ITU-R REPORT BT 961-2-1994 Terrestrial Television Broadcasting in Bands Above 2 GHZ《2 GHZ以上的地面电视广播》.pdf

1、-1- Rep. ITU-R BT.961-2 REPORT ITU-R BT.961-2 TERRESTRIAL TELEVISION BROADCASTING IN BANDS ABOVE 2 GHZ (Questions ITU-R 1/11 and ITU-R 49/11) (1982-1986-1994) 1. Introduction Experimental amplitude-modulation terrestrial television broadcasting systems in Band 10 at 12 GHz have been set up in the Fe

2、deral Republic of Germany CCIR, 1974-78a1, in the Netherlands CCIR, 1974-78b1, and in Switzerland CCIR, 1974-78cI for system G, and in Japan for system M CCIR, 1974-78d and e. Further, an operational station for the same broadcasting system has been working in Japan since 1979 CCIR, 1978-82al. The W

3、orld Administrative Radio Conference for the Planning of the Broadcasting-Satellite Service (Geneva, 1977) (WARC BS-77) has established for Regions 1 and 3 a frequency and orbital position Assignment Plan for the broadcasting-satellite service in the 12 GHz band shared with the terrestrial broadcast

4、ing service. The Regional Administrative Radio Conference, Geneva, 1983 has established an analogous Plan for the broadcasting-satellite service in Region 2. An efficient means for the provision of television services to relatively small communities, (for example as an alternative to, or as an exten

5、sion of, cable television networks) is the microwave multipoint video distribution system (MVDS) Yard, 19921. Within Europe, the CEPT has recommended 40.5 - 42.5 GHz as a harmonized frequency band for MVDS CEPT, 19911. In the United Kingdom a performance specification has been produced for 40 GHz MD

6、VS transmission equipment United Kingdom RA, 19931, and propagation studies are being undertaken to develop appropriate planning parameters. 2. Technical characteristics 2.1 Systems using amplitude modulation 2.1.1 Characteristics of the radiated signal Both amplitude modulation and frequency modula

7、tion are applicable to terrestrial television broadcasting in the 12 GHz band. A system of amplitude modulation requires higher transmitting powers but will allow more television channels. Amplitude modulated television signals in the 12 GHz band should conform to the standards given in Recommendati

8、on ITU-R BT.470 so that they can be received by a conventional television receiver equipped with a frequency converter. 2.1.2 Protection ratio The ratio of wanted-to-unwanted signal power at the receiver input is an important factor in planning terrestrial television systems. The protection ratio re

9、quired when considering interference between two amplitude-modulation vestigial-sideband (AM-VSB) television signals is given in Recommendation ITU-R BT.655. The protection ratio between two frequency modulation television signals can be found in Report ITU-R B0.634. of a terrestrial system in the 1

10、2 GHz band, it is necessary to take into account both signal fading and the frequency stability of transmitters. With regard to the latter, an experiment in Japan has shown that it is not practicable to use precision offset techniques for AM-VSB systems in the 12 GHz band CCIR, 1978-82bI. The requir

11、ed ratios are essentially independent of frequency band. However, in applying them to the planning -2- Rep. ITU-R BT.961-2 2.1.3 Equipment characteristics 2.1.3.1 Transmitter Specifications of AM-VSB transmitters for a terrestrial television service in the 12 GHz band can be virtually In order to si

12、mplify the transmitters, the vision carrier could be amplified together with its accompanying sound carrier, but this may cause intermodulation. In Japan, the ratio of sound to vision power has been altered from 1/4 in Bands III, IV and V, to 1/10 in the 12 GHz band in order to reduce the 920 kHz be

13、at between the sound carrier and the colour subcarrier. the same as those in Bands III, IV and V. 2.1.3.2 Receiving equipment In experiments so far reported, the frequency converters used at the receiving points have only to change the frequency from the 12 GHz band to a frequency within Bands IV an

14、d V. The converter has been mounted directly behind the parabolic reflector, giving rise to negligible feeder loss. Experience gained has led to the conclusion that a converter noise figure of 7 to 10 dB can be realized without excessive cost, and that considering transmitting power, converter noise

15、 figure, mounting facilities, beamwidth and influence of wind, an antenna diameter of 40 cm is reasonable. For establishing the standards for terrestrial television broadcasting in the 12 GHz band in Japan, a converter with a noise figure of 10 dB, equipped with an antenna of 40 cm diameter, was ass

16、umed. In practice, converters with noise figures of 6 to 8 dB have been used in Japan. 2.2 Systems using frequency modulation For FM television systems further studies are required. However, some tests CCIR, 1982-861 to determine basic propagation conditions have been carried out in the United State

17、s of America. 2.2.1 Characteristics of the radiated signal Frequency modulation will normally be the preferred analogue modulation method for systems using 40 GHz, taking account of transmitter output power and available bandwidth considerations. Frequency modulated television signals in the 40 GHz

18、band should provide for compatibility with those radiated in the Broadcasting-Satellite Service (BSS) or the Fixed-Satellite Service (FSS) to enable existing indoor receiver units to be used in conjunction with 40 GHz antennas and down-converters. 2.2.2 Protection ratio The protection ratio between

19、two frequency modulated television signals can be found in Recommendation ITU-R B0.792. 2.2.3 Equipment characteristics 2.2.3.1 Transmitters The transmitter parameters for the 40 GHz analogue MVDS service proposed in the United Kingdom are as shown in Table 2. The limits for the spectrum of the modu

20、lated signal, using either IPAL or D2-MAC signal formats, are as shown in Fig. 1. For the United Kingdom 40 GHz FM MVDS service it has been proposed that a 64“ horn will provide an approximately circular coverage area at the desired service availability (when fed from the perimeter). Such antennas a

21、re considered desirable for frequency planning. However, it is likely that omnidirectional antennas may be specified in certain cases. The maximum gain for these types of antenna is shown in Table 3 and the antenna gain reference patterns for the 64“ antenna are shown in Figs. 2 and 3. 2.2.3.2 Recei

22、ving equipment The receiver parameters for the 40 GHz analogue FM MVDS service proposed in the United Kingdom are as shown in Table 4. The positions of the local oscillator within the MVDS spectrum are shown in Fig. 4 and the envisaged 40 GHz channel plan is shown in Table 5. -3- Rep. ITU-R BT.961-2

23、 2.3 Systems using digital modulation It is envisaged that MVDS will be attractive as a delivery medium for digital televisions services, which will benefit from increased spectrum efficiency over analogue systems. Only limited information on the specific application of digital techniques in Bands 1

24、0 and 11 is available, and further studies are required. 3. The minimum power-flux density 3.1 AM systems At frequencies above 1 GHz it is common practice to use the power-flux density, expressed in W/m2, as a measure for the signal strength. The signal strength in this band has been calculated taki

25、ng account of the above considerations and of the necessity of having a figure for the planning of a terrestrial amplitude-modulation broadcasting network in the 12 GHz band. Table 1 gives the characteristic parameters for the calculation of the minimum power-flux densities, derived from the experim

26、ental and operational systems mentioned above. The power-flux density (dB(W/m2) at the receiving point is given by: F = F + 10 log k T B + (S/N)w - 10 log a dB(W/m2) (1) The proposed minimum power-flux densities for a satisfactory grade picture at the receiving antenna range from -85.5 dB(W/m2) to -

27、70.2 dB(W/m2) for amplitude-modulation systems. The differences in the values are due to different assumptions for the picture quality, the receiver noise performance and the receiving antenna gain, as shown in Table 1. A minimum power-flux density of -70 dB(W/Hz systems (Japan) (Switzerland) 2 I -1

28、4 I -70.2 I I (S/N)RF at the edge of the service area when using an antenna with a cosecant vertical pattern producing the same field strength in the entire service area. Corresponds to grade 4.5 of Recommendation lTU-R BT.500. (S/N)RF at receiver input: modulation index m = 1. Noise bandwidth B = 7

29、 MHz. Noise bandwidth B = 6 MHz. (2) (3) (4) (5) (5 5. Effect of interference In planning a terrestrial network, interference can be a factor which determines the required flux density of the wanted signal. Methods of calculating field strength or transmission loss which are of interest for assessin

30、g interference probabilities are indicated in Reports ITU-R PN.562 and ITU-R PN.569. 6. Effects of propagation For the planning of a terrestrial broadcasting system in the 12 GHz band, losses due to diffraction by buildings are of particular importance; consideration may also have to be given to att

31、enuation due to precipitation. Relevant information is given in Report ITU-R PN.562. During investigations in San Francisco using a 20 MHz bandwidth FM system Bentz, 19821 very little diffraction around obstacles or penetration through obstacles - including foliage - was noted. However, in many case

32、s of obstructed transmission paths, it was possible to use a reflection as a better source of the signal. Because of the highly directional beam of the receiving antenna, whether a horn or parabolic dish, it was possible to select a single reflection. For this reason multipath interference was rarel

33、y encountered. Rain attenuation was considerable, as indicated by long- term measurements at fixed locations, and would have to be taken into account in the system design in the form of adequate transmitter power. Based on the parameters of this specific test, satisfactory reception was reported at

34、approximately 70% of the desired target area. -5- Rep. ITU-R BT.961-2 Transmitter output power per channel Frequency stability of transmission (unmodulated) 7. Frequency-sharing With the broadcasting-satellite service Frequency-sharing between the broadcasting-satellite service (BSS) and terrestrial

35、 services is discussed in Report ITU-R B0.631. Frequency-sharing between the BSS and the terrestrial television service in the 12 GHz band can be accomplished by operating terrestrial transmitters in those parts of the band not used by the BSS in the area where the transmitters are situated. It is i

36、mportant from the viewpoint of spectrum utilization to know the factors affecting the required separation between the operating frequencies of both services. In Japan, field and laboratory tests were conducted using Japans medium-scale broadcasting satellite for experimental purposes SE) and terrest

37、rial broadcasting transmitters in the 12 GHz band. The tests have shown that even in the worst case there is a high probability that interference to reception of a broadcasting-satellite service from unwanted signals is not determined by intermodulation in the receiver but by its selectivity. The re

38、ceivers used for the tests were of a type using a diode-mixer converter (see Report ITU-R B0.473). Interference from the BSE to the terrestrial-broadcasting service in a channel overlapping the BSE signal was not observed during the tests CCIR, 1978-82bI. 35 dB Frequency range Signal input at Ist I.

39、F. to reach fm demodulation threshold and to achieve 48 dB weighted S/N 0.95 - 1.95 GHz -60 dBm (Zm=75 Q nominal) b) Indoor unit Maximum tuning error for worst selected channel I I0.25MHz Rejection of adjacent (N+2) odd or even channels I25dB Channel bandwidth Frequency range of modulated UHF output

40、 Characteristics of baseband video output: Bandwidth Group delay error Peapeak output level 26 MHz nominal Channels 32 - 40 25 HZ - 10.5 MHz I2 dB to 8.4 MHz I3 dB to 10.5 MHz 20 d) De-emphasis selectable to Rec.ITU-R F.405-1 or EBU MACPacket specification Tech. 3258 Baseband video and audio output

41、connection European Standard EN5 0049 PERITELEVIS ION - 11 - Rep. ITU-R BT.961-2 odd channel numbers 61 63 TABLE 5 Proposed channel plan for 40 GHz FM MVDS system increasing in even channel numbers increasing in 29.5 MHz steps 29.5 MHz steps 41.42000 62 41.43475 41.44950 64 41.46425 Groups 1 and 2 c

42、hannel plan odd channel numbers 125 127 Channel Group 1 Horizontal Polarization increasing in even channel numbers increasing in 29.5 MHz steps 29.5 MHz steps 42.42000 126 42.43475 42.44950 128 4 2.4 6 4 2 5 Channel Group 2 Vertical Polarization Channel number Nominal Centre Frequency of Channel (GH

43、z) Channel number Nominal Centre Frequency of Channel (GHz) I 1 I 40.53500 I 2 I 40.54975 I I 3 I 40.56450 I 4 I 40.57925 I Groups 3 and 4 channel plan Channel Group 3 Horizontal Polarization Channel Group 4 Vertical Polarization Channel number Nominal Centre Frequency of Channel (GHz) Channel numbe

44、r Nominal Centre Frequency of Channel (GHz) I 65 I 41.53500 I 66 I 4 1.54975 I I 67 I 41.56450 I 68 I 41.57925 I - IL - Rep. ITU-R BT.961-2 References BENTZ, C. 1982 - Experimenting at 12 290 MHz. Broadcast Engineering Spec. Book. CEPT 1991 - Recommendation T/R 52-01 E (1991) - Designation of a harm

45、onized frequency band for Multipoint MOMOURA, T. and KIKUCHI, S. 1979 - SHF terrestrial broadcasting in Japan. IEEE Trans. Broadcasting, Vol. BC- SAITO, T., ITO, S., OHMARU, K., HASEGAWA, T., ISONO, H. and TAKANO, K. 1977 - Propagation United Kingdom RA 19931 - United Kingdom Radiocommunication Agen

46、cy MPT 1550 (1993): Performance Specification for Analogue Multipoint Video Distribution Systems (MVDS) Transmitters and Transmit Antennas Operating in the Frequency Band 40.5 - 42.5 GHz. GHz within the United Kingdom. IBC July 1992. Video Distribution Systems in Europe. 25,4, 147-151. characteristi

47、cs of the terrestrial television waves in the 12 GHz band in urban area. NHK Lab. Note No. 215. YARD, K. 1992 - Developments towards the introduction of a Multipoint Video Distribution Service (MVDS) at 40 CCIR Documents 1974-781: a. 1 U156 (Germany, (Federal Republic of); b. 1 U172 (The Netherlands); c. 11/22 (Switzerland); d. 11/34 (Japan); e. 1 U308 (Japan). 1978-821: a. 11/79 (Japan); b. 1 U247 (Japan). 1982-861: 1 U320 (United States).