RDS - Radio Data System A Challenge and a Solution Michael Daucher Eduard Gärtner Michael Görtler Werner Keller Hans Kuhr Abstract The launch of the FM broadcasting system in the middle of the 20th century constituted an enormous improve- ment compared to AM. Nevertheless it turned out that car radios cannot reach the performance level of stationary receivers. Therefore in Europe the RDS system has been developed. It provides among other features for increased convenience also specific functions to overcome the performance problems of car radios to a large extent. RDS is the most complex technology to receive analog broadcasting stations. To use this technology to the full extent it requires a lot of know how about the specific reception problems in the field, RDS and reception technol- ogy in general. All this leads to a large and very complex software solution. This paper describes the main reception problems of car radios. The basic features of RDS are explained short- ly. The main part of this essay deals with the software and the required tools. It is shown, based on three key issues, how these problems can be solved with high sophisticated software. The tool for monitoring the behaviour in the field, dedicated for detailed analysis and evaluation, is explained in detail. At the end the results of different test drives show the evidence that this new RDS software developed by Technical Center Nuremberg has reached a performance which is state of the art. 41 FUJITSU TEN TECHNICHAL JOURNAL 1 RDS1 RDS - Introduction. - Introduction. All these influences lead finally to a sum signal at the antenna which is continuously varying in amplitude, The launch of the FM broadcasting system in the phase and frequency. In consequence this fading signal middle of the 20th century constituted an enormous tech- has strong impact onto the quality of the audio signal nological step forward with regard to reception quality after demodulation in the receiver: and stability. The most obvious improvements of FM ・Heavy distortion due to missing parts of the FM sig- compared to AM are a considerable extension of the nal spectrum audio frequency range up to 15 kHz, a much higher S/N ・Fluctuating noise occurring each time the signal ratio, less distortion and no audio signal fluctuations as it level falls below the limiting threshold of the receiver is the case with AM fading ・Periodical noise bursts (paling fence effect) in case The FM system is very effective for stationary the fading signal is dominated by two main paths receivers. More or less directional antennas as dipole or with Doppler shift Yagi antennas outside the buildings are adjusted to the The above described problems of the FM system transmitter's site, so that mainly the signal of the direct show that FM is not suited for mobile transmission. The path is received, excluding reflected and delayed signals extension to FM stereo even increased these effects arriving from lateral paths. Therefore in Europe the RDS system has been devel- During the following decades FM-receivers in cars oped which provides among other very useful features became more and more popular. But it turned out that means for the realisation of network following. The mobile receivers cannot reach the quality level and signal receiver gets via the RDS data channel detailed informa- stability of stationary receivers. Mobile receivers are nor- tion about other frequencies of the same programme or mally operated together with omni-directonal antennas as transmitter chain. That enables a receiver to continuously the reception angle of the radio waves can adopt any check in the background all alternative frequencies and value within 360｠degrees. Therefore car receivers have to always select and tune to frequency with the best quality. cope with all the signals arriving at the receiving anten- By implementing very sophisticated RDS strategies and na, independent of the driving direction and the speed of plausibility checks in the receiver's software the draw- the vehicle. backs of the FM system can be overcome in a very large This so-called "mobile transmission channel" suffers extent. from multipath propagation and from Doppler shift which Since the first RDS specification has been published in is caused by the movement of the receiver itself or by 1984 the RDS system experienced continuous improve- moving reflecting obstacles. ment and optimisation and was finally issued as European Standard EN 50067 in April 1998. RDS has become a real- ly success story in Europe, so that even in America a subset of RDS has even been implemented as RBDS sys- tem. 2 The Radio2. The Radio Data Data SystemSystem -RDS- -RDS- The Radio Data System, RDS, is intended for applica- tion to FM sound broadcasts in the range 87.5MHz to 108.0 MHz which may carry either stereophonic (pilot- tone system) or monophonic programs. The main objec- tives of RDS are to enable improved functionality for FM Fig.1 Multipath propagation receivers and to make them more user-friendly by using features such as Program Identification, Program Service The example of Figure 1 shows two main propagation Name and automatic tuning for portable and car radios, paths where the waves are reflected on discrete obstacles in particular. like tall buildings, hills or mountain ridges. As the aver- The radio can make use of this information by a more age length of the two paths is different, the signals will or less sophisticated software strategy for an almost non arrive at different time instants in the vicinity of the car. disturbed radio reception over a long driving distance Additionally the signals are exposed to local dispersion and period of time. due to further reflections in the immediate surrounding of The data bits are transmitted with 1187.5 bits per sec- the receiving antenna. ond (57kHz/48). The bit stream is structured in blocks. Block A Block B Block C Block D Fig.2 RDS group FUJITSU TEN TECH. J. No.30(2008) 42 RDS - Radio Data System A Challenge and a Solution A block with 26 bits consists of 16 data bits and 10 2.1 Description of important group types check bits (CRC = cyclic redundancy check). This code In all groups are available: can correct 2 random errors in a block. An RDS group PI information (block A), PTY (block B), TP (if it is a consists of 4 blocks (ABCD). traffic program and if it supports traffic announcements Every group contains a block A with the program on related stations, in block B). identification (PI) code, which is a unique identifier of a Group 0A radio station. This information is repeated 11.4 times per Alternative frequency information is transmitted, second. The PI code: either as method A (up to 25 frequencies, normally used ・uniquely identifies a program and the country in to transmit the frequency of neighbor transmitters) or which the program is broadcast method B (more than 25 frequencies, normally every fre- ・allows selection of a program independent of a fre- quency on which the current station is broadcasted). quency Program Service Name is sent in group 0A and 0B. ・allows automatic frequency changes to frequencies TA, a traffic announcement is send in 0A 0B and 15B transmitting the same or related programs. (indicates a starting or ongoing traffic announcement). PI codes must be assigned by national authorities to The same groups apply for the MS bit (music/speech). avoid that different programs share the same PI code. DI the decoder information is send in 0A 0B and 15B. The PI code delivers also information about programs It can be used to signal if a compressed or not com- belonging to the same broadcast chain, for example: pressed program is broadcasted or if the program is Bayern 1, Bayern 2, Bayern 3. Some programs split into recorded in mono, stereo or with an artificial head programs with regional content for a certain period of Group 2A, 2B time. For example: Bayern 1 split into Bayern Franken, Radio text information is transmitted here. Bayern Bamberg and Bayern Ingolstadt. Group 14A The PI code offers the possibility to group the pro- Information about a related station which broadcasts grams of a broadcaster including the regional services. traffic announcement, like the frequency, alternative fre- European customers expect the station list sorted by PI quencies if it is a network and the PI code of this station. code and not only by frequencies or field strength. Group14B Indicates the start of a traffic announcement at the Sorted acc. to field strength Sorted acc. to grouped PI other station with the traffic program code 2.2 How to perform sophisticated network following This was about the signalling which the broadcaster can add to his program. Let us have a focus on the receiver. To reduce it to one sentence: The receiver should be able to perform the best reception under any conditions. The RDS information is one part of this strategy. Another part is determined by the used hardware con- In Europe the PI-code is the key for program identifi- cept and how the signal processing of the radio is per- cation. Selection by frequency is of minor importance. formed. Block B comprises the program type (PTY code), the The radio normally has different detectors for indication for traffic program (TP flag) and the RDS ・Fieldstrength or level detector group number (group type GT) which indicates the type ・Multipath distortion of data encoded in the blocks C and D. The program type ・Ultra sonic noise detector (USN) (for detecting neigh- signals the type of music or information which is current- bour channels) ly broadcast by the tuned radio station (classical music, ・Offset detector music, news ect.).