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Дата: 22 Ноя 2007 19:09:54
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marvel
У меня в кодах с G-TOR тоже самое, при этом в описании сигнала сказано, что Golay Transmission over Radio. A system developed by engineers at Kantronics, Inc. The cycle duration of G-TOR is always 2.4 s. The data frame has a length of 1.92 s, which leaves 0.16 s for acknowledgement from the remote station. At 300 Baud 69 data bytes are transferred, at 200 Baud 45 bytes and at 100 Baud 21 bytes. After the end of the data block a control byte and a 16 bit CRC sum are appended. On the receiving side up to 3 incorrect bits may be corrected using a (24, 12) Golay code. In addition the data bits are interleaved (bit interleaving). The complex G-TOR system is described in detail by the manufacturer KANTRONICS in a booklet (G-TOR, The New Mode, Articles, Charts, Protocol, edited by Shelley Marcotte)., т.е. скорость манипуляции 100, 200 и 300 бод, а CODE300-32 по умолчанию «навязывают» скорость 225 Baud, отсюда вопрос 225 это скорость манипуляции или скорость передачи???
Посмотрел http://www.signals.taunus.de/WAV/G-TOR.HTML и это "вроде G-TOR" , может закрытый?, не знаю, но все равно с кодами что-то не то -- при декодировании одного блока G-TOR выдает всегда разную белиберду, а по идеи должен одинаковую???
P.S. может у кого-то есть образцы сигнала G-TOR, только не с сайта http://www.signals.taunus.de/WAV/G-TOR.HTML, пожалуйста, слейте на эту форум.
Еще интересует описание протокола G-TOR, соответственно не с CODE300-32. |
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Дата: 22 Ноя 2007 21:11:34
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Нашел описание протокола G-TORG-TOR
1. PROTOCOL
G-TOR is a trademark of Kantronics, Inc. G-TOR (Golay-Teleprinting Over Radio)
can be viewed, in part, as a variant of the Automatic Link Establishment (ALE)
protocol, outlined in MIL-STD-188-141A. G-TOR combines the error correcting
properties of ALE, including Forward Error Correction (FEC) coding and
full-frame interleaving, the Automatic Repeat reQuest (ARQ) cycle of Packet and
a new application of the invertibility of the Golay code, to produce a faster
new mode.
2. DATA FRAME STRUCTURE
G-TOR is a synchronous transmission system with a data frame duration of 1.92
seconds and a 0.48-second window between data fraines, for a total cycle time of
2.40 seconds regardless of transmission rate. Data frames are 192, 384, or 576
bits long sent at 100, 200, or 300 symbols/sec, respectively, with the data rate
dependent on band conditions. Each data frame consists of a Data field and
Status byte, followed by a two-byte Cyclic Redundancy Check (CRC). No start or
ending flags are added to any of the frames, thus lowering overhead and
resulting in improved frame efficiency relative to AMTOR and PacTOR. The Data
field contains 21, 45, or 69 eight-bit bytes sent at 100, 200, or 300
symbols/sec, respectively. The Status byte provides the frame number
identification, data format (whether standard 8-bit ASCII or Huffman
compressed), and a command (data, turnaround request, disconnect, or connect)
for a total of 8 bits.
3. ACKNOWLEDGEMENT (ACK) FRAME STRUCTURE
ACK frames are used to acknowledge correct or incorrect receipt of data frames,
to request changes in transmission speed, and to change the direction of
information flow. There are five different ACK frames: Data frame received
without error (send next frame), Data frame error detected, Speed-up,
Speed-down, and Changeover. Each of the ACK frames consists of two eight-bit
bytes sent from the information-receiving station to the information- sending
station at 100 symbols/sec, for a duration of 0.16-second during the 0.48-second
window between data frames. The Changeover ACK frame initiates a changeover in
information flow direction by starting out with a two-byte Changeover ACK (which
causes the information-sending station to stop sending) followed by 19 data
bytes, a single status byte, and a two-byte CRC, for a duration of 1.92 seconds
(the same as a data frame). None of the ACK frames are interleaved; however,
each is generated from a set of pseudorandom numbers and up to three bit-errors
are allowed per ACK, thus reducing needless retransmissions from faulty ACK
signals. Hence the ACKs are called fuzzy. Link quality, denoted by a set number
of consecutive good or bad frames, determines link speed.
4. ASCII CHARACTERS AND HUFFMAN / RUN-LENGTH COMPRESSION
G-TOR frames are sent in normal ASCII or are Huffman and run-length encoded,
depending upon which is more efficient on a frame-by-frame basis. The Huffman
table for G-TOR is unique: It differs from the PacTOR table in that it
emphasizes English over German character usage and upper and lower case
characters are swapped automatically (frame-by-frame) in a third attempt to
compress data—hence Huffman forms A and B.
5. GOLAY ERROR-CORRECTION CODING AND INTERLEAVING
G-TOR uses extended Golay coding which is capable of correcting three or fewer
errors in a received 24-bit code word. The Golay code used in G-TOR is a
half-rate code, so that the encoder generates one error-correction bit (a parity
bit) for every data transmitted. Interleaving is also used to correct burst
errors which often occur from lightning, other noise, or interference.
Interleaving is the last operation performed on the frame before transmission
and de-interleaving is the first operation performed upon reception.
Interleaving rearranges the bits in the frame so that long error bursts can be
randomized when the de-interleaving is performed. When operating at 300
symbols/second, the interleaver reads 12-bit words into registers by columns and
reads 48-bit words out of the registers by rows. The de-interleaver performs the
inverse, reading the received data bits into registers by rows and extracting
the original data sequence by reading the columns. A long burst of errors, for
example 12-bits in duration, will be distributed into 48 separate 12-bit words
before the error correction process is applied. This effectively nullifies the
errors. Both data frames and parity frames are completely interleaved.
In addition, by using the invertibility characteristic of Golay code words, data
frames are always alternated with data frames coded in Golay parity bits. In
this way, G-TOR can maintain full speed (when band conditions are good)—rather
than fall to rate-1/2. Receiving parity bits can be used as data or as parity.
6. LINK INITIALIZATION
To establish a link, the information-sending station transmits the call sign of
the intended receiver. Once the information-receiving station has synchronized,
it sends an ACK to the information-sending station and data transmission begins.
7. SIGNAL CHARACTERISTICS
G-TOR uses frequency-shift keying like PACTOR and packet radio. At 300
symbols/second, and with the recommended frequency shift of 170 or 200 Hz,
G-TOR’s spectral characteristics are almost identical to those of packet radio.
8. ERROR DETECTION AND ARQ CYCLE
G-TOR provides error correction by using a combination of both ARQ
retransmission and forward error-correction. The error-detection code
transmitted with each frame is a 2-byte CRC code, the same used in the AX.25
packet protocol, and it is used to determine if the frame was received correctly
before error correction is initiated and after error correction is completed, to
ensure that the error-correction process has successfully removed all errors in
the packet. Although the CRC error-detection code is used on every frame to
detect errors, the Golay error-correction procedure is skipped unless errors are
detected. This ability to skip unnecessary error correction is extremely
valuable since forward error correction is very costly in terms of throughput.
The Golay code used in G-TOR is a half-rate code, with one error-correction bit
required for every information bit; however, by using the invertibility of the
extended Golay code, the half-rate transmission result normally encountered with
FEC systems is avoided. Frames made up of parity bits can be fully converted to
data frames. Received frames are synchronized, deinterleaved, decoded and
checked for proper CRC. If the frame is found to be in error, the
information-receiving station will request that the matching parity frame be
sent. If the parity (or data) frame that follows is found to be correct, that
frame is acknowledged. If, however, it too is in error, it is combined with the
previous data (or parity) frame in an attempt to recover the original data bits.
In this way the system has three chances to recover the original data from the
transmission of one data and one parity frame. If unsuccessful, the ARQ cycle
begins again. The dispersal of noise-burst errors via interleaving, combined
with the power of the Golay code to correct 3 bits in every 24, usually results
in the recovery of error-free frames.
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