Richard Benbow (Editor: Veronique Autphenne)

Compression and digital technology have introduced audio entertainment alternatives for consumers superior to that of the radio. For audio entertainment, consumers today have the option of listening to compact discs or watching television programs dedicated solely to music or news/information programming rather than listen to the radio.

The creation and development of these alternatives has created a need for the radio industry to compete for the attention of listeners with the same quality and fidelity as its competitors. Radio broadcasters believe that Digital Radio will enable them to aggressively compete for listeners and feel the implementation of digital audio broadcasting (DAB) as a consumer service is necessary for the sustained economic growth of the broadcast industry (http://www.usadr.com/techni.asp).

Digital Radio, or Digital Audio Broadcasting (DAB), is the digital method of transmitting CD-quality audio signals to radio receivers. Digital Audio Broadcast systems are comprised of a digital modulation scheme and a method of encoding digital audio. Developments in broadcast and digital technology have created a plethora of options to form a highly functional digital audio broadcast system, from using microwave broadcasting, digital satellite broadcasting, to creating an entirely new spectrum/band. Nonetheless, research has revealed that the implementation of either one of these options will undermine the economic foundation of radio broadcasting or require extensive renovation of the existing scheme of radio broadcasting.

In an effort to preserve the integrity and economic foundation of existing broadcast radio, without sacrificing optimal quality sound or service, USA Digital Radio developed the ‘In-Band On-Channel’ (IBOC) scheme (http://www.usadr.com/whatis.asp). The IBOC scheme, with the aid of computers, produces a digitally modulated signal that is compatible with the existing analog frequency. With the use of a powerful audio sub-band digital coding techniques, the IBOC scheme economizes the digital information associated with a radio broadcast to fit within the ‘mask’ or frequency slot of each station, both AM and FM (http://www.magi.com). This task is accomplished by using audio coding algorithms, or coding schemes that use hearing curves and other psyche-acoustic measurements (http://www.magi.com). These coding algorithms eliminate parts of a signal that are not heard by the human ear from transmission. By doing so, the use of existing spectrum is maximized and preserved without disrupting the AM and FM allocations already in place. In today’s crowded spectral world, frequency re-use provides a welcome solution to the issues of allocations, regulations and infrastructure associated with starting over in a new band for digital (http://www.magi.com).

In addition to maximizing bandwidth and preserving spectrum, IBOC employs a three-fold defense mechanism that minimizes man-made noise or multipath interference traditionally associated with conventional radio broadcasts.

The first defense method, Orthogonal Frequency Division Multiplex (OFDM), stretches the duration of each data symbol by transmitting more bits per symbol period. By stretching the symbol period, multiple subchannel modulation reduces the effects of delayed radio signals interfering onto nearby data symbols (http://www.magi.com).

The second line of defense against multipath interference is the use of interleaving and forwards error correction (FEC). In the event that OFDM fails to prevent bit errors, FEC corrects errors, and interleaving distributes these errors to optimize the effectiveness of FEC (http://www.magi.com).

The third method to reduce distortion is the use of time diversity. By using the analog channel delayed in time as a backup, the probability of an outage due to multipath interference is reduced by as much as the square of the probabilities of fading occurrence (http://www.magi.com).

With regards to digital encoding systems, IBOC technology aims to reuse a broadcaster's technical infrastructure, i.e. the transmitters, transmission lines and antennae. For example, if an existing AM transmitter plant now generates, amplifies and radiates a good AM stereo signal, IBOC will work through this equipment with minimum modification, adding only a Digital Audio Broadcasting exiter to the existing system ( http://www.usadr.com/techni.asp). Currently, three major U.S. FM transmitter manufacturers are working to provide analog and digital amplification within a common transmitter and provide for an upgrade kit for the existing product (http://www.usadr.com/techni.asp). The goal is for the IBOC digital broadcasting exciters to cost the broadcaster no more than $30,000 to purchase and install. One of the primary advantages of IBOC DAB is the concept of frequency re-use. IBOC signals are designed so that for each station, the IBOC signals fit within the frequencies and spectral occupancy allowed for that station’s conventional AM or FM transmissions.

At its inception, the implementation of Digital Radio required the creation and allocation of a new radio broadcast spectrum. The consensus among radio broadcasters and reality of the situation, during this time, was that the creation of a new spectrum would undermine the economic foundation of broadcast radio by creating an unprecedented parity among radio broadcasters (http://www.usadr.com/why.asp). Under a new spectrum, each radio station would have equal power and equal coverage capabilities. Radio broadcasting, both past and present, rests on the notion that station power and coverage is purchased at a premium price. The implementation of a new spectrum disregards this fundamental principle of radio broadcasting.

Understanding the need to compete for listeners with alternative technologies, USA Digital Radio (USADR) was formed with the intent of creating digital radio without sacrificing the infrastructure of the conventional radio broadcasting industry (http://www.usadr.com/why.asp).

USADR partners include Westinghouse Electric Corporation, CBS Radio, Gannett Company, and Lucent Technologies. The vast and varied resources of each resulted in the creation of the IBOC digital radio scheme (http://www.usadr.com/who.asp). Today, this same entity remains the dominant guide of the industry.

It is expected that IBOC digital radio, in addition to CD quality sound without multipath interference, will be capable of transmitting a large volume ancillary data. Potential applications for ancillary data include station data such as call sign, format, artists and song titles as well as news, financial and stock market data, paging, dispatching, computer communications and networking.

In addition to ancillary data, it is expected that digital radio will be capable of monitoring signal strengths and use this information to switch automatically from a fading signal to a new, more powerful one (http://www.magi.com).

The concept of digital radio was inspired by the need of radio broadcasters to compete for listeners with alternatives to radio listening. While it is clear that the implementation of Digital Radio is advantageous to conventional radio broadcasting, additional technical and economic considerations were evaluated prior to endorsing this method of transmitting radio signals. A technical analysis was performed to establish viable options of providing digital radio service to consumers. An economic analysis was performed to determine the technical option that could be employed most efficiently and cost effectively. Nonetheless, the controlling factor in choosing to implement Digital Radio was minimizing the impact on the conventional radio broadcast infrastructure.

This type of thorough analysis will hold true in the future. In an effort to protect their investment, power, and coverage, the radio broadcast industry will continue to look at these indicators when development opportunities are presented.

The endorsement and implementation of IBOC DAB removes the political and technical nightmare of existing service reallocation and allows for quick regulatory implementation. Consequently, because no new spectrum will be required, the likelihood of an auction or lottery of DAB licenses and FCC administrative intervention in the conversion to DAB will be minimized (http://www.usadr.com/why.asp).

Nonetheless, any proposed modification to the current broadcast system requires approval of the Federal Communications Commission and a Standards Committee. This two-tiered approval system is designed to protect the existing broadcast infrastructure by ensuring that founding principles of radio remain intact.

The benefits of implementing IBOC digital radio are boundless for all parties involved. For the listener, digital radio will be more than just ‘the best sound on the airwaves,’ it will be an intelligent communications device that will offer more services and conveniences than can be provided by conventional analog technology. For the broadcaster, digital radio is not just a way to stay competitive with other forms of digital sound, but it will also offer numerous new business opportunities.

While it is clear that the digital radio services will be competitive with audio alternatives to radio listening, it is unclear how the market will respond. As it stands, the information services market is near saturation. The very same services digital radio expects to provide are currently being provided via pagers, via voice mail, via superwatch. Consequently, digital radio’s impact on the market may be far less that what is expected.

Nonetheless, radio, above all, is a survivor — and a worldwide survivor at that. The key to this survival has been a combination of imagination in programming, flexibility in operations, and most important, portability (http://www.nab.org/conventions/98/radio). Additionally, because radios are practically in every household and car, radio has become less sensitive to the needs of consumers ( http://www.nab.org/conventions/98/radio). This fact alone will carry digital radio to the future and beyond and, if anything, will allow digital radio to be a viable alternative to compact discs, television, and computers.

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