Отчет мсэ-r bt. 2140-1 (05/2009)

Use of Single Frequency Networks (SFNs)

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1.4 Use of Single Frequency Networks (SFNs)

Digital television services have been introduced in Australia, using either a multi-frequency network (MFN) or a single frequency network (SFN) approach. In either case, the digital television service is provided from a network that consists of a high-powered central (or parent) transmitter that may be supported by, or contribute signal to off-air feed, a number of low-powered in-fill or area-extension re-transmitters.

In the MFN case, the re-transmitters operate on a different channel (or channels) from the parent transmitter while, in the SFN case, the re-transmitters may either operate on the same channel as the parent transmitter (if not an off air feed); or on another channel in one or more SFN re-transmission networks, which can be off air feed from the parent3.

In the later case, the parent transmitter is operated in the MFN mode, albeit with SFN timing information embedded into the signal for use by the SFN re-transmission network(s). In a few cases more than one parent transmitter, together with their re-transmitters operate as an SFN.

1.5 Planning parameters and interference threshold limits

Australia’s planning for digital television services takes into account a legislated requirement that “... in SDTV digital mode in that area should achieve the same level of coverage and potential reception quality as is achieved by the transmission of that service in analog mode in the same area”. Following this approach, Australia’s digital services are typically planned with a maximum e.r.p. of 6 dB less than same band analogue television services.

Planning guidelines in Australia also specify minimum median field strengths (referred to a measurement height of 10 m above local terrain) of 44, 50 and 54 dBV/m for Band III, IV and V digital television services respectively4. To minimise the “cliff-effect”, digital television services are planned to achieve the required protection ratio for better than 99% of the time, irrespective of whether the interference is considered to be continuous or tropospheric in nature.

1.6 Comparison of ITU-R and Australian television planning parameters

The following text summarises differences between Australian television planning parameters, including minimum field strengths and protection ratios and the corresponding Recommendation ITU-R BT.1368 parameters for the protection of DVB-T digital television services.

Australian planning for both analogue and digital terrestrial television is based on an assumption of fixed reception using outdoor receiving antennas. Therefore protection ratios relevant to Ricean channels are used where available. The DVB-T mode 64-QAM with 2/3 FEC and a 1/8 guard interval has been adopted as the basis for digital television planning, however to achieve a higher picture quality for the SD/HD simulcast, most broadcasters have selected 64-QAM with 3/4 FEC and 1/16 guard interval.

1.7 Digital television minimum median field strengths

Australian digital television planning is based on provision of minimum median field strength levels of 44, 50 and 54 dBV/m in Bands III, IV and V respectively. These values are reasonably close to the values that can be derived from the sample calculation value provided in Table 44 of Recommendation ITU-R
BT.1368-75. The Australian values are, respectively, 0.1, 0.9 or 2.8 dB higher than values that would be derived from the Recommendation. The differences are due to: inclusion of a 1 dB higher receiver noise figure allowance in Bands III and V; use of 6.7 rather than 7.6 MHz for the receiver bandwidth; inclusion of a 1 dB allowance for man-made noise in VHF Band III; different combinations of antenna gain/feeder loss in Bands III and IV; and, use of frequencies at the top rather than the middle of each band as the reference frequency for the calculation. The Australian minimum field strength calculations also include a 1 dB ‘Interference Margin’ for the support of co-channel, frequency re-use planning.

1.8 Digital television protection ratios

Protection ratios for digital-digital and digital-analogue co-channel and adjacent channel interference from other television broadcasting services were first defined in July 1999. Only minor changes have been made to those original values. The values used in Australian planning are the same as the 64-QAM, 2/3 FEC values set out in Recommendation ITU-R BT.1368-76.

The relevant protection ratios are not to be exceeded for more than 1% of the time. That is,

the E(50,1) value is used for the interfering field strength.

2 Brazil

The digital terrestrial television broadcasting channel planning and the deployment of the DTTB in Brazil.

2.1 Introduction

This chapter presents the work that has been conducted by the National Telecommunications Agency (Agência Nacional de Telecomunicações - Anatel) related to channel planning regarding the introduction of the Digital Terrestrial Television Broadcasting (DTTB) in Brazil and the stages for its deployment. The text consolidates three contributions (RGQ11-1/2/93-E, 95-E and 185-E) submitted by the Brazilian Administration to the Rapporteur’s Group on Question 11-1/2 during the meetings held on September 8th 2003 and May 31st 2004, both in Geneva. The Rapporteur´s Group Meeting of September 2003 “proposed that the contributions of Brazil should be documented on the ITU Web site as a case study on the introduction of digital terrestrial TV broadcasting”(2/REP/012-E). This proposal was approved in the Plenary Session of the Study Group 2 on September 11th 2003. As a result of these decisions, this Annex presents the methodology, the results and the current work Anatel is undertaking on the completion of the DTTB channel planning. In addition, it is important to observe that the country’s channel planning is not related to any specific DTTB standard, since it contemplates the particularities of each existing DTTB standards.

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