Software for Telecoms & Audio
V.32bis Modem TMS320C5000 DSP Code
implements the ITU Data Modem function V.32bis, which provides full-duplex
data transmission at rates of 14.4, 12, 9.6, 7.2, & 4.8kb/s over the
telephone network. Included is V.32 compatibility. Duplex channel separation
is achieved by echo-cancelling for both land-based and satellite calls.
Good error performance is assured by the use of trellis coding and adaptive
equalisation. The assembler software is in the form of callable subroutines,
eg for initialisation and for main-routine processing of input/output
sample blocks and data. The user is responsible for interfacing samples
and data to hardware.
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: 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. 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 14.4kb/s (4kHz BW noise):
#figures are for TMS320C54x operation with the assembler interface including
V.54 Remote Digital Loop sequencing
Availability: NOW - sale is under licence - integration support offered