1、 - STD-ITU-R RECMN H.1222-ENGL 1797 4855232 052733b 2Tb 102 Rec. ITU-R M.1222 RECOMMENDATION ITU-R M. 1222 TRANSMISSION OF DATA MESSAGES ON SHARED PRIVATE LAND MOBILE RADIO CHANNELS (Question ITU-R 213/8) (1997) Summary This Recommendation provides descriptions of channel occupation and access proce
2、dures for the transmission of data messages on different categories of private land mobile radio channels. This Recommendation has been developed to standardize the data transmission procedures for users who share an analogue radio channel in order to minimize interference to other users who also op
3、erate on the channel. The Radiocommunication Assembly, considering 4 for an operator; that the transmission of information in a data format can significantly improve the communications efficiency b) that transmitting messages in data format can considerably improve the spectral efficiency of a chann
4、el; c) essential for fleet management; that the use of data transmission to convey messages such as vehicle status and identification is becoming d) that studies have shown that interference to speech users is minimized by regulating channel access for data transmission on speech channels by only pe
5、rmitting manually initiated channel access procedures and by restricting the length of the message; e) by non-related systems in order to minimize interference to voice users; that automatic channel access protocols are required for the transmission of data messages on speech channels 0 that operato
6、rs who primarily only use data messaging may wish to transmit longer messages; g) interference to other channel users, that automatic channel access protocols are required on data only shared channels in order to minimize recommends 1 for data transmission on two frequency simplex analogue speech do
7、minant channels: 1.1 channel access protocols defined in Annex 1; that for the transmission of data messages on a speech channel both mobiles and base stations should use the 1.2 that the maximum channel occupancy of a single data message should be 650 ms, or 1 o00 ms for systems operating with audi
8、o squelch control circuitry, e.g. continuous tone controlled signalling system (CTCSS), digitally coded squelch CS), selective tone signalling, etc.; 1.3 polling of mobiles causing interference to speech users; that only manual initiation of channel access procedures should be permitted in order to
9、prevent automatic 1.4 that the data message can be either of analogue or digital modulation type; COPYRIGHT International Telecommunications Union/ITU RadiocommunicationsLicensed by Information Handling Services- STD-ITU-R RECMN M-LZ22-ENGL 3977 Li855212 0529337 132 Rec. ITU-R M.1222 103 2 for data
10、transmission on two frequency simplex analogue data dominant channels: 2.1 described in Annex 2 should be used; that for the transmission of data messages by both mobile and base stations the channel access protocol 2.2 be limited to 10 s: that the maximum channel occupancy of a data message on a sh
11、ared channel primarily intended for data should 2.3 that during a transmission period communication between more than two radio units in a fleet is permitted; 2.4 that speech messages should use the same channel access protocols as data messages; 2.5 that the data message can be either of analogue o
12、r digital modulation type; 3 analogue channels: for data transmission on combined speech/data and data only single frequency and two frequency repeater 3.1 described in Annex 3 shall be used; that for the transmission of data messages by both mobile and base stations, the channel access protocol 3.2
13、 that the maximum channel occupancy of a data message shall not exceed 10 s; 3.3 that during a transmission period, communication between more than two radio units in a fleet is permitted; 3.4 that data messages should not account for greater than 0.05% of traffic on combined speecwdata channels; 3.
14、5 that the data message can be either of analogue or digital modulation type. ANNEX 1 Data transmission on two frequency simplex analogue speech channels 1 General The following sections provide an outline description of the channel access and re-transmission procedures as defined in United Kingdom
15、standard MPT 1379 ME, 19941 for the transmission of data messages on two frequency simplex channels. The standard was developed based on the results of a comprehensive study Greensmith, 19921 assessing data interference to speech messages and simulation of channel access procedures for data messages
16、 on a channel. 1.1 Channel occupation time The maximum channel occupancy of any single data transmission which shall not exceed 650 ms. This is to be measured from the start of the rise-time of the transmitter to the end of its decay-time and might for example consist of 100 ms rise-time, 500 ms use
17、d for data transmission and 50 ms transmitter decay-time. For systems permitted to use mobile-to-mobile communication with a CTCSS controlling the base station the maximum channel occupancy of any single data transmission shall not exceed 1 O00 ms. COPYRIGHT International Telecommunications Union/IT
18、U RadiocommunicationsLicensed by Information Handling Services STD-ITU-R RECMN N-2222-ENGL 3777 m 9855232 0527338 O79 m 104 Rec. ITU-R M.1222 1.2 Channel access procedures Figures 1 and 2 show the two channel access and re-transmission procedures which are suited to lightly and heavily loaded speech
19、 channels and these are described in the following sections. Each transmission (including data as a precursor for a voice message) shall only be initiated by a manual action, e.g. pressing a button. FIGURE 1 Flow diagram for channel access and retry procedure option A I Request to transmit Yes No No
20、 I Increase m II Calculate td fp ff+ n 4 I I I I finished? Channel free 10 ms 1, Reset m Transmit message - C Yes End procedure COPYRIGHT International Telecommunications Union/ITU RadiocommunicationsLicensed by Information Handling Services STDWITU-R RECMN M-1222-ENGL 1777 4855232 0527139 TU5 D Rec
21、. ITU-R M.1222 FIGURE 2 Flow diagram for channel access and retry procedure option B Request to transmit 1 Channel free 10 ms Reset m I No free 10 ms Calculate t, Increase m finished? m = maximum value? I No Transmit message 105 0 End procedure COPYRIGHT International Telecommunications Union/ITU Ra
22、diocommunicationsLicensed by Information Handling Services - STD-ITU-R RECMN tl.3222-ENGL 3777 m 4855232 0527340 727 m 106 Rec. ITU-R M.1222 1.2.1 Automatic acknowledgement An automatic acknowledgement to the message from the receiving transceiver is permitted. The maximum duration of the acknowledg
23、ement is 650 ms. This is to be measured from the start of the rise-time of the transmitter to the end of its decay-time and might for example consist of 100 ms rise-time, 500 ms used for data transmission and 50 ms transmitter decay-time. If no response is received in a defined time, automatic retri
24、es of the message are permitted using the procedures described below. 1.2.2 Channel access and retry procedures Transceivers are permitted to access the channel in two ways as shown in Figs. 1 and 2. Both options permit the transceiver to transmit a message if the channel is observed to be clear of
25、traffic but introduce two distinct distribution mechanisms for transceivers waiting to access a channel that has been observed busy. An operator is free to implement either procedure in order to maximize their channel efficiency. in the event of an unsuccessful message transmission the re-transmissi
26、on procedure for each option is as shown in the diagram. 1.2.2.1 Option A (for relatively heavily loaded speech channels) The transceiver shall only attempt to transmit a message if the channel has been observed by the use of carrier sense clear of traffk for an initial period of at least 10 ms. If
27、the channel is not free the transceiver must wait for a random time delay TD (defined below). No channel monitoring is performed during time To. Therefore: The increment time Ti shall be 500 ms f0.5 ms. The number n is a random number between 1, 2, ., m; this means that 1, 2, ., m is the event field
28、 of the random number n. For the first trial, m is set to 4 in the case of a mobile and 2 in the case of a base station. At the end of TD the transmitter must observe with carrier sense, that the channel is clear of traffic for a minimum period of 10 ms prior to a transmission attempt. If the channe
29、l is observed to be busy at the end of TD the event field, in, is increased with each trial. For the second trial m is set to 8 (4 for a base station), for the third trial m is set to 13 (8 for a base station), for the fourth trial m is set to 20 (13 for a base station). Therefore the maximum number
30、 of transmission attempts is set to 5 (this is made up from the initial access attempt plus four attempts using the delay period TD). I 1.2.2.1.1 Retransmission procedures In the event of an unsuccessful transmission attempt (i.e. a message has been transmitted and no response is received) the proce
31、dure defined above shall be repeated with m reset to its initial value of 4 in the case of a mobile and 2 in the case of a base station. The maximum number of re-transmission attempts is set to 3. 1.2.2.2 Option B (for relatively lightly loaded channels) The transceiver shall only attempt to transmi
32、t a message if the channel has been observed by the use of carrier sense clear of traffic for an initial period of at least 10 ms. If the channel is not free the transceiver must wait for the channel to become free. When the channel is observed to become clear using the procedure defined above, the
33、transceiver shall calculate a random time delay TL, (defined below). No channel monitoring is performed during time TD. The fixed part Tjof the observation time shall be 750 ms. The increment time Ti shall be 500 ms +_OS ms. COPYRIGHT International Telecommunications Union/ITU RadiocommunicationsLic
34、ensed by Information Handling Services STD-ITU-R RECMN M-1222-ENGL 1997 LiA552L2 0529141 bb3 Rec. ITU-R M.1222 107 The number n is a random number between 1, 2, ., m; this means that 1, 2, ., m is the event field of the random number n. For the first trial, m is set to 4 in the case of a mobile and
35、2 in the case of a base station. At the end of TD the transmitter must observe with carrier sense that the channel is clear of traffic for a minimum period of 10 ms seconds prior to a transmission attempt. If the channel is observed to be busy at the end of TD the event field, m, is increased with e
36、ach trial. For the second trial m is set to 8 (4 for a base station), for the third trial m is set to 13 (8 for a base station), for the fourth trial m is set to 20 (13 for a base station). Therefore the maximum number of transmission attempts is set to 5 (this is made up from the initial access att
37、empt plus four attempts using the delay period To). 1.2.2.2.1 Retransmission procedures In the event of an unsuccessful transmission attempt (Le. a message has been transmitted and no response is received in TAC) the procedure defined above shall be repeated with m reset to its initial value of 4 in
38、 the case of a mobile and 2 in the case of a base station. The maximum number of re-transmission attempts is set to 3. 1.3 Carrier sensing The carrier sense should be able to detect RF signals with different types of modulation e.g. F3E, G3E, FlD, F2D, G1D. The carrier sense delay shall be less than
39、 or equal to 10 ms. The carrier sense delay is the time which elapses between the application of a carrier to the receiver and the detection of the carrier by that receiver. Data transmission equipment shall implement one of the following options for carrier sensing: a) The channel will be regarded
40、as in use during the observation time if the signal-to-noise ratio is greater than the signal-to-noise ratio observed when an RF signal of 2 pV EMF (- 107 dBm) is applied directly to the receiver input terminals in the absence of extraneous noise. The channel will be regarded as in use during the ob
41、servation time if the RF signal on the channel exceeds a level of 2 pV EMF (- 107 am) as measured at the receiver input terminals. The channel shall be regarded as busy during the observation time if the RF level on the channel exceeds that specified for the frequency band and environment specified
42、in Table 1. These levels are as measured at the receiver input terminals. b) c) TABLE 1 Levels (pV) EMF (dBm) as applied to radio receiver input terminals Band Rural IT Low VHF (-113) (68-87.5 MHz) (138-174 MHz) All UHF I 1 I (-113) Suburban (- 107) Urban I If a transceiver observes a channel to be
43、continuously busy via any one of the mechanisms a), b) laid out in this section for more than 98% of a period of 100 s, the terminal may simply transmit one pending message and if necessary up to four retries. The channel will be regarded as in use during the observation time if the RF level on it e
44、xceeds the current threshold value, which consists of two components, a fixed threshold and a variable amount. The fixed values are shown in Table 1 and the variable amounts may take any number up to + 12 dB, though it is recommended that this should be in discrete steps not larger than 6 dB. No low
45、er limit is specified. d) COPYRIGHT International Telecommunications Union/ITU RadiocommunicationsLicensed by Information Handling Services STD=ITU-R RECMN fl*3222-ENGL 3777 4855232 05273q2 5TT 108 Rec. ITU-R M.1222 Whenever a transceiver is turned on, resets or access a new channel, the variable pa
46、rt of the threshold will be zero. If, after monitoring for a long duration (exceeding 100 s) a channel appears to be busy for a period of 98% of the time or more, then the transceiver may reset the variable threshold by one step of up to 6dB and once more monitor. The threshold may again be increase
47、d after a further 100 s of monitoring if the channel appears to be busy for at least 98% of the time. Provided that channel appears to be busy for more than 80% of time (as observed over a duration of at least 100 s) then the increased value of the variable part of the threshold shall endure. Howeve
48、r, if the channel appears to be busy for less than 80% of such a period then the variable part of the threshold shall be reduced by a step of at least 6 dB, for a period of at least 100 s monitoring at the lower total threshold level. 1.4 Emergency data transmissions The channel access procedure set
49、 out above need not be followed for data transmission for the purpose of indicating the existence of an emergency condition. It is expected that equipment will have some special feature to initiate emergency data transmissions which is separate from the normal mode of transmitting data that adheres to the access protocol. It is recommended that the emergency signal should upon reception generate some form of alarm condition at the recipient and be terminated when an acknowledgement is received. The sending unit may not continuously retry the em
