Research on Priority-Based PLCA in Ethernet Physical Layer

Abstract

The introduction of high-bandwidth technologies in the automotive industry such as Advanced Driver Assistance System (ADAS), Vehicle to Everything (V2X), and Laser Imaging, Detection and Ranging (LIDAR), etc. has increased the complexity and requirements of the vehicle's external and internal systems. As a result, there is a growing trend to replace existing vehicle’s internal and external communication protocols with Ethernet, which features relatively low cost and lightweight. Automotive Ethernet is being standardized internationally by the International Organization for Standardization (ISO), the Institute of Electrical and Electronics Engineers (IEEE), and the Third Generation Partnership Project (3GPP), etc. depending on each speed and requirement. Among these, there is IEEE P802.3cg Task Force standardizing 10 Mbps single-pair Ethernet. To date, the IEEE P802.3cg standard, which is under standardization, introduced the Physical Layer Collision Avoidance (PLCA), which prevents data collisions in the Ethernet physical layer. PLCA is meant to provide improved performance (throughput, max latency, fairness) over standard CSMA / CD method for multi-drop Ethernet networks featuring low number of nodes and low propagation delays. Working principle is detecting transmit opportunities to avoid physical collisions on the data line, and it is defined in an optional Reconciliation Sublayer. However, the existing PLCA may not be suitable for time-sensitive application in vehicle network. This is because safety controlling devices that should operate in case of emergency can exist as nodes in the network to which the PLCA is applied. To cope with this situation, two priority methods that may be introduced to PLCA in the future are discussed in this thesis. The first method is to introduce an alarm signal as a non-design method and assign a high priority to only one single node in the network. This method has significance in that it can be introduced into future international standards by keeping the existing PLCA algorithm as much as possible. The second method is to redesign the existing PLCA transmission cycle into a main-cycle and sub-cycles as a design method. As for the second method, this thesis has mathematically proved that total transmission opportunity of node #0 and node #1 can have up to 2.5 times efficiency over the existing PLCA by giving high priorities to two nodes in the network.