Software for Telecoms & Audio
V.17 Modem DSP C Code
implements the ITU Data Modem function V.17, which provides half-duplex
data transmission at rates of 14.4, 12, 9.6, & 7.2kb/s over the telephone
network for use in Group 3 Fax equipment. Good error performance is assured
by the use of trellis coding and adaptive equalisation. A fast-train algorithm
is implemented for resynchronisation after 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: sophisticated techniques have been incorporated into the software to give excellent performance under noisy or poor line conditions. Over flat channels, near matched-filter performance is obtained. Over very severe channels such as the TAS Telephone Network Emulator ConUS Poor Voice channel 30dB attenuation across the 3kHz band the modem code will still operate at 14.4kb/s. SNR for 10-6 Error Rate at 14.4kb/s (4kHz BW noise):
#example figures from compiling for the TI TMS320C5000(C55x) DSP processor
Availability: NOW - sale is under licence - integration support offered