1、 Rec. ITU-R SM.337-6 1 RECOMMENDATION ITU-R SM.337-6 Frequency and distance separations (1948-1951-1953-1963-1970-1974-1990-1992-1997-2007-2008) Scope This Recommendation provides the procedures for calculating distance and frequency separations for an acceptable interference level. The ITU Radiocom
2、munication Assembly, considering a) that, in the more usual cases, the primary factors which determine appropriate frequency or distance separation criteria include: the signal power and spectral distribution required by the receiver; the power and spectral distribution of the interfering signals an
3、d noise intercepted by the receiver; the distance dependence of the transmission losses of the radio equipments; b) that transmitters, in general, emit radiations outside the frequency bandwidth necessarily occupied by the emission; c) that many factors are involved, among which are the properties o
4、f the transmission medium (which are variable in character and difficult to determine), the characteristics of the receiver and, for aural reception, the discriminating properties of the human ear; d) that trade-offs in either frequency or distance separations of the radio equipment are possible, re
5、commends 1 that the frequency-distance (FD) separations of radio equipment should be calculated by the following method: 1.1 determine the power and spectral distribution of the signal intercepted by the receiver; 1.2 determine the power and spectral distribution of the interfering signals and noise
6、 intercepted by the receiver; 1.3 determine the interactive effects among wanted signals, interference and receiver characteristics for various frequency or distance separations by using the basic equations given in Annex 1 along with, if necessary, simple approximations to the integral expressions
7、and the concept described in Annex 2; 1.4 determine, from these data, the degree of frequency or distance separation that will provide the required grade of service and the required service probability. Account should be taken of the fluctuating nature both of the signal and of the interference, and
8、, whenever appropriate, the discriminating properties of the listener or viewer; 2 Rec. ITU-R SM.337-6 1.5 determine the appropriate ITU-R propagation model to be used; 2 that, at every stage of the calculation, comparison should be made, as far as possible, with data obtained under controlled repre
9、sentative operating conditions, especially in connection with the final figure arrived at for the frequency or distance separation among radio equipment. Annex 1 Basic equations This Annex describes basic equations which quantify the interactive effects among wanted signals, interference, and receiv
10、er characteristics for various frequencies and FD separations. The measures are: frequency dependent rejection (FDR) which is a measure of the rejection produced by the receiver selectivity curve on an unwanted transmitter emission spectra; FD which is a measure of the minimum distance separation th
11、at is required between a victim receiver and an interferer as a function of the difference between their tuned frequencies; relative radio-frequency protection ratio A (see Recommendation ITU-R BS.560) which is the difference (dB) between the protection ratio when the carriers of the wanted and unwa
12、nted transmitters have a frequency difference of f and the protection ratio when the carriers of these transmitters have the same frequency. The FD and FDR are measures of the interference coupling mechanism between interferer and receiver and are the basic solutions required for many interference e
13、valuations. They aid in the solution of co-channel frequency sharing and adjacent band or channel interference problems by providing estimates of the minimum frequency and distance separation criteria between interferer and receiver which are required for acceptable receiver performance. The interfe
14、rence level at the receiver is a function of the gains and losses the interference signal will incur between the source and the receiver and is expressed by: I = Pt+ Gt+ Gr Lb(d) FDR(f ) dBW (1) where: Pt: interferer transmitter power (dB) Gt: gain of interferer antenna in direction of receiver (dBi
15、) Gr: gain of receiver antenna in direction of interferer (dBi) Lb (d ) : basic transmission loss for a separation distance d between interferer and receiver (dB) (see Recommendation ITU-R P.341) and ff+fHfPffPfFDRd )( )(d)(log10)(200=dB (2) Rec. ITU-R SM.337-6 3 where: P( f ) : power spectral densi
16、ty of the interfering signal equivalent intermediate frequency (IF) H( f ) : frequency response of the receiver f = ft frwhere: ft: interferer timed frequency r: receiver tuned frequency. The FDR can be divided into two terms, the on-tune rejection (OTR) and the off-frequency rejection (OFR), the ad
17、ditional rejection which results from off-tuning interferer and receiver. FDR(f ) = OTR + OFR(f ) dB (3) where: =020d )( )(d)(log10ffHfPffPOTR dB (4) +=0202d)()(d)()(log10)(fffHfPffHfPfOFR dB (5) The on-tune rejection also called the correction factor, can often be approximated by: TRRTBBBBKOTR log
18、(6) where: BR: interfered receiver 3 dB bandwidth (Hz) BT: interferer transmitter 3 dB bandwidth (Hz) K = 20 for non-coherent signals K = 20 for pulse signals. 4 Rec. ITU-R SM.337-6 Annex 2 Methodology to determine frequency and distance separation for radio systems 1 Introduction It is well known t
19、hat FD rules are an important part of the frequency management process in most radio services. In channelized services, these rules take the following form: co-channel transmitters must be separated by at least d0(km), the adjacent channel transmitters must be separated by at least d1(km), transmitt
20、ers separated by two channels must be at least d2(km) away and so on. For older technologies the FD rules are usually well known by now. However, the introduction of new technologies raises the question: what kind of FD rules a spectrum manager should apply when new and old systems occupy the same f
21、requency band? The methodology that is required to determine FD separation rules between both similar and dissimilar systems is given below. 2 Methodology The development of a new FD rule requires the computation of the level of interference at the input of the victim receiver, and also requires the
22、 definition of an acceptable interference criterion. 2.1 Interference computation This depends on two primary factors: a spectral factor and a spatial factor. The spectral factor depends on the spectral characteristics of the interfering transmitter and the frequency response of the victim receiver.
23、 For computational purposes one must have accurate knowledge of the power spectral density of the interfering signal which depends on factors such as the underlying modulation technique and the bandwidth of the information signal for analogue systems and the transmitted data rate in the case of digi
24、tal systems. As far as the victim receiver is concerned, one must know the equivalent IF frequency response characteristics of the receiver. Manufacturers specifications such as the 6 dB and the 40 dB bandwidth of the IF stage may be used as a basis for modeling the receivers IF frequency response.
25、The spectral factor is represented by the off-channel-rejection factor OCR(f ), which is defined by the following relationship: +=ffPfffHfPfd)(d)()(log10)(OCR2dB (7) where: P( f ) : power spectral density of the interfering signal in (W/Hz) H( f ) : equivalent IF frequency response of the victim rec
26、eiver f : frequency separation between the victim receiver and the interfering transmitter. Note that equation (7) is not different from equation (2), even though the lower limits of integration are different. Rec. ITU-R SM.337-6 5 It is evident from equation (7) that OCR(f ) is strongly dependent o
27、n the extent of overlapping between the receiver passband and the power spectrum of the interfering signal. As f increases, the extent of overlapping diminishes, thus resulting in lower interference power or, equivalently, higher values for OCR(f ). The spatial factor of the methodology is concerned
28、 with the computation of the distance related signal attenuation; it is closely related to the propagation model to be used and to the statistical distribution of the interfering signal at the front end of the victim receiver. An appropriate propagation model as recommended by ITU-R should be used.
29、The propagation model to be used with this procedure is of course dependent on the system configuration as well as the operating frequency band and the geographical environment surrounding the service area and the system bandwidth. 2.2 Interference criterion This usually is a simple relationship bas
30、ed on which one judges the interference as harmful or tolerable. Such a criterion should ideally be tied to the level of performance degradation the victim receiver may be capable of tolerating. This however is not practical at least from the point of view that there are many different types of syst
31、ems and technologies that may not be capable of dealing with interference the same way. A more generic criterion based on a protection ratio (dB) is therefore adopted. The interference will be considered tolerable if the following inequality is satisfied: idPP (8) where: Pd: desired signal level (dB
32、W) Pi: interfering signal level (dBW) : protection ratio (dB). 2.3 Procedure The procedure for developing a FD separation rule can now be summarized as follows: Step 1: Determine the desired signal level Pd(dBW) at the victim receiver front end. Step 2: Calculate the resulting level of interference
33、at the victim receivers front end using the formula: ()fLGPPprti+= OCR (9) where: Pt: equivalent isotropically radiated power (e.i.r.p.) of the interfering transmitter (dBW) Gr: gain of the receiving antenna with respect to an isotropic antenna (dBi) Lp: propagation path loss OCR (f ) : off-channel-
34、rejection factor for a frequency separation f as expressed by equation (7). The OCR values used in this paper are assumed. The purpose of this Recommendation is to present the methodology rather than the development of OCR values. 6 Rec. ITU-R SM.337-6 Step 3: Substitute Pdand Piof steps 1 and 2 abo
35、ve into equation (8) to derive or numerically compute a relationship between the frequency separation f and the distance separation d such that the interference is considered tolerable. 2.4 Alternative procedure In the real environment, the received signal at the victim receiver experiences shadow f
36、ading which is represented by log-normal distribution. To compensate for this fading effect, the received signal level should be higher than the sensitivity level. An alternative procedure for determining a required isolation between the victim and the interferer, reflecting the shadowing effect, is
37、 presented as follows: Step 1: Calculate the required isolation in order to prevent the interferer from causing radio interference to the victim using the formula: )110log(10)(OCR)(10/+=NminrtIfPGPL (10) where: LI: isolation required between the interferer and the victim to ensure tolerable interfer
38、ence (dB) Pt: equivalent isotropic radiated power (e.i.r.p.) of the interfering transmitter (dBW) Gr: gain of the receiving antenna with respect to an isotropic antenna (dBi) Pmin: minimum desired signal level (dBW) : protection ratio (dB) OCR(f): off-channel-rejection factor for a frequency separat
39、ion f as expressed by equation (7) N: log-normal fading margin (dB). Step 2: Employing an appropriate ITU-R propagation model to equation (10) gives the frequency separation f and the distance separation d at which the interference can be tolerable. 2.5 Consideration of antenna isolation When severa
40、l different radio systems are co-located, the antenna isolation concept can be brought into consideration in the calculation of interference between them. Figure 1 gives generic examples of antenna arrangements which illustrate the isolations of horizontal (HI), vertical (VI) and slant (SI) antenna
41、configurations. The antenna isolation is mainly dependent on distance separation and wavelength, , (m). The distance separation between two antennas is the distance from the centre of interferer antenna to that of victim receiver antenna1. Antenna-to-antenna isolations are normally expressed in term
42、s of dB of attenuation. 1In the practical situation the distance between the interferer antenna and victim receiver antenna may be measured between the nearest edges of both antenna systems for convenience. Rec. ITU-R SM.337-6 7 The isolation between two dipole antennas can be approximately computed
43、 by using the following equations (10a), (10b) and (10c): )/log(2022HI(dB) + x (10a) )/log(4028VI(dB) + y (10b) HI/2HI)(VISI(dB) + (10c) where (rad) is tan1(y/x), x is the horizontal distance, and y is the vertical distance. The equations are applicable when x is greater than 10 and y is greater tha
44、n . These isolations obtained from equations (10a), (10b) and (10c) can be substituted for the basic transmission loss (Lb (d ) of equation (1) or the propagation path loss (Lp) of equation (9) when two stations are co-located. FIGURE 1 Antenna isolation in horizontal, vertical and slant direction 8
45、 Rec. ITU-R SM.337-6 3 Application to land mobile radio systems To demonstrate the methodology described above, an example using two dissimilar land mobile radio (LMR) systems is described in this section. The two systems considered could be digital or analogue with TDMA or FDMA access techniques. O
46、ur computations are based on spectral emission masks and certain receiver selectivity requirements and as such the results are independent of any particular modulation techniques that may be used by either of the two systems. In this example, the receiver selectivity was assumed to have similar char
47、acteristics to the spectral emission masks, a consideration which is expected to be the case for digital systems. The assumptions made for the two systems are summarized in Tables 1 and 2: TABLE 1 Assumed parameters for the example Minimum desired signal level, Pmin145 dBW Required protection ratio,
48、 18 dB Base station antenna height, hb75 m Operating frequency, f 450 MHz Base station e.i.r.p. 20 dBW Base receiving antenna gain 0 dBi Equivalent relative permittivity, 30 Equivalent conductivity, 102S/m In LMR systems there are four modes of interference: base-to-base, base-to-mobile, mobile-to-b
49、ase and mobile-to-mobile. In simplex systems, where the base and the mobiles transmit on the same frequency, all four modes of interference are present. On the other hand, in duplex systems the mobiles and the base transmit on different frequencies and hence only the base-to-mobile and the mobile-to-base modes need to be considered. For the distance of separation analysis purpose however, we only need to look at the worst case; the interference case
