M S Duhan, Deputy Director General (E), DG, DD, New Delhi
The digital terrestrial TV (DTT) platform is important for the broadcasting industry even in those markets that are dominated by other delivery platforms like DTH, cable TV, IPTV, etc. It stimulates competition amongst the delivery platforms but more importantly it is also complementary to other platforms. TV is still the preferred choice for overall viewing and is the most heavily consumed platform for video and audio among adults of all ages. TV continues to play a role in shaping our experiences of live historical events, as consumers continue to watch television as they watch history unfold. People have different perceptions and tastes for different visuals and aural arena. When it comes to viewing habits, the age of the viewer has a lot to do with linear and digital platform usage. As the industry continues to evolve, consumers have endless media options from which to choose across the fragmenting viewing landscape. Listening to radio (audio only) is consistently popular among all age groups. Broadcasters have dilemma for quality and quantity of radio and TV channels but viewers find green pastures. Digital terrestrial is the solution!
DTT Signal's Synthesis: Digital terrestrial TV (DTT) signal received via aerial and decoded for viewing on TV set, supports more free-to-air, TV program channels, radio, text plus high-definition TV. It can also provide t-commerce and application services like e-shopping, ordering services, transaction and payment gateways, third-party integration, delivery tracking, etc. Soft services like on-screen chatting, social media TV, Internet, SMS voting, subscription management system, rating research and analytical CRM, etc., are also feasible through DVB-T2 DTT platform.
The dynamism of DVB-T2 signals with time interleaving becomes highly useful. The signals can be faithfully reconstructed in multipath and lossy environments also. DVB-T2 has support for deep time interleaving, which radically improves the robustness against impulsive noise and interference, and confronts issues of latency and power consumption. The future extension frame gives capability to relay fixed, portable, and mobile service through single multiplex of DTT. Antennas for fixed TV are oriented horizontally and for the portable receivers are often oriented vertically out of habit, and, therefore, favor the reception of vertically polarized waves. Circularly polarized radiation on mobile receivers generates less amplitude variation, i.e., it increases the likelihood of usable field strength, and at the same time serves all forms of linearly polarized receiving antennas. Diversity-2 uses the maximum-ratio-combining algorithm and it increases sensitivity that could triple the coverage area and offers better indoor reception (up to +70 percent). It also improves Doppler effect handling (reception at higher speed). Diversity-4 provides best results. Antenna size for portable receivers reduces with higher frequencies.
Data Capacity: The data capacity of DTT platform depends on various factors like the source and the channel coding, type of content, type of service (fixed/mobile), intended coverage in a given topography/terrain, etc. The content variations may be like "near-static (e.g., near-static shots, TV shows)," "slow and uniform motion (e.g., documentary channels)," "dynamic motion (soccer) (e.g., sports, action movies)," "very dynamic and complex motion (e.g., complex transitions, frequent scene cuts, and occlusions)," etc. The bit rate for each of the above will be different as such type of content has bearing on deciding the program data rate. The compression techniques like MPEG-2, MPEG-4, and HEVC provide efficient coding features. The resolution and data bit rate are different for fixed and mobile devices. Although the video signal takes the majority of the available bit rate, there is some other data that also needs to be transmitted. Audio: 32 kbps to 256 kbps dependent on type and number of audio channels (stereo/surround sound/multilingual); service information and EPG: (SI) about 100 kbps, interactivity/teletex @ 200 kbps, and access services (subtitles/audio description/spoken subtitles): 200 kbps. All of the above are regarded as program-associated data. Typical bit rate requirement for program services in MPEG-2 is SDTV (3.8 Mbps), HDTV (16 Mbps), mobile (1000 kbps), for MPEG-4 data for SDTV (2.5 Mbps), HDTV (8 Mbps) and Mobile (600Kbps). HE AACv2 audio codec is an efficient technique and with it acceptable quality stereo sound may be at 24 to 32 kbps and good "FM-like" sound at 64 kbps or higher. 64 kbps sets the lower limit of audio quality on the speech by HE-AAC. Transparent high-quality stereo sound will be at 128 kbps. It is possible to have better-quality programs with higher data rates for video, and this means that the number of programs in a multiplex would be reduced. Though there is equipment like Picture Quality Analyzer to measure the video quality but expert golden eyes (people who can judge the fine details of picture quality) are best judge for quality measurement. Statistical multiplexing further leads to a reduction in the average video data rate needed per program. DVB-T2 with HEVC is the most significant qualitative and quantitative advancement for terrestrial TV. The RF profile of transmitters like FFT, pilot pattern (PP), guard interval (GI), constellation, code rate, interleaving depth, etc., decide the DTT Tx capacity. So chosen parameters can give data capacity from 15 to 20 SDTV channels for fixed reception. For mobile TV, depending upon tradeoff for coverage versus quantity, 10-19 SDTV are feasible.
DVB-T2 standard has added support for 1.7 MHz bandwidth. This is the same bandwidth that digital audio broadcast (T-DAB) and digital multimedia broadcasting (T-DMB) standard uses in VHF band III and L-band. 1.7 MHz BW: 1.7 MHz channel raster in the VHF band III. With DVB-T2, there are many possible combinations of parameters. One such example is 16QAM, FFT size = 16K ext, GI 1/32 (277.5 µs), PP6, CR 2/3, LDCP 16K, net bitrate: 3770 Mbps. This may provide 48 radio services or 24 radio and one SDTV .
Consumers are increasingly investing in TV sets with larger screens, resulting in higher requirements on picture quality. HDTV services, with resolutions like 1080i/25 or 1080p/50, are already available on DTT in several countries. Furthermore, it is expected that TV requirement for living room viewing of UHD (4 times resolution w.r.t. HDTV) will fast increase. Similarly, the use of smartphones and tablets is on the rise in younger generation. In one study on consumer preference on device size, it is observed that the screen size of the device is divided among young and adults. People up the age group from 16 to 34 in the study conclude to have preference for small screen mobile devices like smartphones/tablets, compared to fixed TV, while people from 35 to 59 have high inclination toward fixed TV. Integrated digital TV with built-in DVB-T2 tuners and some smartphones with embedded DVB-T2 tuners are also available. Multi-room streaming up to 8 tuner configurations including multiple decode/transcode in HEVC/AVC to client boxes and mobile devices is also available. Car receivers for DVB-T2 are also available. But for the growth of broadcasting, perhaps regulation to make it mandatory to provide tuner of DVB-T2 in TVs and smartphones/tablets need to be there. Pocket-size small TVs and radio sets are available in international market. Reception of broadcasting content on portable, mobile, and handheld devices will also become more important in the future as society moves toward more mobile consumption of content. For example, large numbers of people commute daily between home and work, spending hours on the move and choosing to pass their time watching and listening to broadcast content.
Diverse audiences play big role in usage of devices and media for audio and video data. Young generation is the most avid radio listener and spends the most time on their smartphones. In this dynamic media viewing universe, how long the consumer is engaging with content is imperative for content providers and advertisers to assess the opportunities and challenges within this viewing paradigm. DTT provides an excellent opportunity to broadcasters, device manufacturers, and viewers/listeners. Chips are ready, manufacturers are not far behind.