1、 Recommendation ITU-R M.1798-1(04/2010)Characteristics of HF radio equipment for the exchange of digital data and electronic mail in the maritime mobile serviceM SeriesMobile, radiodetermination, amateurand related satellite servicesii Rec. ITU-R M.1798-1 Foreword The role of the Radiocommunication
2、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 Recommendations are adopted. The regulatory and pol
3、icy 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 Common Patent Policy for ITU-T/ITU-R/ISO/
4、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 Patent Policy for ITU-T/ITU-R/ISO/IEC
5、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 Broadcasting service (sound) BT Broadc
6、asting 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 sharing and coordination between fixed-sa
7、tellite 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 Resolution ITU-R 1. Electronic Publication
8、 Geneva, 2010 ITU 2010 All rights reserved. No part of this publication may be reproduced, by any means whatsoever, without written permission of ITU. Rec. ITU-R M.1798-1 1 RECOMMENDATION ITU-R M.1798-1Characteristics of HF radio equipment for the exchange of digital data and electronic mail in the
9、maritime mobile service (2007-2010) Scope This Recommendation describes a MF/HF radio systems and a HF data transfer protocols currently used in the maritime mobile service (MMS) for the exchange of data and electronic mail on frequencies of RR Appendix 17, and on non-RR Appendix 17 frequencies, pro
10、viding a similar functional capability to narrow-band direct printing (NBDP) and many other features. A method of providing completely transparent user interoperability is also described. The ITU Radiocommunication Assembly, considering a) that the use of software-defined radios will in future bring
11、 economical, technical and spectrum efficiency benefits, and that it should be possible to introduce the use of such radios without the need for further regulatory changes; b) that a high-speed data service over HF radio may be useful for low-level graphics, and the updating of Electronic Chart Disp
12、lay and Information Systems (ECDIS); c) that HF data services will enhance operational efficiency and maritime safety; d) that the introduction of new digital technology in the maritime mobile service (MMS) shall not disrupt the distress and safety communications in the MF and HF bands including tho
13、se established by the International Convention for the Safety of Life at Sea, 1974, as amended; e) that the limited use of narrow-band direct printing (NBDP) remains for distress communications in the polar regions (A4), since no coverage from geostationary-satellite networks provides service to mar
14、itime; f) that HF data services may require bandwidths greater than 3 kHz; g) that a maritime HF data system providing automatic connection with internet service providers would improve traffic-handling efficiency; h) that HF has the potential to provide greater coverage in Arctic NAVAREAS than eith
15、er Inmarsat EGC or 518 kHz NAVTEX; j) that there is a continuing need for ship-to-ship digital interoperability; k) the continued expansion of HF maritime digital data services will generate increasing demands for maritime mobile Radio Regulations (RR) Appendix 17 spectrum; l) that multiple standard
16、s for electronic mail could be used to encourage technological development, thus encouraging continued competition, so that users may benefit from continued advances in technology whilst noting the need for interoperability across networks, particularly for future distress and safety purposes, and t
17、he distribution of maritime safety information (MSI), This Recommendation should be brought to the attention of the International Maritime Organization (IMO). 2 Rec. ITU-R M.1798-1 recognizing a) that there is a need to specify the technical characteristics of HF radio systems and equipment for the
18、exchange of HF data and electronic mail on mobile frequencies, including RR Appendix 17 frequencies; b) that there are existing and developing global and regional HF electronic mail services operating on RR Appendix 17 frequencies and mobile frequencies outside of RR Appendix 17 (the use of mobile f
19、requencies outside of RR Appendix 17 by the MMS is in conformity with ITU rules), noting a) that the characteristics for HF data services described in Annexes 2, 3 and 4 can be considered as meeting the requirements for exchange of digital data and electronic mail in the MMS1, recommends 1 that syst
20、em interoperability should be achieved for the transmission of data messages in both the ship-to-shore and shore-to-ship direction should be achieved at the internet protocol (IP) level (see Annex 1); 2 that the examples of HF maritime data services, characteristics and modem protocols given in Anne
21、xes 2, 3 and 4 should be used in systems for the transmission and reception of data to and from ships using HF; 3 that in order to maintain ship-to-ship interoperability and compatibility with existing GMDSS equipment, the system should be capable of automatically accommodating radiocommunications i
22、n accordance with Recommendations ITU-R M.476 and ITU-R M.625 in both the forward error correction (FEC) and automatic repeat request (ARQ) modes; 4 that, if used in the GMDSS, this system should meet the applicable requirements of the IMO. Annex 1 System interoperability 1 Introduction This annex d
23、escribes the system interoperability (ship-to-shore and ship-to-ship) with details of the three HF electronic mail systems given in Annexes 2, 3 and 4 and a glossary is provided in Annex 5. 1Recognizing the need to comply with Chapter VII of the RR. Rec. ITU-R M.1798-1 3 2 System interoperability Sh
24、ip-to-shore In the ship-to-shore direction interoperability is maintained by the internet service provider (ISP) at the IP level. Typically, a ship will enter an e-mail, with or without attachments in the e-mail system and then click on the “send” button in the way that is familiar to all of us. Thi
25、s applies to any location, pole-to-pole, at any time. Shore-to-ship In the system as described in this Recommendation, there are no interoperability concerns on the part of the shore-side user. The shore-based sender of an e-mail to a ship can merely: click on the “reply” button; or address the mess
26、age to or . The e-mail will be delivered via whatever system the ship is using. If there is a system failure, there will be an automatic re-route via an alternate system. These automated decisions are based on the contents of an extensive database. Consequently, the e-mail may be delivered via HF o
27、r an alternate satellite-based system. If there is an overall system failure, addressing problem or non-delivery for any reason, the system support operators will be alerted and take corrective action. This ensures that shore-based users need not be concerned about what system or network the ship is
28、 using. They need only address the e-mail and click on “send”. Annex 2 HF data services modem protocol using orthogonal frequency division multiplexing (OFDM) Overview This annex describes the architecture for an OFDM modem for an HF channel using digital signal processing (DSP). The algorithm defin
29、ition and description of the implementation is provided. This includes the protocol, modulator and demodulator definition. The final section outlines how frequencies are selected and used in a spectrum-efficient manner. There are two basic approaches for implementation of a wideband modem, single ca
30、rrier and multicarrier. The OFDM modem described and in use is a multicarrier approach. The main advantage of using a multicarrier approach is that an equalizer is not required for estimating the fading channel, because the individual subcarrier bandwidth is small and can tolerate moderate fading. T
31、hus, the multicarrier approach is a less complex implementation. Also, the multicarrier approach was selected to make the individual subcarriers similar to narrow-band DATAPLEX. The disadvantage of a multicarrier approach is that it is more sensitive to frequency offset and oscillator phase noise. H
32、F modem protocol Introduction The OFDM waveform uses 32 carriers to transmit 32 blocks every 1 520 ms. Like Recommendation ITU-R M.625 TOR transmissions, OFDM is a half-duplex communication protocol where, at any given time, one station is the information-sending station (ISS) and the other is the i
33、nformation-4 Rec. ITU-R M.1798-1 receiving station (IRS). The basic timing cycle is fixed, and the original calling or MASTER station establishes the cycle timing. In the following sections, this paper describes the OFDM basic timing cycle, the block formats, and the basic link operations such as OV
34、ER, END and link establishment. OFDM modulation The OFDM waveform uses 32 carrier frequencies centred at 1 700 Hz. A full description of the waveform is in the following sections describing the modulator and demodulator. All OFDM transmissions use the 32 carrier (N = 32), 4 phase (M = 4) waveform wh
35、ere the ISS station sends one long data blocks per carrier for a total of 32 data blocks per burst. The IRS station responds with a 32 carrier (N = 32), 4 phase (M = 4) short burst containing 2 bytes per carrier for a total of 64 bytes. Frame timing Like Recommendation ITU-R M.625 TOR, OFDM is a hal
36、f-duplex protocol where one station is the ISS and the other is the IRS. When linked, the OFDM cycle time is fixed at 1 520 ms; the ISS transmits a 1 080 ms long data burst, and the IRS replies with a 216 ms short response burst. The basic timing cycle at the MASTER station is summarized below for M
37、ASTER-ISS and SLAVE-ISS. NOTE RTT is the round-trip propagation and SLAVE station processing time. The OFDM T = 0 cycle time reference is established by the MASTER station when the link starts. When ISS, the MASTER station always starts transmitting at T = 0, and the SLAVE station response must be c
38、ompletely received within the 440 ms receive interval immediately following the MASTERs 1 080 ms data burst. The SLAVE station always transmits the IRS reply as soon as it can after it receives the end of the MASTER ISS burst. When the MASTER is IRS, the 216 ms IRS reply starts 1 304 ms into the 1 5
39、20 ms cycle time so that the end of the reply occurs at the same time the MASTER ISS data burst would have ended. The SLAVE data burst starts at the same time in the cycle as the SLAVE IRS reply. The OFDM cycle timing philosophy follows the example set by Recommendation ITU-R M.625, except that the
40、OFDM cycle time allows a greater path distance (224 ms versus 170 ms) between the two linked stations. M.1798-001 080 ms216 msT = 0 ms T = 1 080 ms + RTT T = 1 520 ms216 msT = 1 304 ms T = 1 520 ms1 080 msT = 1 080 ms + RTT T = 0 msOFDM master timing - Master ISSOFDM master timing - Slave ISSISS dat
41、a burst (master)IRS replyISS data burst (slave)IRS replyISSIRSRec. ITU-R M.1798-1 5 ISS block format The OFDM protocol uses the ISS block illustrated below to transmit both data bytes and control messages to the IRS station. Every ISS transmission sends one data block on each of 32 carriers for a to
42、tal of 32 blocks per long burst. Since the ISS sends a maximum of 32 blocks with 10 bytes per block every 1 520 ms, the resulting maximum data throughput for OFDM N = 32 M = 4 is about 210 bytes or 1 684 bit/s. ISS data block SEQ_NR | LEN (11 bits) (5 bits) DATA (10 bytes) CRC (2 bytes) SEQ_NR 11-bi
43、t block sequence number 1 to 0x7FF 0x000 means discard this block LEN 0 to 10 is the number of valid data bytes in the block 31 signals a CONTROL block DATA 0 to 10 data bytes when LEN is 0 to 10 CONTROL block when LEN is 31 CRC 16-bit CRC sequence Each data block starts with an 11-bit sequence numb
44、er (SEQ_NR) that is used to correctly order the blocks at the IRS end of the link. The sequence number is incremented from 1 to 2 047 (0x7FF) with every new data or control block transmission so that the IRS station can reconstruct the entire data transmission by presenting the blocks in the correct
45、 order at the receive end. The sequence number rolls over from 2 047 to 1 after the 2 047th block has been encoded. The sequence number of a control block indicates when the control block should be decoded. The sequence number is set to 1 when the link starts, and it is not changed during OVERs. Dur
46、ing the link, the ISS station must ensure that no more than MAX_SEQ_NR_DIFF sequence number blocks are outstanding at any time, where MAX_SEQ_NR_DIFF is a programmable value less than (2 047 64) or 1 983. In other words, the difference between the oldest and newest block sequence number in any given
47、 ISS long burst must be less than or equal MAX_SEQ_NR_DIFF. This restriction is meant to limit the number of buffered blocks at the IRS end, and to allow the link to “catch up” if, for some reason, one or more blocks continue to fail to decode error-free at the IRS end. The protocol allows the ISS s
48、tation to repeat blocks in the same long burst. If the ISS station approaches the MAX_SEQ_NR_DIFF difference between the oldest and newest block sequence numbers in any given long burst, the oldest blocks should be repeated in the remaining open long burst slots to improve the probability that the b
49、lock is received correctly. At any time, the ISS station may repeat current blocks if there are no new data blocks pending. The 0000 sequence number is a special case. When a block is transmitted with a 0000 sequence number, this block can be discarded by the IRS station without any further decoding. At the end of an ISS transmission, for example, the 0000 blocks may be used as filler for all blocks after the last block containing valid data. The significance of the 0000 block will become apparent later when discussing the ARQ operation wh
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