Software for Telecoms & Audio
V.27 Modem DSP C Code
implements the data pump function of the ITU Modems V.27bis & V.27ter,
which provide half-duplex data transmission at rates of 4.8 & 2.4kb/s
over the telephone network for applications such as Group 3 Fax. Also
provided is full-duplex transmission for 4-wire leased line operation.
In both cases, an optional independently-controlled backward channel can
be incorporated for rates of up to 75b/s. Good error performance is assured
by the use of adaptive equalisation. The code features train-on-data (V.27bis)
& fast resync. (V.27ter) from initial training.
at the sample interface, the code can operate at 8.0kHz and 9.6kHz sample
rates. Transmit and receive samples are transferred on a common clock,
to which the transmit clock is synchronised. The receive clock is interpolated
in the code for synchronisation to the far-end modem. At the data interface,
data is transferred in buffers under pointer control via subroutine calls.
Performance: over flat channels, near matched-filter performance is obtained. SNR for 10-6 Error Rate (4kHz BW noise):
#example figures from compiling for the TI TMS320C5000(C55x) DSP processor
Availability: NOW - sale is under licence - integration support offered