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V.61 Modem TMS320C5000 DSP Code

Description: 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.
         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. In the assembler interface, the code is re-entrant to facilitate multi-channel operation. A C-callable wrapper can also be provided, allowing individual channels to be called from C to process multiple sample blocks. A comprehensive user's guide together with example application files are provided with the code. Test results are available.

Interfaces: 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.
         At the control interface, the assembler code has one 16-bit control word to sequence operation and to set operating parameters, and two diagnostic words to convey data transfer status and signal quality. With the C wrapper, control and diagnostics are provided by routine call arguments and returned values.

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):

• 26.0dB Flat Channel

Processor Load:

- #figures are for TMS320C54x operation with the assembler interface
- figures apply to both 8.0 & 9.6kHz sample rates
- $allows for 1.3secs. round-trip-delay and is selectable

Availability: NOW - sale is under licence - integration support offered