CEPT T R 25-03 E-1988 Co-Ordination of Frequencies for the Land Mobile Service in the 80 160 and 460 MHz Bands and the Methods to Be Used for Assessing Interference《80、160和460 MHz频.pdf
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1、 25-03 Page E 1 Recommendation T/R 25-03 (Stockholm 1976) CO-ORDINATION OF FREQUENCIES FOR THE LAND MOBILE SERVICE IN THE 80,160 AND 460 MHz BANDS AND THE METHODS TO BE USED FOR ASSESSING INTERFERENCE Recommendation proposed by “Radiocommunications” Working Group T/WG 3 (R) Text of the Recommendatio
2、n adopted by the “Telecommunications” Commission: “The European Conference of Posts and Telecommunications Administrations, considering (a) that it is necessary to harmonize procedures for the Co-ordination of frequencies for the land mobile service in frontier regions, O O (b) that it is important
3、that a simple method of Co-ordination be established which Administrations will be able to implement as widely as possible, (c) that it is a matter of utmost necessity that the available spectrum be used with maximum efficiency, in particular avoiding according land mobile service radio stations gre
4、ater protection than justified by operating requirements, (d) that exceptionally some stations require increased protection, for example stations of the public land mobile radio telephone service, (e) that in practice it is advantageous both for determining the field strength of the wanted signal an
5、d for determining that of the interfering signal to use the same propagation curves, (f) that it may be very useful to determine a maximum permissible value for the field strength of the interfering signal, (g) that account needs to be taken of the variable nature of propagation phenomena, which dep
6、end on location and (h) that the use of certain selective calling devices can to a certain extent improve the quality of the service by time, eliminating a large amount of interference, recommends that in Co-ordinating frequencies in frontier regions for the land mobile service Administrations shoul
7、d be guided by the following provisions: 1. 2. 3. 4. 5. for determining field strength, the CCIR propagation curves valid for 50% of locations and 50% of the time shall be used in every case, calculations shall be made foliowing the procedure set out in part A of the Annex to this Recommendation, th
8、e parameters contained in part B of the Annex shall be used to determine the need for Co-ordination and for dealing with practical cases of Co-ordination, Administrations shall divide stations into 3 groups: Group 1 : stations requiring an exceptional quality of service and consequently a high level
9、 of protection; Group 2: stations requiring a normal quality of service; Group 3: stations requiring no protection, Administrations shall classify under group 2 the largest possible number of stations not classified under group 3. For this purpose users may, for example, be invited to use, as approp
10、riate, selective calling devices and effective methods of coding so as to reduce the effects of interference in the absence of the wanted signal.” Edition of September 15, 1988 CEPT T/R*25-03*E 8 9 2326414 0012409 bT8 TIR 25-03 E Page 3 O Annex A. CALCULATION OF FIELD STRENGTH 1. PRINCIPLE O The sen
11、sitivity of a receiver is determined by the electromotive force which enables a given value for the output signal to noise ratio to be obtained; if the gain of the antenna and the feed line losses are known, the minimum value Co of the electrical field can be deduced from this. The electrical field
12、produced at a distance by a radio-electrical transmitter of known characteristics is subject to propagation variations and its strength varies with time and according to the location. It is accepted that, according to the laws of probability, its value will follow a normal distribution in dB. In tha
13、t case, if the value of the standard deviation is known, it is possible to determine the median value of the field so as to obtain the value Co with a given probability P. The median value must be where O is the value of the standard deviation and x a coefficient. The relationship between P and x is
14、 given by tables or curves. Given the random nature of the distribution of the field, a service quality may be characterised by the percentage of locations where, in a given zone, the field exceeds the value Co. However, this is inadequate if unwanted transmissions reach the receiver, thus causing i
15、nterference. If reception of the wanted signal is not to be disturbed by the interfering signal, the ratio between their values at any given time must be sufficiently high. The minimum value of this ratio is the protection ratio (R,). Given that the variations in the interfering field obey the same
16、statistical laws as those affecting the wanted field, the ratio between them also varies according to a statistical law of the same kind, in accordance with the following rules: - the median value of the ratio between the wanted field and the interfering signal, expressed in dB, is equal - the value
17、 of the standard deviation for the statisticatdistribution of this ratio is: c, = Co + XG to the difference between the median values of these fields; -0 2 G = JO, + 02b where O, = standard deviation for the wanted field ob = standard deviation for the interfering field Since the nature of the two f
18、ields is the same, G, = ub = O and or = fi In order to arrive at a complete definition of a quality of service it is therefore necessary not only to define the percentage of locations in which the zone to be served must be covered, but also at what percentage of locations protection against interfer
19、ence must be provided, in other words, for what percentage of locations the ratio between the wanted field and the interfering field must be greater than R, in dB. If this probability is fixed at P, the median value for this ratio must be Since C, the median value of the wanted field, has been deter
20、mined by the quality of service, the level of protection enables R, to be determined, thus giving the median value for the interfering field: R, = Ro + X. O B, = C, - R, 2. SENSITIVITY OF RECEIVERS The sensitivity to be taken into account for Co-ordination at frontiers shall be 6 dB in relation to o
21、ne microvolt (e.m.f.). Edition of September 15, 1988 CEPT T/R*25-03*E 8 W 232b4/4 OOL24LO 3LT W TIR 25-03 E Page 4 3. CORRESPONDING VALUE OF THE FIELD Power received CL g;hL p, = 120n 4n which gives If the antenna and the receiver have the same impedance of 75 ohms the power received is therefore PI
22、 = C + G, - 20 log f - 105 e2 e p=-=- 4 Z 300 which gives It follows that P, = E - 145 C = E + 20 log f - G, - 40 Account is taken of mismatching loss caused by using antennas and receivers with different input impedances by making a correction D, and of antenna inefficiency by making a correction A
23、, depending on the type of installation. We then obtain For example, in the case of an antenna h/4 and receiver input impedance of 50 ohms, we can admit from which it follows that This gives the following values for the field C in the different frequency bands: C = E + 20logf - G, - 40 + D +A (6) Gd
24、 = 3dB D = 2dB A= 3dB C = E + 20 log f - 38 80 MHz 160 MHz 460 MHz 6 dB 12 dB 21 dB p, P, c C gi = isotropic gain Gd h = wavelength in metres f = frequency in MHz e E Z = receiver input impedance D = antenna mismatch correction A = antenna efficiency correction = power received in watts = power rece
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