Vehicles’ Ethernet Emerging Trends And Challenges

By V.P. Sampath


Maintaining compatibility also eliminates the need for any special drivers, making it easily interoperable with Ethernet devices that support IEEE 1588 remote timing and clock synchronisation protocol. Precise timing and synchronisation that IEEE 1588 provides will be critical in automotive sub-systems such as braking, engine control, active suspension and anywhere else where real-time operations are performed.

Incoming data is divided into blocks that are partitioned in up to three levels with different degrees of coding and then mapped to a 2D constellation. Bits in the first level are protected with a BCH code that provides powerful error correction, while the second level is protected with another BCH code and the last level is not coded. These are then mapped such that those from levels two and three are far apart (that is, coset partitioning).

The first level is always enabled by using QPSK modulation. The second level, depending on bit-rate configuration, uses BPSK or QPSK modulations. For BPSK, BCH code is shortened to 1008-bit length. The third level directly maps the information into configurable size modulations over Z2 or RZ2 lattices. After mapping, 2D lattice transformations are used to implement the coset partitioning. Finally, MPAM symbols are generated by time multiplexing from 2D symbols.

Fig. 5: Driver-assistance and infotainment systems

This is a process for configuration in which the numbers of bits in each level are 1,1 and 1.5. This corresponds to 16-PAM modulation and bit rate of 1Gbps, with symbol frequency of 312.5MHz. By using different numbers of bits at each level, multiple speeds can be obtained depending on channel conditions. This results in a flexible scheme that can adapt to many POF channels.

Transmission of data is structured in frames that are sent continuously. Each frame contains 112 data blocks (MLCC code words) and also additional information related to the physical layer. This information is in the form of two pilot signals (S1 and S2) and the physical header (PHS). Pilots are intended to aid the receiver in performing linear and non-linear equalisation and timing recovery.

Non-linear equalisation is implemented in the receiver while linear equalisation is implemented in part in the transmitter using Tomlinson-Harashima Precoding (THP) to avoid error-propagation issues, and in the receiver using a feed-forward equaliser. The physical header is used for physical-layer signaling, which includes selection of MLCC configuration and transmission of THP coefficients. GigaPOF scheme also provides good energy efficiency.

Fig. 6: Ethernet in automotives (Source: Bosch)

The Ethernet moves packets through networks on a best-effort, non-deterministic basis, which makes it poorly suited for use in mission-critical real-time systems used to control drivetrain or braking systems or support driver-assist functions. But later developments have added mechanisms like IEEE 802.1tsn (time-sensitive networking) protocol that provide assured, non-conflicting delivery of data and command packets within strict time parameters.

Additional standards for specific timing-critical applications are also available, including IEEE 802.1AS/802.1Q/802.1Qca protocols, which support transport, switching and management of latency-sensitive connections used in high-speed real-time control applications.



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