VOCAN - Voice over CAN

Sprachdatenübertragung über CAN

Michael Kugelmann, Michael Mayer, Werner Zimmermann

CAN, originally developped for automotive applications, now is an established solution in the sensor - actuator - fieldbus sector of the automation business. In some automation applications in parallel to process data a speech communication is needed.
In a research project at the FHTE (University of Applied Sciences) Esslingen, Germany, we studied voice transmission over CAN, using the same microcontroller and CAN for process control and for speech transmission without additional hardware (except of course micro and speaker amplifiers).
We investigated the following speech coding and compression algorithms with respect to bus and microcontroller load:
For implementation we used evaluation boards with Siemens 80C167CR microcontrollers with integrated CAN controllers. The major results of our investigations can be found in the table below. Details can be found here (unfortunately this paper is only available in German). Source code of the ADPCM-software is also available.
ADPCM provides a good compromise between bus and microcontroller load, whereas with PCM bus load and with GSM microcontroller load will not be acceptable in most applications.

Algorithm
PCM
ADPCM
GSM (RPE-LTP)
Sampling Frequency
8kHz
4 kHz
4 kHz
4 kHz
Data Rate *1
64kBit/s
32 kBit/s
16 kBit/s
6,5 kBit/s
CAN Bus Load *1
102%
51%
25%
10%
Microcontroller Load *2
 
 
 
 
---Transmitter
8%
4%
12%
82%
---Receiver
2%
1%
10%
42%

*1 Half duplex operation, CAN bitrate 125kBit/s, allowing a CAN bus length of approx. 400m and an effective data rate of 64kBit/s

*2 Siemens 80C167CR @ 20MHz, 16bit non-multiplexed bus, program and data memory without wait states

 


Prof. Dr.-Ing. Werner Zimmermann, Hochschule Esslingen, Germany