1、INTERNATIONAL TELECOMMUNICATION UNION)45G134 TELECOMMUNICATIONSTANDARDIZATION SECTOROF ITU).4%2.!4)/.!,G0G0!.!,/5%G0G0#!22)%2G0G03934%-3%.%2!,G0G0#(!2!#4%2)34)#3G0G0/1.2 47 500 pW0p, psophometrically weighted,2)one-minute mean power,3)for more than 0.1 % of any month;1.3 1 000 000 pW0, unweighted (w
2、ith an integrating time of 5 ms), for more than 0.01% of any month.“Adding these values to the 2500 pW0p of psophometric power allowed for multiplexing equipment(Recommendation G.222, 3) gives the recommended objectives shown in Recommendation G.222, 1.1 for thetelephone transmission and signalling
3、aspect. CCIR Recommendation 393 1 gives the conditions for applying theseobjectives to radio-relay systems; these conditions are in general the same as those given in Recommendation G.222, 2and in Recommendation G.223.The CCIR has not yet recommended any noise objectives in connection with voice-fre
4、quency telegraphtransmission. CCITT Recommendation G.442 covers this aspect.2 Noise on real circuits(See CCIR Recommendation G.395 3.)References1 CCIR Recommendation Allowable noise power in the hypothetical reference circuit for radio-relay systems fortelephony using frequency division multiplex, V
5、ol. IX, Rec. 393, Dubrovnik, 1986.2 CCIR Recommendation Allowable noise power in the hypothetical reference circuit of transhorizon radio-relaysystems for telephony using frequency division multiplex, Vol. IX, Rec. 397, Dubrovnik, 1986.3 CCIR Recommendation Noise in the radio portion of circuits to
6、be established over real radio-relay links forFDM telephony, Vol. IX, Rec. 395, Dubrovnik, 1986._1)This Recommendation relates only to “line-of-sight“ radio-relay systems. Trans-horizon radio-relay systems are dealt with inRecommendation 397 2.2)The level of uniform-spectrum noise power in a 3.1-kHz
7、 band must be reduced by 2.5 dB to obtain the psophometrically weightednoise power.3)For carrier transmission systems with one minute mean noise power distributions which are not well defined, the inclusion ofanother one minute mean noise clause would be desirable to ensure equivalent performance fo
8、r all systems. This clause would specifythat:The mean psophometric noise power over one minute shall not exceed 20 000 pW0p for more than 3% of any month.This clause has not been specifically included because CCIR has determined that for radio-relay links the application of clauses1.2.1 and 1.2.2 are sufficient to ensure, with high probability, that the additional clause will also be satisfied.
