Radio Data System (RDS) is a communications protocol standard for embedding small amounts of digital information in conventional FM radio broadcasts. RDS standardizes several types of information transmitted, including time, station identification and program information.
The standard began as a project of the European Broadcasting Union (EBU), but has since become an international standard of the International Electrotechnical Commission (IEC).
Radio Broadcast Data System (RBDS) is the official name used for the U.S. version of RDS. The two standards are only slightly different.
Both carry data at 1,187.5 bits per second on a 57-kHz subcarrier, so there are exactly 48 cycles of subcarrier during every data bit. (Note that kHz frequencies discussed here are before composition with the underlying carrier, which is in FM broadcast band somewhere from 87.5 to 108 megahertz.) The RBDS/RDS subcarrier was set to the third harmonic of the 19-kHz FM stereo pilot tone to minimize interference and intermodulation between the data signal, the stereo pilot and the 38-kHz DSB-SC stereo difference signal. (The stereo difference signal extends up to 38 kHz + 15 kHz = 53 kHz, leaving 4 kHz for the lower sideband of the RDS signal.
The data is sent with error correction. RDS defines many features including how private (in-house) or other undefined features can be "packaged" in unused program groups.
Maps, Directions, and Place Reviews
Development
RDS was inspired by the development of the Autofahrer-Rundfunk-Informationssystem (ARI) in Germany by the Institut für Rundfunktechnik (IRT) and the radio manufacturer Blaupunkt. ARI used a 57-kHz subcarrier to indicate the presence of traffic information in an FM radio broadcast.
The EBU Technical Committee launched a project at its 1974 Paris meeting to develop a technology with similar purposes to ARI, but which was more flexible and which would enable automated retuning of a receiver where a broadcast network transmitted the same radio programme on a number of different frequencies. The modulation system was based on that used in a Swedish paging system and the baseband coding was a new design, mainly developed by the British Broadcasting Corporation (BBC) and the IRT. The EBU issued the first RDS specification in 1984.
Enhancements to the alternative frequencies functionality were added to the standard and it was subsequently published as a European Committee for Electrotechnical Standardization (CENELEC) standard in 1990.
In 1992 the U.S. National Radio Systems Committee issued the North American version of the RDS standard, called the Radio Broadcast Data System. The CENELEC standard was updated in 1992 with the addition of Traffic Message Channel and in 1998 with Open Data Applications and, in 2000, RDS was published worldwide as IEC standard 62106.
RDS 2.0
The RDS-Forum (Geneva / CH) decided at its annual meeting (8-9 June 2015) in Glion/Montreux to bring the new standard RDS2 on the way. The standard will be created in close collaboration with U.S. colleagues from NRSC RBDS-Subcommittee and should offer a unified platform for FM broadcasting and data services worldwide.
- Seamless support for frequencies from 64 MHz to 108 MHz (AF, EON)
- New character coding: UTF-8 (old EBU Charset remains for compatibility mode for the old 0A/2A Groups).
- New ODA handling, "B" groups are assigned as signalling group to the "A" groups.
- Long PS-Name, up to 32 byte with UTF-8 character set. (Indian, Chinese, Arabic, and more)
- RadioText (eRT) 128 byte long with UTF-8
- Increased capacity from 11.4 up to 57 "A"-groups per second. (2,109 bit/s. net capacity with the single modulation-type multiple subcarriers (SMMS) technology)
- Graphical RadioText - supports HTML/CSS templates (for smartphones, car radios, computers/tablets)
- Supports return channel over gRT if the receiver has IP or SMS capability.
- Broadcaster's graphical logo - a maximum 4 kilobyte picture (JPEG, PNG, or GIF)
- Hybrid Radio feature (partly based on Radio France development)
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Content and implementation
The following information fields are normally contained in the RDS data:
RDS support
As far as implementation is concerned, most car stereos will support at least AF, EON, REG, PS and TA/TP.
- More expensive car stereos will offer TMC, RT and / or PTY, perhaps with "NEWS" override.
- Home systems, especially hi-fi receivers, will mainly support functions like PS, RT and PTY.
There are a growing number of RDS implementations in portable audio and navigation devices thanks to lower-priced, small-footprint solutions.
Program types
The following table lists the RDS and RBDS program type (PTY) codes and their meanings:
The later RBDS standard made no attempt to match the original RDS plan, therefore several identical radio formats were given different numbers, including jazz, weather, sports, and rock. Other similar formats such as varied/college and phone-in/talk are also mismatched. This is mainly a problem for Americans taking portable radios out of their country.
RDS Technical Specification
The RDS standard as specified in `EUROPEAN STANDARD EN50067` is separated into these sections according to the OSI model (Excluding network and transport layer, since this is a broadcasting standard).
- Data Channel (Physical Layer)
- Baseband Coding (Data-Link Layer)
- Message Format (Session And Presentation Layer)
Data Channel (Physical Layer)
The physical layer in the standard describes how the bitstream is retrieved from the radio signal. The RDS hardware first demodulates the 57 kHz RDS subcarrier signal to extract a Biphase encoded signal which contains both the bitrate clock and the differentally encoded bitstream. This allows for retrieving the RDS bitstream via a differential decoder, which requires a synchronised clock and a differentally encoded bit-stream.
Baseband Coding (Data-Link Layer)
The data-link layer describes the baseband coding of which the largest element in the structure is called a "group" sized 104 bits wide. Within each group are 4 blocks sized 26bits wide. Each block contains a 16bit data word and a 10 bit checkword. In the case of the FM Tuner RDA5807M IC, it displays a group in separate 16bits blocks over four i2c registers. All group is sent most significant byte first, with no gap between groups or blocks.
Synchronisation of the baseband coding structure from the RDS bitstream
The identification of a RDS message blocks and groups is done via a 10bit offset table containing offset word: A, B, C, C' , and D (In RBDS this also includes "E" ).
Message Format (Session And Presentation Layer)
A RDS message group consist of two versions of the group structure, designated in the standard as type A, and type B.
Within Block 1 and Block 2 are structures that will always be present in both group versions, for fast and responsive identifications. First block of every group, will always be the program identification code. The second block dedicates the first 4 bits for Application/Group Type
Meaning of Block 2 Bits
- GTYPE : Group Type
- B0 : If B0=0 then Message Group Type A else Type B
- TP : Traffic Program. Indicates if this is a traffic alert radio program.
- PTY : Program Type
- ???? : Rest of the bits are group type dependent
Message Version A
Message Version B
Block 3 is used for repeating program identification code.
Program Identification Code (PI Code)
This allows for quick identification of radio program type, based on country, coverage area, and program reference number. While the country code is specified by the standard, bit 11 to bit 0 is specified by each country local authorities.
Group Type
This is a short list of the full group type. Each group type may have a secondary version available
RDS Message Examples
These are non comprehensive examples that covers just the simple messages likes station name, radio text, and date time.
Group Type 0 - Version B - Station Name
As we have already described previous fields above, these dot points below show just the application specific fields.
- TA : Traffic Announcement
- M/S : Music/Speech
The station name and decoder identification code is sent progressively over 4 groups, where the offset is defined by bit C1 and C0.
Group Type 2 - Radio Text
As we have already described previous fields above, these dot points below show just the application specific fields.
- A/B : Text A/B flag is used to detect if a screen clear is requested.
- C3 to C0 : Is the text segment offset value
The station name and decoder identification code is sent progressively over 4 groups, where the offset is defined by bit C1 and C0.
Group Type 4 - Version A - Clock Time and Data
When group type 4A is used, it shall be transmitted every minute according to EN 50067.
The clock time group is inserted so that the minute edge will occur within +/- 0.1 seconds of the end of the clock time group.
Time and date are packed as these:
Note: The local time offset is expressed in multiples of half hours within the range -12h to +12h
- LOS : Local Offset Sign ( 0 = + , 1 = - )
Example RDS usage
The following three images illustrate how RDS can be used on an FM radio station; the latter two were taken when the radio was tuned to Nottingham radio station Trent FM. All the images are of the display on the Sony XDR-S1 DAB/FM/MW/LW portable radio.
RDS chipsets
Companies such as ST Microelectronics, Silicon Labs in Austin, Texas and NXP Semiconductors (formerly Philips) offer single-chip solutions that are found in these devices.
Source of the article : Wikipedia
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