HC-ARQ is a simplex system operating at a symbol rate of 240 Bd on the radio link.
|
Parameter |
Value |
|
Frequency range |
HF |
|
Operation modes |
Simplex ARQ |
|
Modulation |
FSK |
|
Symbol rate |
240.0 Bd, variable 30-650 Bd |
|
Receiver settings |
DATA, CW, LSB or USB |
|
Input format(s) |
AF, IF |
|
Additional Info |
ITA-2 with block coding |
HC-ARQ does not use a fixed timing cycle so data blocks of the information sending station (ISS) and the acknowledgement blocks of the information receiving station (IRS) have no fixed timing frame.
Synchronization is achieved by a long bit sequence at the start of each block. The start sequence consists of the bit pattern 1000 1011 10101 0010 and 16 subsequent control bits. After the start sequence sixty ITA-2 characters and 32 check bits for each block follow.
HC-ARQ may be set to one of three data block lengths with 30, 60 or 180 characters (150, 300 or 900 data bits). However, the system is not adaptive and the block length must be set to the same value by both stations before transmissions start.
HC-ARQ was originally intended for use in telephone line based data transmission, but it is also found on short-wave.