Radio Data System
The Radio Data System (RDS; literally translated: Radio Data System) allows the transmission of additional information for radio.
- 3.1 Control of RDS transmission
History
RDS was designed about 1983 by the European Broadcasting Union and reached around 1987 for the market. Radio Data System is standardized in DIN EN 62106. Currently valid version is EN 62106:2010-07 (English version ), which replaces the version of 2002.
The RDS pilot plant was recorded from 1984, official launch was April 1, 1988.
The first car radio with RDS was available in the Volvo 760 surcharge Volvo radio type SR- 701.
The RDS - recognition was initially mainly used in car radios, since it is possible by the transmission of alternative frequencies ( alternative frequencies ) to change automatically, without user intervention, the frequency, and thus to follow a set program once. This saves to manually search for the new frequency when the vehicle leaves the transmission range of a transmitter on the ride. The RDS signal must be generated specifically for each transmitter location, usually directly at the transmitter.
Services of the RDS
The services of the RDS are certain types of data which are sent and analyzed in accordance with the data type of the radio receivers. When transmitting, the data in transmission blocks (see below for the format ) of the service is defined in part by the type of group (group type, GT). Here are 16 types of groups in two versions A and B (32 in total ) are available.
RDS offers in addition to the common functions used for program identification, traffic and alternate frequencies of further options for additional information / services that are used but only occasionally by the transmitters and supported by many devices only partially.
Program Service Name (PS, GT 0A/0B )
Program Service Name ( PS) is the best-known service in the RDS. It allows the transfer of the station name in up to eight alphanumeric characters. Older car radios could only numbers and uppercase letters as well as restricted represent special characters, which was sometimes little room for meaningful PS text. Newer RDS receiver, especially radio text enabled devices must include extensive code tables, including the standard Latin briefs and other European characters ( see EN 62106 ).
More recently, it has become fashionable to transmit a longer station names, additional information such as the music currently playing, or even advertising by changing PS displays. However, this application violates the RDS specification and often hinders the transmitter memory management in the car stereo, to which some radio manufacturers are trying to filter out with intelligent software implementations the program name, so as to obtain the benefits of the PS again.
Programme Type (PTY in all broadcast GT)
Programme Type refers to the classification of stations by division, for example, pop music, news, classical or jazz. PTY select one of the standard features of conventional RDS receiver. PTY is not used by many broadcasters, or at best statically assigned (usually " pop" or "Classic ").
PTY -31 ( GT 9A)
PTY -31 provides theoretically an automatic Ein-/Umschaltlösung for emergency and disaster messages, but partly not implemented in newer receivers, since it was never or only misused at least in Europe. RAI, the Italian public broadcaster said in this respect some cautions against private broadcasters for "Station Kidnapping " from. The radio station had admonished radios forcibly changed by PTY -31 signal on their program because PTY -31 has the highest priority and the receiver switches automatically and the listener unintentionally.
Traffic Programme (TP, in all broadcast GT)
A traffic signal programs ( TP) is sent when a station offering the so-called traffic, that is, when information about traffic jams and hazards of a special signal to be announced. The TP identifier existed since the dawn of RDS and ARI has the previous function on 1 April 2005 completely replaced, which had been broadcast in parallel for backward compatibility to non- RDS - capable receivers until then.
Traffic Announcement (TA, GT 0A/0B, and 14B, 15B)
If TP is activated, causes a Traffic Announcement ( German: TA, abbreviated TA) for the time of announcement, for example, an increase in the volume (device dependent) or changing the playback of CD to the radio and then back again.
Enhanced Other Network ( EON, GT 14A, 14B)
Enhanced Other Networks ( EON ) enables the reception of traffic information (TA ), although the selected channel does not offer a TA program. This function is mainly used by the public radio stations that do so, for example, students of the waves of culture (eg, MDR Figaro ) the traffic messages of pop and youth waves (eg MDR Jump) accessible. Germany radio culture uses EON to refer to regional or federal state specific traffic (such as MDR 1 Radio Sachsen ).
When a traffic message is sent from the traffic radio station, this is signaled via RDS group 14, which carries the EON receiver causes switch for the duration of the traffic message to the other program with the message (typically from the same family of channels ) and after the message back to the TP -less output program. With the signaling of an announcement once some link -related information with broadcast, such as PI of the relevant traffic information station, and possible frequencies ( AFs ) for fast tuning of the EON receiver.
EON is theoretically well suited to switch to other program types ( PTY) such as messages on a connected transmitter, if there begins a program of the same PTY concerned. This function is not used by the transmitters and receivers.
If EON is supported, is mostly found an EON icon on the front panel.
Traffic Message Channel ( TMC, GT 8A)
The Traffic Message Channel ( TMC) contains coded traffic messages which can be displayed by a navigation system and used directly for route planning. In foreign countries, the receiver can generate constructs messages in their own language.
Alternative Frequency (AF, GT 0A/0B )
The function Alternative Frequency (AF) enables automatic switching of the receiving frequency when leaving the reception range of a transmitter. In the AF table in the RDS constantly alternate frequencies of surrounding stations are broadcast, which also convey the set program. Normally, the receiver should continuously monitor the quality of the received signal and optionally switch to a different specified in the AF frequency table. The change is only successful if the programs - Identification code ( PI, see below) matches. This avoids, that a change to a radio frequency which is assigned to this point, by another program.
Program Identification (PI, in all broadcast GT)
The Program Identification Code (PI) is a transmitter internal identification code, which is used, inter alia, in the search for AFs ( alternative frequencies ). It consists of a 16 -bit number, which allows a unique identification of the transmitter. In the 4- digit identification number country code is included as well as a region identifier (Reg -bit). In addition, one of the transmitter chain associated, individual numbering.
Radio Text ( RT, GT 2A, 2B)
Radio Text ( RT) submitted additional information such as the current song and artist, or contact the sender. The text transmission line by line, one line contains a maximum of 64 characters. For most car radio, however, omitted for security aware to this function so as not to draw the driver's attention on the displayed text. In the current RDS specification EN 62106 also radio text / Radio text plus ( RT ), was integrated. In parallel, now multiply the implementations, including even already at " Original Radio" (so called OEMs) that are tightly integrated into modern vehicles.
Music / Speech (MS, GT 0A/0B, 15B)
With Music / Speech (MS ), a distinction in a bit between music and voice transmission, so that a radio can switch for example between two sound profiles.
Clock Time (CT, GT 4A)
The clock -time signal (CT ) is used for time synchronization. If the signal is broadcast, inaccuracies of the clock in the receiver, this signal can be corrected. This function is mainly used by the public broadcasters.
Open Data Applications ( ODA GT 11A, 12A, 3B, 4B, 7- 13B)
Open Data Applications ( ODA) has been introduced to easy to make the RDS system extensible, and thus to be able to quickly implement additional data services without the need to adjust the default explicitly for it. Examples of ODAs are ( besides the above- mentioned TMC) the transmission of DGPS correction data; RT (Radio text plus), a machine-readable evolution of the radio text; or iTunes tagging, which allows identification of a broadcast song from the iTunes Music Store (currently only HD Radio ).
Technical Basics
The data bits are transmitted at a data rate of 1187.5 bits per second. The modulation method, a digital two- sideband method (2 -PSK) is used, is being used as the carrier of the 90 ° rotated ARI pilot tone of 57 kHz. The 90 ° phase rotation, the ARI signal and the RDS signal can be received independently of one another, since the two signals are orthogonal to each other. In addition, the carrier is suppressed. Support and transfer rate are in a Relationship: carrier frequency ( 57 kHz) / 48 requirement for the independent reception is the coherent demodulation. The necessary phase information is derived from the phase of the stereo pilot tone at 19 KHz (1 /3 of the RDS carrier frequency) in the receiver.
With RDS, form each 26 bits a block which in turn consists of 16 data bits and 10 check bits. Here is a linear code for the application, which has a minimum Hamming distance of 5, that is, it can be corrected two random error within a block. The code is designed to leave that up to 11 more correct errors when they are present as bundles disorder, ie directly next to each other. With the aid of check bits and the block boundaries, and the type of the block can be detected. Each four blocks (ABCD or ABC'D ) form a RDS group.
Important still, the synchronization of the blocks. Data transfers are normally always synchronized with a special data word having a high probability of detection in a noisy signal. But this method can not be applied here as a continuous data stream is present. For this purpose, a different procedure is used: Considering the above error correction method in more detail, one finds that there are more possibilities of error in addition to the specified error corrections that can not be used because they fit into a schema. For these words are not usable error 5 is selected and assigned to the blocks. Blocks A, B, C, D, and C '. These errors are added corresponding to the blocks at the transmitting side. As the type of errors on the receiver side can be recognized, a receiver searches for these errors. Can 3 errors in the proper group order are detected, one starts from a correct synchronization and can then analyze the data. However, there are still on the receiving end of appropriate strategies for positive and negative bitslip to develop.
The specifications are found in the DIN standard DIN EN 62106th
In block A, the 16- bit channel ID ( Identification Programs, PI) is always transmitted. In block B is found the program type ( PTY), an indicator for traffic information (TP ) and the RDS group number ( Group Type GT). This provides information on the use of the remaining five bits of the block B and the 32 bits of block C and D. There are a number of RDS groups that are used for various additional data services, such as group 11A (see Beispielbitmuster ) or group 3A for Open Data Applications ( ODA).
Control of the RDS transmission
As long as the use of RDS largely limited to the transmission of static data such as TP / TA or AF, control of acoustic signals (sounds, as Hinz- trill ) is possible. For the procedure " control of the RDS / VRF system by Hinz- trill " with the letter FTZ 175 AB 33 was given by the German Telekom. There were only a few devices approved for control (including Rudolph HT090 ). If in addition, other services are used, is a transmission in other ways to the RDS encoder required (such as a separate data line ). A suitable method can be found at UECP.
Radio data systems
The RDS method can be used in the described form only for broadcasting on the FM band. By phase modulation of the carrier but can also broadcast transmitters in long, medium and short wave range for the receiver imperceptible additional information transmit (amplitude modulated data system, AMDS ).