oa Visible Light Communication for Intelligent Transport Systems

Introduction

Road safety is a world-wide health challenge that is of great importance in Qatar. According to WHO [1], global traffic fatalities and injuries are in the millions per year. Qatar has one of the world's highest rate of traffic fatalities, which causes more deaths than common diseases [2]. Traffic congestion and vehicle fuel utilization are two other major problems. Integrating vehicle communication into intelligent transport systems (ITS) is important as it will help improve road safety, efficiency and comfort by enabling a wide variety of transport applications. Radio frequency communication (RFC) technologies do not meet the stringent transport requirements due to spectrum scarcity, high interference and lack of security [3]. In this work, we propose an efficient and low-cost visible light communication (VLC) system based on CMOS transceivers for vehicle-to-vehicle (V2V) and infrastructure-to-vehicle (I2V) communication in ITS, as a complementary platform to RFC.

Objective

The proposed VLC system is designed to be low cost and efficient, supporting various V2V and I2V communication scenarios as shown in Fig. 1. The VLC LED transmitters (Tx) are responsible for both illuminating and information broadcasting. They are designed to support various existing transport infrastructures (such as street lamps, guideboards and traffic lights) as well as vehicle lights, with low cost and complexity. The receivers (Rx) will be available on both the front and back sides of vehicles with both vision and communication capabilities. Robustness of communication is enhanced by the added vision capability.

System implementation

The VLC system implementation in Fig. 2 is an optimized joint design of the transmitter, receiver and communication protocol. The LED transmitter will focus on the design of LED driver with efficient combination of illumination and communication modulation schemes. Light sensor is integrated to provide adaptive feedback for better power efficiency. Polarization techniques are utilized to cancel background light so as to not only enhance image quality but also improve robustness of VLC, as shown in Fig. 3.(a) [4]. A polarization image sensor using liquid crystal micro-polarimeter array has been designed as illustrated in Fig. 3. (b). The CMOS visible light receiver will be designed based on traditional CMOS image sensor but with innovative architecture specifically for V2V and I2V VLC. It features dual readout channels, namely, a compressive channel for image capture and a high-speed channel for VLC. Novel algorithms for detection and tracking are used to improve communication speed, reliability and security. Compressive sensing is applied for image capture. The compression is facilitated by a novel analog-to-information (AIC) conversion scheme which leads to significant power savings in image capture and processing. A prototype AIC based image sensor has been successfully implemented as shown in Fig. 4 [5]. A VLC protocol is specifically tailed for V2V and I2V based on the custom transceivers. The PHY layer is designed based on MIMO OFDM and the MAC layer design is based on dynamic link adaption. The protocol is to be an extension and optimization of IEEE 802.15.7 standard for V2V and I2V VLC. A preliminary prototype VLC system has been designed to verify the feasibility. A Kbps-level VLC channel has been achieved under illumination levels from tens to hundreds of lux. It's anticipated better improvement will be obtained with further research using the novel techniques described above.

Conclusion

An efficient and low-cost visible light communication system is proposed for V2V and I2V VLC, featuring low cost and power-efficient transmitter design, dual-readout (imaging and VLC) receiver architecture, fast detection and tracking algorithms with compressive sensing, polarization techniques and specific communication protocol.

References

[1] Global status report on road safety 2013, World Health Organization (WHO).

[2] Sivak, Michael, “Mortality from road crashes in 193 countries”, 2014.

[3] Lu, N.; Cheng, N.; Zhang, N.; Shen, X.S.; Mark, J.W., “Connected Vehicles: Solutions and Challenges,” IEEE Internet of Things Journal, vol. 1, no. 4, pp. 289–299, Aug. 2014.

[4] X. Zhao, A. Bermak, F. Boussaid and V. G. Chigrinov, “Liquid-crystal micropolarimeter array for full Stokes polarization imaging in visible spectrum”, Optics Express, vol. 18, no. 17, pp. 17776–17787, 2010.

[5] Chen, D.G.; Fang Tang; Law, M.-K.; Bermak, A., “A 12 pJ/Pixel Analog-to-Information Converter Based 816 × 640 Pixel CMOS Image Sensor,” IEEE Journal of Solid-State Circuits, vol. 49, no. 5, pp. 1210–1222, 2014.