1、CCIR VOLUME*IV-1 90 W 4855232 0509887 T Rec. 482-2 31 RECOMMENDATION 482-2 MEASUREMENT OF PERFORMANCE BY MEANS OF A SIGNAL OF A UNIFORM SPECTRUM FOR SYSTEMS USING FREQUENCY-DIVISION MULTIPLEX TELEPHONY IN THE FIXED-SATELLITE SERVICE (Question 20/4) (1 974- 1978-1986) The CCIR, CONSIDERING (a) that i
2、t is desirable to measure the performance of satellite links in the fixed-satellite service for frequency-division multiplex telephony under conditions closely approaching those of actual operation; (b) that a signal with a continuous uniform spectrum (white noise) has statistical properties similar
3、 to those of a multiplex signal when the number of channels is not too small; (c) that the use of a signal with a continuous uniform spectrum to measure the performance of such links is already widespread; (d) that it is necessary to standardize the frequencies and bandwidths of the measuring channe
4、ls to be used for such measurements: (e) that for reasons of international compatibility it is necessary to standardize the minimum attenuation and the bandwidth of the stop filters which may have to be used in the white-noise generator; (f) that the CCIT has indicated, for the planning of telephone
5、 circuits, a mean value of speech power in the baseband of a multiplex telephone system to be taken into consideration during the busy hour (CCITT Recommendation G.223, Vol, III-2), UNANIMOUSLY RECOMMENDS 1. that the performance of frequency-division multiplex satellite links in the fixed-satellite
6、service should be measured by means of a signal with a continuous uniform spectrum in the frequency band used for the telephone channels: 2. that the nominal power level of the uniform spectrum test signal should be in accordance with the conventional load, specified in CCITT Recommendation G.223 *;
7、 2.1 that the sending equipment should be capable of providing, at the output of an inserted band-stop filter, a loading level of at least up to + 10 dB, relative to the nominal power level defined above; 2.2 that, within the bandwidth corresponding to the baseband of the system under test, the r.m.
8、s. voltage of the white noise spectrum measured in a band of about 2 kHz should not vary by more than f 0.5 dB. This degree of spectrum uniformity should be met in the level range of up to +6 dB, relative to the nominal power level; 2.3 that the white noise test signal should be available at the out
9、put of the sending equipment with a peak factor of about 12 dB with respect to the r.m.s. value; 3, that the nominal effective cut-off frequencies (the cut-off frequencies of hypothetical filters having ideal square cut-off characteristics and transmitting the -same power as the real filters) and to
10、lerances, for the band-limiting filters proposed for the various bandwidths of systems to be tested, should be as specified in Table I. (To reduce the number of filters required, compromises have been made between the nominal effective cut-off frequency and the system bandwidth-limiting frequency in
11、 some cases. The tolerances ensure that consequent calibration errors do not exceed +. 0.1 dB and errors in measurement of intermodulation noise do not exceed f 0.2 dB assuming system pre-emphasis conforming to Recommendation 464); 3.1 that the discrimination of a low-pass filter should be at least
12、20 dB at a frequency of more than 10% above nominal cut-off and at least 25 dB at frequencies of more than.20% above nominal cut-off. The discrimination of a high-pass filter should be at least 25 dB at frequencies of more than 20% below nominal cut-off; * The level of the conventional load in dBmO
13、is given by: - 1 + 4 log N, for N 240 channels. P t CCIR VOLUMEKV-L qo rn 4855232 osow88 I, m 32 Rec. 482-2 3.2 that to limit discrimination against measuring channels, the spread of losses introduced by any pair of high-pass and low-pass filters should not exceed 0.2 dB over a range of frequencies
14、which includes the upper and lower measuring channels; 4. that values of the characteristics for the discrimination in each stopband at the output of a sending equipment are given in Table II. The passband of each band-stop filter shall be designed to cover at least the largest baseband frequency ra
15、nge with which it is to be used, as indicated in the column entitled “Limits of band . , .“ in Table I. These characteristics are intended to apply over a temperature range from 10“ to 40 “C; 5. that, when the receiving equipment is connected directly to a sending equipment provided with band-stop f
16、ilters which only just meet the requirements of item 4, the ratio of the noise power indicated by the receiving equipment when the band-stop filter is by-passed, to that indicated when the filter is in circuit, should be a minimum of 67 dB; this requirement applies when a conventional load is applie
17、d. The minimum effective bandwidth of the receiver should be 1.7 kHz. The maximum reading of absolute noise power arising from leakage given by a receiver OP 1.74 kHz effective bandwidth and which just meets the foregoing leakage requirement is -85.6 dBmOp; 6. that additional measuring channels may
18、be provided by agreement between the administrations concerned; 6.1 that for the selection and technical characteristics of any new measuring or band-limiting filters the technical details indicated in the Annex I to Report 553 should be taken into account. Note - An overall accuracy of f 2 dB and b
19、etter, is assumed for systems in operation in the fixed-satellite service. Attention is also drawn to CCITT Recommendation G.228, Annex 1 and Annex 2 which discuss the method of measurement and the measuring accuracy. TABLE I Capacity (channels) 12 24 36 48 60 72 96 132 192 252 312 372 432 492 552 6
20、12 792 972 1 092 1 200 1332 .1 872 Limits of band occupied by telephone channels (kHz1 12- 60 12- 108 12- 156 12- 204 12- 252 12- 300 12- 408 12- 552 12- 804 12-1 052 12-1 300 12-1 548 12-1 796 12-2 o44 12-2 292 12-2 540 12-3 284 12-4 028 12-4 892 12-5 340 12-5 884 12-8 120 Effective cut-off frequen
21、cies of band-limiting filters (kH4 High pass 12 f 0.5 12 I: 0.5 12 f 0.5 12 f 0.5 12 f 0.5 12 f 0.5 12 i: 0.5 i2 f 0.5 12 f 0.5 12 f 0.5 12 i: 0.5 12 f 0.5 12 f 0.5 12 f 0.5 12 f 0.5 12 i 0.5 12 f 0.5 12 f 0.5 12 f 0.5 12 f 0.5 12 f 0.5 12 f 0.5 Low pass 60 -+ 0.5 108 f 1.0 156 f 1.0 204 f 1.5 252 i
22、 2.0 300 f 2.0 408 f 3.0 552 f 4.0 804 f 6.0 1052 f 8.0 1296 i 8.0 1548 f 10 1796 f 12 2044 f 14 2292 f 17 2600 f 20 3284 f 25 4 100 f 30 4892 f 40 5340 f 45 5884 f 50 8160 f 75 Frequencies of recommended measuring channels () (kHz1 16 56 16 98 16 140 16 185 16 240 16 270 16 240 394 16 240 534 . 16
23、394 770 16 534 1002 16 534 1248 16 534 1002 1490 16 534 1002 1730 16 534 1248 1940 16 770 1730 2150 16 770 1730 2438 16 1002 2438 3 150 16 1002 2438 3 886 70 1002 2438 4650 70 1002 3150 4650 70 1 002 3 150 4 650 5 340 70 1002 3150 5340 7600 (I) See also Recommends 6.1 of this Recommendation. ,- - -
24、-.! 70 70 (4) 98 f 1.5 rr 2.2 f 3.5 - f 1.5 f 1.7 f 2.0 - f 1.5 f 1.8 f 2.1 - 240 270 394 f 1.5 f 1.8 f 2.2 - I: 1.5 f 2.3 f 2.9 - f 1.5 f 3.0 f 4.5 - 1002 1248 -i 1.5 f 4.0 f 9.0 - f 1.5 f 4.0 f 11.0 - 1 940 2 150 f 1.5 f 4.3 f 15.0 - f 1.5 f 4.4 f 17.0 - f 15.0 f 1.8 3 886C) 1 f 1.5 f 30.0 - f 3.5
25、 -k 8.0 4 650 5 340 f 1.5 f 2.0 f 3.8 i 8.5 -f 1.5 f 2.2 f 4.0 f 8.5 CCIR VOLUME*IV-L 90 = 4855232 0509889 3 W - Rec. 482-2 33 TABLE II Centre Bandwidth (kHz) in relation to fe, over which the. discrimination should be at Ieast: (I) frequencyAll (kH4 3 dB () Bandwidth (kHz) in relation to fe outside
26、 of which the discrimination should not exceed: 3 dB 1 0.5 dB 16 I f 1.5 I f 2.1 I f 2.7 I - f 51 f 7 56 I f 1.5 I i 1.8 (j) I f 2.1 (3) I - ; 1; 1. f 18 f 10 f4 f9 140 I f 1.5 I f 1.8 I f 2.2 I - f 5 I f14 185 I f 1.5 I f 1.8 I f 2.2 I - I5 I f17 I -+y+ f 11 f 35 534 I f 1.5 I f 3.5 I f 7.0 I - f15
27、 I f48 I 770 I f 1.5 I f 3.8 I f 8.0 I - f 35 f 110 1490 I f 1.5 I f 4.1 I +. 12.0 I - f 42 I I: 135 I 1730 I f 1.5 I f 4.2 I f 14.0 I - f 48 I f 155 I f 175 &I 2438 I f 1.5 I f 4.5 I f 19.0 I - i 60 I f 220 I 3 150 I f 1.5 I f 9.0 I f 22.0 I - f 350 f 12 I 100 f 13 f 120 , f 14 f 16 I f200 I (I) Th
28、e discriminafion values quoted are relative referred to the minimum attenuation of band-stop filters within the baseband frequency range defined by high-pass and low-pass filters in Table I. (2) New 3 dB-column from CCIT Recommendation G.228. (3) The values accepted at the Final Meeting of Study Gro
29、up 4 were: f 2.0 (55 dB) and (4) New band-stop filter from CCITT Recommendation G.230. (5) The characteristics recommended for the filters 16 kHz to 3150 kHz inclusive are based on inductor-capacitor type filters. Those characteristics recommended for the filters at 4650 kHz and above are based on c
30、rystal-type filters. Optional characteristics are recom- mended for the 3886 kHz fiiter to permit a choice of design between a coil-capacitor type (upper line in table) or crystal-type filter (lower line in table). The design of the receiver selectivity of 3886 kHz should be matched to the characteristic of the crystal-type band-stop filter. It is suggested that in the range from 3150 kHz to 7600 kHz the receiver selectivity should be related to the Characteristics of crystal-type band-sfop filters. f 2.5 (30 dB).
