Why Radio Data System (RDS)?

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Radio Data System

Transmitting radio information

RDS, or Radio Data System, is a system for simultaneous transmission of FM signals and digital data, analogous to Teletext transmission on TV. Parallels between the two services should stop here, because RDS in contrast to Teletext has no independent life, but is transmitted solely to assist in trouble-free reception and to render additional information to the FM programme. The System is now included in many of Bang & Olufsen's current product line-up including BeoSound Ouverture, BeoSound 3000 and BeoSound 9000.

RDS has been developed under the auspices of the European Broadcasting Union (EBU) since 1974. The aim of the system is the instant and unique identification of the FM station in order to help the radio listener to find his/her way in the over-burdened FM radio band.

The System was developed primarily as a service for car radio reception, where reception conditions may change within seconds, due to the nature of FM broadcasting in relation to a moving car. When driving from one place to another, the RDS circuit constantly monitors the FM station and automatically changes to the same programme on an alternative frequency/transmitter if the reception is unsatisfactory.

Stationary radio receivers do not face the same problem as car radios. But the number of FM radio stations in Europe exploded in the 1980's and the '90s. Today there are more than 20,000. In many areas today up to 30 - 40 different stations can be received and this makes it extremely difficult to find out which station you are actually listening to and whether the right station has been found. A basic benefit of RDS is its ability to identify individual stations and show the identity on a display.

RDS fundamentals

The RDS standard can be summed up as follows:

The data signals are compatible and inaudible in monophonic and stereophonic programmes

The data signals are suitable for mobile reception. The area coverage of the data signal to be at least that of monophonic broadcast (in real life it is not expected that this specification is met; a more realistic coverage would be that of stereophonic broadcast). The system provides flexibility for a large number of applications, be open for future extensions and be standardised for use in all countries of Europe. RDS data does not interfere with existing transmission systems (ARI)

RDS modernises FM broadcasting with several optional features, while others are still on the drawing board; RDS is a technology that allows further features to be developed and transmitted in the future without problems of compatibility.

Static and dynamic data

RDS features can be split into two groups: static data and dynamic data. The static data have been implemented with most national broadcasting companies in Europe and a lot of private companies as well. Transmission of static data is cheap and only requires very little hardware - i.e. a generator in the transmitter chain and no extra maintenance. But transmission of dynamic data requires an operator with the broadcast company and is resource-demanding. Thus it is likely that full-scale implementation of dynamic RDS data will be prolonged into the future, although a lot of testing is already being carried out, e.g. in the UK and Germany.

Development of RDS since 1974:

1974: EBU starts the development of a system for the identification of individual FM stations

1982: tests show the Swedish contender PI to be the superior of 5 system, and PI is chosen as the basis for further RDS development

1984: in March, EBU settles the standard for RDS and thus paves the way for its commercial development

1987: RDS is presented to the public at the Internationale Funkausstellung in Berlin. The first car radios and stationary tuners with RDS are presented as prototypes

1987: RDS transmissions begin in the UK and Sweden

1988: RDS transmissions of static data with most European national FM stations

1989: RDS dynamic data testing with BBC and ARD

RDS description

RDS signals are carried on an amplitude modulated sub carrier at three times the 19 kHz pilot tone (57 kHz). A few European countries transmit other data on this frequency (ARI) and when both are transmitted, the two data signals will be sent with a phase difference of 90 degrees. The RDS sub-carrier is suppressed to avoid cross-talk in phase-locked loop stereo decoders.

The digital signals are transmitted in separate groups, each consisting of 104 bits. Each group is divided into 4 blocks of 26 bits each. The 26 bits of each block is divided into a 16-bit information parcel and a 10-bit error correction check word. The data rate is 1187.5 bits per second (57 kHz/48). Transmission of a complete group takes approximately 88 ms, i.e. slightly less than a tenth of a second, followed by the immediate transmission of the next group. By combining different blocks in a given pattern the RDS groups can transmit different messages; more important groups must be sent with a minimum amount of repetition in order to avoid drop-outs in the reception especially for car radio use.

RDS receiver

The first stationary receivers were shown at the Funkatisstellung in Berlin 1987 and at the 1989-Funkausstellung receivers from a number of manufacturers were available. Use of the RDS services requires a display with a capacity of at least 8 characters to show static data and 32/64 characters for dynamic data. As an alternative, dynamic data can be shown on a smaller display with a scrolling action. The characters are generated by an alphanumeric display controlled by the emitted codes. The alphanumeric display can be made available for other manual programming functions such as station naming, similar to station naming on TV receivers using the text generator in the Teletext decoder. In this way the user can name stations that are not using RDS, or override the RDS Programme Service Name with personal favourite names. The RDS module is placed in the tuner signal paths.

Conclusion

RDS is no revolution of the radio, but it effectively updates possibilities for both stationary and mobile receivers. In a historic situation where the sheer amount of radio stations threatens to confuse the user rather than give him/her extended possibilities, RDS restores the balance by offering a simple and logic identification of programme, station etc. Furthermore, RDS is not a static application or an emergency solution, it is a well-designed and dynamic system that could lead FM radio reception well into this century. The radio manufacturers have accepted RDS as a viable and desirable technology and most Research and Development departments are busy putting RDS decoders together for the more expensive receivers in the future range of the individual manufacturers. The key to the future is now in the hand of the radio stations and if they support RDS implementation wholeheartedly and in concert, RDS will boost radio services considerably on a mutual European basis. If not, RDS could be another of those technological dinosaurs...

Appendix

RDS services - 16 different application have been defined for RDS transmission. As described above, only a few of these have been implemented, i.e. mainly the static data. Below find a listed description of these applications. The list is based on the officially approved application names and abbreviations and are the ones most likely to be used in future publications.

Programme Identification (PI)

PI is used in the RDS decoder in the receiver. None of the PI data is shown on the display. The PI code identifies the radio station according to country, area coverage (options: local/national) and programme reference number of the station. PI is the most significant data and must be broadcast in every group - in some versions PI is sent in two of the blocks of a group.

Programme Service Name (PS)

PS is the data used for showing the name of the station on the display. It consists of up to eight characters, in ASCII format and can be displayed on all types of alphanumeric displays. PS data is important and must be relayed once in every group.

Alterative Frequencies (AF)

AF is mainly for car and portable radio reception, in so far as it renders information on up to 25 alternative frequencies for the programme that is actually being received. AF thus enables the receiver to automatically select an alternative frequency for the reception if the alternative frequency can be received at higher signal strength. AF uses a code system to list the frequencies of the alternative transmitters, the number of frequencies available and how many kHz the alternative station is offset from the one being received:

Code 0 = 87,5 MHz - the frequency being received

Code 249: 25 alternative frequencies available

Code 254: the offset of the alternative station is + 50 kHz. AF, is being transmitted in every group, as it is necessary for optimal car radio reception

The three applications listed above are the static and basic data. EBU lists the two first as necessary features in a RDS transmission, whereas AF and the one listed below, TP, TA and DI, are listed as desirable and the rest as optional.

Traffic Programme identification (TP)

TP provides information that the station being received regularly broadcasts traffic information. The service can be used for automatic search for a traffic programme, e.g. in a car radio. TP is transmitted simply as a one-bit code, denoting that the station in question carries traffic programmes or that it does not carry traffic programmes. TP is transmitted in all groups.

Traffic Announcements (TA)

If TP is provided, TA can be transmitted alongside so that the receiver may automatically switch from other sources, from stations without TP, or from stand-by to the traffic announcements. After the traffic announcement the receiver switches back to the original mode. As with TP, TA works with a simple either/or situation and thus only use 1-bit to denote that a traffic announcement is being broadcast at present/no traffic announcements. TA is transmitted in some of the possible group combinations

Programme Type Identification (PTY)

Up to 31 different programme types can be identified if PTY is implemented. PTY must be dynamic and usually change at least as often as the programme changes. Programme types include for children, news, pop, jazz, serious classical music, light classical music, entertainment. Code 31 is an alarm code intended to have priority. It should switch the receiver to the station transmitting the alarm message, no matter what mode the receiver was left in. PTY can be used for selection of favourite programme types in the receiver with automatic switching if the programme changes to another programme type. PTY also allows the user to make a scan search for types instead of just flipping through the available programmes indiscriminately.

Decoder Identification (DI)

DI provides information on the FM signal, i.e. mono/stereo/compression/artificial head stereo or if a noise reduction system (or combinations) has been employed. Up to 16 different DI codes can be broadcast with combinations of 4-bits.

Music/Speech Identification (MS)

MS enables the receiver to automatically switch between two volume control settings. MS is a simple on/off switching and thus only requires 1-bit for on/off decision.

Other Network (ON)

Information on other networks, e.g. local stations and the services they offer. Used in conjunction with AF to render data on 25 alternative frequencies for each of up to 8 other networks. Also data on TP and TA.

Programme Item Number

A service that can be compared to VPS (Video Programming System) on Teletext, in so far as it gives each programme its own identification code. With the function, e.g. a timer record can be started correctly even in the event of a transmission delay. PIN can also switch from sources/programmes to another programme and thus be used as an update function, e.g. for the news. PIN data comprises time and day in the month.

Clock and Time (CT)

With CT, a built-in clock in a receiver can be locked to the CT data and thus synchronised precisely, with automatic switching between summer/winter time. CT transmits Coordinated Universal Time (UTC) and Modified Julian Day (MJD), the international specification for time measurements and displays. The receiver still has to have its own clock, since the cyclic CT may not be decoded accurately every time. Local time and date will be converted in the receiver.

Radio Text (RT)

Radio Text is analogous to Teletext on TV, but with a maximum of 64 ASCII characters. This could be a list of radio programmes, traffic announcements, sport results, telephone numbers, questions in a quiz, melody titles etc. Future application could include printed messages from a built-in printer or messages rendered by a speech synthesiser. This application would be of value especially in car reception, where displays could interfere with traffic safety. RT is presently being tested with various national broadcasting companies, e.g. Finland, Germany and the UK

Transparent Data Channel (TDC)

For transmission of Radio Text data not suitable for the 64-character display but, e.g. for a television or computer monitor: graphics, alphanumerics, computer programmes etc.

Traffic Information Channel (TIC)

TIC displays traffic announcements (TA), either on the display, via printer or using a speech synthesiser.

Paging (PG or RP for Radio Paging)

Paging using FM programmes. PG can transfer up to 18 alphanumerics per pager.

In-house Application (IH)

Service for the transmitting company only, i.e. for internal communication between stations. It can be used for, e.g. remote switching or testing of RDS encoders from the central transmitter, internal paging etc.

Created: 9th January 2007
Modified: 2nd April 2007

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