Vehicles’ Ethernet Emerging Trends And Challenges

By V.P. Sampath

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One-Pair Ethernet

A proprietary PHY standard, BroadR-Reach, enables longer distances of copper Ethernet connectivity at 100Mbps (up to 700 metres). This PHY uses technologies from 1GE copper including multi-level PAM-3 signaling and better encoding (to reduce the bandwidth required on the cable) and using echo cancellers, so bi-directional data could be transmitted on a single pair. Due to the lower bandwidth (~27MHz bandwidth, 62.5MHz for 100BASE-T), this standard met automotive EMI requirements and Broadcom started marketing this to the automotive world.

As the industry realised that 100Mbps is enough for video transmission but not enough to act as a backbone in the car, it pushed for the creation of a task force for 802.3 (802.3bp) to define a standard for 1G over a single twisted pair for links of up to 15M for the automotive market. The new PHY is known as 1000BASE-T1 (where 1 stands for one pair). Based on current timelines, it is expected that prototypes will be available this year, and this will become a standard by 2017.

Power-over Ethernet

To further reduce the wiring needed in a car, Power-over Ethernet (PoE) may be used to power devices. IEEE 801.3bu (One-Pair Power-over Data Lines, or PoDL) task force is working on standardising PoE over a single pair. This is a minor modification to the current PoE, and this standard is expected to be approved soon.

Energy-Efficient Ethernet

A car’s electrical components do not all turn off when the engine is turned off. When the engine is off, battery capacity is limited. In order to minimise power consumption when the engine is off and when the engine is on, Energy-Efficient Ethernet (EEE), which turns off the network when not in use, is used. Those components that do not need to be powered on at all when the engine is off will have their network segments completely turned off. Those that need to be on will use EEE to minimise power consumption.

Gigabit Ethernet

A single-pair version of Gigabit Ethernet intended as a high-speed aggregation backbone for 1TCPE traffic reduces cable weight. It could also serve as a direct connection between network backbone and diagnostics, ADAS cameras, infotainment video and other applications with data requirements above 100Mbps.

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Fig. 3: Compatiability requirement

It meets automotive system EMC requirements, supports 15 metres over unshielded automotive cabling. It has a standard Gigabit Ethernet MAC interface (SGMII/RGMII/GMII), which is defined through IEEE standardisation process. Gigabit Ethernet is targeting to penetrate the vehicle market in 2018.

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Fig. 4: PHY technology for Gigabit Ethernet over POF

Two essential factors are completion of IEEE standards and a roadmap for the future. With the completion of IEEE 100BASE-T standard, chip vendors expect to follow the trends in vehicles Ethernet. Upcoming 100BASE-T1 standard will be based on BradR-Reach specifications. Gigabit automotive Ethernet PHY transceiver chip is based on 1000BASE-T1 draft standard.

Advantages of 1000BASE-T1 are:

      • Supports machine vision for ADAS and is suitable for high-speed video links
      • Supports more video channels and can uplink 100Mbps domains
      • Can use cost-effective unshielded cables
      • Ethernet cables are lightweight and flexible
      • Possibility to support 100BASE-T1 and 1000BASE-T1, and can define systems with choice of resolution by replacing a single module
      • Adds video paths through software

Uncompressed high-definition video needs greater than 100Mbps. At 100Mbps, strong compression is required that can degrade images. Compression algorithms add latency, which limits the applications for the Ethernet. At 1Gbps, little or no compression is required. Low latency supports higher quality image transport. For machine vision, high-definition navigation and instrument cluster that has a high bandwidth compression algorithm are required.

The standard that defines 100BASE-T1 was developed outside of IEEE 802.3 committee’s governance. But it is strictly based on IEEE 802.3 framework. PHY is fully compatible with a standard Ethernet MAC that allows seamless interoperability with nearly any Ethernet-capable microcontroller or embedded system element, provided its MAC’s Media Independent Interface (MII) is compatible with One-Pair Ethernet PHY.

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