In Stat/MDR suggests that 1.4 billion Bluetooth devices will have been shipped by 2005. Figures from Forrester also highlight that applications for Bluetooth are shifting away from just mobile phones, to PDAs, laptops and other applications including in-car use. In fact, market analyst firm ABI expects there to be 25 million Bluetooth equipped cars worldwide by 2008. So given the growth of in-car use, how is Bluetooth likely to fit into these vehicles, what are its applications, and what are the technological developments driving this wider adoption?
We look at some of the current and future applications of Bluetooth, and examine some of these recent developments in the Bluetooth standard. Some of these developments are helping the wireless technology fine-tune its performance in the rigorous demands of the cabin's environment; whilst some are opening Bluetooth up to new application areas.
Bluetooth is already widely in use in the car as a replacement for wired headsets. A growing number of countries around the world ban the use of a phone unless a hands-free kit such as a Bluetooth car kit, or Bluetooth headset is employed. In many countries hefty fines are being used to enforce this. Asian countries such as Hong Kong, India, Japan, Malaysia, Philippines, Singapore, Korea, Taiwan and Thailand have some level of ban currently in place.
Hands-free mobile phone operation in vehicles clearly offers a huge potential market for Bluetooth wireless technology, and solutions are already finding their way into both after-market (add-ons bought from mobile phone or electronics shops) and embedded designs. Audi, BMW, Saab, Daimler Chrysler, Honda and Toyota are some of the companies already offering models with embedded Bluetooth options, which work through the car's multimedia interface such as those used for car navigation.
Alongside hands-free mobile phone operation, future Bluetooth applications in-vehicle will include Internet access, wireless additions to the infotainment system, vehicle personalization and even vehicle diagnostics. In the past 12 months, Bluetooth has been going through developments in its specifications that make the technology even more suitable for these potential applications. Version 1.2 (v1.2) specification of Bluetooth was finalized in 2003 and the Bluetooth special interest group (SIG) announced enhanced data rate (EDR) Bluetooth in June 2004.
To embed Bluetooth in the vehicle there are problems that need to be overcome. Bluetooth technology was originally developed to withstand harsh environments, such as that found in a vehicle cabin. This is the reason behind its rapid adoption by some of the world's leading car-makers. CSR's BlueCore silicon for example, operates over the required temperature range of -40 to +85°C for in-cabin applications and operates up to +105°C.
In addition to temperature, other RF devices in a vehicle, such as car stereos, GPS navigation equipment, Satellite Digital Audio Radio Service (SDARS), GSM transceivers and other electrical devices, can all potentially cause interference, or can be susceptible to interference. A car is effectively a reflective "tin-can", where radio waves are reflected within the vehicle cabin. This potentially results in a phase shift that, with superposition, can effectively cancel out or corrupt the desired signal.
All this RF activity can be detrimental to the data throughput of a wireless system in a vehicle. As the applications for Bluetooth expand into infotainment, Internet diagnostics and others, Bluetooth implementations are likely to become more widespread around the car, further compounding the potential risk of interference.
Bluetooth has an existing arsenal of defenses to combat interference designed into the standard. The first line of defense built into the Bluetooth radio specification is frequency hopping which requires both the receiver and transmitter to tune/hop to one of its 79 different channels 1600 times per second in a pre-determined pattern. This provides a good level of immunity to interference but even with frequency hopping in place, the high amount of RF activity in the vehicle cabin can still be detrimental to data throughput and link reliability.
The Bluetooth specification includes measures to combat any potential sources of RF interference, which are magnified in a vehicle cabin. Called CQDDR (Channel Quality Data Driven Rate), this technology monitors the noise in the environment allowing the Bluetooth device to gauge how much of the data is being corrupted on transmission and then dynamically adjusts the packet types to best suit the environment. The result is that it maintains the most efficient data rates. Given the potentially busy RF environment in a vehicle cabin it is important that silicon chosen for automotive applications incorporates CQDDR to assure the highest data rate, especially in data applications such as Dial-up Networking-not all Bluetooth systems incorporate CQDDR.
In the latest Bluetooth specification, v1.2, there is further support to help Bluetooth devices maintain an even more robust connection, as well enhancements to smoothen Bluetooth's coexistence with other wireless standards such as WiFi (802.11).
Hopping sequenceAFH (Adaptive Frequency Hopping) is one of these. AFH allows the Bluetooth devices to monitor the link quality, and then determine if there are common poor channels present on specific frequencies. In such a case, the Bluetooth devices adjust their hopping sequence to avoid the bad channels, therefore improving data throughput.
eSCO (extended Synchronous Connection Orientated) is another valuable addition to the Bluetooth specification particularly to the automotive market. SCO is the data transport mechanism for transferring voice over a Bluetooth link. eSCO links improve audio quality and flexibility.
With the known harsh RF environment within a vehicle cabin, it is possible to hear audio corruption on a SCO link between two Bluetooth devices due to the synchronous nature of the transport. With eSCO it is now possible to have a limited number of retransmissions of this synchronous voice data, which greatly improves the audio quality in a noisy RF environment such as the vehicle cabin.
SCO in Bluetooth version 1.1 (v1.1) only used single slot packets. Extended SCO in v1.2 allows the use of 3 slot packets for synchronous voice or data. This means it is possible with eSCO to get connection speeds of 100Kbps, compared with the fixed 64Kbps from v1.1. This is possible because with single slot packets a lot of link capacity is lost to gaps between packets whilst the radio changes frequencies.
In eSCO, each packet has a CRC (Cyclic Redundancy Check) so the receiver can check that packets have been received correctly. This uses an acknowledgement scheme, so packets that have been received with errors or lost altogether are negatively acknowledged. Retransmission windows allow opportunities to retransmit unacknowledged packets.
The CRC means that there will be fewer errors in the audio, giving better quality, and the retransmission means that, from the CODEC's viewpoint, there are less dropped packets, so there will be fewer clicks in the audio. Overall, eSCO means the same CODECs will give better quality audio.
Figure 1 illustrates the eSCO system. At each eSCO instant the master transmits an eSCO packet, the slave responds using the normal SCO rules (the slave is allowed to respond even if it does not receive the packet from the master). Then the differences from SCO appear: there is a retrans-mission window during which unacknowledged packets can be re-sent until acknowledged. The spacing of the eSCO instant is negotiable. With v1.1 SCO there was a choice of 3 different packet intervals all giving the same 64Kbps. With eSCO both packet length and intervals can be negotiated in both directions of the link allowing asymmetric traffic.
>Figure 1: eSCO enables a limited number of retransmissions of synchronous voice data with improved audio quality in a noisy RF environment.Figures 2 and 3 illustrate the difference between the automotive environment with standard SCO (
Figure 2) and with eSCO in place (
Figure 3). As with CQDDR, eSCO is an optional feature of v1.2 and not all Bluetooth silicon vendors incorporate it.
In June 2004, the Bluetooth SIG announced EDR (Enhanced Data Rate), an addition to the v1.2 specification that offers data rates 3 times faster than standard v1.2. EDR makes possible maximum data transfer rates of 2.1 Megabits per second (Mbps) compared to the current 721 Kilobits per second (kbps) for v1.2. This increase in transfer rate also means that, for a given amount of data, the EDR radio will be active up to 3 times less than a v1.2 radio, hence reducing power consumption, which greatly benefits battery-dependent mobile devices.
Figure 2: The difference between the automotive environment with standard SCO.
Figure 3: The difference between the automotive environment with standard SCO and eSCO.EDR will also permit the simultaneous transmission to multiple devices. In the automotive environment, this may be applied to in-seat entertainment systems, connected to DVD or games consoles (controllers for which can also be wireless). Given that EDR is, strictly speaking, an addendum to the v1.2 specification, it employs the same interference avoidance technologies as standard Bluetooth therefore it is still suitable for such in-cabin application.
So, Bluetooth is a fundamentally robust radio technology and a globally accepted standard available in consumer products today-recent developments in v1.2 and EDR Bluetooth have made it even more suitable for use within the vehicle as well as opening up the potential for wireless infotainment systems.
