Twisted Pair
Twisted pair cable is currently the most common physical layer cable in automotive Ethernet. It consists of two insulated wires that are twisted together according to a certain pattern (usually clockwise). This wiring form can effectively reduce electrical interference between adjacent pairs and improve the reliability of data transmission. Twisted pair cables are divided into shielded twisted pair (STP) and unshielded twisted pair (UTP).
Unshielded twisted pair (UTP)
UTP is the most commonly used type of twisted pair cable in automotive Ethernet due to its low cost and ease of installation. The two wires in a UTP cable transmit signals with equal amplitude but opposite phase, and this differential signal transmission method can effectively resist external noise interference. In automotive Ethernet, UTP cables are commonly used for simultaneous transmission and reception of data, and the cable end needs to be equipped with a hybrid transceiver to distinguish between the transmitted and received data.
Common UTP cable specifications include Cat5e, Cat6, and Cat7. Cat5e cables support a maximum transmission speed of 1Gbps and are suitable for most internal network connection needs of vehicles, such as audio systems, navigation systems, and entertainment devices. Cat6 cables are superior in terms of transmission speed and performance, supporting transmission speeds of up to 10Gbps, making them suitable for scenarios that require processing large amounts of data, such as high-definition video transmission or real-time communication between in vehicle devices. Cat7 is the highest level product, surpassing Cat6 in transmission speed, bandwidth, and anti-interference ability, suitable for vehicles equipped with advanced driving assistance systems, safety monitoring devices, or remote diagnostic tools and other high-end features.
Shielded Twisted Pair (STP)
STP cable adds a metal shielding layer between the twisted pair and the outer insulation cover, which can more effectively shield electromagnetic interference and improve the stability of data transmission. STP cables are typically used in situations where electromagnetic interference is more demanding, such as complex electromagnetic environments inside vehicles or situations where long-distance data transmission is required.
Fiber Optics
Fiber optic, as an emerging transmission medium, also has its unique advantages in automotive Ethernet. Fiber optic cables are made of pure quartz glass or plastic fibers and can transmit data in the form of optical signals, with higher bandwidth and anti-interference ability. The transmission rate supported by fiber optic can reach 100Gbit/s, far higher than twisted pair cables.
Fiber optics are divided into two types: single-mode fiber and multi-mode fiber. Single mode fiber can only transmit light of one mode, without mode to mode dispersion, and is suitable for long-distance high-speed transmission. Multimode optical fibers allow different modes of light to be transmitted on a single fiber, but due to their large mode to mode dispersion, they are mainly used for short distance transmission in local area networks.
In automotive Ethernet, optical fiber is often used in applications that require high-speed and stable data transmission, such as on-board cameras, Advanced Driver Assistance System (ADAS) and auto drive system. Fiber optic transmission is not affected by electromagnetic interference, which is particularly important for highly reliable data transmission in automotive systems. In addition, fiber optic transmission is not limited by distance and is suitable for scenarios that require data transmission over a large area, such as fleet collaboration or communication between vehicles.
Coaxial Cable
Coaxial cables also have certain applications in vehicle Ethernet, especially in some scenarios with high requirements for anti-interference. A coaxial cable consists of a central conductor, an insulating medium, a mesh conductive layer, and an outer insulating layer. This structure can provide good shielding performance and effectively prevent interference from external signals.
However, compared to twisted pair cables and fiber optic cables, coaxial cables are relatively less used in automotive Ethernet. This is mainly due to the high cost of coaxial cables and the relatively complex installation and wiring. Therefore, coaxial cables are usually only used in situations where high data transmission quality is required and cost is not a major consideration.
Considerations for cable selection
When choosing cables for automotive Ethernet, multiple factors need to be considered, including bandwidth requirements, transmission distance, cost, and feasibility.
Bandwidth requirement: If large capacity data needs to be transmitted, fiber optic may be a better choice because it can transmit data at higher speeds and support the demand for larger bandwidth. Twisted pair cables are suitable for applications with lower bandwidth.
Transmission distance: If data transmission is required over a long distance, fiber optic is a more reliable choice. The transmission distance of twisted pair cables is usually short and is greatly affected by interference. However, with the development of technology, some new twisted pair cables (such as Cat6 and Cat7) have been able to stably transmit data over longer distances.
Cost and feasibility: Considering factors such as manufacturing and installation costs, as well as feasibility and adaptability, it is crucial to choose a transmission medium that is suitable for project budget and resource constraints. Twisted pair cables are widely used in automotive Ethernet due to their cost-effectiveness and ease of installation. Although fiber optics have higher performance, their cost is relatively high.
