ITU-R SF 766-1992 Methods for Determining the Effects of Interference on the Performance and the Availability of Terrestrial Radio-Relay Systems and Systems in the Fixed-Satellite rfer.pdf
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1、CCIR RECMN*7bb 72 W 4855232 0538579 42T Rec. 766 27 SECTION 4/9B: CO-ORDINATION AND INTERFERENCE CALCULATIONS RECOMMENDATION 766 MEXHODS FOR DETERMINING THE EFFECTS OF INTERFERENCE ON THE PERFORMANCE AND THE AVAILABILITY OF TERRESTRIAL RADIO- RELAY SYSTEMS AND SYSTEMS IN THE FIXED-SATELLITE SERVICE
2、(Questions 32/4 and 109/9) (1992) The CCIR, considering that it is necessary to evaluate the effects of interference on the performance and the availability of terrestrial that, in general, the determination of interference criteria requires suitable calculation methods; that calculation methods for
3、 determining interference to FDM-FM systems are fairly well established; that calculation methods for interference to single-channel-per-carrier (SCPC) FM telephony are to be a radio-relay systems and systems in the fixed-satellite service; b) C) i) established; e) f) 8) h need to be established; j
4、formulation, that calculation methods for interference to FM television are to be established; that calculation methods for interference to amplitude modulated (AM) telephony are to be established; that calculation methods for interference to digital transmissions are to be established; that, in fut
5、ure, calculation methods for interference to systems employing new modulation techniques may that it is desirable to provide spectra of signals for determination of interference from the general recommends that the methods described in Annex 1 be used for calculation of interference to FDM-FM system
6、s; that in the absence of more accurate information the methods described in Annex 2 be used provisionally for 1. 2. wanted signais other than FDM-FM. ANNEX I* Calculation methods for the interference of FDM-FM systems Given below is the method of calculation to determine the effects of interference
7、 to the FDM-FM systems in terrestrial radio-relay systems and systems in the fixed-satellite service. * Note from the Director, CCIR - For information, derivation of the formulae and historical development of this Annex are given by References contained in CCIR Report 388 (Dsseldorf, 1990). CCIR REC
8、flN*7bb 92 4855252 05i18580 i145 28 Rec. 766 1. Calculation methods 1.1 General formulation The relationship (this linear relationship is only valid for the lower levels of interference into FDM-FM telephony signals) between baseband interference power in a telephone channel and the carrier-to-inter
9、ference ratio involves the interference reduction factor B (in dB), defined as follows: S/Ni B= lOlogC/I where: S : test signal power in a telephone channel = 1 mW Ni : unweighted interference power in a telephone channel (bandwidth: 3.1 kHz) C : power of the wanted signal carrier (W) i : power of t
10、he interfering signal carrier (W). The weighted interference power Np (pW) is obtained as unweighted power in 1.75 kHz, which gives: 10 log Np = 87.5 - B - 10 log (C/l The interference reduction factor i3 is expressed as: with: r.m.s. test tone deviation (without pre-emphasis) of the wanted signal (
11、kHz) centre-frequency of channel concerned, within the wanted signal baseband (WZ) upper frequency of the wanted signal baseband (kHz) pre-emphasis factor for cetitre-frequency of channel concerned, within the wanted carrier baseband bandwidth of telephone channel (3.1 kJ3z) separation between carri
12、ers of the wanted and interfering signals (kHz) continuous part of the normalized power spectral density of the wanted signal with pre- emphasis (Hz-1) normalized vestigial carrier power of the wanted signal continuous part of the normalized power spectral density of the interfering signal (Hz-1) no
13、rmalized vestigial carrier power of the interfering signal amplitude-frequency response of the wanted signal receiving filter, the origin of the frequencies being the centre frequency of the interfering signai carrier. CCIR RECMN*7bb 72 4855232 0538583 088 Rec. 766 29 The power spectral densities ar
14、e normalized to unity and are assumed to be one-sided (only positive frequencies). The expression of Np in terms of the ratio C/Z is derived from expressions (2) and (3). In order to determine Np, it is necessary to determine: - - the interfering signal spectrum. The expressions of these spectra are
15、 given in 0 2 below and in D 3 of Annex 2. the wanted signal spectrum (analogue telephony), 1.2 Interference from a low-rnodulation-index FDMIFM signal to a high-modulation-index FDM-FM signal This case represents a terrestrial radio-relay system interfering into a system of the fixed-satellite serv
16、ice. The baseband channel which receives the most interference is not easily identified. However, the worst interference condition results when the wanted-to-unwanted carrier frequency separation is equal to, or less than, the top baseband frequency of the wanted signal. The factor B can be determin
17、ed from the following formula: If the modulation index of the wanted signal is greater than 3, the signai spectrum shape is near Gaussian, and formula (7) takes the following form: 7a) The definitions of the parameters in formulae (7) and (7a) have been given in 0 1.1 with the exception of the follo
18、wing: f, : r.m.s. multi-channel deviation of the wanted signal (Hz) LF : load factor, which is less than unity when not in the busy hour; y = (-15 + 10 log Nc)/20 for Ne 2 240 = (-1 + 4 log Nc)/20 for 60 5 Ne 3, the signal spectrum shape is near Gaussian. If the modulation indices of the wanted and
19、interfering signals are greater than 3, formula (7) should be applied to calculate interference, taking into account 0 1.3. In certain special cases, where the interfering signal may be characterized by its ramas. modulation index, and the upper baseband frequency is equal to the wanted signal (i.e.
20、fin, I fm2 = fm) there is the possibility of calculating the. interference function, Du, fo), very simply from the normalized curves of Fig. 1. 10 O 3 - 10 i2 - 20 E 6 2 .CI O -30 N - 40 -50 .- - i - 60 - 70 FIGURE 1 Normalized spectral density of FDM-FM signals Modulation iiidex, 111 The equivalent
21、 modulation index is determined by: m = .: + 41 !h and for this value of tti on the curves in Fig, 1 we find the values f,S(fi) atid fn,Scf2), where: and further: - CCIR RECMN*7bb 92 W 4855212 0538583 950 r- I 1.6 Interference from angle-modulated digitul signals into FDM-FM signals Digital systems
22、using PSK or FSK modulation are classes of angle-modulated systems. Consequently, the interference from these systems into analogue, angle-modulated systems is computed by the convolution integral. However, the spectral densities of digital, angle-modulated signals cannot be easily generalized; a sp
23、ecific spectrum is, however, provided in Q 3.2 of Annex 2. More generalized computation would involve the calculation of the digital spectral density (see Q 3.2 of Annex 2), the calculation of the analogue spectral density, the convolution of the two densities, and the computation of the factor B. I
24、 When a high-modulation-index FDM-FM carrier receives interference from angle-modulated digital signals that occupy a bandwidth small compared with that of the wanted signal, factor B is given roughly by formula (7). If a wanted FDM-FM signal suffers interference from an unwanted PCM-PSK or DPSK-PM
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