Wireless Video Interface Options

Since the first public demonstration of television in 1935, there have been tremendous advances in the state of the art of video delivery from a local source to a remote display. Despite these advances, the transport of video across a distance remains one of the most demanding technical requirements placed on communications systems, be they wireless or wireline. The principle reason for this difficulty is the high and increasing data rate associated with delivering video. This high data rate drives either bandwidth or signal to noise ratio as described the Shannon-Hartly Theorem for an analog communications channel subject to additive white Gaussian noise:

where C is the channel capacity in bits per second; B is the bandwidth of the channel in hertz; S is the total signal power over the bandwidth and N is the total noise power over the bandwidth. S/N is the signal-to-noise ratio of the communication signal to the Gaussian noise interference expressed as a straight power ratio (not as decibels). This theorem tells us that once the channel capacity C, by which we mean the maximum rate of zero or low bit error rate (BER) communications, requirements are known, then the designer can tradeoff bandwidth for Signal to Noise ratio.

There are several wireless options for transporting data within the vehicle, including Bluetooth, Zigbee, IEEE 802.11 Wireless LAN, and UltraWide Band (UWB, also known as WiMedia). Of these four, only 802.11 and UWB have the necessary bandwidth to support video transmission. A key difference between 802.11 and UWB is the amount of spectrum used. For 802.11 the maximum spectrum assignment is 40MHz, limiting usable data rates to 100Mbps. With over 7500MHz of spectrum allocated by the FCC in 2002 for unliscenced use of UWB communications, and with typical sub-band channel allocations of 500MHz, the usable data rate of UWB over short distances could be in excess of 1Gbps. At the 2007 Consumer Electronics Show, Dr. Wieland Holfelder, DaimlerChrysler’s vice president and chief technology officer, predicted that more and more wireless devices and options will find their way into future vehicles. A Mercedes-Benz R500 enabled with the ability to stream high-definition video live from a consumer electronic device using ultra-wideband (UWB) to a rear seat entertainment system was also demonstrated. This demo in an automobile is the first of its kind using WiMedia UWB, and sets the stage for all sorts of technology and content possibilities that capitalize on rear seat entertainment systems in family vehicles. But although proponents say the technology is robust enough to convey a vehicle's electrical control signals through UWB chipsets located within every ECU, reliability will need to be proven beyond a reasonable doubt in the interference prone automotive environment, and that is still years away.

What can be said now, though, is that wireless looks likely to be choice for interfacing between consumer devices and the car infotainment system, but is unlikely to replace in-vehicle wireline or POF interfaces and networks.