Experimental comparison of pulse-amplitude and spatial modulations for vehicle-to-vehicle visible light communication in platoon configurations.

Visible light communication (VLC) is an attractive complementary communication technology for vehicular applications such as platooning. Although data rates around 100 kbps are enough for crucial data transmission, it may be useful to reach a few megabits per second for other applications like networking. Such data rates can be reached by using appropriate modulations and clock rates. In this paper, three forms of pulse amplitude modulations (PAM) are compared in a vehicular context: on-off keying (OOK), PAM-4 and generalized space-shift keying (GSSK). A prototype based on off-the-shelf light-emitting diodes (LED) headlamps is used for static tests in straight line configuration, with an inter-vehicle distance up to 30 m, and curves of minimum radius 100 m and inter-vehicle distance of 10 m. These tests show that OOK and GSSK are the most interesting modulations for highway platooning applications. OOK provides indeed a good mobility while remaining simple to implement. A 1 Mbps link of BER below 10-6 is thus demonstrated. In GSSK, the data rate reaches 2 Mbps for an equivalent BER. These performances are obtained by using, in particular, two spatially distinct receivers, which limits strongly the complexity of GSSK decoding.