Optical CDMA MAC Evaluation in Vehicle-to-Vehicle Visible Light Communications

Abstract

One of the most critical challenges in vehicle-to-vehicle (V2V) visible light communications (VLCs) is the access capability of multi-users over the same channel. VLC links are known to be line of sight (LOS) and highly directional compared to the commonly used radio-frequency (RF) technologies, but multi-user interference can still be problematic. Consequently, it is necessary to develop a medium access control (MAC) protocol for VLC. In the present work, we propose a novel optical code division multiple access (OCDMA) protocol. The fundamentals of the VLC channel are presented, and the interference problem is discussed in more detail. We also explain the CDMA MAC protocol and its adaptation from optical fiber communications. The simulations with our OCDMA protocol based on pseudo-noise (PN) sequence codes are presented, and the results are compared with those obtained using a solution based on VLC and optical orthogonal codes (OOCs) from the OCDMA gold standard. Finally, the results show that PN sequence OCDMA can provide sufficiently high performance and is particularly attractive because there are no synchronization requirements between nodes in real V2V scenarios.

A Comprehensive Investigation on Multi-User Interference Effects in Vehicular Visible Light Communications

“…On the other hand, the development of vehicular VLC prototypes has been mainly focused on PHY layer development, whereas MAC development has been rather neglected, being addressed in relatively few works [27][28][29]. Nevertheless, the results presented in this work emphasize the necessity of the MAC layer development in parallel to the PHY layer development, as also suggested in [28,[30][31][32]. The issues associated with multiusers interference have been partially addressed in [31].…”

“…On the other hand, it must be emphasized that the work focused on multi-user access and on multi-user interference mitigation is mostly orientated toward indoor VLC applications rather than vehicular VLC utilization. Examples of studies focused on vehicular VLC applications are found in [30,31], where an optical CDMA solution is proposed, or in [29,49], where solutions based on Space-Division Multiple Access (SDMA) using vehicle matrix headlights are analyzed. Additionally, [33] provides a detailed analysis focused on the problems associated with MUI in vehicular VLC applications and on the benefits of optical CDMA utilization.…”

Addressing Multi-User Interference in Vehicular Visible Light Communications: A Brief Survey and an Evaluation of Optical CDMA MAC Utilization in a Multi-Lane Scenario

“…Before developing new MAC solutions for improved vehicular VLC systems, demonstrating their necessity is important. Therefore, in [25], it has been experimentally demonstrated that a typical VLC emitter developed based on a vehicular tail-lamp set has an emission angle up to 60 • , enabling signal reception from a neighboring lane for a distance of more than 60 m. In [32], analytical and simulation investigations showed that the effects of MUI on inter-vehicle VLC links are dependent on the V2V separation distance, on the number of lanes, and on the vehicle density. The authors of [33] have evaluated the use of VLC in platooning applications and concluded that the technology is suitable for such uses, but it is strongly affected by MUI, which significantly increases message failure rate.…”

“…In addition, it provides a complex simulation analysis concerning the utilization of Optical Code Division Multiple Access (OCDMA) techniques as a solution to mitigate the effects of MUI in vehicular VLC applications. This work carries on the work begun in [28] by providing a more complex analysis of existing solutions to address MUI in vehicular applications. In addition, different from [28], which investigated the benefits of two OCDMA codes in MUI mitigation, this new article provides additional results and a more comprehensive analysis, focusing on the evaluation of four optical CDMA codes.…”

“…This work carries on the work begun in [28] by providing a more complex analysis of existing solutions to address MUI in vehicular applications. In addition, different from [28], which investigated the benefits of two OCDMA codes in MUI mitigation, this new article provides additional results and a more comprehensive analysis, focusing on the evaluation of four optical CDMA codes. Thus, this work emphasizes that different sub-codes may have different cross-correlation properties, which, in turn, can lead to variable performances.…”