1、Rec. 598-1 1RECOMMENDATION 598-1*FACTORS INFLUENCING THE LIMITS OF AMPLITUDE-MODULATIONSOUND-BROADCASTING COVERAGE IN BAND 6 (MF)(Question 44/10, Study Programme 44F/10)(1982-1990)Rec. 598-1The CCIR,CONSIDERING(a) that amplitude-modulation sound-broadcasting coverage within a given frequency band ca
2、nnot be improvedbeyond a certain limit imposed by physical and technical factors;(b) that improved coverage within a given frequency band is directly related to improved spectrum-utilizationefficiency;(c) that improved spectrum-utilization efficiency can only be achieved by: maximizing the useful ef
3、fects of all transmitters belonging to the network considered; minimizing the interference effects of all transmitters of that network; selecting an appropriate channel width; arranging frequency channels in such a way that interference throughout the network is minimized;(d) that a coverage factor
4、can be defined in a way that it is representative of spectrum-utilization efficiency;(e) that among the factors influencing the limits of broadcasting coverage in band 6 (MF) there are: the minimum usable field strength; the power level in the network; the radio-frequency protection ratios; the dist
5、ance between transmitters sharing the same channel; the channel spacing; the bandwidth of emission; wave propagation and the factors by which propagation is influenced; the channel distribution,UNANIMOUSLY RECOMMENDSthat in frequency planning and for the solution of frequency assignment problems in
6、band 6 (MF) advantageshould be taken of existing knowledge of the interrelations between the various factors influencing the limits ofbroadcasting coverage as they are described in Annex I.The information contained in Annex I was derived from studies based on regular lattices and linear channeldistr
7、ibutions and takes account of omni-directional transmitting antennas only.Practical aspects of MF coverage are given in Annexes II, III, IV and V._*This Recommendation incorporates, in Annexes II to V, the contents of Reports 616-3 (Dubrovnik, 1986) and 461 (Dubrovnik,1986) which are hereby deleted.
8、2 Rec. 598-1ANNEX I1. IntroductionIn the decade preceding the LF/MF Broadcasting Conference for Regions 1 and 3, Geneva, 1974-75, thefactors influencing the limits of sound-broadcasting coverage in band 6 (MF) and their interrelations were extensivelystudied in various countries. The results obtaine
9、d so far permit a deep insight into the complex problem and may evenappear to provide a conclusive answer to it.For obvious reasons, it was assumed in the studies, that because of the limited MF broadcasting band available,no channel would be assigned exclusively to one transmitter throughout the wo
10、rld. The assignment, however, of thesame frequency channel to more than one transmitter supposed to be sufficiently distant from one another inevitably ledto co-channel interference problems.2. Definition of coverage factorIt is first assumed that in an infinitely extended area all transmitters (inf
11、inite in number) are operating on thesame frequency with an equal power p (kW). The distance between neighbouring transmitters is D (km). The highestdensity in this co-channel transmitter network can be obtained when three neighbouring transmitters each form anequilateral triangle of the sidelength
12、D (see Fig. 1), and it is supposed that under these conditions spectrum utilization isalmost optimal. In the presence of noise and interference from the surrounding co-channel stations the coverage rangeR (km) of each individual transmitter depends on: the frequency; the propagation characteristics
13、affecting the field strength of the wanted (Ew) and unwanted (Ei) signals; the minimum usable field strength (Emin); the radio-frequency protection ratios ai.The coverage range is that distance from the wanted transmitter at which field strength of the wantedtransmitter is equal to the usable field
14、strength Eu:Eu= Ew= E 2min+ i = 1n(Ei ai) 2(see Report 945)Note Where field strengths or protection ratios are expressed in dB(V/m) or dB, respectively, the conversion can bemade by means of the following formulae:E _(V/m) = 10E (dB(V/m)20a = 10A (dB)20In the absence of noise or when interference is
15、 by far predominant, the coverage range does not depend on thetransmitter power level, whereas in the opposite case it does.Quite generally, the coverage factor, c, may be defined to be the ratio of the sum of all areas, Sn, covered bythe individual transmitters operating on the same frequency in a
16、very extensive area to the total area, S:c = Sn/ SRec. 598-1 3For the determination of the coverage factor in the theoretical case of a regular network the infinitely extendedarea is subdivided into unit areas, each of which consisting of two equilateral co-channel triangles having one side incommon
17、. Under these conditions each unit area corresponds to just one of the co-channel transmitters (see Fig. 1). Thus,the coverage factor (per channel) may be defined as: either the ratio of the coverage area piR2to the unit area 1/2 3 D2(area coverage):c = 2pi3RD2 100 (%) or the ratio of the population
18、 in the aforementioned two areas (population coverage).The concept of area coverage will be retained for the remainder of Annex I because additional information onpopulation distribution would be required if the concept of population coverage were to be used. However, studies of ageneral nature woul
19、d be difficult for the latter case.The influence of the remaining channels as potential sources of interference (e.g. adjacent channels, secondchannel) should also be considered. In principle, in a unit area, each channel can be assigned to one transmitter only.Depending on whether an even coverage
20、is wanted or not, the channels will either have to be distributed evenly over theunit area in a geometrically regular manner and according to an appropriate (e.g. linear) channel distribution scheme or in the case of irregular coverage will have to be arranged differently, maintaining however, suffi
21、ciently largedistances between transmitters that may cause or suffer interference.The coverage factor c is normally expressed as a percentage. If the area coverage obtainable by means of allthe channels available in band 6 (MF) exceeds unity (100%), this number represents, on the average, the number
22、 ofprogrammes that can be received at any location throughout the whole area under consideration.D01-scFIGURE 1 D01 = 10 cm4 Rec. 598-13. Coverage factor c as a function of the distance D between co-channel transmitters3.1 GeneralTo establish curves showing the dependence of the coverage factor c on
23、 the distance D between co-channeltransmitters under varying conditions for the remaining parameters two different approaches, A and B, were made,however with the following common bases: transmitters of equal power p; ground-wave propagation curves of Recommendation 368; sky-wave propagation curves
24、of Recommendation 435 (type 1) or Report 575, (type 2); radiation constant in all azimuthal directions and at all angles of elevation.The two approaches, A and B, differ with respect to the following parameters:Approach A (results shown in Fig. 2): the power level remains unchanged (p = 1 kW); there
25、 is no noise limitation (Emin= dB); the radio-frequency protection ratio varies, in steps of 5 dB, between the limits A = 20 dB and A = 45 dB; the ground conductivity is = 3 103S/m.Approach B (results shown in Figs. 3 and 4): the power level varies, in steps of 5 dB, between the limits p = 1 kW and
26、p = 1000 kW; the minimum usable field strength is Emin= 60 dB (V/m); the radio-frequency protection ratio values are A = 40, 30 or 27 dB; the ground conductivity values are = 103, 3 103or 102S/m.As a matter of fact, the rigorous and systematic use of directional antennas was also studied for aproach
27、 B. Theresults obtained indicated that no substantial improvement in spectrum utilization efficiency can be expected under suchconditions. This does not mean, however, that no advantage can be gained when directional antennas having horizontalpatterns suitably adapted to the individual interference
28、and coverage problem are used to a large extent (see Annex II).3.2 Results obtained for a plane Earth modelThe curves in Figs. 2, 3 and 4 are given as examples. They show the dependence of the coverage factor c onthe co-channel distance D for a frequency of 1 MHz under varying conditions. The figure
29、s take account of theinterfering co-channel stations on the two nearest hexagons surrounding the wanted transmitter (see Fig. 1). Thus,interference from 18 stations, i.e. 6 stations at the distances D, D 3 or 2 D was included in the computation. Forreasons of symmetry the coverage range was determin
30、ed as the root mean square of the values obtained for twosignificant azimuthal directions: direction towards interfering stations at the distances D and 2 D, direction towards interfering station at the distance 3 D.In particular, Fig. 2 shows the results obtained with approach A and is valid when g
31、round-wave coverage islimited by sky-wave interference and when, in the absence of noise, there is no power dependency. The parameterindicated on the curves is the radio-frequency protection ratio A. Also shown in decibels relative to 1 V/m is thefield E1, of the wanted transmitter at the limit of t
32、he coverage area, for a transmission power of 1 kW with a shortvertical antenna. For instance, the points of intersection on a curve shown by alternating dots and dashes, for E1= 40 dB,and the curves c = f (D), for A = 20 dB derived for interference by sky waves of type 1 (shown by a full line) or o
33、f type 2(shown by dashes), mean that if the co-channel distance is D (abscissae of the points of intersection, i.e. 2800 km or4800 km, respectively) and for a protection ratio A = 20 dB, the field at the limit of the area, where the radio-frequencyprotection ratio is 20 dB, is 0.1 mV/m.Rec. 598-1 5F
34、igure 2 shows that: the coverage factor increases with decreasing values of radio-frequency protection ratio, regardless of the type ofpropagation of the interfering sky-wave signals; the general shape of the curves varies considerably with the type of propagation; for distances beyond about 1500 km
35、 the coverage factor increases when the interfering sky-wave propagation is oftype 1; the coverage factor is largely independent of the co-channel distance with propagation of type 2; there is no pronounced optimum separation between co-channel transmitters as long as there is no limitation bynoise.
36、D02-scFIGURE 2 D02 = 15 cm6 Rec. 598-1The curves of Figs. 2, 3 and 4 presenting the results obtained with approach B show the influence of thepower p (which is the parameter indicated on the curves) in the presence of noise for the three protection-ratio valuesmentioned above. The coverage factor c
37、is represented on a logarithmic scale to facilitate, in each of the Figures, acomparison between the five examples shown: ground-wave service interfered with by ground-wave signals (day-time conditions): group A of curves; ground-wave service interfered with by sky-wave signals (night-time condition
38、s) for the two types of sky-wavepropagation curves under study: groups B1and B2of curves; sky-wave service interfered with by sky-wave signals (night-time conditions) for the two types of sky-wavepropagation curves under study: groups C1and C2of curves.Figures 3 and 4 show that in the presence of no
39、ise: the optimum separation between transmitters using the same channel varies considerably with transmitter power; the optimum separation is completely different under day-time and night-time conditions; the lowest coverage will result when a ground-wave service is interfered with by the sky-wave s
40、ignals of theunwanted transmitters.Moreover, the figures show that at co-channel distances below the optimum distance interference ispredominant so that an increase in power is only of limited use and that a power reduction may result in no loss incoverage.When the sky wave is of type 1 it can, more
41、over, be seen that: the optimum separations between transmitters using the same channel are not very different, under night-timeconditions, both for a ground-wave or a sky-wave service; at least with high-power transmitters (p 30 kW), a sky-wave service would give a coverage similar to that ofground
42、-wave service in the day-time.The results are remarkably different, however, when the sky-wave propagation is of type 2. In this case: the optimum separations, if any, between transmitters using the same channel are noticeably different, under night-time conditions, for a ground-wave and a sky-wave
43、service; the coverage of a sky-wave service would be more or less inferior to that of a ground-wave service in the day-time.Finally, depending on the ground conductivity, the ground-wave coverage during night-time may increase atshort distances with decreasing co-channel distance. This effect result
44、s in higher coverage at lower co-channel distanceswhereas the service ranges decrease to a few kilometres only.The influence on coverage of the radio-frequency protection ratio can be derived from Figs. 3a and 3b,whereas a comparison of Figs. 3b, 4a and 4b permits the influence of the ground conduct
45、ivity to be ascertained.As may be expected an increase in the protection ratio leads to reduced coverage which can, at least partly, becompensated for if the co-channel distance is increased. This loss in coverage is particularly pronounced for the night-time sky-wave service obtained with the curve
46、s of type 2.Similarly, decreasing ground conductivity leads to decreasing ground-wave coverage at both the day and thenight-time. This can be remedied to some extent by a reduction of the co-channel distance, however, under day-lightconditions only. There is, of course, no effect of the ground condu
47、ctivity on sky-wave coverage.3.3 Results obtained for a spherical Earth modelFor interference from sky-wave signals either to a ground-wave or to a sky-wave service, suitable co-channeldistances are of the order of the radius of the Earth, so that the spherical nature of the Earth must be taken into
48、 account.This has been done in Eden and Minne, 1969 where only a sky-wave service is considered and where potentialinterference from the nearest co-channel transmitters, all equally spaced, has been taken into account.An attempt has been made, therefore, to cover a sphere with a network of equilater
49、al spherical triangles. It canbe shown that this can be done by approximating the sphere to a polyhedron. A tetrahedron, octahedron and icosahedronprovide surfaces consisting of 4, 8 and 20 equilateral triangles, respectively. These triangles may be developed on to aplane and it is then possible to apply, without difficulty, a linear channel distribution to this development.Rec. 598-1 7However, when reconstituting the polyhedron, some of the triangles will share sides or a
