1、 Recommendation ITU-R BT.1735-3 (02/2015) Methods for objective reception quality assessment of digital terrestrial television broadcasting signals of System B specified in Recommendation ITU-R BT.1306 BT Series Broadcasting service (television) ii Rec. ITU-R BT.1735-3 Foreword The role of the Radio
2、communication Sector is to ensure the rational, equitable, efficient and economical use of the radio-frequency 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 regu
3、latory and policy functions of the Radiocommunication Sector are performed by World and Regional Radiocommunication 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 IT
4、U-T/ITU-R/ISO/IEC referenced in Annex 1 of Resolution ITU-R 1. Forms to be used for the submission of patent 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/
5、ITU-R/ISO/IEC and the ITU-R patent information database can also be found. Series of ITU-R Recommendations (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 (so
6、und) BT Broadcasting service (television) F Fixed service M Mobile, radiodetermination, amateur and related 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 be
7、tween fixed-satellite and fixed service systems SM Spectrum management SNG Satellite news gathering TF Time 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. Electron
8、ic Publication Geneva, 2015 ITU 2015 All rights reserved. No part of this publication may be reproduced, by any means whatsoever, without written permission of ITU. Rec. ITU-R BT.1735-3 1 RECOMMENDATION ITU-R BT.1735-3 Methods for objective reception quality assessment of digital terrestrial televis
9、ion broadcasting signals of System B specified in Recommendation ITU-R BT.1306 (Question ITU-R 100/6) (2005-2012-2014-2015) Scope The purpose of this Recommendation is to make available methods to assist in quality assessment of the reception of digital terrestrial television broadcasting services f
10、or digital television broadcasting in System B. This Recommendation takes into account relevant ITU-R Recommendations. For the stated purpose, two methods are available, one for multi-frequency network (MFN) and one for single frequency network (SFN). The ITU Radiocommunication Assembly, considering
11、 a) that Recommendation ITU-R SM.1682 Methods for measurements on digital broadcasting signals, specifies in 2.6 the parameters to be measured for coverage evaluation; b) that in Recommendation ITU-R BT.1368 planning parameters such as minimum field strength, protection ratio and relation between mi
12、nimum field strength and receiver voltage input are defined and widely used by administrations; c) that in Recommendation ITU-R P.1546 field strength prediction methods and clutter height for field evaluation are indicated and widely used by administrations; d) that ITU-R established Recommendation
13、ITU-R BT.500 as a methodology for the subjective assessment of the quality of television pictures; e) that, with the introduction of digital television services, it has been observed that subjective assessment of digital television pictures is considered less relevant in quality assessment, as the p
14、erformance of digital technologies do not provide the tolerances experienced with analogue; f) that with the assessment of digital television systems, a critical requirement is that the system is above the threshold; g) that subjective analysis of the picture quality cannot be used as a measure of t
15、he interference level or required protection ratio of digital systems; h) that satisfactory planning of digital systems requires a determination of operation with a sufficient margin above the threshold point of quasi error free (QEF) signal, taking into account time and location variability; i) tha
16、t BER after Viterbi decoding (vBER) is used to determine the threshold of QEF condition; j) that the SFP method is used to determine the threshold of visible errors; k) that there is a need for in-field methodologies to assist administrations and Sector Members to assess the reception quality of dig
17、ital terrestrial television broadcasting (DTTB) coverage, 2 Rec. ITU-R BT.1735-3 recommends 1 that the model to describe the objective reception quality of digital signals based on measured bit error rates (BER) and measured field strength, in accordance with 3 of Annex 1 should be used; 2 that for
18、MFN the quality scale presented in Tables 1 and 2 of 3.1 of Annex 1 should be used; 3 that for SFN the quality scale presented in Table 3 of 3.2 and Table 2 of 3.1 of Annex 1 should be used; 4 that the methods of measurement described in 5, 6 and 7 of Annex 1 should be used. Annex 1 Standard method
19、for objective reception quality assessment for digital television broadcasting signals for System B 1 Objective quality assessment of reception The coverage of a specific area, as determined by a prediction method, should be verified by “in-field” measurements in order to assess prediction results.
20、In terms of quality, by means of a prediction method, it is possible to identify the coverage area using “location probability”. In the same way, the “perceived quality” concept, related to the end user, could be evaluated by means of measurement methods. The digital terrestrial television reception
21、 system works on the basis of a “threshold” and the perceived quality depends on three factors: the access to the service, the time availability and the location availability. Signal level assessment and quality assessment are two different processes within the application of this method. Applicatio
22、n of the reception environment is not relevant in the quality assessment process1. It is assumed that the quality assessment process is based upon the minimum signal level applied for a specific environment within an administrations DTTB planning regime where the derivation of minimum signal level w
23、ould take into account the relevant reception environments. It is also assumed that the DTTB planning regime takes into consideration location availability. If the field strength in a particular reception environment is not achieved according to the planning regime, then the service automatically fa
24、ils to meet the quality assessment requirement. 1 The main application is for fixed reception and steady receiving conditions. Caution should be taken for tropospheric propagation when detectable contributions fall closed or outside GI. For fixed reception and time variable receiving conditions, a s
25、tatistical method has to be applied. Several samples of field strengh and BER have to be taken over a significative period of time and Q values have to be calculated for each sample. A Q value exceeded for more than a specific percentage of time (e.g., 90%) of the samples is the value of the Quality
26、 coverage. Rec. ITU-R BT.1735-3 3 2 Parameters to be evaluated As reported in the current version of Recommendation ITU-R SM.1682 at 2.6, the parameters to be evaluated are: field strength and bit error ratio (BER) after different decoding stages (here it is suggested to get the BER before and after
27、 Viterbi decoding (cBER and vBER). The BER after Viterbi decoding (vBER) is used to determine the threshold of quasi error free (QEF) condition. One more parameter should also be recorded during measurement activities. It is the modulation error ratio (MER) at the transmitting site. MER represents a
28、 synthetic form of constellation analysis. If the MER value at the transmitting site is lower than an established value, e.g. 36 dB2, the measurement activities should be stopped due to possible transmission failure. It has been noted that within some administrations there can be distinct classes of
29、 MER performance where there appear to be three distinct classes of MER performance corresponding to tiers of services for different types of transmission services as follows: Type of service Service performance target (MER) Primary transmission service which may feed secondary transmission services
30、, requires a reference quality suitable for coverage of urban, suburban and rural areas. 35 dB Secondary re-transmission service which is RF fed from the primary transmitter service and reconstituted or re-modulated for re-transmission on a different output channel to the input. 33 dB Tertiary trans
31、lator or on channel repeater service which is RF fed off-air from the primary transmitter service and is IF processed only to transmit on either a different channel or the same channel in the case of on-channel repeater (OCR), is intrinsically a lower power service and has a relatively smaller cover
32、age area and may be fed from a secondary re-transmitter service. 30 dB The Modulation Error Ratio (MER) is defined as the sum of the squares of the magnitude of the ideal symbol vectors in a modulation constellation of M points divided by the sum of the squares of the magnitudes of the symbol vector
33、s. The result, expressed as a power ratio in dB, is given by the equation: = 10 log10 (2+2)=1 (2+2)=1 (dB) where N is the total number of received symbol coordinate pairs (Ij+Ij, Qj+Qj) and N is significantly larger than the number of modulation constellation points, M. The ideal symbol coordinate p
34、air is (Ij, Qj). For each received symbol the error vector is defined as the distance from the ideal position in the constellation to the actual position of the received symbol. The difference is expressed by the vector dj = (Ij, Qj). Figure 1 illustrates a constellation diagram for a 64-QAM modulat
35、ion format (M = 64). Each of the received symbols at the ith point deviated from the ideal position (Ij, Qj) by a distance (Ij, Qj). 2 Minimum MER acceptable is contained in the purchase specification for the transmitters. 4 Rec. ITU-R BT.1735-3 FIGURE 1 Example of a constellation diagram for a 64-Q
36、AM modulation format where the ith point has been enlarged to illustrate the coordinates of the symbol error vector B T . 1 7 3 5 - 0 1ththId ea l v ec t o r( )I Qj jId ea l v ec t o r p o i n tis y mb o liA cq u i re d v ec t o r( + , + )I I Q Qj j j j QQjIjI Ij QjdjdjThe definition of MER does not
37、 assume the use of an equalizer, however the measuring receiver may include a commercial quality equalizer to give more representative results when the signal at the measurement point has linear impairments. When an MER figure is quoted it should be stated whether an equalizer has been used. 3 The o
38、bjective quality scale for System B It is well known that field strength measured at receiving sites varies with location and receiving antenna height. The variability, at fixed power flux-density (pfd), depends on amplitude and phase combination of several paths that reach the receiving antenna. Va
39、riability is more accentuated for continuous wave (CW) signals than wideband signals. The reflected paths can give either possible positive or negative contributions. Negative contributions are connected to the intersymbol interference that happens when the delay of one or more paths is greater than
40、 the guard interval. Possible positive contributions are generated when path delay is lower than the guard interval. The presence of several paths falling into the guard interval frame can result in additive or subtractive contributions depending on implementation of Viterbi soft decision, fixed or
41、moving research window and paths phase. The intrinsic non-linear relationship among Viterbi decoding, protection levels, temporal and spatial dispersion gives as a result a low correlation between field strength and BER, as shown by analysis of thousands of field survey data reported in Report ITU-R
42、 BT.2252. Rec. ITU-R BT.1735-3 5 The quality evaluation system for an analogue signal has been based on both field strength and the five quality (Q) grades subjective assessment scale. Q5 grade corresponds to “excellent”, Q1 grade corresponds to “very bad”. The acceptance threshold is fixed to Q3 gr
43、ade. In a digital environment the situation is quite different and it is important to note the difference between compression video quality evaluation methods and broadcasting coverage quality evaluation. For the compression methods evaluation, such as MPEG, the five-grade assessment scale has been
44、maintained. For the objective of broadcasting reception quality evaluation, it would seem more difficult to maintain a method based on the five-grade scale because of rapid transition from a service to a no service condition. Nevertheless, it is possible again to maintain a five-grade scale if, at e
45、ach grade, the meaning of distance from the transition point is attributed. For a deeper analysis of transition zone, a three-grade scale can be used. Evaluation of the distance from the transition point is very important because the measurement equipment is usually placed before the end users recep
46、tion system, usually composed of an antenna, distribution system and set-top box. Interpretation of digital objective quality reception assessment is not to be confused with interpretation of the analogue quality assessment. Therefore, this Recommendation defines the following reception quality grad
47、es in terms of the margin to failure of the received signal. Grade Q1 Signal level is below minimum planning target. Grade Q2 Signal level is below minimum planning target or margin to failure is too low (reception may be possible but signal is very susceptible to failure). Grade Q3 Signal level and
48、 margin to failure have some margin above minimum planning targets. Grade Q4 Signal level and margin to failure above planning targets. Grade Q5 No measurable defects can be reasonably detected. 3.1 Multi-frequency network (MFN) For MFN fixed reception, Table 1 should be used. TABLE 13 DTTB MFN sign
49、al quality scale BER Field strength vBER SFP QEF 100 E SFP QEF SFP QEF Q4 curve vBER Q4 curve and vBER Q5 curve vBER Q5 curve E 2 1 0-4QEFCas e E 2 1 0-4Cas e E Exx4.2 Table 2 scale interpretation Q2 read on the first horizontal line of Table 2 means that the field strength is lower than the minimum value assigned in the planning procedure. In such cases, no protection against interference can be guaranteed. Its interpretation is given in Fig. 2A above. Q2 read on the second horizontal line of T
