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V.34 Data Pump Software for Texas TMS320C54x/C55x & C2xx/C5x DSPs

This software implements the ITU Data Modem function V.34, so offering full-duplex(FD) and half-duplex(HD) data transmission at rates from 2.4kb/s to 33.6kb/s (in 2.4kb/s steps) over the telephone network.

To achieve such rates, the software adapts the signal bandwidth for each telephone call connection by selecting the best symbol rate / carrier frequency combination following channel sounding. The symbol rate can differ in each transmission direction. The data rate can be matched automatically to line conditions and to direction. As conditions change during transmission, the data rates can be renegotiated. Optimal error performance is assured by the use of 4D trellis coding, equalisation by flexible pre-coding and pre-emphasis, shell mapping and signal "warping". Full-duplex channel separation is achieved by echo-cancelling. In half-duplex transmission eg for V.34 fax, an additional function is a separate full-duplex control channel with rates of 1.2 or 2.4kb/s for signalling purposes. The software includes common rate conversion at the sample interface for the different V.34 symbol rates.

The software is in the form of two callable subroutines, one for initialisation and one for processing of input/output data and sample blocks. The user is responsible for interfacing sample and data input & output to hardware. By making multiple sub-routine calls, the code can operate on blocks of samples. Data memory is offset-addressed in the ‘C54xC55x version, so the code re-entrant for implementing multiple modems on a single DSP. A comprehensive user's guide is provided with the code. Test results are available.

Interfaces: at the sample interface, the code can operate at 9.6kHz or 8.0kHz 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 transfer is via word blocks with associated counters. At the control interface, three 16-bit control words sequence operations and set parameters, and two diagnostic words convey data transfer and receiver status.

Performance: the software algorithms have been carefully designed for excellent performance under noisy or poor line conditions. Over flat channels, near matched-filter performance is obtained. Over the very severe "ConUS Poor Voice" channel in the TAS Telephone Network Emulator - 30dB attenuation across the 3kHz band - the modem code still operates up to 16.8kb/s.

• SNR for 10^-6 error rate (flat channel): 17.0dB - 14.4kb/s ; 25.5dB - 24kb/s ; 34.0dB - 33.6kb/s

DSP Load - C54x/C55x version:

• MIPS: 20.3(FD) or 13.8(HD)

• Data memory: 7.9kwords(FD - 1.2secs. RTD) or 2.3kwords(HD)

• Program memory: 12.5kwords(FD), 12.4kwords(HD), 14.3kwords(FD+HD)

Figures are for optimum performance in full-duplex operation including V.8. Complexity is selectable. For a small cost in SNR performance, load figures can be reduced by: 3.6MIPS, 0.8kwords data memory, and 0.4kwords program memory. The data memory allocation for far-end echo cancellation of 1.2secs. round-trip delay (RTD) is selectable.

DSP Load - C2xx/C5x version: MIPS figures are worst-case for full-duplex operation - receiver complexity and internal / external memory partitioning are selectable - internal data memory use may be set as low as 512 words - MIPS figures vary from 19.4 to 31.8 according to configuration:

• MIPS: 23.9 (both 8.0 & 9.6kHz s.r.)

• Data memory: 12.5kwords (for 1.2secs. RTD)

• Program memory: 14.0kwords (includes V.8)

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