Wavecom W40PC, Manual

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Transmission Modes WAVECOM Decoders v6.15 W40PC, W41PC, W51PC
Symbol rate 3125 Baud
Bit rate 6250 bps
Modulation 4-PAM/FM
Receiver settings FM narrow, 15-30 kHz
Signal source IF (only)
Alphabet ITA-5
Introduction
ERMES is a new Europe-wide high speed paging system with a data rate of 6250 bps in
comparison to POCSAG which has a maximum rate of 2400 bps. ERMES radio data may be
transmitted using frequency or time multiplex or both. All transfer modes do however utilize
the same modulation format on the same frequency. ERMES is now operating in several
European countries whereas Asian countries tend to standardize on FLEX, which is a
technically comparable Motorola system.
Radio Link
ERMES employs a radio link transfer protocol conforming to the ETSI prETS 300 133-4
standard (ETS 300 133-1 to ETS 300 133-7). Transmissions are within the range from
169.4125 MHz to 169.8125 MHz all over Europe. Channel spacing is 25 kHz. The nominal
frequencies and the channel numbering are defined as:
fn = 169.425 + n*0.025 MHz
n = Channel number = 0...15
ERMES transmitter allocations follow the CEPT T/R 25-07, annex 1 recommendation.
Modulation
ERMES modulation is 4-PAM/FM. The four frequency pulse-amplitude modulation carries
two bits (di-bit) per frequency step. In addition to coherent phase keying ERMES also utilizes
pre-modulation pulse shaping. To decrease bit error rate, data is encoded using the Gray code.
The nominal frequencies are:
Carrier Di-bit symbol
+ 4687.5 Hz 10
+ 1562.5 Hz 11
- 1562.5 Hz 01
- 4687.5 Hz 00
The ERMES Protocol
A sequence of 60 seconds is partitioned into 60 cycles. The sequences are synchronized to
UTC. The cycles have a duration of exactly one minute and synchronize the various ERMES
networks (transmitters). In this way the receivers will only receive one or more cycles and thus
power consumption is substantially reduced.
Each cycle is subdivided into five subsequences of 12 seconds each. In order to maintain
synchronism between networks the subsequence number (command SSN = 0) is transmitted
preceding every UTC minute marker.
A subsequence may also have a duration of less than 12 seconds. The remaining time is used
for transmitter switching.
Each subsequences is further divided into 16 batches designated A to P. Thus the pagers are
divided into 16 groups. The transfer mode (tone call only, numerical call, alphanumerical call)
is controlled by the position of the batch number.