was ich damit machen will???
steht in der überschrift, aber noch nicht, hmm. für die, die noch nich wissen was ein RDS signal is, hier n kleiner informativer text(leider nur auf englisch)
:
Viel Spa´beim lesen:
RDS
The Radio Data System standard is widely adopted on pretty much every
modern FM radio, 99.9% of all car FM radio models feature RDS nowadays.
The standard is used for transmitting data over FM broadcasts and RDS-TMC
is a subset of the type of messages it can handle. The RDS standard is
described in the European Standard 50067.
The most recognizable data transmitted over RDS is the station name which
is often shown on your radio display, other information include alternate
frequencies for the station (that can be tried when the signal is lost),
descriptive information about the program type, traffic announcements (most
radio can be set up to interrupt CD and/or tape playing and switch to radio
when a traffic announcement is detected), time and date and many more
including TMC messages.
In a FM transmission the RDS signal is transmitted on a 57k subcarrier in
order to separate the data channel from the Mono and/or Stereo audio.
FM Spectrum:
Mono Pilot Tone Stereo (L-R) RDS Signal
^ ^ ^ ^ ^^
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--------------------------------------------------------------------------
19k 23k 38k 53k 57k Freq (Hz)
The RDS signal is sampled against a clock frequency of 1.11875 kHz, this
means that the data rate is 1187.5 bit/s (with a maximum deviation of +/-
0.125 bit/s).
The wave amplitude is decoded in a binary representation so the actual data
stream will be friendly '1' and '0'.
The RDS smallest "packet" is called a Block, 4 Blocks represent a Group. Each
Block has 26 bits of information making a Group 104 bits large.
Group structure (104 bits):
---------------------------------------
| Block 1 | Block 2 | Block 3 | Block 4 |
---------------------------------------
Block structure (26 bits):
---------------- ---------------------
| Data (16 bits) | Checkword (10 bits) |
---------------- ---------------------
The Checkword is a checksum included in every Block computed for error
protection, the very nature of analog radio transmission introduces many
errors in data streams. The algorithm used is fully specified in the
standard and it doesn't concern us for the moment.
Here's a representation of the most basic RDS Group:
Block 1:
--------------------- PI code = 16 bits
| PI code | Checkword | Checkword = 10 bits
---------------------
Block 2: Group code = 4 bits
B0 = 1 bit
--------------------------------------------------- TP = 1 bit
| Group code | B0 | TP | PTY | <5 bits> | Checkword | PTY = 5 bits
--------------------------------------------------- Checkword = 10 bits
Block 3:
------------------ Data = 16 bits
| Data | Checkword | Checkword = 10 bits
------------------
Block 4:
------------------ Data = 16 bits
| Data | Checkword | Checkword = 10 bits
------------------
The PI code is the Programme Identification code, it identifies the radio
station that's transmitting the message. Every broadcaster has a unique
assigned code.
The Group code identifies the type of message being transmitted as RDS can
be used for transmitting several different message formats. Type 0A (00000)
and 0B (00001) for instance are used for tuning information. RDS-TMC
messages are transmitted in 8A (10000) groups. Depending on the Group type
the remaining 5 bits of Block 2 and the Data part of Block 3 and Block 4
are used according to the relevant Group specification.
The 'B0' bit is the version code, '0' stands for RDS version A, '1' stands
for RDS version B.
The TP bit stands for Traffic Programme and identifies if the station is
capable of sending traffic announcements (in combination with the TA code
present in 0A, 0B, 14B, 15B type messages), it has nothing to do with
RDS-TMC and it refers to audio traffic announcements only.
The PTY code is used for describing the Programme Type, for instance code 1
(converted in decimal from its binary representation) is 'News' while code
4 is 'Sport'.
Und für die, die noch nicht wissen, was ein TMC(oderTCM
) signal ist, hier noch ein kleiner text...(auch auf englisch)...
TMC
Traffic Message Channel packets carry information about traffic events,
their location and the duration of the event. A number of lookup tables are
being used to correlate event codes to their description and location
codes to the GPS coordinates, those tables are expected to be present in
our SatNav memory. The RDS-TMC standard is described in International
Standard (ISO) 14819-1.
All the most recent SatNav systems supports RDS-TMC to some degree, some
systems requires purchase of an external antenna in order to correctly receive
the signal, modern ones integrated in the car cockpit uses the existing FM
antenna used by the radio system. The interface of the SatNav allows
display of the list of received messages and prompts detours upon events
that affect the current route.
TMC packets are transmitted as type 8A (10000) Groups and they can be
divided in two categories: Single Group messages and Multi Group messages.
Single Group messages have bit number 13 of Block 2 set to '1', Multi Group
messages have bit number 13 of Block 2 set to '0'.
Here's a Single Group RDS-TMC message:
Block 1:
--------------------- PI code = 16 bits
| PI code | Checkword | Checkword = 10 bits
---------------------
Block 2: Group code = 4 bits
B0 = 1 bit
----------------------------------------------------- TP = 1 bit
| Group code | B0 | TP | PTY | T | F | DP | Checkword | PTY = 5 bits
----------------------------------------------------- Checkword = 10 bits
T = 1 bit DP = 3 bits
F = 1 bit
Block 3: D = 1 bit
PN = 1 bit
------------------------------------- Extent = 3 bits
| D | PN | Extent | Event | Checkword | Event = 11 bits
------------------------------------- Checkword = 10 bits
Block 4:
---------------------- Location = 16 bits
| Location | Checkword | Checkword = 10 bits
----------------------
We can see the usual data which we already discussed for RDS as well as new
information (the <5 bits> are now described).
We already mentioned the 'F' bit, it's bit number 13 of Block 2 and it
identifies the message as a Single Group (F = 1) or Multi Group (F = 0).
The 'T', 'F' and 'D' bits are used in Multi Group messages for identifying if
this is the first group (TFD = 001) or a subsequent group (TFD = 000) in the
stream.
The 'DP' bit stands for duration and persistence, it contains information
about the timeframe of the traffic event so that the client can
automatically flush old ones.
The 'D' bit tells the SatNav if diversion advice needs to be prompted or
not.
The 'PN' bit (Positive/Negative) indicates the direction of queue events,
it's opposite to the road direction since it represent the direction of the
growth of a queue (or any directional event).
The 'Extent' data shows the extension of the current event, it is measured
in terms of nearby Location Table entries.
The 'Event' part contains the 11 bit Event code, which is looked up on the
local Event Code table stored on the SatNav memory. The 'Location' part
contains the 16 bit Location code which is looked up against the Location
Table database, also stored on your SatNav memory, some countries allow a
free download of the Location Table database (like Italy[1]).
Multi Group messages are a sequence of two or more 8A groups and can
contain additional information such as speed limit advices and
supplementary information.