Adaptive Flow Control for Traffic Data Collection based on Low Bandwidth iDEN Wireless Network

This paper describes a cost-effective traffic data collection system which is based on low bandwidth iDEN mobile network. An adaptive flow control protocol over the TCP/IP stack was developed to ensure a "best-effort" style data transmission over the low bandwidth network while the data link status is monitored to avoid unnecessary drop-offs caused by excessive demand of the wireless bandwidth. The iDEN handsets communicate via serial port with Caltrans field master signal controller using AB3418 standard. Signal phase and timing (SPAT) data from up to 10 signal controllers could be collected with one client at a maximum sampling rate of 200ms. Lab testing at California PATH showed that the data collection system based on the adaptive flow control provides an average upload data rate of 2.68kps per remote client for over 95% of the time, which could support SPAT sampling rate up to 200ms. Overall for more than 98% of the time the measured system availability is greater than 98%. The lab testing of the data collection showed significant improvement in the availability of the data collection system when compared with the transmission without our adaptive flow control protocol.