Building robust wireless LAN for industrial control with the DSSS-CDMA n cell phone network paradigm

Wireless LAN for Industrial Control (IC-WLAN) provides many benefits, such as mobility, low deployment cost, and ease of reconfiguration. However, the top concern is robustness of wireless communications. Wireless control loops must be maintained under persistent adverse channel conditions, such as noise, large-scale path loss, fading, and many electromagnetic interference sources in industrial environments. The conventional IEEE 802.11 WLANs, originally designed for high bandwidth instead of high robustness, are therefore inappropriate for IC-WLAN. A solution lies in the Direct Sequence Spread Spectrum (DSSS) technology: By deploying the largest possible processing gain (slowest bit rate) that fully exploits the low data rate feature of industrial control, much higher robustness can be achieved. We hereby propose using DSSS-CDMA to build IC-WLAN. We carry out fine-grained physical layer simulations and Monte Carlo comparisons. The results show that DSSS-CDMA IC-WLAN provides much higher robustness than IEEE 802.11/802.15.4 WLAN, so that reliable wireless industrial control loops become feasible. We also show that deploying larger processing gain is preferable to deploying more intensive convolutional coding. The DSSS-CDMA IC-WLAN scheme also opens up a new problem space for interdisciplinary study, involving real-time scheduling, resource management, communication, networking, and control.