Editing Digital Audio Broadcasting (section)

===Use of frequency spectrum and transmitter sites===
DAB can give substantially higher [[spectral efficiency]], measured in programmes per MHz and per transmitter site, than analogue systems. In many places, this has led to an increase in the number of stations available to listeners, especially outside of the major urban areas. This can be further improved with DAB+ which uses a much more efficient codec, allowing a lower bitrate per channel with little to no loss in quality. If some stations transmit in mono, their bitrate can be reduced compared to stereo broadcasts, further improving the efficiency.

For example, analog FM requires 0.2&nbsp;MHz per programme. The [[frequency reuse]] factor in most countries is approximately 15 for stereo transmissions (with lesser factors for mono FM networks), meaning (in the case of stereo FM) that only one out of 15 transmitter sites can use the same channel frequency without problems with [[co-channel interference]], i.e. cross-talk. Assuming a total availability of 102 FM channels at a bandwidth of 0.2&nbsp;MHz over the Band II spectrum of 87.5 to 108.0&nbsp;MHz, an average of 102/15 = 6.8 radio channels are possible on each transmitter site (plus lower-power local transmitters causing less interference). This results in a [[system spectral efficiency]] of 1 / 15 / (0.2&nbsp;MHz) = 0.30 programmes/transmitter/MHz. DAB with 192&nbsp;kbit/s codec requires 1.536&nbsp;MHz * 192&nbsp;kbit/s / 1,136&nbsp;kbit/s = 0.26&nbsp;MHz per audio programme. The frequency reuse factor for local programmes and multi-frequency broadcasting networks ([[multi-frequency network|MFN]]) is typically 4 or 5, resulting in 1 / 4 / (0.26&nbsp;MHz) = 0.96 programmes/transmitter/MHz. This is 3.2 times as efficient as analog FM for local stations. For single frequency network (SFN) transmission, for example of national programmes, the channel re-use factor is 1, resulting in 1/1/0.25&nbsp;MHz = 3.85 programmes/transmitter/MHz, which is 12.7 times as efficient as FM for national and regional networks.

Note the above capacity improvement may not always be achieved at the L-band frequencies, since these are more sensitive to obstacles than the VHF band II frequencies, and may cause [[shadow fading]] for hilly terrain and for indoor communication. The number of transmitter sites or the transmission power required for full coverage of a country may be rather high at these frequencies, to avoid the system becoming noise limited rather than limited by co-channel interference.