1、 Recommendation ITU-R SM.1875-2 (08/2014) DVB-T coverage measurements and verification of planning criteria SM Series Spectrum management ii Rec. ITU-R SM.1875-2 Foreword The role of the Radiocommunication Sector is to ensure the rational, equitable, efficient and economical use of the radio-frequen
2、cy spectrum by all radiocommunication services, including satellite services, and carry out studies without limit of frequency range on the basis of which Recommendations are adopted. The regulatory and policy functions of the Radiocommunication Sector are performed by World and Regional Radiocommun
3、ication Conferences and Radiocommunication Assemblies supported by Study Groups. Policy on Intellectual Property Right (IPR) ITU-R policy on IPR is described in the Common Patent Policy for ITU-T/ITU-R/ISO/IEC referenced in Annex 1 of Resolution ITU-R 1. Forms to be used for the submission of patent
4、 statements and licensing declarations by patent holders are available from http:/www.itu.int/ITU-R/go/patents/en where the Guidelines for Implementation of the Common Patent Policy for ITU-T/ITU-R/ISO/IEC and the ITU-R patent information database can also be found. Series of ITU-R Recommendations (
5、Also available online at http:/www.itu.int/publ/R-REC/en) Series Title BO Satellite delivery BR Recording for production, archival and play-out; film for television BS Broadcasting service (sound) BT Broadcasting service (television) F Fixed service M Mobile, radiodetermination, amateur and related
6、satellite services P Radiowave propagation RA Radio astronomy RS Remote sensing systems S Fixed-satellite service SA Space applications and meteorology SF Frequency sharing and coordination between fixed-satellite and fixed service systems SM Spectrum management SNG Satellite news gathering TF Time
7、signals and frequency standards emissions V Vocabulary and related subjects Note: This ITU-R Recommendation was approved in English under the procedure detailed in Resolution ITU-R 1. Electronic Publication Geneva, 2014 ITU 2014 All rights reserved. No part of this publication may be reproduced, by
8、any means whatsoever, without written permission of ITU. Rec. ITU-R SM.1875-2 1 RECOMMENDATION ITU-R SM.1875-2 DVB-T coverage measurements and verification of planning criteria (2010-2013-2014) Scope This Recommendation describes methods for DVB-T coverage measurements and their evaluation. Keywords
9、 Coverage measurements, DVB-T, monitoring, planning Abbreviations/Glossary BER Bit error ratio C/N Carrier-to-noise ratio C/I Carrier-to-interference ratio also referred to as protection ratio in this Recommendation FEC Forward error correction DVB-T Terrestrial Digital Video Broadcasting GE06 Agree
10、ment Regional Agreement and its annexes together with its associated Plans as drawn up by the Regional Radiocommunication Conference 2006 for the planning of the digital terrestrial broadcasting service in Region 1 (parts of Region 1 situated to the west of meridian 170 E and to the north of paralle
11、l 40 S, except the territories of Mongolia) and in the Islamic Republic of Iran, in the frequency bands 174-230 MHz and 470-862 MHz (Geneva, 2006) MFN Multi-frequency network QEF Quasi-error-free QoS Quality of service RF Radio frequency SFN Single frequency network Related ITU Recommendations Recom
12、mendations ITU-R BT.419, ITU-R P.1546 and ITU-R P.1812. NOTE In every case the latest edition of the Recommendation/Reports in force should be used. The ITU Radiocommunication Assembly, considering a) that the GE06 Agreement defines the receiving conditions, necessary signal-to-noise ratios and mini
13、mum field strength values for the reception of DVB-T; b) that monitoring services have to measure the coverage of DVB-T transmitters and networks to verify compliance with coverage predictions used in the planning process or to assess the receiving condition at a location where interference is repor
14、ted, recommends that the method described in Annex 1 together with corrections described in Annex 2 should be used for DVB-T coverage measurements and verification of planning criteria. 2 Rec. ITU-R SM.1875-2 Annex 1 1 Introduction Monitoring services have to measure the coverage of broadcast networ
15、ks for different purposes: To verify predictions of computerized tools used for the planning of the network. To verify compliance with license conditions if part of the broadcast license is that a certain area, percentage of an area or percentage of the population is covered by the broadcast service
16、. To assess the receiving conditions at certain locations where interference is reported. Due to certain circumstances and principles inherent in the reception of digitally modulated systems, the coverage of digital terrestrial television networks has to be measured different from analogue networks.
17、 This Recommendation describes the measurement principles, procedure and necessary equipment for fixed and mobile coverage measurements of DVB-T transmitters and networks. However, much of the information provided is also valid for measurements of other digital terrestrial broadcasting systems. Meas
18、urements of the quality of service (QoS) and measurements to verify technical transmitter parameters are not covered in this Recommendation. 2 Terms and definitions for the purpose of this Recommendation The following terms and definitions are used throughout this Recommendation. In case of generall
19、y known terms, their definitions are interpreted and specialized only to coverage issues related to the DVB-T system throughout this Recommendation. 2.1 Antenna diagram for fixed reception The antenna diagram characterizes the relative output level of an antenna when the signal is received under dif
20、ferent angles. Recommendation ITU-R BT.419 defines the directivity of a standard antenna used for fixed broadcast reception as in Fig. 1. To reproduce the actual receiving conditions of a customer installation, measurements for fixed coverage should be made with a measurement antenna having the same
21、 directivity. Rec. ITU-R SM.1875-2 3 FIGURE 1 Relative antenna directivity for fixed broadcast reception Mobile coverage measurements should be made with omnidirectional measurement antennas. The maximum relative loss in any direction is 3 dB. 2.2 Antenna factor The antenna factor is used to calcula
22、te the field strength from the antenna output level. Because it is usually specified in dB, the calculation formula is as follows: E = U + K dB(V/m) where: E: electrical field strength at the antenna (dB(V/m) U: measured antenna output voltage (dB(V) K: antenna factor (dB(1/m). The antenna factor de
23、pends on frequency and gain according to the following formula: K = 20 Log(f ) Gi 29.774 (for 50 Ohm systems) where: f: frequency (MHz) Gi: antenna gain relative to an isotropic radiator (dB) K: antenna factor (dB(1/m). Figure 2 shows the antenna factor of the standard antenna used for fixed broadca
24、st reception according to Recommendation ITU-R BT.419 in the direction of the main beam which is the same as the antenna used for measurements of fixed reception. S M .18 75 -01-200A ngl e ( de gr e e s )B a nd IB a nd I I IB a nd I V / VAttenuation(dB)-4-6-8- 10- 12- 14- 16- 1820 40 60 80 100 120 1
25、40 160 1804 Rec. ITU-R SM.1875-2 FIGURE 2 Antenna factor for fixed broadcast reception S M .18 75 -0218170F r e que nc y ( M H z )Antennafactor(dB)171615141312111098270 370 470 570 670 770 8702.3 Assignment area An assignment area is a coverage area, realized by one or more transmitters where all pa
26、rameters relevant for the planning process such as transmitter power, antenna height and directivity, are known. The assignment area is limited by interference from sources outside this area. 2.4 Bit error ratio Generally, the bit error ratio (BER) is the number of false bits divided by the total nu
27、mber of bits transmitted during a given time. It is a measure of the receiving quality of a digital signal. Because DVB-T uses inner and outer error protection, it is possible to determine the BER after the Viterbi and after the Reed-Solomon decoder off the air. A BER of 104 after the Viterbi decode
28、r is regarded sufficient for DVB-T reception. 2.5 C/N See protection ratio. 2.6 The term “covered” A certain area is regarded as being “covered” by DVB-T, when the median field strength for the particular receiving situation in a specified height above ground (often 10 m) and the protection ratio re
29、ach or exceed the values given in the relevant planning documents (e.g. the GE06 Agreement). The fact of a certain area to be covered or not is a result of the calculation process done with a coverage prediction tool that assumes defined conditions and/or values for: the receiving condition (e.g. fi
30、xed or portable reception); Rec. ITU-R SM.1875-2 5 the field strength loss with distance due to topography and morphology; the receiver model (e.g. sensitivity and selectivity); the receiving antenna (height, gain and directivity); the reception channel (Gaussian, Rice or Rayleigh). Attached to the
31、attribute “covered” is also a certain probability in time and location. Using planning tools, the coverage area is calculated for this probability (e.g. 50% of the time and 50% of the locations). It can therefore not be assumed that DVB-T reception with a standard receiver is possible at every singl
32、e location inside the area defined as being covered. Verification of coverage cannot be done with a standard DVB-T receiver by simply checking whether it works at a certain location. Instead, the technical parameters such as field strength have to be measured, preferably under the same receiving con
33、ditions as assumed in the planning tool. 2.7 The term “reception possible” The DVB-T reception is regarded possible if at a certain location a standard receiver can correct (nearly) all errors in 99% of the time and produce a picture. The BER after the Viterbi decoder should be below 2*104. The actu
34、al necessary field strength for a successful DVB-T reception depends on: the DVB-T system variant; the receiver performance; the antenna gain; the type of reception channel (Gaussian, Rice or Rayleigh). Verification of a general reception possibility can be done by measurement of the following param
35、eters: median receiving field strength; median interfering field strength; type of reception channel. Alternatively, a reception test with a standard DVB-T receiver can be done. Experience from these tests shows that, for portable reception, sometimes higher field strengths than median values given
36、in the relevant agreements are necessary. 2.8 Coverage prediction Coverage prediction is a procedure to calculate the geographical area inside which reception of the service is possible. It is based on transmitter parameters, terrain and propagation models and is done with computerized tools. The re
37、sult represents a defined location and time probability. In the GE06 Agreement, the minimum field strength values for DVB-T to be reached at the coverage border are valid in 10 m height above ground and assume fixed reception with a directional antenna according to Figs 1 and 2. They are medians of
38、the minimum equivalent field strength values and depend on the system variant and the reception channel. 2.9 Crest factor The crest factor is the ratio between the peak and r.m.s. level value of an RF emission. Usually, it is given in dB and is then the difference between peak and r.m.s. levels (dB)
39、. 6 Rec. ITU-R SM.1875-2 2.10 Guard interval To make use of all incoming signal components from co-channel transmissions and reflections that arrive at different times at the receiver, and to prevent interference of two subsequent symbols, each symbol is transmitted longer as would be necessary to d
40、ecode the signal. The additional time is called guard interval. The actual decoding process inside the receiver can start after the guard interval has passed. The length of the guard interval depends on the system variant and the maximum distance between neighbouring transmitters in a single frequen
41、cy network (SFN). 2.11 Height loss This is the field strength difference in 10 m above ground (reference for DVB-T planning) and the receiving field strength at an antenna being closer to the ground (e.g. 1.5 m for portable reception). Its value is statistical. 2.12 Interfering field strength The in
42、terfering field strength is produced by signals from transmitters on the same frequency that are not part of the investigated SFN or transmitter, by signals from neighbour channel transmitters and by signals from transmitters of the investigated SFN that are received outside the guard interval. It i
43、s formed by the vector addition of the directly received signal component from the interferer and reflections due to obstructions in the field. It varies with the location of the receiver, and because the reflecting obstacles may not be stationary, it also varies with time. The actual interfering fi
44、eld strength inside a certain area can therefore only be described statistically by a median value and a standard deviation. Practical measurement of the interfering field strength can be difficult, especially if its level is well below the wanted signal level and both interferer and wanted transmit
45、ter are received from the same direction. Possible ways of improving the measurement conditions for the interfering field strength are: Use of a measurement antenna with a high directivity to separate wanted and interfering signals by changing the azimuth. Measurement of a signal on a different freq
46、uency that is emitted from the same location as the interfering transmitter. In this case, corrections for different attenuation loss from the frequency difference and for different transmitter power on the measurement frequency may have to be applied. Switch off the wanted transmitter or SFN during
47、 the measurement. When the interfering signal is more than 30 dB below the wanted field strength, its influence on the reception of the wanted transmitter or SFN can be neglected. 2.13 Median The median is calculated from a total of many samples (e.g. a series of measured field strengths) so that 50
48、% of all samples exceed the median value, the other 50% of the samples are lower. The median is a statistical value and specifies a 50% confidence or probability. Example: The field strength is measured at 100 locations inside a certain area. The median of all measurement values is 42 dB(V/m). This
49、means that the probability of the actual field strength at any location in this area being at least 42 dB(V/m) is 50%. The advantage of using the median when specifying field strength statistically is that single values far off do not influence the result as much as the average or mean. Rec. ITU-R SM.1875-2 7 2.14 Minimum median field strength (Emed) This is the median field strength based on calculations at a certain percentage of the locations inside a receiving area. In relevant planning texts such as t
