Wavecom W74PC V8.7.0 - Manual (Page 156)

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Transmission Modes WAVECOM Decoder W74PC, W-PCI/e, W-CODE, W-CLOUD Manual V8.7.0
 Custom-defined LSR initialization for derandomization - expects a seven-digit hexadecimal
value for initialization (note that it is important to enter leading zeros). This option should be
used if the initialization value is known, or if it is not possible to calculate the value automatically
due to poor signal conditions.
The CODAN-9001 decoder has the following output options:
 Store channel data. The channel data output is very useful for analysis purposes. In the channel
data output every channel packet is stored in a file.
(C:\Users\Public\Documents\WAVECOM\W61PC\Data-Output\CODAN9001[SN])
 Enable frame status messages. It is possible to activate frame status messages, with the rele-
vant checkbox. The frame status messages are printed in the decoder output. They show [PREAM-
BLE FOUND] and [EXTENDED PREAMBLE FOUND].
 Decompress. The user can control the decompressor and the channel data output. Please refer
the section Compressed Mode specifics for further information on Compressed Mode. The user can
set the decoder/decompressor into the initial state with the Mode-Resync button in the
WAVECOM Toolbar.
 RAW DATA - the output consists of synchronized and demodulated multichannel symbols in hex-
adecimal representation. Every symbol consists of 32 bits (16 channels * 2 bits/channel).
 TEXT DATA - the demodulator output is processed into readable text.
 TEXT & RAW DATA - if possible the decoder decodes into readable text, otherwise it outputs the
demodulated multichannel symbols as RAW DATA.
 7 or 8-bit-ASCII. CODAN-9001 can use a 7-bit or an 8-bit alphabet, the choice being made by
selecting the appropriate radio button. The 7-bit alphabet is often used in transmissions handled
by the CODAN-9102 software.
The data is presented in two ways: hexadecimal-form, and ASCII-form.
At the beginning of every line the user can find the following information about the channel data packet:
 CRC OK or CRC NOK (not O.K.)
 SEQ [Nr] (Sequence number, a counter from zero up to the length of the packet)
 ARQ [Nr] (ARQ number used from the modems to request packets not received correctly)
At the end of a packet some statistical data is stored.
In secure mode the channel data packet output is adapted, as the secure interactive packets have a
slightly different structure.
The extended preamble gives an indication as to whether the transmission is a group or broadcast call.
The frame type, shown in the decoder status bar, indicates if the current package is ACK, IDLE or DATA. If
a data package with a known length is recognized, the decoder shows its length.
DECODING OF CODAN DATA MODEM SIGNALS
Introduction
This section intends to offer an overview of the issues related to the practical decoding of the CODAN data
modem protocol using WAVECOM decoders. It is important for the user to be aware of any constraints and
limitations inherent in the decoding process during non-cooperative interception of this mode, and so pos-
sible issues are explained below.
Protocol overview
The CODAN-9001 modem uses 16 DQPSK carriers for the transport of payload data. Each carrier is inde-
pendently modulated with data.
Each individual channel carries a channel packet. All 16 concurrent channel packets constitute a frame and
a number of frames constitute a multi-frame.
CODAN-9001 modem frame structure:
CH Frame 1 Frame 2 Frame 2 ... Frame n
1 Chnl packet 01 Chnl packet 17 Chnl packet 33 .... ...