question: What is RDS protocol and how does it apply to car radios that display a readout of the station/song/program?
comment: RDS - Radio Data System. It is a signal that is carried by station's transmission in what's called a "subcarrier". That subcarrier is outside the frequency range that the music is carried on. On the RDS signal, stations will often broadcast the title/artist for the current song and sometimes they'll transmit weather & traffic as well.
passages: The identification of a RDS message blocks and groups is done via a 10-bit offset table containing offset word: A, B, C, C' , and D (in RBDS this also includes "E").
  
  Section::::RDS Technical Specification.: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.
  
  Section::::RDS Technical Specification.:Message Format (Session And Presentation Layer).:Shared Structure.
   RDS-TMC is a low-bandwidth system. Each RDS-TMC traffic message comprises 37 data bits sent at most 1–3 times per second, using a low capacity data channel primarily designed for FM radio station name identification and tuning. Compressing traffic incident descriptions in multiple languages into 16 bits for a location, 11 bits for an event description code, plus 3 bits for the event's extent and a few extra bits for the duration/system management was necessary due to pre-existing constraints in the RDS standard. Almost all the other broadcast data bits were already assigned from each 104-bit RDS Group.
   Section::::Development.
  
  Detailed technical proposals for an RDS-TMC broadcasting protocol were first developed in the European Community's DRIVE programme research project RDS-ALERT, a partnership of the BBC, Philips, Blaupunkt, TRRL and CCETT led by Castle Rock Consultants (CRC). The main goal of the project was to develop and build consensus upon a draft standard for broadcasting RDS-TMC traffic messages in densely coded digital form.
   XDAIS algorithms
  
  XDAIS or eXpressDsp Algorithm Interoperability Standard is a standard for algorithm development by Texas Instruments for the TMS320 DSP family. The standard was first introduced in 1999 and was created to facilitate integration of DSP algorithms into systems without re-engineering cost. The XDAIS standard address the issues of algorithm resource allocation and consumption on a DSP. Algorithms that comply with the standard are tested and awarded an "eXpressDSP-compliant" mark upon successful completion of the test.
   The following information fields are normally contained in the RDS data:
   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.
  
  Section::::Development.:RDS 2.0.
   Section::::RDS Technical Specification.:RDS Message Examples.
  
  These are non comprehensive examples that covers just the simple messages likes station name, radio text, and date time.
  
  Section::::RDS Technical Specification.:RDS Message Examples.: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.
  
  BULLET::::- TA : Traffic Announcement
  
  BULLET::::- 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.
  
  Section::::RDS Technical Specification.:RDS Message Examples.:Group Type 2 - Radio Text.
   BULLET::::- Conducted immunity : Low frequency signals (usually 10 kHz to 80 MHz) are injected onto the data and power lines of a device. This test is used to simulate the coupling of low frequency signals onto the power and data lines, such as from a local AM radio station.
  
  BULLET::::- Conducted emissions : Similar to radiated emissions, except the signals are measured at the power lines with a filter device.
   A basic SDR system may consist of a personal computer equipped with a sound card, or other analog-to-digital converter, preceded by some form of RF front end. Significant amounts of signal processing are handed over to the general-purpose processor, rather than being done in special-purpose hardware (electronic circuits). Such a design produces a radio which can receive and transmit widely different radio protocols (sometimes referred to as waveforms) based solely on the software used.
   BULLET::::- VHF FM Radio Data System (RDS): RDS can send a clock signal with sub-second precision but with an accuracy no greater than 100 ms and with no indication of clock stratum. Not all RDS networks or stations using RDS send accurate time signals. The time stamp format for this technology is Modified Julian Date (MJD) plus UTC hours, UTC minutes and a local time offset.
   BULLET::::- MSB VMA report, 
  
  BULLET::::- http://www.interactive-radio-system.com/docs/EN50067_RDS_Standard.pdf
  
  Section::::External links.
  
  BULLET::::- FARWAY IRFC, TV and Radio Transmission , Radio Data System Encoders
  
  BULLET::::- Specification of the RDS standard, available via the RDS Forum
  
  BULLET::::- "NRSC-4 National Radio Systems Committee United States RBDS Standard – Specification of the radio broadcast data system (RBDS)"
  
  BULLET::::- The RDS Forum is the professional association of the users of the Radio Data System broadcast technology
  
  BULLET::::- RDS: "The Radio Data System", "The Broadcasters Guide to RDS"
  
  BULLET::::- RDS Features Serving as Tuning Aids
  
  BULLET::::- xRDS "Extending the RDS data transmission capacity"
   BULLET::::- TMC (traffic message channel): Digitally encoded traffic information. Not all RDS equipment supports this, but it is often available for automotive navigation systems. In many countries only encrypted traffic data is broadcast, and so an appropriate decoder, possibly tied to a subscription service, is required to use the traffic data. The subscription is often paid by the vehicle manufacturer and is therefore transparent to the user.
  
  Section::::RDS support.
  
  As far as implementation is concerned, most car stereos will support at least AF, EON, REG, PS and TA/TP.
   An initial proposal for defining RDS-TMC data fields had been made to the European Conference of Ministers of Transport (ECMT) in Madrid, based on a scheme developed by CCETT and Philips in the Eureka-sponsored CARMINAT research project. This proposal required the use of at least two 104-bit RDS data groups for each message. Within these RDS Groups, 32 bits per group would be used for traffic data, giving a total traffic message length of 64 bits. A second proposal, by Bosch-Blaupunkt and the German Road Research Institute BASt, sought to use just a single RDS Group per traffic message. Then, in 1987, the CEC invited Castle Rock Consultants to lead a joint team that would take TMC development a stage further. CRC produced a proposal for a modified BASt/Blaupunkt single group message definition, which became known as the ALERT A coding scheme. Tests also continued at CCETT and BBC on the CARMINAT approach, which formed the basis of an alternative ALERT B coding proposal.
   RadioVIS
  
  RadioVIS is a protocol for sideband signalling of images and text messages for a broadcast audio service to provide a richer visual experience.
  
  It is an application and sub-project of RadioDNS, which allows radio consumption devices to look up an IP-based service based on the parameters of the currently tuned broadcast station.
  
  In January 2015, the functionality of RadioVIS was integrated to Visual Slideshow (ETSI TS 101 499 v3.1.1). The original RVIS01 document is now deprecated.
  
  Section::::Details.
   The GNU Radio project already successfully demonstrated that purely software-based demodulators can exist and the hardware rule is not fully enforceable.
  
  Section::::Current status.
   RDM has been designed with the traditional DMX-512 serial interface in mind. It relies heavily on a few assumptions that could affect its compatibility with other lighting technologies.
   BULLET::::- PS (programme service name): This is simply an eight-character static display that represents the call letters or station identity name. Most RDS capable receivers display this information and, if the station is stored in the receiver's presets, will cache this information with the PI code, frequency and other details associated with that preset. In some countries, stations use the PS to dynamically send other information. This is prohibited in some countries and was not its intended use within the RDS system.
   WebSDR is a project initiated by Pieter-Tjerk de Boer providing access via browser to multiple SDR receivers worldwide covering the complete shortwave spectrum. Recently he has analyzed Chirp Transmitter signals using the coupled system of receivers.
  
  Section::::See also.
  
  BULLET::::- List of software-defined radios
  
  BULLET::::- List of amateur radio software
  
  BULLET::::- Digital radio
  
  BULLET::::- Digital signal processing
  
  BULLET::::- Radio Interface Layer
  
  BULLET::::- Softmodem
  
  BULLET::::- Software defined mobile network
  
  BULLET::::- Software GNSS Receiver
  
  BULLET::::- White space (radio)
  
  BULLET::::- White space (database)
  
  Section::::Further reading.
  
  BULLET::::- "Software defined radio : architectures, systems, and functions." Dillinger, Madani, Alonistioti. Wiley, 2003. 454 pages.
   A second method of prevention is by using cryptography. Rolling codes and challenge-response authentication (CRA) are commonly used to foil monitor-repetition of the messages between the tag and reader; as any messages that have been recorded would prove to be unsuccessful on repeat transmission. Rolling codes rely upon the tag's id being changed after each interrogation, while CRA uses software to ask for a cryptographically coded response from the tag. The protocols used during CRA can be symmetric, or may use public key cryptography.
   BULLET::::- EON (enhanced other networks information): Informs the receiver about other networks or stations, linked to the one being listened to, for dynamically changing data such as the TA flag turning on for a particular station of the network in a particular moment due to a traffic programme being broadcast, and automatically and temporarily allows the radio to tune into that station.
   The RDS-enabled receiver can be set to pay special attention to this TA "flag" and e.g. stop the tape/pause the CD or retune to receive a Traffic bulletin. The related TP (Traffic Programme) flag is used to allow the user to find only those stations that regularly broadcast traffic bulletins, whereas the TA flag is used to stop the tape or raise the volume during a traffic bulletin.
   The important thing to keep in mind is that the WS-RM specification only deals with the contents and behavior of messages as they appear "on the wire". How messages are sent from the AS to the RMS, how they are delivered from the RMD to the AD, whether messages are persisted on-disk or held in memory, etc.; none of these considerations are part of the WS-RM specification.
  
  The WS-RM protocol defines and supports a number of Delivery Assurances. These are:
   AES11 recommends using an AES3 signal to distribute audio clocks within a facility. In this application, the connection is referred to as a Digital Audio Reference Signal (DARS).
  
  AES11 Annex D (in the November 2005 or later printing or version) shows an example method to provide isochronous timing relationships for distributed AES3 structures over asynchronous networks such as AES47 where reference signals may be locked to common timing sources such as GPS.
   The RDM standard addresses this problem by ensuring that in all cases (except discovery) only one device is authorized to be transmitting at any given time (somewhat similar to the token passing approach). Only the controller (of which there can be only one) can start an RDM exchange. Responders can speak only if spoken to. The controller will always initiate all RDM communication.
  
  All RDM devices have a unique identifier (UID) that consists of a manufacturer ID and serial number.
  
  RDM communication can be broken down into three types:
  
  BULLET::::- Discovery
  
  BULLET::::- Unicast communication
  
  BULLET::::- Broadcast communication
  
  Section::::Technical Details.:Discovery.
   A fast PC performs the digital signal processing (DSP) operations using software specific for the radio hardware. Several software radio efforts use the open source SDR library DttSP.
  