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V.22bis Modem TMS320C5000 DSP Code

Description: implements the ITU Data Modem functions V.22bis and V.22, which provide full-duplex data transmission at rates of 2.4, 1.2, & 0.6kb/s over the telephone network. The code can also send the V.25 2100Hz auto-answer signal. Duplex channel separation is achieved by band splitting with 1200Hz and 2400Hz carriers for each channel. An (optional) 1800Hz guard tone is sent in the high channel. 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: near matched-filter performance is obtained over both flat and very severe channels. SNR for 10-6 Error Rate (4kHz BW noise):

  • 2.4kb/s:13.5dB Flat Channel; 14.0dB Bell 3002 Channel
  • 1.2kb/s: 6.5dB - Flat Channel; 7.5dB - Bell 3002 Channel
  • 0.6kb/s: 3.5dB - Flat Channel; 4.5dB - Bell 3002 Channel

Processor Load:

Sample rate MIPS# Data memory (words) Prog memory (bytes)#
8.0kHz 3.6(3.5) 244 2.6k(2.4k)
9.6kHz 3.2(3.1) 224 2.4k(2.2k)

- #figures are for TMS320C54x operation with the assembler interface including Remote Digital Loop
- figures in ( ) for V.22-only ie 1.2-0.6kb/s

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

 
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