1、INTERNATIONAL TELECOMMUNICATION UNION)45G134 TELECOMMUNICATIONSTANDARDIZATION SECTOROF ITU).4%2.!4)/.!,G0G0!.!,/5%G0G0#!22)%2G0G03934%-3%.%2!,G0G0#(!2!#4%2)34)#3G0G0/&G0G0).4%2.!4)/.!,#!22)%2G0G04%,%0(/.%G0G03934%-3G0G0/.2!$)/G0G13G02%,!9G0G0/2G03!4%,)4%G0G0,).+3G0G0!.$).4%2#/%#4)/.G0G07)4(G0G0-%4!,
2、)#G0G0,).+32!$)/G0G13G02%,!9G0G03934%-G0G0$%3)./“*%#4)6%3G0G0&/2G0G0./)3%G0G0!4G0G04(%G0G0&!2G0G0%.$/&G0G0!G0G0(90/4(%4)#!,G0G02%&%2%.#%G0G0#)2#5)47)4(G0G02%&%2%.#%G0G04/G0G04%,%2!0(942!.3-)33)/.)45G134G0G0RecommendationG0G0 (Extract from the “LUEG0“OOK)NOTES1 ITU-T Recommendation G.442 was publishe
3、d in Fascicle III.2 of the Blue Book. This file is an extract fromthe Blue Book. While the presentation and layout of the text might be slightly different from the Blue Book version, thecontents of the file are identical to the Blue Book version and copyright conditions remain unchanged (see below).
4、2 In this Recommendation, the expression “Administration” is used for conciseness to indicate both atelecommunication administration and a recognized operating agency. ITU 1988, 1993All rights reserved. No part of this publication may be reproduced or utilized in any form or by any means, electronic
5、 ormechanical, including photocopying and microfilm, without permission in writing from the ITU.Fascicle III.2 - Rec. G.442 1Recommendation G.442Fascicle III.2 - Rec. G.442RADIO-RELAY SYSTEM DESIGN OBJECTIVES FOR NOISE AT THEFAR END OF A HYPOTHETICAL REFERENCE CIRCUIT WITHREFERENCE TO TELEGRAPHY TRA
6、NSMISSION(modified at Geneva, 1964)As is shown in Recommendation G.222, if the intention is to use on radio links, amplitude-modulated voice-frequency telegraph equipment for 50 bauds conforming to Series R Recommendations, then in order to obtain telegraphconnections with the quality indicated in R
7、ecommendation F.10 1, the design of these radio links should include theobjectives recommended for telephone transmission and signalling and, in addition, should include the objectives set outbelow:On any telephone channel constituted in accordance with the hypothetical reference circuit for the typ
8、e of radiolink considered, the unweighted noise power, measured or calculated with a time-constant (integrating time) of 5 ms andreferred to a zero relative level point, should not exceed 106pW0 during more than 10-5(i.e. 0.001%) of any month, normore than 0.1% of any hour.Provided that short bursts
9、 of high-level noise due to causes other than propagation have been reduced tonegligible proportions, and assuming that the fine structure of the noise is the same as white noise, it is assumed that, indesigning line-of-sight radio links, the objective during any month is in practice equivalent to t
10、he following objective:The unweighted noise power on a telephone channel at a zero relative point, calculated from measurementsmade with an integrating time of 1 second, should not exceed 2 x 105pW0 for more than 10-4(i.e. for more than 0.01%)of any month.With regard to the objective to be met durin
11、g any hour, it may happen that on certain radio links unforeseenexceptional propagation conditions may result in this objective not being met during certain most unfavourable hours.These hours, called “hours of interrupted telegraph traffic“, will be those during which a noise level of 106pW0 isexce
12、eded for more than 36 seconds.Every effort should be made to reduce the number of such hours to a very small fraction of the total time. Sinceit follows from the recommended objective for telephone signalling that the 5 ms unweighted noise power should notexceed 106pW0 during more than 10-4(i.e. 0.0
13、1%) of any month, there should never be more than seven “hours ofinterrupted telegraph traffic“ during a month.It may then be expected that the telegraph service will be satisfactory. Nevertheless, to achieve this object, itmay be necessary in certain cases to select the channels allocated to amplit
14、ude-modulated voice-frequency telegraphy for50 bauds from among those which are the least sensitive to propagation noise.Note 1 - Use of a measuring instrument having a 5-ms time constant (integrating time) is recommended so as todetect, in particular, the presence of short high-level noise bursts,
15、such as those caused by power supplies and by theequipment. Administrations should take all possible practical steps to eliminate such noise.It is expected that on the majority of line-of-sight radio links (if not on all) it will be possible to reduce shortnoise bursts to negligible proportions, and
16、 that for the majority of radio links, any remaining short high-level noisebursts will be due to propagation. Noise surges having a mean power in excess of about 105pW0 will then last from 1 to10 seconds and will have an approximately constant level during this period. Under these conditions, for pr
17、opagationmeasurements and preliminary design measurements for radio links, instruments having a time constant (integratingtime) of 1 second could be used.Note 2 - The fraction 10-5of a month, for a 2500-km circuit, leads to impracticably small fractions of the timefor shorter circuits (for example,
18、10-6for a 250-km circuit). It is for this reason that the practical objective refers to agreater fraction of the time (10-4for 2500 km), together with a reduced power (2 x 105pW0), the latter measured with atime constant (integrating time) of 1 second.Reference1 CCITT Recommendation Character error rate objective for telegraph communication using 5-unit start-stopequipment, Vol. II, Rec. F.10.
