1、 Report ITU-R BT.2209(10/2010)Calculation model for SFN receptionand reference receiver characteristicsof ISDB-T systemBT SeriesBroadcasting service(television)ii Rep. ITU-R BT.2209 Foreword The role of the Radiocommunication Sector is to ensure the rational, equitable, efficient and economical use
2、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 regulatory and policy functions of the Radiocommunication Sector are performed by World and
3、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 ITU-T/ITU-R/ISO/IEC referenced in Annex 1 of Resolution ITU-R 1. Forms to be used for the
4、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/ITU-R/ISO/IEC and the ITU-R patent information database can also be found. Series of ITU
5、-R Reports (Also available online at http:/www.itu.int/publ/R-REP/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
6、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 between fixed-satellite and fixed service systems SM Spectrum management Note: This ITU-R Report w
7、as approved in English by the Study Group under the procedure detailed in Resolution ITU-R 1. Electronic Publication Geneva, 2011 ITU 2011 All rights reserved. No part of this publication may be reproduced, by any means whatsoever, without written permission of ITU. Rep. ITU-R BT.2209 1 REPORT ITU-R
8、 BT.2209 Calculation model for SFN reception and reference receiver characteristics of ISDB-T system (2010) TABLE OF CONTENTS Page Summary 2 Chapter I SFN with delays less than guard interval duration . 2 1 In the case of a single SFN wave 2 1.1 Mathematical equations used in this text 3 1.2 Increas
9、e in the required CNR . 4 1.3 Noise characteristics in receivers 6 1.4 Conditions that gives SFN failure . 8 1.5 SFN non-failure conditions . 10 1.6 Location variation . 11 1.7 Location correlation 12 2 In the case of multiple SFN waves . 12 Chapter II SFN with delays exceeding guard interval durati
10、on 14 3 In the case of SFNs with delays exceeding the guard interval duration . 14 3.1 SFN wave with a large delay exceeding guard interval duration . 14 3.2 SFN with relatively small delays (but larger than guard interval duration) . 14 3.3 Aliasing affects of scattered pilot signals . 16 3.4 Calcu
11、lation method for the required DUR 19 3.5 Setting of FFT window . 22 3.6 Protection ratios for analogue to digital interference . 25 3.7 Receiver characteristics to be specified 25 3.8 GI Mask characteristics of receivers on the market 26 Chapter III Fading . 26 Appendix 1 Fading margin for less tha
12、n 1% of time (Kumadas law) 28 2 Rep. ITU-R BT.2209 Summary This Report provides detailed considerations on receiver characteristics under single frequency network (SFN) conditions for ISDB-T system. It introduces new technical parameters that dominate receiver performances, in addition to the conven
13、tional planning parameters. The new parameters are amplitude proportional noise (APN), FFT window setting margin and interpolation filter characteristics used for reference carrier recovery. Using these parameters, the overall receiver characteristics can be expressed by a single parameter called gu
14、ard interval mask characteristics, which is useful in estimating whether or not the signal is received correctly. Furthermore, the Report gives a reference receiver characteristic that would be applied in frequency planning and/or network design of ISDB-T based broadcasting systems. The calculation
15、method for SFN reception and the reference receiver characteristics have been established in ARIB TR-B14, which is successfully applied in planning and designing of broadcasting networks in Japan. It is shown that SFN does not work unconditionally, but works well only when the reception signals are
16、kept under certain conditions in terms of reception voltages, DURs, delays between main and SFN signals and so on. Chapter I SFN with delays less than guard interval duration First we will derive the condition that gives single frequency network (SFN) failure when a single SFN wave exists. Then, we
17、will discuss about the conditions when multiple SFN waves exist. Also we will give some considerations on the receiver characteristics that are necessary to estimate the area of failure. We call SFN with delays less than guard interval duration as “inner-GI SFN” in short. 1 In the case of a single S
18、FN wave The received signal exhibits ripples in frequency response when the desired signal is received with SFN waves. In this case, the bit error rates (BER) of the OFDM carriers positioned at peaks in frequency response becomes better, because the input signal levels are high for those carriers. O
19、n the other hand, the BER of the carriers positioned at dips in frequency response become worse because the input levels are low. We can estimate the occurrence of SFN failure by calculating the BERs for every carrier and summing up them to check whether or not the total BER is worse than the requir
20、ed value. Figure 1 shows an example of frequency response of received signal. Figure 1a) is the case where the desired signal is just at the level that gives the required carrier-to-noise ratios (CNR). In this example, we assume the total BER being worse than the required value, as there are many ca
21、rriers of which BER is worse than the reference value. If we increase the levels of both desired and SFN signals, the number of carriers having worse BER is decreased, and then the signal is correctly received, as shown in Fig. 1b). The SFN failure takes place depending not only on the desired to un
22、desired ratios (DUR) but also on the levels of the received signal itself. Rep. ITU-R BT.2209 3 FIGURE 1 Example of received signal 1.1 Mathematical equations used in this text The relationship between BER and CNR are to be following: for QPSK ()BERErfcNCNCNCErfcBERppaapp=22and21211(1) for 16-QAM =B
23、ERErfcNCNCNCErfcBERppaapp3810and101831(2) for 64-QAM =BERErfcNCNCNCErfcBERppaapp72442and4212471(3) where: Cp: average power of signal Ca: r.m.s. amplitude of signal Np: noise power Na: r.m.s. amplitude of noise and () ()=xdttxErfc2exp2-30-0.1周波数受信信号振幅（）level increasedCNR increasedrecovered by Error
24、Correction Few carriers having BERworse than required Frequency Amplitude Response (dB)(b) in the case of signal level increased -30-0.1周波数受信信号振幅（）noise level reference level required CNRnot recovered by Error CorrectionMany carriers having BERworse than required Frequency Amplitude Response (dB)(a)
25、 in the case of reference signal level Level increase CNR increase4 Rep. ITU-R BT.2209 The relationship between the Erfc above and Ndist (normal distribution function) generally used in mathematics are as follows: () ()dt2exp212=xtxNdist () ()() ()()xNdistuutxErfcxxx22du2exp2122du2exp2dtexp222222=(4
26、) where: u: t2 The relationship between the inverse functions of the above are: by using: () ( )()()=2212212222111PNdistPErfcPNdistxxNdistPxNdistxErfcP(5) 1.2 Increase in the required CNR In the case of a single SFN wave, the frequency response of the received signal is given by equation (6). () ( )
27、+= cos212aaaUUF (6) where: Ua: amplitude of SFN wave relative to desired wave : delay of SFN signal. Figure 2 shows examples of increase in the required CNR when an SFN wave exists. The horizontal axis of the graphs denotes the input power of the SFN wave relative to the desired signal, that is, the
28、 inverse figures of DUR. The vertical axis denotes the increase in the required CNR. The actual values of CNR necessary for correct reception are obtained by adding these increases to the reference CNR such as 20 dB for 64-QAM-FEC3/4, 22.5 dB for 64-QAM-FEC7/8, and so on. The curves in Fig. 2 are ob
29、tained by calculating the CNR that gives BER of 8.5 103for FEC3/4 or 1.1 103for FEC7/8 against a number of SFN waves of which amplitude and delay are given randomly. The relationships given by these curves are called “CNR Increase Functions” in this document. Since CNR Increase Function cannot be ex
30、pressed by simple mathematical formula, we introduce approximated function for it, as below: () )0dB(dBdBdBexp)0dB(dBexpdB+=UUAUUUUUCNup(7) Rep. ITU-R BT.2209 5 where: UdB: denotes the power of SFN wave expressed (dB) CNup(UdB): denotes the increase in the required CNR expressed (dB) The values of t
31、he coefficients, , and are given in Table 1. The value for A in equation (7) should be zero in usual cases. FIGURE 2 Example of increase in the required CNR TABLE 1 Coefficient for CNR increase function Coefficient Modulation FEC:7/8 FEC:5/6 FEC:3/4 FEC:2/3 FEC:1/2 64-QAM 27.749 20.257 12.090 8.1386
32、 3.8797 16-QAM 29.800 22.163 13.874 9.8342 5.4002 QPSK 32.255 24.378 15.953 11.827 7.2391 64-QAM 0.5592 0.4117 0.2953 0.2527 0.2074 16-QAM 0.6074 0.4453 0.3171 0.2702 0.2251 QPSK 0.6702 0.4876 0.3450 0.2922 0.2437 64-QAM 1.0662 0.7253 0.9096 1.0341 1.2100 16-QAM 0.5954 0.6936 0.8616 0.9776 1.1378 QP
33、SK 0.5710 0.6608 0.8115 0.9172 1.0662 (a) FEC = 3/4 (b) FEC = 7/8 -100102030-20 -10 0 10Total Power of SFN Signals (dB)Increase ofRequired CNR(dB)Random Waves（0dB）SFN Wave x 1Trend CurveModulation: 64QAMCoding Rate: 3/4Number of SFN: 1-100102030-20 -10 0 10Total Power of SFN Signals (dB)Increase ofR
34、equired CNR (dB)Random Waves（0dB）SFN Wave x 1Trend CurveModulation: 64QAMCoding Rate: 7/8Number of SFN: 16 Rep. ITU-R BT.2209 The value of corresponds to the maximum increase in the required CNR, which takes place at DUR = 0 dB. A large difference is found in the maximum CNR increase between FEC 3/4
35、 7/8, comparing to 2-3 dB in the case without SFN waves. This difference must be noted in the design of broadcasting networks, in other words, FEC of 7/8 could not be applied in the actual world where SFN is more or less used. 1.3 Noise characteristics in receivers The noise that affects the recepti
36、on performance can be summarized in two categories; one is the noise of which amplitude is independent of the input signal, such as thermal noise, and the other is the noise of which amplitude increases/decreases according to the input signal level. The former is called “fixed noise” and the latter
37、“amplitude proportional noise” (APN) in this text. Fixed noise consists of thermal noise, man-made noise, noise figure of receivers, and so on. An example of link budget reported by the National Council on Information and Telecommunication in Japan applies thermal noise of 300 K, man-made noise of 7
38、00 K, and noise figure of 3 dB. The value of fixed noise is estimated to be 8.5 dB(V) (75) in this case. Amplitude proportional noise is mainly determined by the receiver characteristics, such as the quantization noise of A/D conversion, clipping noise, phase jitter of local oscillator. The words “f
39、ixed” and “amplitude proportion” come from the features of noise when expressed equivalently at the receiver input terminal. 1.3.1 Clipping noise Since the amplitude distribution of OFDM signal exhibits a normal distribution, an enormous dynamic range is required for the receiver signal processing t
40、o treat without distortions. Normal receivers clip the signals exceeding a certain level, and generate clipping noise in some extent. Figure 3 explains the affect of clipping. The clipped waveform is equivalent to the input waveform with adding the signal components that exceed the clipping level in
41、 the opposite polarity. The component that exceeds the clipping level has a pulse waveform, as shown in the Figure. The probability that the OFDM signal takes a level of x is written by Gauss(x/Srms), where Srmsdenotes the r.m.s. amplitude of the signal, and Gauss(*) the probability density function
42、 of a normal distribution. The amplitude of the pulse component that exceeds the clipping level is written by (x CL), where CL denotes the clipping level. Using the above, we can estimate the power of the pulses or clipping noise as below: () ()=rmsSCLrmsclipxSxGaussCLxNP d2(8) The spectrum of clipp
43、ing noise can be regarded as flat noise, because the intervals of these pulses are considerably large and isolated pulse has flat spectrum. Rep. ITU-R BT.2209 7 FIGURE 3 Clipping noise 1.3.2 Quantization noise of A/D conversion It is assumed for normal receivers that the clipping level is set equal
44、to the full scale of the A/D converter. Then, the quantization noise is given by the well-known equation (9). () 122122122222NNadcCLCLLSBNP=(9) where: LSB: denotes the amplitude of the least significant bit N: denotes the bit-length of A/D converter. The noise power given by equations (8) and (9) is
45、 in proportion to square of clipping level, that is, the amplitude of the noise is in proportion to the clipping level. As the receivers usually adjust the signal amplitude by AGC to a certain level corresponding to the clipping level, we can regard these noises to be in proportion to the input sign
46、al level. Figure 4 shows examples of amplitude proportional noise. It is seen from the figure that the clipping level should be set at approximately 4 times (+12 dB) of the r.m.s. signal amplitude and that the optimum clipping level depends on the bit-length of A/D conversion. -0.500.50 100時刻信号振幅Cli
47、pping levelClipping = equivalent to add thesignal components exceeding theclipping level in opposite polarityClipping noise = Power of pulses in opposite polarityAverage level (r.m.s.)TimeSignal Amplitude8 Rep. ITU-R BT.2209 FIGURE 4 Amplitude proportional noise 1.3.3 Other amplitude proportional no
48、ises There are a lot of amplitude proportional noise sources other than described above, such as phase jitter of PLL, computational errors, and so on. In addition, transmitted signals include APN such as inter-modulation components generated in the power amplifiers, noises included in the reception
49、signal (in the case of relay stations with broadcasting wave relay), etc. We can treat these transmitter noises to be equivalently generated in the receiver, and we will express the APN including all noise sources in a single value relative to the r.m.s. signal amplitude. 1.4 Conditions that gives SFN failure Now we will express the factors that are used in the digital reception estimation. They are:
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