Software for Telecoms & Audio
V.61 Modem DSP C Code
implements the ITU Data Modem function V.61. This operates in two full-duplex
modes over the telephone network: audio+data for Simultaneous Voice Data
(SVD) where the data rate is 4.8kb/s, and data-only for rates of 14.4,
12, 9.6, 7.2, & 4.8kb/s. In the data-only mode, an auxiliary channel
of up to 343b/s is available. Operation can be switched at the user interface
during data mode and can be independent in each direction, though both
ends send at the same rate in data-only mode. Duplex channel separation
is achieved by echo-cancelling for both land-based and satellite calls.
Good error performance is assured by the use of adaptive equalisation.
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 DSP code for synchronisation to the far-end modem. At the data
interface, data is transferred in buffers under pointer control.
Performance: over flat channels, near matched-filter performance is obtained. The software can automatically set the data rate according to line conditions and can renegotiate the data rate during data transmission as conditions change to maintain good throughput/error performance. The decision criteria can be adjusted at the user interface. SNR for 10-6 Error Rate at data-only 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