Pol-Arq - Wavecom W40PC Manual

For reasons of compatibility with older pagers two different bit rates (512 Bit/s and 1200 Bit/s
or 1200 Bit/s and 2400 Bit/s) are often used on the same frequency. In some countries
POCSAG and GOLAY systems are on the same frequency. By selecting the "Auto speed"
function all baud rates are automatically detected and switch-over between 512, 1200 and 2400
bps is performed.
POCSAG Signaling
Generally activation of the HF carrier is followed by the transmission of a preamble or bit
synchronization pattern which slaves the receiver to the clock frequency. The preamble
contains at least 576 bits and represents a continuously alternating sequence of 010101...0101.
Following the preamble, data batches containing the actual information are transmitted, each
batch being 17 x 32 bit or 544 bits long.
The structure of a batch is fixed : Each batch starts with a 32 bit synchronization codeword
with a fixed content.
The synchronization word is followed by eight frames (frame 0 - 7 ) containing 2 x 32 bits in
total. Only the first 32 bits are however used for transmitting a pager address. It would
therefore be possible to double the maximum number of subscribers in the group by utilizing
the frame contents to its full extent.
The message contents of the codewords may include pager addresses or messages destined for
specific pager addresses. The frames contained in a batch are numbered from 0 to 7. All pagers
are similarly divided into 8 groups with each pager only receiving frames for the group to
which it has been assigned. A pager synchronizes itself to the batch synch codeword (SC) and
ignores the seven frames which are not applicable.
Following the address at the beginning of a frame, a message of any desired length may be
sent. In the case of numeric pagers, digits are sent in BCD code while for alphanumeric pagers
the message is transmitted using 7 bit ASCII codes.
The example shows the transfer of a message of 350 bits in frame 3. The first 32 bits of frame
3 are the address codeword (Add). Then follow 4 1/2 frames equivalent to 9 x 32 bits which
extend up to the next synch word (SC). The remaining 62 bits fit into frame 0. If the frame
containing the end of a message is not required to send a new address, it is filled with IDLE
codes until a new address or a new synch word must be sent.
POCSAG mode uses direct frequency modulation. Proper decoding is only possible from the
receiver IF output (455 kHz, 10.7 MHz or 21.4 MHz).

POL-ARQ

Parameter
Frequency range
System
WAVECOM Decoders v6.15 W40PC, W41PC, W51PC
Value
HF
DUPLEX, Single Channel Duplex System
Transmission Modes • 175