodicity of the any message file; specify the recipient of any message file; manage the file mess
27、age encryption. Some of these functionalities may be automated. As an example, the priority and the periodicity of a message may be selected according to the source it comes from or the source may specify the priority in the message. 1.1.3 Shore transmitter manager The shore station manager is a man
28、 machine interface connected to the transmitter through the network; it makes it possible to supervise the transmitter status indications such as: transmit acknowledgment; alarms; effective transmit power; synchronization report; and to change the transmitter parameters, such as: transmit power; 6 R
29、ec. ITU-R M.2010 OFDM parameters (pilot subcarriers, error coding, etc.); transmission schedule. 1.2 Shore network The shore network can use a broadband link, a low data rate link or a local file sharing. 1.3 Shore transmitter description A coastal transmitting station consists of this minimum confi
30、guration: one local server connected to a protected access; one OFDM modulator; one 500 kHz amplifier; one transmit antenna with matching unit; one GNSS receiver or atomic clock for synchronization; one monitoring receiver with its antenna. 1.3.1 Shore system architecture Figure 3 shows the block di
31、agram of a 500 kHz digital transmitter. FIGURE 3 NAVDAT 500 kHz transmitter functional block diagram M.2010-03ShorenetworkControllerMatchingunitMessage filesControls/signalisations500 kHzmonitoringreceiverRFamplifierRFgeneratorModulatorDSTISMISControls/signalisationsControls/signalisationsControls/s
32、ignalisationsGNSS receiverorreference clockTxantenna1.3.2 Controller This unit receives some pieces of information: message files from SIM; Rec. ITU-R M.2010 7 GNSS or reference clock for synchronization; 500 kHz signal from monitoring receiver; 500 kHz modulator and transmitter control signals. The
33、 function of the controller is: to check if the frequency band is free before transmission; to synchronize all signals on the coast station from synchronization clock; to control the transmission parameters, time and schedule; to format the message files to be transmitted (split files into packets).
34、 1.3.3 Modulator Figure 4 shows the diagram of the modulator. FIGURE 4 NAVDAT 500 kHz modulator functional block diagram M.2010-04PilotgeneratorOFDMbase bandgeneratorEncoderEnergydispersalOFDMmapperOFDM base bandEncoderEncoderEnergydispersalEnergydispersalPre-encoderPre-encoderPre-encoderDSTISMIS1.3
35、.3.1 Input streams In order to operate, the modulator needs three input streams: modulation information stream (MIS); transmitter information stream (TIS); data stream (DS). These streams are transcoded and then placed on the OFDM signal by the cell mapper. 1.3.3.1.1 Modulation information stream Th
36、is stream is used to provide information about: the spectrum occupancy; the modulation for transmission information stream and data stream (4, 16 or 64-QAM). This MIS stream is always coded on 4-QAM subcarriers for good demodulation into the receiver. 8 Rec. ITU-R M.2010 1.3.3.1.2 Transmitter inform
37、ation stream This stream is used to provide information to the receiver about: error coding for data stream (should be different for surface wave propagation at day time and for surface + sky wave propagation at night time); identifier of the transmitter; date and time. This TIS stream can be coded
38、on 4 or 16-QAM. 1.3.3.1.3 Data stream It contains the message files to transmit (these message files were previously formatted by the file multiplexer). 1.3.3.2 Error encoding The error correction scheme determines the robustness of the coding, The code rate is the ratio between useful and raw data
39、rate. It illustrates the transmission efficiency and can vary from 0.5 to 0.75 depending on the error correction schemes and modulation patterns. 1.3.3.3 OFDM generation The three streams (MIS, TIS and DS) are formatted: encoding; energy dispersal. A cell mapper organizes the OFDM cells with the for
40、matted streams and the pilot cells. The pilot cells are transmitted for the receiver to estimate the radio channel and synchronize on the RF signal. An OFDM signal generator creates the OFDM base band according to the output of the cell mapper. 1.3.4 500 kHz RF generator A 500 kHz RF generator trans
41、poses the base band signal to 500 kHz RF output carrier. An amplifier brings the RF signal to the desired power. 1.3.5 RF amplifier The function of this stage is to amplify the 500 kHz signal from the generator output to the necessary level to obtain the desired radio coverage. The OFDM transmission
42、 introduces a crest factor on the RF signal. This crest factor must stay in the range 7 to 10 dB at the RF amplifier output for a correct modulation error rate (MER). 1.3.6 Transmit antenna with matching unit The RF amplifier is connected to the transmit antenna through the impedance matching unit.
43、1.3.7 Global navigation satellite receiver and a backup atomic reference clock The clock is used to synchronize the local controller. 1.3.8 Monitoring receiver The monitoring receiver checks that the frequency is free before transmission and offers possibility to check the transmission. Rec. ITU-R M
44、.2010 9 1.4 Transmission channel: Radio coverage estimation The coverage could be calculated based on Recommendations ITU-R P.368-9 and ITU-R P.372-10. See Report ITU-R M.2201 for an example. Annex 3 NAVDAT technical characteristics 1 Modulation principle The system uses OFDM which is a modulation t
45、echnology for digital transmissions. 1.1 Introduction The bandwidth of the radio transmission channel is divided in the frequency domain to form subcarriers. The radio transmission channel occupancy is organized in the time to form OFDM symbols. An OFDM cell is equivalent to one subcarrier in one OF
46、DM symbol. 10 Rec. ITU-R M.2010 FIGURE 5 OFDM introduction M.2010-05RadiotransmissionChannelbandwidthOFDM symbolTimeFrequencySub-carrierOFDM cellAmplitude1.2 Principle The OFDM uses a large number of closely-spaced (41.66 Hz) orthogonal subcarriers to obtain high spectral efficiency to transmit data
47、. These subcarriers are frequency-spaced (Fu = 1/Tu), where TUis the OFDM symbol duration. The phases of subcarriers are orthogonal one to each other to enhance signal diversity caused by the multipath, especially in long distance. A guard interval (Td) is inserted in the OFDM symbol to reduce multi
48、path effect, thus reducing the inter-symbol interference. The OFDM symbol duration is Ts = Tu + Td The OFDM symbols are then concatenated to make an OFDM frame. The OFDM frame duration is Tf. Rec. ITU-R M.2010 11 FIGURE 6 Spectral representation of an OFDM frame M.2010-06BandwidthOFDM frameTimeFrequ
49、encyAmplitudeFIGURE 7 Temporal representation of an OFDM frame M.2010-07S: OFDM symbolTimeTfS1 S2 S3 SNTs1.3 Modulation Every subcarrier is modulated in amplitude and phase (QAM: Quadrature amplitude modulation). Modulation patterns can be either 64 states (6 bits, 64-QAM), 16 states (4 bits, 16-QAM), or 4 states (2 bits, 4-QAM). The modulation pattern depends on the desired robustness of the signal. 12 Rec. ITU-R M.2010 FIGURE 8 4-QAM constellation M.2010-084
