Hf-Acars (W51Pc, W40Pc) - Wavecom W40PC Manual

HC-ARQ was originally intended for use in telephone line based data transmission, but it is
also found on short-wave.

HF-ACARS (W51PC, W40PC)

Parameter
Frequency range
System
Baudrate(s)
User data rate
Modulation
Receiver settings
Signal source(s)
Alphabet
HF Data Link (HFDL) protocols are defined in the ARINC (Aeronautical Radio, Inc.)
Specification 635-3, published on December 29, 2000. The development of HF Data Link
service builds on the experiences of ACARS (Aircraft Communications Addressing and
Reporting System), therefore HFDL is also known as HF-ACARS.
The protocols are compatible with the OSI model and enable the ground stations and avionics
systems on aircraft to communicate with each other in a bit-oriented message format.
HF Data Link employs M-ary Phase Shift Keying (M-PSK) to modulate a carrier centered at
RF+1440 Hz, where RF is the used HF frequency. The carrier is modulated with 1800 symbols
per second (baud). However, the rate at which user data is transmitted can be selected : 300,
600, 1200 or 1800 bps.
HFDL air/ground protocols employ a slotted Time Division Multiple Access (TDMA)
protocol.
Every frame has a duration of 32 seconds and is divided into 13 slots. The first slot is called
Squitter, which carries various information, including slot acknowledgement and assignment
codes.
The next 12 slots of a frame are called Medium access Protocol Data Units (MPDU). They are
used by aircrafts and ground stations to exchange different kind of data, e.g. aircraft logon /
logoff request, aircraft position and frequency assignment etc. Each MPDU contains several
Link Protocol Data Units (LPDU), which may consist of Basic Data Units (BDU).
Each slot (Squitter of MPDU) has the same structure:
Parameter
Prekey
Preamble
Data
The following diagram shows the TDMA slotted frame structure.
WAVECOM Decoders v6.15 W40PC, W41PC, W51PC
Value
249 ms
295 ms
1.8 sec (single slot)
or
4.2 sec (double slot)
Value
HF
M-ary Phase Shift Keying (M-PSK)
1800.0 Baud
300, 600, 1200 or 1800 bps
SSB
USB
AF-IN, IF-IN-VAR, IF-IN-10.7 or IF-IN-21.4
Remarks
1440 Hz single tone
Known BPSK symbols for synchronization purposes
Data section structured in data-probe pair (45 M-
PSK symbols each : 30 user data symbols and 15
known BPSK symbols for synchronization purpose)
Transmission Modes • 153