FM Radio - Any Digital Alternative?

FM radio is a well known and used technology. It is used all around the world. There are some minor differences in modulation parameters and frequency bands but the basic principle is the same. It is amazing how popular this radio has become. FM radio receivers are found everywhere, even in mobile phones. In the last decade broadcasting has made a big step toward digital technologies. We are now in a phase of transition from analog television broadcasting to various forms of digital broadcasting. And television is far more complex than radio--simple stereo sound service. Why is there no suitable technology for digital radio?

The answer is pretty simple. We have to look at key aspects of the transition of television broadcasting. Analog television uses one frequency channel (from 6 to 8 MHz bandwidth ) for one program. Digital television broadcasting is using the same radio-frequency channel to broadcast multiplex--a digital package of many TV programs and other services. The advantage is obvious--using the same radio-frequency spectrum we can now broadcast many TV channels and other services. Therefore, digital television broadcasting means more efficient use of frequency spectrum. There is another very important aspect of digital TV broadcasting. Since both technologies are using radio-frequency channels with the same bandwidth it is possible to switch from analog to digital step by step. Such change from one technology to another usually takes years and needs detailed preparations on a large scale.

To switch from analog FM to digital broadcasting we need a suitable technology that will offer comparable quality, mobile reception, capacity for more radio stations, efficient use of radio spectrum, step by step transition and cheap receivers. There are many digital technologies that are already available for sound broadcasting. Unfortunately, none of those technologies is suitable for a direct replacement of existing analog broadcasting.

Currently there are already many efficient audio codecs that can be used with any digital technology. There are also digital transmission technologies suitable for digital sound broadcasting like T-DAB, DRM and DRM+. DVB-T and DVB-T2 in particular can also be used for radio. All those technologies can provide excellent quality and mobile reception. But this is not enough.

FM radio uses about 250 kHz wide channels. Channel spacing is 100 kHz in most parts of the world and 200 kHz in USA and some other countries. This combination of channel bandwidth and spacing makes it very difficult to simultaneously use analog and digital broadcasting. Therefore, the transition with existing technologies will be difficult. Some partial solutions like HD radio are nothing more than additional data and audio transmitted along main analog carrier.

There are probably only two possible approaches for the digitalization of FM band. Either to find a suitable technology that will satisfy all the above mentioned requirements or to select one technology that is future proof enough and make a totally new frequency plan for fast transition. Currently, the digitalization of frequencies used for FM radio will have to wait for a while.