ARQ-E

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ARQ-E is a radio transmission method used to send data over short wave radio. ARQ-E is a full duplex synchronous data communications system that requests repeats if data is not received correctly. It uses an alphabet that can detect errors. Another name for this is ARQ-1000 duplex [1] or ARQ-1000D.

Contents

Alphabet

The alphabet used in the ARQ-E protocol is an extension of the CCITT Telegraph Alphabet No. 2 more commonly known as Baudot. [2] This alphabet has five bits, and therefore has 25 or 32 different possible symbols. The ARQ-M alphabet being synchronous always has to send data and does not have gaps between characters. It does not include start and stop bits that would be used in asynchronous transmissions. In asynchronous transmissions a steady stop signal indicates that there is nothing to send.

The ARQ-E characters are extended with an identification bit or signal element at the start to indicate whether it is a normal character or a function signal. [2] This would add another possible 32 combinations to the code. But of the 32 only three are used. [2]

An extra symbol labelled α shows a start polarity, and another symbol labelled β indicates a steady stop polarity. So a stream of β characters will be sent if there is nothing else to send. The α and β symbols are called idle signals. The third symbol used is the RQ signal used to request a retransmit. [2]

A seventh bit is added to the character to indicate parity. Odd parity is used so that the number of stop polarity elements (1) is always odd. The parity bit is checked by the receiver to tell if an error has occurred in the transmission of the character. The return channel will include the RQ signal if an error is detected. [2]

Letters shiftfigures shift1 id23456parity 7
A-0110001
B?0100110
C:0011100
Dwru0100101
E30100000
F0101100
G0010110
H0001011
I80011001
Jbell0110100
K(0111101
L)0010011
M.0001110
N,0001101
O90000111
P00011010
Q10111011
R40010101
S'0101001
T50000010
U70111000
V=0011111
W20110010
X/0101111
Y60101010
Z+0100011
crcr0000100
lflf0010000
ltrs0111110
figs0110111
space0001000
0000001
RQ1110000
α1000110
β1001001

[2]

ltrs is the symbol to activate the letters shift.

figs is the symbol to activate figures shift.

Space is equivalent to the space bar

cr is carriage return

lf is line feed

cells with blank entries are undefined for international communications, but may have meaning within one country.

Marking

After the five bit characters are extended to seven bit, the polarity may be inverted to form a marking pattern, Either every fourth or every eighth character has its 0s and 1s (space and mark elements) transposed. There is also a variation with a cycle length of five characters, to be used when encrypters are in-line. [3]

Transmission

The seven bits resulting are converted from parallel to serial, sending the left-most element first, and then modulated onto a radio carrier using frequency-shift keying. Standard baud rates are 48, 64, 72, 86, 96, 144, and 192 baud. [4]

Repeat request

When an error is detected in a character received, then an RQ symbol is sent, along with a repetition of the last characters in the cycle. When an RQ is received, then an RQ is sent along with repeated characters starting from the one flagged as having a problem. The repeated characters would be three in the four character cycle, and seven in the eight character cycle. For the five character cycle, three characters are repeated after two RQ characters. For encrypted characters streams, it is very important to get the position in the sequence precisely correct, and it cannot afford to make a mistake with repeated data. [3]

Variants

Different variants of ARQ-E include ARQ-E3 which uses a different alphabet, ITA3 as in ARQ-M. ARQ-E3 can also be called CCIR 519. [5] ITU standard F.519 introduces this as a variant of ARQ-M, but with one channel. Standard bit rates are 48, 72 and 96 baud. [6]

ARQ-N is similar to ARQ-E but there is no marking pattern. [5]

Monitoring

Software is available for professionals and hobbyists to receive and decode utility transmissions that use ARQ-E. [7] Software includes go2MONIOR which can handle the variants [8] and multipsk, [9] the Rohde & Schwarz GX401DC, [10] the Hoka Code2-32P, [11] and Code200-32, Wavecom, the WiNRADiO Universal FSK Decoder,. [12] Early software included Radioraft. [13]

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IEEE 1355

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Hybrid automatic repeat request is a combination of high-rate forward error correction (FEC) and automatic repeat request (ARQ) error-control. In standard ARQ, redundant bits are added to data to be transmitted using an error-detecting (ED) code such as a cyclic redundancy check (CRC). Receivers detecting a corrupted message will request a new message from the sender. In Hybrid ARQ, the original data is encoded with an FEC code, and the parity bits are either immediately sent along with the message or only transmitted upon request when a receiver detects an erroneous message. The ED code may be omitted when a code is used that can perform both forward error correction (FEC) in addition to error detection, such as a Reed–Solomon code. The FEC code is chosen to correct an expected subset of all errors that may occur, while the ARQ method is used as a fall-back to correct errors that are uncorrectable using only the redundancy sent in the initial transmission. As a result, hybrid ARQ performs better than ordinary ARQ in poor signal conditions, but in its simplest form this comes at the expense of significantly lower throughput in good signal conditions. There is typically a signal quality cross-over point below which simple hybrid ARQ is better, and above which basic ARQ is better.

ARQ-M, short for Automatic Repeat reQuest, Multiplex, is a radio telegraphy protocol used to reliably forward telex messages over partially reliable radio links. It is a low-speed system designed to match the performance of landline telex systems and allow those messages to be forwarded over long distances using shortwave radios. The first ARQ-M link was built in the Netherlands, and began exchanging messages with a counterpart in New York in 1947.

References

  1. ↑ ITU Radiocommunication Assembly (1994). "Rec. ITU-R SM.1052 AUTOMATIC IDENTIFICATION OF RADIO STATIONS" (PDF). Retrieved 26 August 2014.
  2. 1 2 3 4 5 6 Wiesner, Lothar (1975). Telegraph and Data Transmission over Shortwave Radio Links. Berlin: Siemens Aktiengesellschaft. pp. 103–104. ISBN   3800912325.
  3. 1 2 Barbi, Luca (2011). "ARQ-E e ARQ-N / ARQ 1000 DUPLEX" . Retrieved 26 August 2014.
  4. ↑ Klingenfuss, Joerg (1991). Radioteletype Code Manual (11 ed.). Klingenfuss Publications. p. 70. ISBN   3924509115.
  5. 1 2 Proesch, Roland (May 2013). Technical Handbook for Radio Monitoring Hf. Books on Demand. pp. 146–147. ISBN   9783732241422 . Retrieved 26 August 2014.
  6. ↑ ITU Radiocommunication Assembly (July 1978). "Rec. ITU-R F.519 SINGLE-CHANNEL DUPLEX ARQ TELEGRAPH SYSTEM" . Retrieved 26 August 2014.
  7. ↑ RD, Baker (24 January 1996). "Hoka Electronics News Release" . Retrieved 17 August 2014.
  8. ↑ Van Horn, Larry (April 2013). "What's New" (PDF). Monitoring Times: 59.
  9. ↑ "Primary Changes from v. 4.26.1 to v. 4.27". Archived from the original on 2014-09-02. Retrieved 5 Sep 2014.
  10. ↑ "Industry-leading technology group" (PDF). Rohde & Schwarz. Retrieved 1 Sep 2014.[ permanent dead link ]
  11. ↑ "Hoka Code3". Archived from the original on 2014-09-07. Retrieved 5 Sep 2014.
  12. ↑ "WiNRADiO Universal FSK Decoder". Archived from the original on 2014-09-05. Retrieved 5 Sep 2014.
  13. ↑ Guillet, Francois (2004). "RADIORAFT 3.21 RADIO SIGNAL DECODER SOFTWARE" . Retrieved 5 Sep 2014.
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