Bluetooth paves the way for truly wireless car interiors

Many would say that the automotive market is like a slow-moving tanker in its hesitance to adopt new technologies or to change course. This has certainly been the case for wireless applications in the automotive environment. From the introduction of simplistic remote locking to today’s concept cars offering living-room comfort, wireless electronics have certainly come a long way.



Bluetooth wireless technology has experienced reasonable growth in the automotive sector thanks to its adoption first by hands-free kit designers, and then by after-market navigation and infotainment designers, and now increasingly by the big automotive manufacturers in Japan, Germany and the US. However, the cabin, or interior environment, still presents a real challenge for robust wireless communications. The growing range of applications demands ad-hoc wireless connectivity and the ability for those connections to resist the high levels of interference inherent in the cabin.



RISE OF BLUETOOTH IN AUTOMOTIVE SPACE

Due to the costs involved in designing new technology into cars, the industry has been watching the rise in consumer adoption of Bluetooth technology before deciding if it has reached the critical mass required to be recognized as a desirable feature for cars. In the early days of automotive Bluetooth, the main application for such short-range wireless connectivity was hands-free use of a mobile phone. Wired systems were often prohibitively expensive for consumers as they had to be fitted professionally. Alternatively, they could choose a wired mono headset that was often uncomfortable, but it was reliable and low cost.

EXISTING CHALLENGES

There are a number of factors to consider when evaluating the challenges of the car environment for RF applications. Automotive electronics must be able to safely withstand certain levels of humidity, and temperatures typically ranging from -10°C to +70°C. For OEM fitted systems, this increases to a universal minimum requirement of -40°C to +85°C, and under severe humidity and vibration conditions. These temperature requirements are particularly challenging for RF-based systems which are dependant on stable clock performance over temperature.



It is also important to consider the expected life of a car. Unlike the mobile phone market where users change handsets every year in order to keep up with technology trends, a car may be in use for over a decade. Therefore, the integrated electronic systems must be robust enough to continue to work efficiently during this lifetime, and to be easily upgraded to add new technology.



However, the most critical aspect of RF integration is the ability to guard against interference from other electronic systems in the vehicle, including the ignition system, other in-car entertainment modules and things like GSM transceivers and WiFi. A car’s interior is highly reflective, and RF signals can cancel out elements of the desired signal, leading to poor audio performance.



TECHNOLOGY EVOLVES TO MEET NEW CHALLENGES

The demands on Bluetooth in the automotive environment are increasing as consumers take the technology to heart, and designers recognize the added value of integrating Bluetooth connectivity within the car. There is growing interest in connecting multiple Bluetooth devices (mobile phone, PDA, MP3 player, GPS, navigation) to the central infotainment console and operating all those devices via the dashboard controls.

Bluetooth has gone through a series of evolutionary changes to address these issues. The need to withstand extreme temperatures, as well as consistent usage throughout the life of the car, must be considered continuously from initial silicon straight through packaging design which must be more rugged than that used in consumer electronics.



New versions of the Bluetooth specification developed by the Bluetooth SIG also introduced new ways of avoiding interference and boosting coexistence between Bluetooth and other wireless technologies such as WiFi. Elements such as eSCO (extended synchronous connection oriented) channels and AFH (adaptive frequency hopping) were introduced to complement the original CQDDR (channel quality data driven rate) which monitored the noise in the environment and allowed the Bluetooth device to gauge how much of the data is being corrupted on transmission and adjust the packet types to best cope with the environment.

eSCO allows the receiver device to check that all packets have been received, and it requests the retransmission of any dropped packets. AFH monitors the link quality and identifies poor channels on specific frequencies so that they can be avoided by the Bluetooth signal.



Enhanced data rate (EDR) Bluetooth, introduced with the v2.0+EDR Bluetooth specification, also added coexistence support and provides data rates of up to 3Mbps. These two features make it possible for multiple devices to operate simultaneously, increasing the complexity of applications but increasing the number of scenarios that can co-exist in a vehicle.



UWB/BLUETOOTH HYBRID RADIO

In March 2006, the Bluetooth SIG announced that it would work with the WiMedia Alliance to integrate its version of UWB wireless technology into a future version of the Bluetooth specification. UWB is a very high-speed RF technology that transmits information at low power over a large range of radio frequencies. UWB differs from other wireless technologies in that it transmits at levels very close to what is considered the “noise floor” — normal background noise. This requires UWB radios to have sophisticated receivers in order to detect signals at a level that is lower than normal background interference.



Although different, Bluetooth and UWB are two very complementary technologies. Bluetooth has historically provided low rate data transfer with low cost and low power. UWB radios use about 20 times more power when active, but they will offer data rates of up to 480Mbps, meeting the requirements of increasingly data-heavy applications. This will enable data to be transferred quickly at lower power per bit than Bluetooth.



The introduction of a hybrid Bluetooth/UWB architecture will help to support the developing trend for even more complex in-car multimedia systems. Although the technology is still only at the R&D stage, it is easy to envision “Ultra Wide Bluetooth” (as CSR is informally calling it) being used to transfer the contents of personal media players, packed with videos and music, to an in-car infotainment system. The system can then stream video to rear-seat screens while passengers listen to the audio over Bluetooth stereo headphones and use wireless controllers to either select new content or play games.



INTEGRATION OF THE FUTURE

Wireless technology for in-car systems with applications ranging from infotainment to vehicle diagnostics is here to stay. Bluetooth, in particular, has now been recognized as an established system that can add value to a commercial car design and, with the standard evolving to incorporate hybrid radio combinations that offer much higher data rates, the possibilities are virtually endless.