As analogue fades, India eyes a digital leap with DTT and D2M—reshaping how we watch TV, stream on mobiles, and access free public broadcasting without the internet.
Bringing TV into the digital era
The analogue TV is obsolete for now, and all the analogue transmitters of Doordarshan (DD) have been shut down since 2018. The digital terrestrial television (DTT) standard was supposed to take its place as the basic public telecasting network. The digital video broadcasting terrestrial (DVB–T/T2), or DTT, utilises VHF/UHF carriers in the 174–862MHz range to transmit eight data-compressed digital sub-channels within 8MHz wide bandwidths formerly used by analogue TV. Since signal is prone to multipath and fading, orthogonal frequency division multiplexing (OFDM) transforms a digital bit stream into a frequency multiplex.
The frequency range allotted for DTT in India extends from 470–562MHz, and can easily be received by a suitable Yagi antenna. At locations of high field strength, a very simple telescopic antenna could be successfully used to receive DTT signals. A set-top box (STB), designed for DVB–T/T2 operation, may be used to recover and decode the digital bit stream, as well as reconstruct video and audio. However, older TV receivers with analogue tuners require a separate DTT tuner or STB for signal decoding. The integrated digital TV (iDTV) receivers are, however, designed to receive DTT signals, and are available in the market.
The DTT broadcasting was started by DD in 2014. Each transmitter channel is 8 MHz wide and could accommodate five video sub-channels: DD National, DD News, DD Bharati, DD Sports, DD Regional/DD Kisan, and a few audio channels. Due to advanced data compression and coding, DTT performs well even with weak signals in dense or moderately covered regions.
Small Screen, Big Impact
A smartphone has nearly overtaken the regular domestic TV in terms of time spent viewing videos. The idea of providing TV service on the mobile phone is not new. Even during the early days of mobile phones, some handsets incorporated circuitry to receive VHF analogue TV with the help of a small whip antenna. The FM receiver is a popular section in mobile phones and often uses a headphone wire as an antenna, and occasionally, the specially tailored antenna is incorporated within the mobile phone, popularly termed as ‘wireless FM’. Therefore, the introduction of DTT reception on mobile phones should not have been far behind. In the meantime, the ‘over the top’ (OTT) service has caught up fast, apart from many video sources proliferating on the internet. These services require extensive use of internet bandwidth. The DTT receiver/decoder circuitry can also be integrated within a mobile phone, except it would require some extra signal processing hardware. As with early analogue TV in mobiles, integrating DTT hardware with some added processing capability is feasible.
The RF carriers used in the DTT, as well as some of the bands of mobile phones, are close to each other. Thus, there is a clash of interest between the two services. The UHF band has high demand from mobile phone services, and the introduction of G5 has enabled the use of the 600MHz region for mobile services. The close carrier frequencies facilitate the use of common RF front-end sections for telephony as well as TV reception. The built-in antenna, which is small in size at these frequencies, can also be common as well. The video signal processing required is, however, substantial, but not insurmountable.
No internet? No problem—D2M arrives
The merger of DTT circuitry within the mobile phone hardware has opened a new possibility of utilising mobile phone towers for extended broadcasting of Digital TV signals. The direct-to-mobile (D2M) utilises high-power terrestrial digital transmitters as well as low-power transmitters of mobile towers in an integrated way to facilitate use of UHF carriers in the 526–582MHz range for downloading high-speed data on smartphones, without the need for internet connectivity. It can support video sources as available on OTT, and a public interest information dissemination service. It obviates the need for satellite-based relays like direct-to-home (DTH) service, which requires a rather elaborate antenna arrangement.
India’s Broadcast Crossroads
The DTT transmitters of DD have been shut down, effective 1 October 2022, to facilitate testing of D2M, which is poised to start in 2025. Possibly the ideal solution would have been to either assign the carrier frequencies in the UHF 470–526MHz region, or even in the VHF 174–230MHz region for DTT, and utilise the 526–578 MHz region for testing the D2M system.
This way, DTT would have been continued for the viewers of local TV channels in densely populated regions. The closure of the entire DTT system pushed the users more towards DTH and OTT, which are paid services, by and large. Individual mobile phone users are drifting towards videos distributed over the internet, paying substantial charges. The suspension of DTT in 2022, without ready D2M alternatives, has created a vacuum in public terrestrial broadcasting. The introduction of D2M would require smartphones to have the facility to handle a TV bit stream. Smartphone manufacturers, however, do not seem to be in the mood to make such changes. In the meantime, there is pressure on internet bandwidth, as users are dependent on the internet protocol (IP) for watching video on smartphones, which is essentially a one-way traffic as far as data is concerned. The D2M is still on the horizon and its success will also depend upon how soon it is introduced in the country. The delay in the introduction of D2M has allowed more and more penetration of strong rivals DTH and OTT.
References
- The Journey of TV Technology in India, R N Misra, Electronics For You , March 2020, pp 52-54
- What is D2M Technology: Everything You Need to Know, Shashank Shakya, Feb 15 2024 ,
Author: R.N. Misra, The author was formerly associated with the Physical Research Laboratory, Ahmedabad
