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deviation, limited to 7.5 kHz in the standard, but typically broadcast at about 2 kHz; therefore, RDS is generally

difficult for the receiver to decode unless a signal is fairly strong. In urban environments with many large

broadcasting stations, an FM tuner with modest performance can typically receive many signals which exceed the

requirements for decoding RDS.

*Note: RDS/RBDS will be noted as only RDS throughout this paper since the two standards are largely unified.

Figure 1. MPX Signal Spectrum

RDS in Europe and RBDS in North America are identical at the physical layer, and nearly identical at the data-link

and presentation layers, with exceptions highlighted in Section 7. Differences between the data-link layers are

managed internally by the device. Key differences at the presentation layer are discussed later in this document.

The remainder of this document refers to RDS and RBDS simply as RDS where a distinction is not required.

RDS is transmitted in a continuous stream of four data blocks each containing 26 bits of content and error-

correction information. Each set of four blocks constitutes a group. There are required repetition rates in the

standard to which all RDS-certified transmitting devices must adhere (shown in Table 2), but aside from this, all

information related to presenting the content of an RDS group is contained within the four blocks of data.

Figure 2. Structure of the Baseband Coding

The blocks each contain 26 bits; 16 bits in the information word, and 10 bits in the checkword and offset word. The

checkword and offset word contain error correction, synchronization, and block identification information. The

information word contains the coded content of the data blocks including RDS group types and associated content,

and represents 64 total bits per group of four data blocks (16 x 4 = 64).

There are 32 possible group types ranging from basic tuning information and emergency warnings, to "Open Data

Applications (ODA)" which can support many content types. In most of the North American and European markets,

only a few RDS groups are used by the broadcasters conveying station identifiers, alternative frequencies between

broadcast coverage areas, traffic alerts and locations, and relevant information to the broadcast content. Other

markets are currently using similar group patterns.

The information coded into each RDS group has a common fixed structure according to the RDS group type. The

structure dictates a standard repetitive data format and repetition rate to maximize reliability in all environments,

while allowing for content flexibility. The structure for all RDS group types is shown in Figure 3.

057

53

38

23

19

15

Frequency (kHz)

Stereo Audio

Left - Right

RDS/

RBDS

Mono Audio

Left + Right

Stereo

Pilot