1、 Rec. ITU-R SF.1486 1 RECOMMENDATION ITU-R SF.1486*SHARING METHODOLOGY BETWEEN FIXED WIRELESS ACCESS SYSTEMS IN THE FIXED SERVICE AND VERY SMALL APERTURE TERMINALS IN THE FIXED-SATELLITE SERVICE IN THE 3 400-3 700 MHz BAND (Questions ITU-R 255/4 and ITU-R 227/9) (2000) Rec. ITU-R SF.1486 The ITU Rad
2、iocommunication Assembly, considering a) that the frequency band 3 400-3 700 MHz is allocated worldwide on a primary basis to the fixed service (FS) and the fixed-satellite service (FSS); b) that this band is in use by the FSS, particularly by systems using very small aperture terminals (VSATs); c)
3、that this band is used for terrestrial point-to-multipoint (P-MP) systems operating in the FS for providing fixed wireless access (FWA) and that this use is growing rapidly in many countries; d) that in ITU Regions 2 and 3 the band 3 400-3 600 MHz is also allocated to the radiolocation service on a
4、primary basis by RR No. S5.433; e) that there is a need to protect co-primary services and to assess further the sharing conditions between FWA systems and these services, noting a) that there is interest in harmonized use of FWA systems in this band; b) that co-frequency sharing between VSAT and P-
5、MP systems may be difficult for VSATs operating at low elevation angles; c) that some FWA systems are capable of using a range of frequencies, but in some administrations only part of the 3 400-3 700 MHz band may be available; d) Recommendation ITU-R F.1488 on frequency block arrangements, for FWA s
6、ystems in the range 3 400-3 800 MHz, recommends 1 that to facilitate sharing between VSAT earth stations in the FSS and FWA stations in the FS in the band 3 400-3 700 MHz, the methodology as outlined in Annex 1 should be used; 2 that to facilitate substantial frequency sharing within the coordinatio
7、n distance, administrations are encouraged to adopt precautions during the planning and deployment of such systems, taking into account the interference mitigation methods described in Annex 2, and in particular those for the installation at the VSAT and P-MP central and terminal stations, including
8、 judicious location of antennas to exploit natural and man-made features or the use of diffraction screens close to the VSAT antennas (see Note 1). NOTE 1 Co-frequency sharing between such systems depends to a considerable extent on the usage of this band by the two services, especially on the densi
9、ty of deployment, on geographical and other factors. _ *This Recommendation should be brought to the attention of Radiocommunication Study Group 3. 2 Rec. ITU-R SF.1486 ANNEX 1 Methodology for calculating separation distances for sharing in the 3 400-3 700 MHz range between FSS VSATs and P-MP FWA sy
10、stems 1 Introduction Generally it is acknowledged that the 3.5 GHz range is suitable for P-MP FWA systems. For FSS systems the range 3 400-3 700 MHz is commonly referred to as extended C-band. The characteristics of typical VSAT and (TDMA based) P-MP FWA systems in this band are given in Tables 1 an
11、d 2. The two modes of possible concern are: a) interference from P-MP central station (CS) and/or terminal station (TS) into the FSS earth station (VSAT) receiver; b) interference from the FSS spacecraft into the P-MP CS and/or TS receivers. The methodology addressed in this Annex is for interferenc
12、e mode a), and makes certain general assumptions regarding system characteristics and propagation conditions. Other methodologies employing the actual system parameters and path loss specific to the case under study may provide a more precise separation distance. Interference mode b) is currently ad
13、dressed by the power flux-density (pfd) requirements of Article S21 of the RR, but may require future studies. 1.1 Interference criteria It is considered that interference to the FSS terminal is significant when the victim receiver (VSAT) is subjected to an interference level equivalent to a degrada
14、tion of the thermal noise floor by 0.4 dB, corresponding to an interference level 10 dB below the receiver thermal noise floor for more than 20% of any month (see Recommendation ITU-R SF.558). 2 Sharing methodology 2.1 System parameters P-MP FWA system parameters used for calculations are shown in T
15、able 1. The FWA example described here uses TDMA, but generally the calculations for other FWA technologies may be considered similar in this context (see also Recommendation ITU-R. IS.847). The technology is designed for wireless access for the delivery of telephony and data services to businesses
16、and residential users. Typical VSAT parameters for this band are given in Table 2. The antennas used in 3 400-3 700 MHz VSATs and those used in FWA CSs and TSs, are not sufficiently large to afford substantial off-beam rejection; side-lobe discrimination levels are modest due to the apertures involv
17、ed. Nevertheless the type of VSAT antenna typically used for this band is of parabolic reflector type with good offset horn type feed. However, practical FWA TS and CS antennas are predominately of planar design, of relatively lower efficiency and side-lobe performance. Terrestrial P-MP FWA systems
18、normally feature air-side traffic concentration, which from a RF viewpoint may be considered deployed in a manner similar to that of terrestrial mobile cellular, that is in a contiguous cellular arrangement using frequency reuse. 2.2 FWA TS interference into VSAT station The example P-MP FWA system
19、occupies the frequencies 3 475-3 492 MHz (CS to TS) and 3 425-3 442 MHz (TS to CS). Because the e.i.r.p. of the TSs is higher than that of the CS, as well as their greater number and distribution and hence the greater likelihood that the TS will be directed towards the VSAT station (downlink band),
20、it is appropriate to calculate the interference from the TS. From Table 1, the e.i.r.p. from the FWA TS = 27 + 18 30 = 15 dBW. The TS directional antenna typically has a nominal beamwidth of 20 (at 3 dB). Rec. ITU-R SF.1486 3 TABLE 1 P-MP FWA system parameters TABLE 2 Typical VSAT system parameters
21、The interference level depends upon the FWA TS transmit output power, antenna gain, antenna height and the direction of the antenna main beam. The FWA TS interference can be determined as a function of the separation distance, d, and the off-axis angles of the VSAT () and FWA TS () for various assum
22、ptions regarding the digital modulation techniques for the VSAT and FWA systems, side-lobe envelope, power level of the FWA TS carrier, centre frequency offset between carriers, required protection ratio, and the amount of shielding of the VSAT stations. Transmission frequency band (TS to CS) (MHz)
23、3 425-3 442 Reception frequency band (CS to TS) (MHz) 3 475-3 492 Channel spacing (kHz) 307.2 Access technique TDMA Duplex spacing (MHz) 50 or 100 Number of frequency channels 48 Modulation /4 DQPSK Traffic channel bit rate/time slot (kbit/s) 32 CS(1)transmit power (dBm) 29 CS antenna gain (dBi) 10
24、(omnidirectional), 12 (tri-sector) Receiver sensitivity (dBm) 102 TS(2)transmit power, maximum (dBm) 27 TS antenna gain (dBi) 18 TS feeder loss (dB) 0 TS height (m) 10 (1)CS: P-MP FWA central (base) station. (2)TS: terminal (subscriber or remote) station. Frequency band (GHz) 3.4-3.7 Transmit rate (
25、kbit/s) 64 Modulation 2-PSK FEC rate 1/2 Channel bandwidth (kHz) 153.6 Antenna diameter (m) 1.8/2.4 Antenna gain (dBi) 35.7/38.2 Noise temperature (K) 114.8 Tx e.i.r.p. (maximum) (dBW) 38 Receiver sensitivity (dBm) 126.1 Height of VSAT station (m) 10 4 Rec. ITU-R SF.1486 The total interference power
26、, I, from the FWA TS at the VSAT input to the antenna, is given by: I = e.i.r.p.FWA() LFWA(d ) + GVS() R F (1) where: a) e.i.r.p.FWA(): off-axis e.i.r.p. from the FWA TS transmitter (dBW) = P + Gmax 2.5 103(D /)2for 0 4.8 for 1.8 m and 3.6 for 2.4 m. d) R: the isolation from the site shielding. One
27、study found that up to 40 dB of isolation may be obtained by providing physical or natural shielding at the VSAT stations. However, this may not be achievable at all earth station sites, so we illustrate here the results of 20, 30 and 40 dB shielding. e) F: centre frequency offset factor. Depending
28、upon the FWA frequency plan, it may be possible to select a VSAT carrier centre frequency which is completely outside of the assigned bandwidth of an interfering FWA carrier. In this example, we assume 0 dB frequency offset improvement factor, the worst case. Rec. ITU-R SF.1486 5 2.3 Required protec
29、tion distance The required protection distance, d, can be found from: 20 log (d) = C/I C + P + (sidelobe pattern in equation (2) 92.5 20 log ( f ) 18.5 + 32 25 log () R for 48 and 48 (5) where: C/I: required protection ratio for the VSAT downlink. C is based on the assumed values for C/N correspondi
30、ng to: clear-sky BER 1 1010 99.96% availability 10% noise budget allocation for FWA interference. It is assumed that the required clear-sky C/N will be reduced by 0.4 dB due to the interference (see Recommenda-tion ITU-R SF.558). From the link budget for the VSAT with 1.8 m antenna (64 kbit/s downli
31、nk with 2-PSK, 1/2 rate FEC), C/I = 10 + 5.7 = 15.7 dB C = C/N + 10 log (k TsB) = 5.7 + (228.6 + 20.6 + 51.9) = 150.4 dBW From equation (5): 20 log (d) = 15.7 + 150.4 3 + (sidelobe pattern in equation (2) 92.5 20 log ( f ) 18.5 + 32 25 log R = 73.2 + 18 0.0267 2 25 log R for 0 17.6 = 73.2 + 9.7 25 l
32、og R for 17.6 30.6 = 73.2 + 46.9 25 log 25 log Rfor 30.6 48 These equations are valid over the range 4.8 48. Figure 1 indicates the required separation distances, derived according to this methodology, between the FWA TSs and the VSAT stations, based on the following systems parameters: FWA terminal
33、 station height: 10 m VSAT elevation angle: 20 FWA system characteristics: as per 2.1 VSAT system characteristics: as per 2.1 Additional interference attenuation due to the site shielding isolation at the VSAT terminal: 20, 30 and 40 dB It should be noted that in some cases the FWA TS units may be s
34、ited higher than the VSAT and require considerable antenna downtilt. In these cases the separation distances will be increased equivalent to a corresponding reduction in the VSAT elevation angle. 2.4 FWA CS interference into VSAT station The FWA CS, despite having an e.i.r.p. some 5 dB lower than th
35、at of the TS, is usually located higher to clear the local clutter, has an antenna with wide sectoral coverage, and a higher probability of activity than the TS end. Similar analysis is required for sharing between the FWA CS and VSATs, and care is needed in selecting an appropriate propagation mode
36、l (including duct type fading). 6 Rec. ITU-R SF.1486 1486-011 3 5 7 9 11 13 15 17 19 21 23 25 27 29 31 33 354030201005060708090Requiredseparationdistance,d(km)FWA TS off-axis angle (degrees)FIGURE 1Required separation distances(20 elevation angle)Shield, R = 20Shield, R = 30Shield, R = 40FIGURE 1486
37、-01 2.5 Site shielding To provide insight into the practicality of affording shielding isolation in a range about 30 dB, Appendix 1 addresses the possible isolation calculated in accordance with Recommendation ITU-R P.526. The advantages of mounting the VSAT antenna closer to the ground can be appre
38、ciated, together with typical isolation values for diffraction edge to VSAT spacings that would be consistent with mounting near to, say, a one-story building wall, etc. APPENDIX 1 TO ANNEX 1 Examples of shielding isolation attainable by suitable measures at the VSAT To effect tolerable separation d
39、istances, use normally needs to be made of additional diffraction or other losses in the vicinity of the VSAT. For analysis a single edge diffraction can be taken to approximate the case of a building, tree grove or similar which is not too close (see Fig. 2). Clearly the diffraction source should b
40、e clear of the Fresnel zone. For guidance, at this frequency this can be taken as extending in a cone some 9 m out from the VSAT reflector dish to a diameter of some 3.2 m and then of this same diameter out to at least 17 m from the antenna. The calculated sensitivity of the diffraction loss with tr
41、ansmitter/edge distance, d1may readily be shown to be negligible for all practical cases here. Predicted diffraction losses for a notional single edge model calculated and summarized within the examples studied here are in the range 2-33 dB; this covers plausible situations corresponding to values f
42、or p of 5 m, spacings d2of 5 to 20 m and heights dvof 1 to 6 m. Rec. ITU-R SF.1486 7 The TS units are generally seldom sited higher than around 10 m. A common situation is that of exposed roof-top mounting for a VSAT, and the effect of this rather than the more desirable siting at ground level prote
43、cted by suitable shielding can be approximately 33 dB, as calculated in accordance with Recommendation ITU-R P.526. 1486-02pd1d2dvFIGURE 2Edge diffraction lossFIGURE 1486-02 ANNEX 2 Interference mitigation methods for the shared deployment of FSS VSATs and FWA terrestrial systems The following are s
44、uggested as an initial basis, where satellite elevation angles may permit co-location in the same geographical area as described in Annex 1 (see Note 1): VSATs, wherever possible, should be sited so as to maximize shielding from possible FWA interferers; VSATs and P-MP FWA stations should not be sit
45、ed higher than is necessary for the application; where practicable, FWA TSs should generally be sited such as to reduce rear radiation, for example by mounting against walls, below roof lines, etc. and by avoiding reflections back in the direction of the VSAT; when deploying such FS and FSS systems,
46、 economical use should be made of available terrain, i.e. depressions, natural screening to increase obstructive/diffraction losses; if no natural screening exists use should be made of artificial obstructions such as judicious siting of systems amongst buildings, etc.; in some cases it may be possi
47、ble to tailor the pattern of the VSAT antenna feeds to provide greater interference rejection; advantage may be taken in some cases by use of more directional FWA TS or CS antennas. NOTE 1 Although it is possible to exploit orthogonal polarization as an inter-sector and/or inter-cell discriminant within the FWA systems (typically some 5 dB), it is not possible to use this feature to minimize the interference into the VSAT due to the widespread use of circular polarization in the space-to-Earth link for these FSS systems.
