Japanese Digital Television Project: An informed choice?

by Shanthilal Nanayakkara

Retired Principal Engineer, Digital Transition Division, Australian Communications and Media Authority

A Japanese delegation recently announced the resumption of the previously stalled digital television project in Sri Lanka following a meeting with the newly-elected President Anura Kumara Dissanayake. The commencement of the digitisation project is now imminent.

Once terrestrial television transmissions are digitised in Sri Lanka, it will replace the old analogue terrestrial television forever. Therefore, it is critically important that the final outcome is better than the current analogue television, if not far superior. Setting such a goal prior to the implementation of the project is crucial for its fruitful completion.

To achieve this outcome, deficiencies in the current parameters in the Japanese Digital Plans need to be revisited and appropriately addressed for the benefit of all stakeholders. Otherwise, as it stands today, there is a high potential for rural and regional viewers in Sri Lanka to miss out on the digital coverage. (This is further illustrated below). Such an unwarranted outcome could become a highly ‘politically sensitive’ issue for the new government .

Why Digital

In analogue transmissions, radio waves encounter several problems. When radio waves are subjected to multipath, ghosting images appear on television screen. They are also subjected to cancellation of their own signals and interference.

Digital technology overcomes these analogue transmission weaknesses and, as a huge value addition, is able to carry more information than its analogue counterpart. As this capacity enhancement feature helps carry multiple programmes on one frequency or channel, digital television transmission technology is considered to be highly spectrum productive. Once analogue is switched off, the vacant spectrum that can be harnessed, commonly known as Digital Dividend (DD), becomes an income earner for the Government, as spare spectrum can be sold to Telcos for broadband internet use. Thus, this digitisation project is effectively a self-financing venture for the government and a win-win for all stakeholders.

Stakeholder benefits of digital

Many countries in the world have now moved or are in the process of moving to the digital domain.

Irrespective of the digital television transmission standard adopted in Sri Lanka, benefits of a conversion from analogue to digital television are many for the majority of stakeholders.

These are listed below against the various stakeholders:

Funding arrangements or self-financing

The current funding arrangement for digitisation of television in Sri Lanka is a ‘soft loan’ from the Japanese government, and it is tied up in ‘one bundle’ with loans for other projects. This loan is also based on the premise that the deployment of the Japanese digital television standard, Integrated Services Digital Broadcasting-Terrestrial (ISDB-T) is mandatory. As the vacant spectrum can be sold after Analogue Switch Off (ASO), the venture could also be a self-financing project, albeit with bridging finance.

Purpose of this essay

The main purpose of this article is to suggest ways of optimising the benefits of the digitisation project while retaining the support of the Japanese government. If the bulk of problems for viewers and broadcasters can be removed by making appropriate adjustments to the current plans at a minimal cost, with broadcasters becoming willing participants, the digitisation of television in Sri Lanka would no doubt be a success for all stakeholders, including the new government. Otherwise, there is an urgent need to review the bi-lateral agreement that was signed previously.

The broadcasting fraternity in Sri Lanka is fully aware that the Japanese system is not as efficient as the second generation European standard, Digital Video Broadcast-Terrestrial 2 (DVB-T2).

Understanding Digital

Simply put, digitisation of analogue vision and sound enables radio waves to carry more information within the same channel or bandwidth than in the analogue era. This allows producers of visual and aural content to be more creative than before. The technology also facilitates easy communication in both fixed and mobile environments and facilitates two-way communication more than in the analogue era. However, there are two main pitfalls that one needs to address in order to make the venture a success. They are as follows:

Cliff effect (sudden loss of signal): –

* to avoid the ‘cliff effect’ a robust signal (with higher reliability and availability at a receive location than in analogue era) is needed at the receiver to prevent momentary picture pixelation and/or sudden loss of signal; and

* it is also necessary to ensure that all television digital services reaching viewer locations are of the same signal strength to ensure equity of services and therefore must originate from ONE location such as the Lotus Tower.

* Absence of ‘graceful degradation’ and its effect on signal level – even with a degraded signal with ‘snowy pictures’, analogue signal is still watchable. It is not so with digital due to ‘cliff effect’. Therefore, there is a need to ensure that the digital coverage is the same or better than the existing watchable analogue coverage that is defined by a signal level of 43 dBuV/m in VHF Band III.

This limit was adopted for digitisation in Australia.

Deficiencies of the Japanese standard/plan

In planning to deploy the ISDB-T system in our country, everyone should aim for a cost-beneficial outcome as it is of paramount importance to all stakeholders. There are several issues in the Japanese documentation of 2014/2018, which should be addressed to suit the needs of the public/consumers, broadcasters and government. They range from policy issues at the outset, technical areas during planning and management issues during the proposed phases of ASO and Digital Switch On (DSO).

Spectrum for Digital: VHF/UHF issue

In particular, the proposal to use only a part of the available broadcast spectrum has an impact on the eventual DD income for the Government. The Japanese have deployed both VHF and UHF spectrum in Brazil, strangely not offered to Sri Lanka. In that context, it is not clear why the Japanese team has not proposed a VHF and UHF combined solution as deployed in Brazil. This was pointed out by the writer when a Japanese team, including a senior Embassy official Sato Takefumi, met him in 2017 in Colombo to discuss Lotus Tower issues (after his disclosure in an article in The Island about the Lotus tower) and digitisation in general. Their response was ‘no one asked for it’.

As it stands today in Sri Lanka, analogue television transmissions are based on frequencies using both VHF and UHF Bands, but the proposed Japanese digital conversion is not utilising the VHF Band. In particular, VHF Band III exhibits superior propagation characteristics, while contributing to lower the consumption of electricity by the transmitters. More importantly, VHF radio waves carry longer distances than UHF due to lower propagation losses, are able to travel around obstacles comparatively and therefore VHF is more suitable for wide coverage transmissions.

Currently, the VHF spectrum is occupied by three television broadcasting networks i.e. Rupavahini, ITN and TNL. These networks will lose their inherent wide coverage VHF Band advantage. They also have the additional burden of occupying a digital channel in the UHF spectrum, especially when the earmarked UHF channels for digital are almost at the bottom of the UHF Band V, where propagation losses are higher than in UHF Band IV.

ISDB-T New Coder H.265

It is a known fact that the Japanese ISDB-T standard, in payload capacity terms, is second to the second generation European Standard DVB-T2 that provides 45 Mb/s capacity. However, the Japanese standard can only carry about 1/2 of the European standard per channel at 23 Mb/s. But as the Japanese are now offering to change the content source coder to H.265, they will be able to provide HD at 1080P at a rate of 2-4 Mb/s. This change would now allow all HD TV ready broadcasters to provide True HD content at 1920 x 1080P and possibly can accommodate all television channels in Colombo. But the downside is that the receivers are going to be more complex with the new coder. This may then lead to more expensive ISDB-T receivers or STBs in Sri Lanka.

Vacant VHF Band III

The unused VHF Band III is likely to reduce the DD for the government though the Japanese strategy is to achieve some productivity by the use of single frequency networks in the UHF Band (SFNs-a technique to use the same frequency multiple times to improve spectrum productivity). However, in practice receiving of SFNs is not simplistic as the reception of SFN signals are subject to receiver complexities.

The Telecommunications Regulatory Commission (TRC) may be exclusively reserving the VHF band for future digital radio, but the same band could be co-shared with digital television without any problems. For example, Australia is co-sharing VHF Band III for both digital television and radio without any issues.

Once all analogue transmissions are switched off with the deployment of UHF band per se for digital, the unused VHF Band III spectrum, where 7 MHz bandwidth, 8 VHF Frequency channels exists, will become vacant.

This is clearly a waste of unused spectrum. Additionally, as Restacking [restack is the re-arrangement of frequencies ideally in the two bands of VHF and UHF, to maximise the spectrum productivity] is in the Japanese Plan, additional expenditure on broadcasting infrastructure is also on the cards. Where are the funds coming from?

There is no mention of new funding arrangements for Restacking of the spectrum, and it also raises questions about the STB/Receiver specifications as frequencies may need to change after Restacking.

If some broadcasters are not keen to use ISDB-T, they may canvass for the opportunity to use the vacant VHF Band for the potential deployment of DVB-T2 standard. This MUST be avoided at all costs! If this happens, there will be two digital systems in Sri Lanka. This issue, in particular, could become another potential headache for the government as it is likely to be under heavy pressure from commercial broadcasters to release the vacant VHF Band III for the more efficient DVB-T2. This issue, too, was pointed out by the writer when another Japanese team consisting of a Senior Engineer from Yacheo Engineering along with Sato Takefumi of the Japanese Embassy met him in 2017/2018.

Unless there are plans to use the vacant VHF Band III by Restacking the spectrum, this spectrum specifically allocated for broadcasting would go to waste.

Digital Signal Reliability & Availability

Unlike in the analogue domain, television signal reliability and its availability becomes crucial in digital reception. In the analogue era, television broadcasting service field strength was planned for 50% of the locations and 50% of the time at a receiving height of 10 m. But in digital this becomes 80%-95% of the locations and 90% of the time to ensure reliability and availability of the digital signal. Hence the planned field strength would need to be adjusted to ensure the required reliability and availability at a higher field strength. In Australia, field strength used was 50 dBuV/m for Band IV and 54 dBuV/m for Band V frequencies in a rural environment

However, it is not clear from the published documents of the Japanese plans 2014/2018 whether this issue had been addressed or otherwise. The signal level at 51 dBuV/m identified in the 2018 Japanese documentation is certainly not adequate for a rural grade of service in the UHF Band! It ought to be in the region of 54-74 dBuV/m in the UHF Band V. For example, the Australian Broadcasting Planning Handbook for Digital Television Broadcasting has clearly identified these requirements and provided information on how they were derived.

Duplication Parameter

The potential impact of the proposals for duplication of coverage is illustrated in the diagram. (See Figure 01)

The signal threshold of a planned analogue coverage is 50 dBuV/m for VHF Band III. However, some regional and rural viewers in Sri Lanka are currently receiving watchable analogue signals well below this value. If, as planned by the Japanese studies in 2014, the analogue coverage is converted at the planned cut-off level of 55 dBuV/m, then the majority of regional and rural viewers, who are currently watching the analogue television with no issues, will not be able to receive digital television coverage. This could potentially become a political nightmare for the new government. Therefore, the cut-off signal level, as illustrated above, should be lowered to 43 dBuV/m.

Though Single Frequency Networks (SFNs) are a solution to mitigate this difference in coverage, it is not easy to implement them at the receiver-end due to the variation in receiver profiles of Set-Top-Boxes (STBs) and complexities in receiver SFN signal detection.

The Japanese designers, while being aware of this issue, may have been heavily constrained due to the requirement for spectrum productivity. Most probably, given the limits of the available UHF spectrum for digital and the lower data efficacy of the Japanese ISDB-T standard, this higher limit of duplication may have been proposed by the designers in order to preserve some spectrum productivity.

One Network Operator for Digital

The advent of digital terrestrial television also signifies the end of individual transmission facilities for broadcasters, as several content feeds are carried on one frequency or the channel and the requirement to consolidate all transmissions at one site. A combined digital transmission service provider may, in the future, be an independent entity and the facilities may be offered to the broadcasters on a fee-levying basis, based on a pragmatic business plan. In a future digital broadcasting landscape, the broadcasters will essentially be ‘content’ providers. Perhaps, there ought to be some sort of protection provided to the existing broadcasters in the event new content providers also express a desire to use digital transmissions.

Cost to viewers and broadcasters

All consumer television sets require digital receivers to extract video and audio content from digital transmissions. Therefore, either in-built ISDB-T receivers or compatible STBs are required. For example, there are flat TVs that do not have in-built ISDB-T receivers. The cost of an STB for ISDB-T with H.265 decoders, is likely to be around US $ 50-100, depending on their complexity and economies of scale. If in the event, there is likely to be a Restack of frequencies including the VHF Band, two band STBs or receivers may be needed; one during the first phase and another after the Restack of channels with the ability to tune into the VHF Band. Additionally, at some household locations, there may also be a requirement for new receiver antenna installation to receive VHF/UHF channels. If so, this is also an additional cost to the viewer.

There is also a significant cost to the commercial television broadcasters to provide HD ready studios, Outside Broadcast (OB)/Electronic News Gathering (ENG) equipment, and content feeding arrangements. However, once the commercial television broadcasters elect to use consolidated broadcast towers, analogue era transmission costs would also disappear as their independent transmission networks are no longer needed, in a digital environment. It is noteworthy to highlight that the Japanese financial proposal for digitisation of television is primarily for Rupavahini, and limited to funding the analogue to digital transfer of Rupavahini facilities, including the provision of a True HD studio, OB unit, Transmission equipment and a Central Command centre for the proposed Digital Broadcast Network Operations (DBNO) at the Lotus Tower.

At this stage, there are no signs of any discussions with the broadcasters to develop a ‘road map’ to facilitate the smooth transition from analogue to digital of commercial channels. If Restack is to take place, there is likely to be additional costs but there is no mention of further Japanese funding for Restack of channels either.

As additional costs to the commercial television broadcasters are likely, strategic government policy initiatives to compensate for the additional capital expenditure in a highly competitive market are in order.

Way forward

It is heartening to note that the Japanese plan has now incorporated the more efficient coder in H.265 with an intention to maximise the use of limited payload capacity of an ISDB-T channel, which then will result in providing True HD transmission (1920 x 1080P) for ALL licensed television channels in Colombo.

If Japanese consultants can pay attention to the issues of using VHF Band III, changing receiving the field strength requirements to that of the ITU signal level requirements for UHF and address the duplication parameter issue, then ALL stakeholders including the government and broadcasters will no doubt look forward to the venture of digitisation of television in Sri Lanka.