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84 Focus | Infotainment systems audio systems, because analogue wiring requires expensive shielded cables for microphones and loudspeakers. These ANC and RNC systems require several microphones inside the car, adding many other inputs to the audio network. An alternative approach is the Automotive Audio Bus (A2B). This carries acoustic data over a low-cost single unshielded twisted-pair (UTP) cable with a maximum latency of two cycles. The protocol is simple and is implemented in the transceiver without the need for a microcontroller or software. This can be used for connecting up the microphones and speakers for ANC and RNC designs. The A2B protocol provides a 50 Mbit/s bandwidth that supports up to 32 upstream and up to 32 downstream audio channels using standard audio sample rates (44.1 and 48 kHz) and channel widths (12-bit, 16-bit, 24-bit). Maintaining a completely digital audio signal chain between audio ECUs ensures the highest quality audio is preserved without introducing the potential for audio degradation with ADC and DAC conversions. Up to 11 slave nodes can be daisy- chained together with a master device, with a maximum of 15 m between nodes and a total length of 40 m so that it can easily run around a cabin. Multiple buses can be used to provide the different zones in the cabin, and can be linked to a gateway with a digital signal processor to provide the ANC capability. The bus also includes system-level diagnostics, as all the nodes have the capability to identify various fault conditions including open circuits, wires shorted together, wires reversed or shorted to power or ground. This is important from a system integrity standpoint, because in the case of open circuits, wire shorts or reversed wire faults, the nodes are still fully functional upstream of the fault. The diagnostic capability also provides efficient isolation of system-level failures. Alongside audio data, the bus also carries control signals using the standard SPI, I2C and I2S protocols. A new generation of the bus can carry 50 W of power over the same wire, up from 2 W in the current version. This allows the single wire to drive small speakers for the personalised zones without having to have separate power supplies, simplifying the cabin design. All of this gives a 75% reduction in the weight of the wiring harness for the audio system. The same technology is also used for camera feeds. The Car Camera Bus (C2B) carries uncompressed HD video over an unshielded UTP cable. The bandwidth on the cable is 72 MHz, and it uses an analogue multi-level protocol to meet EMI requirements to carry the equivalent of 1.5-2 Gbit/s links but without the need for shielded connectors. This can also carry data from sensors in the cabin such as a time-of-flight sensor. This could be used to monitor the position of people in the cabin or display feeds from 2 MP rear or side cameras with 2 MP and 1080p30 displays. This is not the only serial camera technology available. For example, the CoaXPress (CXP) consortium has developed an asymmetric high-speed point-to-point serial comms standard for the transmission of video over coaxial cables, This supports a high-speed downlink of 12.5 Gbit/s alongside a 42 Mbit/s uplink for comms and control, as well as power. It can run for 35 m at 12.5 Gbit/s and 100 m at 3.125 Gbit/s, with real-time behaviour and a fixed low latency. This has been adopted by the Automotive SERDES Alliance for serial/ deserialiser (SERDES) technology to combine parallel data lines into April/May 2020 | Unmanned Systems Technology Driverless vehicles could be used as travelling hotel rooms, dramatically increasing the data rates they would need (Courtesy of Toyota)