World Broadcasting Unions Digital Radio User Manual - page 11

DIGITAL RADIO GUIDE

TERRESTRIAL TRANSMISSION SYSTEMS - DRM

11

4

Terrestrial Transmission Systems

This section provides a technical overview of the various digital radio systems available

for terrestrial application: DRM, DAB, ISDB-TSB, and HD Radio.  These systems operate 

in various frequency bands and offer different attributes and features.

4.1

DRM – Digital Radio Mondiale

The DRM system encompasses a high level of flexibility in its design. These are noted in 

this subsection in the signal flow sequence going from the delivery from a program studio 

or network control centre to a transmission site and on to reception and decoding in a

receiver.

4.1.1

Key Features of the System Design for the Markets to be Served by the 

DRM System

The DRM system is a flexible digital sound broadcasting system for use in the terrestrial 

broadcasting bands below 30 MHz.

It is important to recognize that the consumer radio receiver of the near future will need to 

be capable of decoding any or all of several terrestrial transmissions; that is narrow-band

digital (for 30 MHz RF), and analogue for the LF,

MF, HF and VHF (including the FM) bands. In addition there is the possibility of satellite

delivery reception in the L- and S-bands. The DRM system will be an important

component within the receiver. It is unlikely that a consumer radio designed to receive

terrestrial transmissions in the near future with a digital capability would exclude the

analogue capability.

In the consumer radio receiver, the DRM system will provide the capability to receive

digital radio (sound, program related data, other data, and still pictures) in all the

broadcasting bands below 30 MHz. It can function in an independent manner, but, as

stated above, will more likely be part of a more comprehensive receiver – much like the

majority of today’s receivers that include AM and FM analogue reception capability.

The DRM system can be used in either 9 or 10 kHz channels, or multiples of these

channel bandwidths. Differences on how much of the total available bit stream for these

channels is used for audio, for error protection and correction, and for data transfer

depend on the allocated band (LF, MF or HF) and on the intended use (for example,

ground wave, short distance sky wave or long distance sky wave, with a data application 

service or without one). In other words, there are modal trade-offs available so that the

system can match the needs of broadcasters worldwide. 

As noted in more detail in subsequent parts of this subsection, the DRM system has the 

following structure. It employs advanced audio coding (AAC), supplemented by spectral

band replication (SBR), as the main digital audio encoding. These are parts of the

MPEG-4 audio standard. SBR significantly improves perceived audio quality so that the

overall audio quality of a DRM signal is similar to that of FM (mono). Orthogonal

Frequency Division Multiplexing (OFDM) and Quadrature Amplitude Modulation (QAM)

are used for the channel coding and modulation, along with time interleaving and forward 

error correction (FEC). Pilot reference symbols are injected to permit a receiver to

“equalize” the channel by comparing a known stored bit sequence with the corresponding 

received sequence of these special bits, and adjusting accordingly if there are differences 

in the received compared to the stored sequence.