1、STD.CEPT ERC REPORT 33-ENGL 3994 D 232b414 0035423 7YT ERC REPORT 33 w EIXODW adiocommunications Committee (ERC) within the European Conkrence of Postai and Telecommunications Administrations (o THE USE OF RADIO FREQUENCIES ABOVE 20 GHz BY FIXED SERVICES AND ENGIOB Bonn, December 1994 STD=CEPT ERC R
2、EPORT 33-ENGL 3994 2326434 0035424 686 Copyright 1994 the European Conference of Postal and Telecommunications Administrations (m ERC REPORT 33 Page 1 THE USE OF RADIO FREQUENCIES ABOVE 20 GBz BY FiXED SERVICES AND ENGIOB ABSTRACT The ever-increasing demand for new communications systems and service
3、s in Europe, as well as the trend towards employing higher data-rate transmission in systems, has resulted in a rapid increase in the demand for spectrum allocations in recent years. Overpopulation of the frequency bands allocated to fixed services has meant that it is becoming increasingly difficul
4、t to accommodate new services in these bands. In order to ease the growing congestion in the frequency bands currently used by fixed service operators, and to provide additional channel capacity for future communications services, preliminary planning work began in Europe around 10 years ago to deve
5、lop the use of the millimetric region of the radio spectrum for future fixed and mobile systems. ETSI defines millimetric frequencies to be those above 20 GHz, and ETS specification work on millimetric systems currently covers a frequency range of 20 - 60 GHz. As a result of the work of ETSI and oth
6、er organisations, a number of frequency bands above 20 GHz are now being used in Europe to provide fixed and mobile communication services, and work is ongoing within ETSI to prepare equipment specifications for these systems. The aim of this report is to consider the use and applications of the rad
7、io spectrum above 20 GHz, and the potential benefits to be gained from operating radio-relay systems in this region of the spectrurr Factors such as millimetrewave propagation, the type of systems currentiy in operation in the 20 - 60 GHz ikequency bands and potential future applications for the mil
8、limetric bands will be considered, in order to highlight the benefits of further utilkiing the spectrum above 20 GHz for fixed seMces and other applications. The role of European administrative and regulatory bodies in developing the use of the millimetric bands will also be considered, along with t
9、he experiences of system operators and equipment manufacturers in providing reliable radio links above 20 Ga. Finally, the cost and availability of components for systems operating in the millimetre bands and the advancements in millimetre-wave technology over recent years will be considered. NB: Th
10、e compatibility issue between FS and EESS between 50.2 and 66 GHz is being studied by CEPT/ERC Working Group - SE. The results of the study may influence the following paragraphs. ERC REPORT 33 Page 2 CONTENTS 1 . BACKGROUND . 3 2 . MILLIMETRE WAVE PROPAGATION 3 2.1 WTRODUCTION 3 2.2 HYDROMETEOR ATT
11、ENUATION . 4 2.2.1 Attenuation by Rain . 4 2.2.2 Attenuation by Fog 5 2.2.3 Attenuation by Snow 5 2.2.4 Attenuation by Atmospheric Gases . 5 2.3 RESEARCHATIES 5 2.3.1 The Work of the UKS RutherfardAppleton Laboratory 5 2.3.1.1 Studies of Hydrometeor Attenuation . 5 2.3.1.2 Investigation into the Sca
12、ttering Effects of Buildings in Urban Areas . “. . 6 2.3.1.3 Studies of Co-polar Attenuation and Cross-polar Discrimination at 55 GHz . 6 2.3.2 Propagation above 20 GHz by France Telecom Research Centre (CNET) 6 2.3.3 Research into propagation above 20 GHz by BT 6 3 . REGULATION AND HARMONISATION OF
13、 THE SPECTRUM ABOVE 20 GHZ . 7 3.1 EUROPEAN REGULATION OF THE MILLIMETRIC BANDS . 7 3.2 EUROPEAN “ISATION OFMILIMETRICUENCIES AND SERVICES . 9 4 . APPLICATIONS OF MILLIMETRE WAVES . 10 4.1 NTRODUCIION 10 4.3 POTENTIAL APPLICATIONS . 12 4.5 MULTIPOINT VIDEO DISTRIBWIION Sym (MVDS) 14 4.6 RACE MBS PRO
14、JECT 15 4.7 DEDICATEDROAD INFRASTRUCTUREFOR VEHELE SAPETYINEUROPE (DRNE) 15 5 .USE OF THE SPECTRUM ABOVE 20 GHZ . 15 5.1 FREQUENCY ALLOCATIONS IN THX MILcBANDs 15 5.2 USE OF THE MILTIUC BANDS IN EUROPE . 16 5.3 RADIO TECHNOLOGY ABOVE 20 GHz 18 5.4 EXPERIENCES OF MILLIMETRIC SY OPERATION 18 5.4.1 23
15、and50 GHz Radio Links in the UKMercury Network . 18 5.4.2 Radio-relay links above 20 GHz in Sweden 19 6 . CONCLUSIONS 19 18 4.2 ADVANTAGES OF USING THE-C BANDS 11 4.4 NETWORK APPLICATIONS 13 18 7 . FUTURE USE OF MILLIMETRIC FREQUENCIES AND REQUIREMENTS FOR FURTHER WORK . 20 7.2 REQUIREMENTS FOR FURT
16、HER WORK 21 8 . REFERENCES 22 7.1 FUTURE USE OF THE MILLlMEiTRIC REGION OFTHE SPEC TRVM 20 ERC REPORT 33 Page 3 1. BACKGROUND Until around 10 years ago, the millimetre-wave region of the radio spectrum was relatively unused, and fixed services tended to be accommodated in frequency bands up to 10 GH
17、z. In the early 1980s, however, factors such as, predicted congestion in the frequency bands allocated to ked services, the large number of new communication services emerging around Europe and the requirement for higher data-rate transmission in networks, ail led radio regulators and operators to c
18、onsider the use of the millimetric region of the spectrum for future fixed and mobile systems. Although the absorption and attenuation of signal energy due to rain, water vapour and oxygen imposes severe constraints on the coverage distance of radio systems operating in the spectrum above 20GHz, the
19、 propagation characteristics in this region of the spectrum are ideal for providing short distance communication 1%. Purthermore, there are a number of advantages to be gained from operating radio systems in the millimetre-wave region of the spectrum, such as the availability of wide bandwidths and
20、the possibility of multiple frequency re-use over very short distances. There are a number of additional advantages to be gained from operating systems in the millimetric region of the spectrum, such as the ability to operate transmission links using compact antennas and equipment, due to the short
21、wavelengths invoved2. The milliietre bands in the spectrum are therefore very well suited to providing short distance connections in communication networks. During the last decade, considerable amounts of time and effort have been invested in developing millimetrewave systems in Europe. Research has
22、 been devoted to developing the technology required to implement millimetrewave systems, as well as to providing sufficient data with which to create propagation prediction models, which can be used to assist network planning and overcome the restraints imposed on system designs due to the high leve
23、l of atmospheric attenuation occurring in the spectrum above 20 GHz. Equipment specifications and protection critena have been produced by European radio authorities in order to regulate the use of the millimetric bands in countries throughout Europe. Channel plans have been produced for these bands
24、 by the -R. Harmonisation of the Frequency Allocation Table in the frequency range 3.4 to 105 GE is undertaken by CEPT, to ensure that national frequency plans, equipment specifications and regulatory constraints do not conflict3. This ensures commonality of equipment standards, frequency management
25、 and system planning throughout Europe. Work is going on to agree European harmonised frequency plans for the spectrum above 20GHZ, in order to standardise the use of these bands by the year 2008. A number of equipment ETS for systems operating above 20 GHz are also now available, to ensure commonal
26、ity of the equipment used in millimetric systems. Work is also ongoing within ETSI to develop an equipment standard for systems operating at 29 GHz. This prETS will shortly be issued for public enquiry. 2. MILLIMETRE WAVE PROPAGATION 2.1 Introduction Signal transmission at frequencies above 20 GHz i
27、s influenced by various meteorological conditions, which impose severe limitations on the line of sight coverage distance of radio systems operating in the miliiietric region of the spectrum4. Absorption and scattering of signal energy by rain, snow, fog, water vapour, oxygen and other gases in the
28、atmosphere all affect the propagation of radio waves at frequencies above 20 GHZ, and these effects must be taken into consideration when designing millimetre-wave systems. STD*CEPT ERC REPORT 33-ENGL 1994 232b414 0015428 221 ERC REPORT 33 Page 4 To ensure that millietric communication systems are a
29、ble to achieve the same degree of availability and performance as systems operating in the lower frequency bands of the spectrum, accurate propagation models are required to estimate the effect of atmospheric attenuation on the performance of the system over specified periods of time. It is therefor
30、e very important for system planning tools, such as propagation prediction models, to be widely available to system designers, so that the probability and severity of signal fading Occumng due to signal attenuation and absorption by hydrometeors and other atmospheric effects can be estimated. Consid
31、erable effort has therefore been devoted in recent years to studying the propagation of millimetre waves, so that accurate attenuation prediction models can be produced to aid the design of millimetric systems. Much of the research has concentrated on quantifying more precisely the effects of rain,
32、since rain is the most dominant attenuation factor at frequencies above 20 GE1. The aim of this research has been to gather sufficient propagation data so that attenuation effects can be predicted probabilistically. These probabilities can then be incorporated into system planning tools, to facilita
33、te the development of future millietre-wave communications systems. A considerable amount of work in this area has been carried out within Europe15v6. A number of ITU-R reports and recommendations have been published containing millimetre-wave propagation data and prediction models, and these are re
34、ferred to in the ETS equipment specifications for millmetric ystems. This Section of the report is devoted to describing the propagation effects that occur in the millmetre-wave region of the radio spectrum, as well as research into these effects that is being carried out in Europe at this time. 2.2
35、 Hydrometeor Attenuation 2.2.1 Attenuation by Rain The theory relating to attenuation and scattering of radio waves by rain is based on the calculation of the attenuation and scattering cross sections of a single raindrop19. In the millimetrewave range of the radio spectrum the shape of raindrops is
36、 important, since the cross-section of the drop is comparable to the wavelength of the radio-wave. For a particular raindrop, the drop shape will depend on its size and the rate at which it is falling. In order to model the effects of rain attenuation and scattering on radio-waves, rainfall is usual
37、ly characterised by drop-size distribution, NO), which is defined as the number of raindrops falling per cubic metre, with drop diameters, D, within a specified range. The drop-size distribution is a function of the rain rate, R which is usually measured in millimetres-per-hour (mm/hr). Attenuation
38、of radio waves by min at millimetre frequencies is therefore dependent on a number of factors relating to the water particles making up the rainfall at a certain time, including the size of the raindrops, the velocity at which the drops are falling, the time of year and the drop-size distribution. T
39、heoretical predictions of attenuation due to rain are often shown graphically, illustrating specific attenuation occurring over a range of frequencies for various intensities of rainfall. A range of curves showing calculated levels of attenuation due to the atmosphere, as well as due to various inte
40、nsities of rainfall, is shown graphically in Figure 1. In order to predict accurately the attenuation of millimetre-waves due to rain, it is necessary to measure the rainfall occurring in a specified geographic area over periods of time, and then to accumulate the data gathered to form statistical m
41、odels of the events that have occurred. The data collected can then be used to form cumulative distributions of the degrees of signal attenuation, rainfall rate, temperature and humidity occurring within a specific geographic area monthly and annually. These distributions can then be compared to ave
42、rage distributions for that particular geographic area, to illustrate when and by how much the measured data exceeds the average distribution for various percentages of time. STD.CEPT ERC REPORT 33-ENGL 1994 2326414 0035429 Lb& - ERC REPORT 33 Page 5 This information can then be used by system plann
43、ers, to estimate averages and extremes of system performance and predict the reliability of a particular communications system under a range of geographic and meteorological conditions. Various statistical models describing the effects of rain and other hydrometeors on the transmission of radiowaves
44、 have been developed in Europe. The most widely accepted rain attenuation models for the planning and design of line-of-sight radio systems are summarised in ITU-R Report 721-2, “Attenuation by hydrometeors, in particular precipitation, and other atmospheric particles“*. 2.2.2 Attenuation by Fog The
45、oretical predictions of the attenuation of millimetre-waves by fog are derived in roughly the same way as for rain. The main difference is that fog consists of a suspended mist of water drops with very small diameters 1.49.19 . Radio wave attenuation by fog is therefore less significant than that of
46、 rain. In general, therefore, if a particular communication system is designed to overcome rain attenuation, then attenuation by fog will have no additional effect on the performance of the system. 2.2.3 Attenuation by Snow Snow and hail consist of a complex mixture of water, air and ice crystals. H
47、ence the attenuation of radio waves due to snow is wnsiderably harder to estimate than that of rain. The problems involved in measuring radiowave attenuation due to snow are made further complicated because the shape of snow and ice crystals is very varied. Hence it is very difficult to create accur
48、ate probability distributions of snow flake sizes and shapes. Experimental data so far indicates that the effect of snow on the propagation of millimetre-waves depends on the consistency of the nowl. Studies have shown that the attenuation of radio waves above 20 GHz in dry snow is less than in rain
49、, for the same precipitation rate. Investigations into wet snow, however, have indicated that the attenuation that occurs is in excess to that of rain. 2.2.4 Attenuation by Atmospheric Gases Attenuation by atmospheric gases at millimetric frequencies occurs because of absorption by oxygen molecules and water vapour in the atmsphere.?*. This effect is highly frequency-dependent, which means that attenuation due to atmospheric absorption is much greater in some frequency bands than in others. A band of very high atmospheric absorption occurs near 60 GHz, for inStan
