M. S Duhan, DDG(E), Doordarshan
Radio is a lifeline of communications to and from the widely scattered audiences in mainland, in oceans, and people in distress/warzones. It has a major part in opening the way to victory over various fronts, particularly in preserving culture and dialects, building harmonization among the society, developing scientific temperaments, informing the happenings, andproviding entertainment to common masses. Hence the driving force of radio is continually gaining momentum to reach the goal of triumph for all citizens. All India Radio is the main pillar of modern-day society in India.
Compared with legacy analog systems (like FM), digital radio networks provide more capacity from the same number of frequencies and greater voice clarity at low received signal levels near the edge of coverage. In traditional analog modulation schemes, the frequency, amplitude, or phase of the radio signal is continuously varying whereas in digital modulation methods only certain states of frequency, amplitude, and/or phase are defined. These states are called symbols and each symbol conveys several bits of data.
The biggest advantage of digital radio standards is their capability to greatly enhance the quality and efficiency of radio broadcasting compared to analog AM/FM radio. Digital radio standard adoption is taking place in many countries around the world. The adoption process has been rather slow due to different local policies on spectrum and broadcasting. Each country is trying to select a standard that best suits its interests. Socio-economic impact factors are also taken into account when choosing the digital transition period. As a result, the development of digital radio receiver chipsets has been rather stagnant, with relatively slow progress, over the past years.
With digital radio, listeners can have access to more diverse and pluralistic radio content and enjoy better sound quality and new functionality. Digitization can also greatly improve the emergency preparedness system, facilitate increased competition, and offer new opportunities for innovation and development. So, digitizing the radio media is part of the modernization of any country.
Norway decided to switch off FM transmission on 11th January 2017 and start the digital radio. The switch to digital audio broadcasting, a first for any country, will be watched closely by other nations across the world, some of which are starting to question the benefits of shutting down aging analog networks, as FM is very popular and receiver ecosystem is well established. The switch to digital broadcasting is intended to save money, but critics are worried about the effect on drivers and listeners of small radio stations.
There are presently five digital radio standards across the world. Each of these standards has its strengths and weaknesses. All use orthogonal frequency division multiplexing (OFDM) modulation and the main differences are in spectrum use and data capacity. The other factors for digitization of radio include the use of single frequency network (SFN) and reduced power consumption for more number of channels. While FM has better quality compared to medium wave, but digital standards like DAB+, DRM+, IBOC (HD radio), China Digital Radio (CDR), and DVB-T2 have various advanced features for optimal utilization of spectrum. A comparative sketch of these standards, considering spectrum use and data capacity, is shown in the diagram.
- In-band on-channel (IBOC) or HD radio is a hybrid method of transmitting digital radio and analog radio broadcast signals simultaneously on the same frequency. It is used in US, Mexico, Brazil, etc. It facilitates data services, album art, traffic services, and news headlines and a wide range of similar value-added services. With bandwidth (BW) of
400 kHz, it operates in 55–1705 kHz and 87.5–108 MHz. The data capacity is 96/124 kbps (1–4 channels).
- The Chinese government's Academy of Broadcast Science (ABS) has developed its own FM digital radio standard called China Digital Radio (CDR). Its spectral range is 88–108 MHz and BW is 400 kHz. Data capacity may be 96 kbps, 1.5 Mbps (1-4 Channels or more).
- Digital Radio Mondiale (DRM) also allows for simultaneous transmission of multiple data streams alongside an audio signal and is being used in Africa, Russia, India, etc. The frequency range is 47–68 MHz,87.5–108 MHz, and 174–230 MHz and useful data capacity is 96 kbps (1–3 channels). Besides radio, text messages program, electronic program guide, MOT slideshow program accompanying images plus animation, traffic information, etc., are feasible with DRM+.
- T2-Lite is a new light version of DVB-T2 to enhance mobile performance. Ireland has become the first country that in its Irish Digital Terrestrial Television DVB-T2 specifications made DVB-T2 with 1.7 MHz raster within VHF band III mandatory from January 1, 2013. About 37 countries across the world have started radio transmission using DVB-T/T2 standard. DVB-T2 has support for deep time interleaving and longer symbol period, which together radically improve the robustness against impulsive interference. T2-Lite provides data capacity of 3.177 Mbps (18–48 channels) in VHF or UHF bands for radio, TV, etc. It can relay radio, emergency messages, graphics, video, and text signals.
- Digital audio broadcasting (DAB) is a digital radio standard for broadcasting digital audio radio services, used in more than 40 countries across Europe and Asia-Pacific. It is capable of transmitting data of 1.5 Mbps (9–24 channels). There is a large variety of DAB+ digital radio-enabled devices on the world market.
For transmission of, say, 40 radio channels, requirement of radio transmitters will be approximately: for FM 40 No. of transmitters, for HD radio/DRM+ and CDR 9 transmitters, for DAB+ 3 transmitters, while DVB-T2 will require only a single transmitter. The impact of energy consumption and other associated overheads can be compared accordingly.
DVB-T2 versus DAB
Higher data capacity can be achieved using DAB+ and DVB-T2-Lite standards. Compared to DAB+, up to three times more capacity will be available with DVB-T2. Further, with chosen modulation parameters and using same capacity as DAB, which requires C/N as 13.5 dB, the broadcasting strength with DVB-T2, capable to decode with C/N as 4.1 dB, could reduce more than eight times (13.5–4.5 dB=9 dB) with an equivalent reduction of transmission costs.
With the developments, single chip which can receive and process multi-standard digital radio broadcasts, the chasm in digital radio standards has been truncated and it gives added dimension while selecting the standards. The DVB-T2-Lite has highest data capacity, DRM+ has the advantage of larger coverage area and DAB+ has the advantage of developed ecosystem. Digitization is an important milestone in broadcasting arena, but broadcasters need to select the option of digital radio standards after analyzing and testing various standards. Digital radio would benefit all stakeholders, including listeners, manufacturers, broadcasters, and regulators. A large amount of radio listening in India takes place in the car and the adoption of a specific radio technology by car manufacturers can be integral to its take up and success. Like other digital technologies, digital radio works well in coverage range but has a cliff edge drop off at the boundary of reception.
But the most vital factor is availability of affordable receivers in handheld devices and cars. The advancement of chips and high-gain antenna is a critical issue. Norway has, though, been an early mover in digital radio; it is to be seen when globally digital radio takes over FM. In any case, the future of radio will be in digital domain and end result will be merriment and jubilation for the common people.