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83 analogue-to-digital converters (ADCs) and digital-to-analogue converters (DACs) needed for these systems increase total system cost while introducing potential areas of audio performance degradation. Bus standards such as 150 Mbit/s media-oriented systems transport (MOST) were designed to transport audio, video, voice and data signals to tackle this challenge. It defines all seven layers of the ISO/OSI model, from the physical level up to the application layer. Similarly, the 100 Mbit/s Ethernet Audio Video Bridging (AVB) standards have been widely adopted in current- generation infotainment systems to simplify the wiring complexities of analogue audio implementations. For 100 Mbit/s designs, the IEEE 802.3bw (100Base-T1) standard is a physical layer (PHY) comms protocol that uses techniques such as superposition, encoding and scrambling schemes, along with a few passive components, to reduce electromagnetic interference (EMI), cabling weight, cost and footprint size compared to traditional Fast Ethernet (100Base-TX) solutions. However, the added performance and flexibility of MOST and Ethernet AVB carry an added cost of microcontrollers to manage their associated software protocol stacks. These are also inherently non- deterministic, with variable system delays from node to node. That means existing digital bus architectures are not acceptable for latency-sensitive speech and voice- based applications such as ANC. These technologies have been overtaken by the need for higher performance data links of more than 1 Gbit/s using Ethernet (although that is still non-deterministic) and simpler technologies operating at 50 Mbit/s but with lower latency for audio and acoustic applications. Developers want to create individual sound cocoons where passengers are acoustically separated from each other. One way to do that is with ANC, which takes the output of an array of microphones and creates soundwaves that cancel out the sound. That is then played back through speakers to cancel out the sound and create the cocoon. All of this requires deterministic networking links and high- performance digital signal processing This can also be used to provide active road noise cancellation (RNC), detecting the road noise and cancelling it to make the cabin quieter. This combination of demand for the audio domain for infotainment and the acoustic domain for ANC is driving new audio networking technologies in the cabin and new approaches to the design of an autonomous platform. The traditional architecture of an entertainment system (also called the head unit) and audio amplifier, both integrated into the dashboard for the convenience of the driver, is no longer relevant in an autonomous vehicle design. That means higher performance system-on-chip and Class D amplifiers can be distributed around the cabin if the networking is sufficiently deterministic. That allows more flexibility in the power and thermal management, as these power-hungry subsystems can be placed in different places around the vehicle. ANC also relies on microphones and small speakers in non-standard places such as headrests and pillars to create the acoustic cocoon, which also increases the complexity and weight of the wiring harness. A major contribution to the total cabling weight comes from car Infotainment systems | Focus Unmanned Systems Technology | April/May 2020 The latest concept designs for driverless cars turn the passenger cabin into an infotainment centre with multiple screens (Courtesy of Mercedes-Benz) The Automotive Audio Bus is a low-latency bus for noise-cancelling systems in the cabin (Courtesy of Analog Devices)