1、CCIR RECPlN*364-5 92 4855232 053930B 2T5 = Rec. 364-5 43 RECOMMENDATION 364-5* PREFERRED FREQUENCIES AND BANDWIDTHS FOR MANNED AND UNMANNED NEAR-EARTH RESEARCH SATELLUES (Question 132/7) (1963- 1966- 1970- 1978- 1986- 1992) The CCIR, considering a) missions are determined by propagation factors and
2、technical considerations; that suitable operating frequencies and required radio-frequency bandwidths for near-Earth space research b) that two-way communication is required for many near-Earth missions, and is vital for manned missions; C) conditions; that requirements for telecommunication reliabi
3、lity must be satisfied during periods of adverse atmospheric d) that it is practical and desirable to effect telecommunication functions on a single link, e) desirable; that to effect precision tracking, a pair of coherently related Earth-to-space and space-to-Earth frequencies is 0 space-to-Earth f
4、requencies should be separated by at least 7%; that for sUnultaneous transmidreceive operations involving a single antenna, the paired Earth-to-space and g) growth and development of near-Earth investigations in the space research service; that space-to-space and EarWspace relay satellite telecommun
5、ications are necessary to accommodate the h) with power flux-density limits or to guard against multipath and/or interference effects, that particular modulation and channel coding techniques may be required for some links in order to comply recommends 1. purpose of the link and to the feasibility o
6、f sharing, in the preferred frequency ranges listed in Table 1; that frequency bands for near-Earth missions in the space research service be located, with due regard to the 2. that the widths of the allocated bands at preferred frequencies satisfy the individual link bandwidth requirements listed i
7、n Table 2 in order to provide for present and future near-Earth telecommunications in multi- spacecraft, multi-mission systems, within the space research service. * This Recommendation should be brought to the attention of Study Groups 1,4,7,8,9, 10 and 11. 44 - _ - - CCIR RECMN*364-5 92 m YB55212 0
8、519309 131 Rec. 364-5 ANNEX 1* Procedure for the selection of frequency bands preferred for transmission to and from manned and unmanned spacecraft for near-Earth space research 1. Background - propagation effects This Annex discusses the procedure used for the selection of frequencies preferred for
9、 near-Earth missions, based upon propagation and technical considerations within the range of 100 MHz-350 GHz. The link performance is critically dependent upon the propagation conditions which are determined primarily by atmospheric gases and by precipitation. Parameters which model these effects a
10、re derived from Study Group 5 texts. Typical values of attenuation and sky noise have been obtained for clear-sky conditions and for rain rates of 20,50, 100 and 140 mm/h for elevation angles of 5“ and 20“. Ionospheric effects arise due to the interaction of the transmitted radio wave, the Earths fr
11、ee electron density, which varies as a function of geomagnetic latitude, diurnal cycle, yearly and solar cycle, etc., and the Earths magnetic fields. Ionospheric effects above 10 GHz are generally small and not considered significant. In the absence of precipitation, tropospheric effects are unlikel
12、y to produce serious fading in space telecommunications systems at frequencies below about 10 GHz. Signal attenuation due to absorption by molecular oxygen and water vapour and due to absorption and scattering by rain can severely affect link performance and therefore the selection of frequencies. 2
13、. Technical and operational considerations equipment factors. Technical considerations may be divided into two categories, namely mission requirements and hardware or 2.1 Mission frequency support requ iremen 13 2.1.1 Telecommand and maintenance telemetering The basic requirement of any mission is i
14、ts safety and success. In order that this requirement be met, the telecommand and maintenance telemetry link must function with the spacecraft in any orientation. As this can only be achieved through the use of a broad-beam, omni-type antenna aboard the spacecraft, the use of such an antenna must be
15、 considered when selecting frequencies. Telecommand bandwidths of 10-50 kHz are adequate .for most missions, although more sophisticated spacecraft may require link bandwidths of the order of 500 kHz or more. Maintenance telemetry link bandwidths range from several kilohertz to several hundred kiloh
16、ertz. 2.1.2 Mission telemetry For many missions, telemetry data are gathered and stored for play-back to Earth. For some of these missions, there may only be a single opportunity for the spacecraft to transmit the recorded data; these missions must therefore be capable of operating under all weather
17、 conditions. For missions which do not need to operate under such constraints, a frequency may be selected where data rate can be maximized for clear-sky conditions. Link bandwidths depend on the complexity and sophistication of the spacecraft. For direct spacecraft-to- Earth station links, bandwidt
18、hs of 100 k?Iz to 100 MHz can be expected. Bandwidths for relay satellite space-to-Earth links presently range from 225 to 650 MHz; however, this is expected to increase to above 1 GHz to meet future requirements. * Note from the Director, CCIR - Report 984 (Dsseldorf, 1990) was used in the preparat
19、ion of this Annex. _I_- CCIR RECMN*3bY-5 92 = 4855232 0539330 953 - Rec. 364-5 45 Space-to-space link bandwidths presently range from about 5 to 225 MHz for direct user satellite to relay satellite communications. Inter-relay satellite bandwidths will be considerably wider, possibly greater than 1 G
20、Hz. 2.1.3 Tracking Near-Earth space research involves various methods for determining spacecraft orbital information. For interferometer tracking, consideration of factors such as a good omnidirectional antenna on a spacecraft, transmitter efficiency, and earth-station antenna beamwidth, usually fav
21、ours a frequency below 1 GHz. More elaborate moving antenna interferometers have been built for frequencies greater than 5 GE, but atmospheric attenuation and noise usually limit their performance at frequencies greater than 6 GHz. Typical bandwidths range from several hundred hertz to several kiloh
22、ertz. Range and range-rate systems which must operate with the minimum of disturbances from ionospheric and trans-atmospheric effects are in the 1-8 GHz range for precision tracking systems. The main factor which dictates the maximum bandwidth needed per one-way channel is the range resolution requi
23、red. Range resolutions of the order of metres can be obtained by using appropriate modulation with bandwidths of about 1-3 MHk. Radar tracking is also employed although atmospheric attenuation usuaily limits the use of frequencies above about 6 GHz for tracking by primary radar systems. For many of
24、these systems, a bandwidth in the range of 1-10 MJ3z is usually sufficient. Bilateration ranging is designed to supply precise information on the location of a relay satellite so that its movement can be taken into account when determining the orbital parameters of user spacecraft via the relay sate
25、llite. Typical links must be weather independent, and have bandwidths of about 5 to 6 ME. 2.2 Equipment factors Equipment factors which have an effect on link performance and whose characteristics depend on frequency to some extent are transmitter power, antenna gain (for a fixed-size antenna) and t
26、he receiver noise temperature. Of these three, the antenna gain is a function of the square of the frequency, whereas the transmit power and receiver noise are indirectly coupled to the frequency of operation. Their performance is therefore considered uniform over a wide frequency range. The existen
27、ce of proven space equipment and systems must also be considered in the selection of frequency bands to provide operational consistency. Because of practical limits of diplexers, Earth-to-space and space-to-Earth pairs of frequencies should be separated by at least 7% to allow simultaneous trammithe
28、ceive operations using a single antenna. 3. Link performance I In this Annex, the impact of propagation effects on the signal strength and system noise in a basic link equation has been considered, and an index of link performance, determined as the ratio of received signal power to noise spectral-d
29、ensity (P, /No), has been established as the criterion for frequency selection. The link analyses which follow are based upon a fixed diameter earth-station antenna, and cover both a fixed diameter and a fixed beamwidth space-station antenna. The fixed-diameter space station antenna is included to a
30、ccount for situations where a large antenna is employed on the spacecraft, and there are no pointing limitations. The fixed beamwidth case is included to account for situations where antenna pointing accuracy determines the minimum beamwidth, or where an antenna must provide wide coverage to permit
31、communication without regard to spacecraft orientation as in the case of an emergency telemetry or command link. CCIR RECMN*3bY-5 92 w Y855212 0519311 9T 46 Rec. 364-5 In the analyses, the effects of precipitation are considered only for frequencies below about 22 GHz. The effects of precipitation a
32、bove 22 GHz are not considered because even low rain rates can seriously degrade communications on trans-atmospheric links. Therefore only clear weather usage is assumed above 22 GHz. The results apply to an elevation angle of 5 which represents a “worst case” situation. Maximum data rate capability
33、 is obtained by using the frequency bands where Pr/No is a maximum for the weather conditions and space-station antenna limitations considered. A concise presentation of preferred frequency bands is shown in Table 1 and is obtained from the normalized Pr/No curves given in this Recommendation. The g
34、eneral width of the bands was determined by noting the frequencies corresponding to the levels approximately 1 dB below the peaks of the curves. A high rain rate was assumed when determining the width of all-weather frequency bands in Table 1 in order that the results be applicable worldwide. Bands
35、outside this range may be suitable for areas of lower rain rates. 3.1 Calculation of link performance as a function offrequency The index of link performance, received power-to-noise spectral density ratio, is given by the basic link equation: where: P, : received power (W) No : noise spectral densi
36、ty (W/Hz) Pt : transmitted power (W) Gt : transmitting antenna gain Ls : free-space loss La : transmission loss due to attenuation in the clear atmosphere Lr : transmission loss due to rain attenuation Gr : receiving antenna gain (dBi) k : Boltzmanns constant (JK) T : total system noise temperature
37、(K). Assuming no waveguide loss Tis given by: T = Tr i- Ts i- Tg where: Tr : receiver noise temperature (K) Ts : sky contribution (due to atmospheric and precipitation effects) to antenna noise temperature (K) Tg : ground contribution to antenna noise temperature (K). By isolating the frequency-depe
38、ndent terms in equation (l), the equation may, for a fixed distance between space and earth station, be written as follows: Case I: Earth and space-station antenna diameters are fixed: dB CCIR RECMN*364-5 72 m 4855232 0539312 726 m Rec. 364-5 47 Case 2: Earth-station antenna diameter is fixed, space
39、-station antenna beamwidth is fixed: dB (3) - pr = ci + lolog= 1 NO where: C and Cl are constant in equations (2) and (3) respectively and expressed in dB and the terms in the brackets are the frequency-dependent terms. Any change in the value of the constant wil merely raise or lower the PJNo curve
40、s, the overall shape of the curves will remain unchanged. 3.2 Application to near-Earth space research mksions Assumed system and receiver noise temperatures for space and earth stations are shown in Figs. 1 and 2 respectively. The noise temperatures are depicted as a step function because of the as
41、sumption that the receiver noise temperature will not change significantly over its frequency of operation, but rather remain fairly constant over the operating frequency ranges for which it is designed. FIGURE 1 Assumed satellite system noise temperature 2 O00 ?5 +8 5 1500 E - LI a c B 1000 w .* 50
42、0 LI c 2 v1 O 0.1 0.25 0.5 1 10 20 30 40 50 60 70 80 90 100 200 300 350 Frequency (GHz) FIGURE 2 Assumed earth-station receiver noise temperature 300 - 250 2 v 2 200 c! E C 150 I LI P . c LI o g 100 .- 50 V 0.1 0.2 0.3 0.6 1 10 15 20 30 40 50 60 70 80 90 100 150 200 300 350 Frequency (GHz Note 1 - T
43、he values in Figs. 1 and 2 are derived from a number of technical references. They are typical of existing equipments in bands below about 20 GHz and represent anticipated developments in bands above 20 GHz. -. O - 10 h m 2 ! 5 Q E -20 % a = a -30 5 2 - 40 - 50 FIGURE 3 Normalized Earth-to-space lin
44、k performance. Space station antenna diameter fixed - - - _ _ CCIR RECNN*364-5 92 4855232 0539333 662 48 Rec. 364-5 Using the above data together with the relevant propagation data from Study Group 5 and the formulae derived in 0 3.1, a set of normalized link performance values was computed for bidi
45、rectional propagation through the atmosphere and for the two cases of antenna restrictions. These normalized iink performance values are plotted in Figs. 3 to 6 for the frequency range 0.1-22 GHz, and in Figs. 7 to 10 for the frequency range 22-350 GHz. 4. Discussion and conclusions In each of Figs.
46、 3 to 6, a set of parametric curves is shown for precipitation conditions with rain rates of 20, 50,100 and 140 mm/h and for clear-sky conditions. From these figures, it can be seen that rain has a pronounced effect on the optimum range of frequencies, shortening and shifting the optimum range to lo
47、wer frequencies for higher rain rates. For countries located in regions of high rain rate, the choice of suitable frequencies is critical if they are to maintain a high quality of performance despite adverse weather conditions. For the frequency range 22-50 GHz, Figs. 7 to 10 show a series of normal
48、ized link performance curves for clear-sky conditions only. The important features of the link performance curves are the locations of the maxima and the effect of the weather on the optimum frequency range. The optimum frequency range was determined by noting those frequencies on either side of a c
49、urve maximum, which correspond to a link performance value of approximately 1 dB below that of the maximum. A decrease of the order of 1 dB below a curve maximum was considered sufficient to represent a relatively flat portion of the curve about its maximum. -_ 10 2 5 1 2 Frequency (GHz) 5 Curves A: rain rate = 20 mm/h B: rain rate = 50 mm/h C: rain rate = 100 mm/h D: rain rate = 140 mm/h S: clear sky 10 2 3 CCIR REC!N*364-5 92 4855232 0539314 5T9 W Rec. 364-5 FIGURE 4 Normalized Earth-to-space link performance. Space station antenna beamwidth fixed .i 2
