Sharing the Broadcasting Spectrum: digital dividend, white spaces, power line telecommunication (PLT) system - (by Mr. N. Venkatesh, Counsellor ITU-R Study Group 6)

Digital Dividend

The introduction of digital terrestrial broadcasting, which is underway in many parts of the world, provides many benefits, among which is the professed digital dividend. Digital compression technology and coding systems allow for several television programme channels to be carried within the same bandwidth that is used by an analogue television channel. Digital terrestrial television (DTT) delivers an increasing number of quality television programmes within the same amount of spectrum that is used by an analogue channel and uses spectrum more efficiently.

So as television broadcasting migrates from analogue to digital, it is clear that all existing analogue television channels can be accommodated in less spectrum than used previously and many additional television channels can be introduced in the available broadcasting spectrum. One might say that some spectrum may be released after the analogue TV services have closed down. This release of spectrum is referred to as the ‘digital dividend’. This released spectrum could be used for many purposes, such as:

  • providing many more digital television broadcasting services
    of conventional quality and resolution;

  • providing a new service concept (partially or totally) that allows for indoor, portable and mobile reception including digital TV services for reception on hand-held receivers;

  • providing enhanced sound and picture quality, like High Definition TV, Three-Dimensional TV;

  • providing non-broadcasting services, like IMT, WiMAX, Wifi, etc.

It is anticipated that this 'digital dividend' is likely be used by the Member States for various purposes reflecting their political, social, and cultural considerations. Already, the digital dividend has resulted in the availability of some of the broadcasting spectrum in the UHF band in Region 1 - specifically from 790- 862 MHz, for mobile broadcasting on a primary basis from 17 June 2015. Furthermore, Agenda item 1.17 of the 2012 World Radiocommunication Conference (WRC-12) tasks the ITU-R Sector to consider results of sharing studies between the mobile service and other services in the band 790-862 MHz in Regions 1 and 3, in accordance with Resolution 749 (WRC-07) - to ensure the adequate protection of services to which this frequency band is allocated, and to take appropriate action to assure this.

ITU-R Joint Task Group 5-6 (JTG 5-6) - 'Studies on the use of the band 790-862 MHz by mobile applications and by other services' was established by the first session of the Conference Preparatory Meeting (CPM 11-1) in order to carry out these studies and to develop the text for the 'Draft CPM Report on Agenda item 1.17 (WRC-12)'. The JTG 5-6 completed its work at the meeting held from 30 April – 7 May 2010.

White spaces

Another aspect of the switch-over to digital terrestrial television broadcasting is the thorough review of the UHF broadcasting spectrum that is taking place in Administrations undertaking this transition. The terrestrial TV networks in the UHF bands have been traditionally planned as Multi-Frequency Networks (MFNs), in order to support regional TV planning and to facilitate international frequency coordination. In this type of planning, there are locations within a country where particular UHF channels are not used in order to avoid interference to TV services in adjacent regions. These channels are known as UHF white space and have been used by the broadcasters for low-power applications like radio microphones and wireless in-ear monitors, known as Programme Making and Special Events (PMSE) applications. This sharing of the broadcasting spectrum is the subject of many ITU-R Recommendations (ITU-R BT.1368 - 'Planning criteria for digital terrestrial television services in the VHF/UHF bands' and ITU-R BS.1786 - 'Criterion to assess the impact of interference to the terrestrial broadcasting service (BS)', etc.) which provide the necessary criteria for the interference-free operation of such equipment.

There is now a demand for this UHF white space (spectrum) by fixed and mobile devices, which are looking to deliver improved Wifi systems for mobile broadband and for multimedia streaming in the home. These devices are based on a combination of spectrum sensing (Cognitive Radio - CR) and geolocation (database of locally “unused” channels in an area) techniques. CR technology is under study in WRC-12 Agenda item 1.19. The broadcasting community is particularly uneasy about the impact that these ubiquitous devices could have on TV reception in the home. The CR process is difficult and requires high performance Radio Frequency (RF) circuitry and potentially complex signal processing as the licensed Digital terrestrial television (DTT) signal to be detected will be received at a very low level. In addition, the database to be developed and maintained for the geolocation poses many questions as to its accuracy, timeliness and reliability. In addition to the broadcasters who are affected by the use of large numbers of such unlicensed devices, the cable industry have pronounced concerns by the ingress of these signals into cables (which have no white spaces).

Power Line Telecommunication (PLT) system

PLT system is a communication system which uses the electrical infrastructure wiring to transfer high-frequency data signals from place to place. It is superimposed on electrical wiring that is used within the house or office, from power sockets to all spurs or branches that go to the light fittings, ceiling/wall outlets, etc. In some countries this technique is referred to as 'Broadband over Powerline (BPL)'.

As electrical wiring is not designed or engineered for the transmission of wide bandwidth data, radiation from the wiring is a consequence. So PLT systems will increase the level of ambient noise at locations where they operate; and radiation from such unlicensed devices will impact the potential performance of any broadcast receiver (or any other licensed/authorized service) operating at that location.

The ITU-R Sector has been studying the impact of PLT on radiocommunication services and in 2009 published Report ITU-R SM.2158 - 'Impact of power line telecommunication systems on radiocommunication systems operating in the LF, MF, HF and VHF bands below 80 MHz'.

Initially PLT systems operated in the frequency bands below 80 MHz and consequently Report ITU-R SM.2158 focused on these bands. However, developments in PLT technology have extended the frequency of PLT operation beyond 300 MHz. Further studies are thus required to investigate the effect of PLT in the VHF broadcasting bands up to at least 230 MHz (i.e. the top of the VHF broadcasting bands).

ITU-R Study Group 6 (Broadcasting service) is actively studying the above-mentioned areas by undertaking tests and measurement programmes and is developing pertinent Reports and Recommendations.

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