Group 3 Fax Modem
for the TMS320C5x
by Signals and Software Limited

Software Overview

DSP software that implements the ITU V.21, V.27ter, and V.29 modem standards for use in Group 3 
facsimile. This operates under the T.30 and T.4 protocols, using V.21 channel 2 to transmit control 
information at 300 bps. Data transfer is then achieved using V.27ter, which provides data rates of 
2400 bps and 4800 bps, or V.29, which provides data rates of 7200 bps and 9600 bps.

Features and Benefits

Modem types:	V.21, V.27ter, V.29
Data rates:		300, 2400, 4800, 7200, 9600 bps
Symbol rate:	300, 1200, 1600, 2400 baud (1–4 bits/symbol)
Sample rate:	9.6 kHz 
V.21 channel 2:	1750 Hz ±100 Hz FSK  0 = 1850 Hz  1 = 1650 Hz
V.27ter:		1800 Hz ±600 Hz 4-phase PSK - 2400 bps
			1800 Hz ±800 Hz 8-phase PSK - 4800 bps
V.29:			1700 Hz ±1200 Hz   8-point QAM - 7200 bps
			1700 Hz ±1200 Hz   16-point QAM - 9600 bps
Rx performance	300 bps	  9-dB SNR for 1e-5 block error rate (1000 bits/block)
(flat channel):	2400 bps	13-dB SNR for 1e-5 block error rate (1000 bits/block)
			4800 bps	19-dB SNR for 1e-5 block error rate (1000 bits/block)
			7200 bps	20-dB SNR for 1e-5 block error rate (1000 bits/block)
			9600 bps	24-dB SNR for 1e-5 block error rate (1000 bits/block)

Processor and System Requirements

Group 3 Fax Modem
Program Memory (Words)
Data Memory
(Words)
Processing Load (MIPS)
V.21
500
100
3.5
V.27ter
2000
400
4.0
V.29
2500
500
4.5

Usage Limitations or Performance Considerations

•	The software is implemented as subroutines. The V.21 functions are called at the sample rate 
(9600 Hz), and the V.27ter and V.29 functions are called at their respective symbol rates. A 
control word is used to set modem speed, and a status word provides signal quality, clear-to-send, 
and carrier detect information.
•	Interpolator: Signals and Software can also supply an 8/9.6-kHz sample interpolator to enable 
modem operation over ISDN or other applications that require 8-kHz sampling.

Availability

First quarter 1996, under licence, for a one-off payment and/or royalties depending on the 
commercial application. An Application Note is available. Support consultancy for code integration 
is also available.
V.17 and T.30 will also be available in 1996 subject to demand.

Company Background and Contact Information

Signals and Software Limited (SASL), based in Harrow, Middlesex, UK is a design consultancy 
specializing in the area of Digital Signal Processing (DSP). From concept and algorithm design 
through to real-time DSP implementation, SASL is able to offer its clients fast and cost-effective 
solutions to their DSP needs. Services include: feasibility studies, DSP software to order, DSP 
research and algorithm design, computer simulations (C or PASCAL), and hardware design. In support 
of these services, SASL offers a range of "off-the-shelf" software that includes audio/speech 
coding, modems, acoustic echo cancellation, video coding, and general telecommunications functions. 
Key technology areas include: GSM/PCN mobile comms, video conferencing, video telephony, and 
PSTN/ISDN voice and data transmission.
Contact:	David Morley
		3 Jardine House
		Bessborough Road
		Harrovian Business Village
		Harrow, Middlesex, HA1 3EX
		United Kingdom
		+44 (0) 181 426 9533
		Fax: +44 (0) 181 869 1182
		e-mail: davem@sasl.demon.co.uk