[Technology Report]
With Devices Ready To Go, Bluetooth Is Poised To Make Its Move
As semiconductor manufacturers gear up to mass-produce Bluetooth silicon, they're concentrating on solving technical and price hurdles.
One of the hottest topics in Europe is Bluetooth. The new standard was created by the Swedish telecommunications equipment manufacturer Ericsson. Named after the Danish King Harald II, who received the nickname "Bluetooth" when he unified Denmark and Norway in the 10th Century, the Bluetooth communications standard is now about to conquer the world. Over 1800 companies are already members of the Bluetooth Special Interest Group (SIG) and intend to use this RF short-range networking technology within their products. Members of the Bluetooth SIG can use the standard without paying royalties.
Perhaps this licensing factor was the reason why it took less than two years for Bluetooth to develop from scratch into a world standard. Currently, several companies are starting to develop commercial products. So far, Bluetooth is one of the fastest-growing technologies. Considering Europe alone, market researcher Frost & Sullivan predicts European revenues with Bluetooth devices of $36.7 million this year and almost $700 million for 2006.
Bluetooth is intended to provide an energy-saving, safe, and low-cost RF technology in order to eliminate cable connections over short distances. Bluetooth may be integrated in almost all kinds of electronic data-communications devices. Compared with equipment using infrared (IR) links, Bluetooth-based devices can communicate amongst each other without having a line-of-sight connection.
In principle, a Bluetooth unit consists of a baseband controller and an RF part. The controller needs an interface to the host system, such as a mobile cellular phone, cordless phone, laptop computer, PC, printer, headset, and PC peripheral. Bluetooth works in the industrial, scientific, and medical (ISM) band with frequencies between 2.402 and 2.480 GHz by using a frequency hopping mechanism, where 1600 frequency changes occur every second. A single Bluetooth connection uses 79 different frequencies with a channel separation of 1 MHz.
There are two main reasons for using frequency hopping. First, it provides a higher level of security against both eavesdropping and fraudulent access (in addition to existing encryption protection). The other reason is that RF disturbances may be eliminated. This is important in view of the fact that the operating frequencies of microwave ovens and several radio services are close to those of the ISM band used by Bluetooth. The use of forward error correction (FEC) by Bluetooth limits the impact of random noise on long-distance links. Whenever interferences occur on a specific frequency, this frequency isn't assigned during frequency hopping, resulting in a high level of robustness against external distortions. In most cases for such situations, the antenna will be implemented by assigning a short segment of conducting track on a pc board.
Communicating Over Distances Currently, maximum transmission power for Bluetooth is 1 mW. This is enough to communicate through walls and briefcases over a distance of up to 10 m (or 33 feet). To enable communication over longer distances, power amplifiers capable of providing an output power of 100 mW will be used. This will allow communication up to 100 m (330 ft). On the receiver side, the Bluetooth specification describes an input sensitivity of −70 dBm working with an IF of 1 MHz.
Between two and eight devices may communicate within a so-called Piconet. Within two seconds, individual Bluetooth controllers inside of a Piconet identify themselves by using a unique 48-bit serial number. The first device identified takes over the master function, which includes determining the 1600 frequency hops per second. All users participating on the same Piconet are synchronized to this hopping sequence.
Several Piconets operating with individual frequency-hopping algorithms can communicate within a larger multiple-Piconet environment known as a Scatternet. In this case, communication takes place via the individual Piconet masters. Compared to other RF LAN technologies, Bluetooth works with significantly shorter data packets. The full-duplex data rate within a Scatternet that has 10 fully loaded independent Piconets is more than 6 Mbits/s. This is due to a data throughput reduction rate of less than 10% according to system simulations based on 0-dBm transmitting power at the antenna.
By combining circuit and packet switching techniques, the baseband controller not only prepares the data for transmission, but also controls the entire procedure. When voice audio data is transmitted, Bluetooth works with a transmission rate of 64 kbits/s in a synchronous mode. Every single data packet is transmitted at another hopping frequency. In most cases, a data packet is assigned to a single time slot. But, data packets may be extended to assign up to five slots.
Nonvoice data may be transmitted either asynchronously at net data rates of 721 kbits/s upstream and 57.6 kbits/s downstream, or synchronously at 432.6 kbits/s in both send and receive directions. If one adds the control and protocol bits, this adds up to a total data rate of 1 Mbits/s that needs to be transmitted physically. The next-generation Bluetooth protocol might offer a 2-Mbit/s option. The current Bluetooth specification is version 1.0, but version 2.0 is expected before the year's end.
Bluetooth supports the simultaneous transmission of a synchronous data channel together with three synchronous voice audio channels. In addition, it allows the simultaneous transmission of asynchronous data and synchronous voice audio data within a single channel.
Voice channels use the continuous variable-slope delta-modulation (CVSD) voice-coding scheme and never retransmit voice packets. The CVSD method was chosen for its robustness in handling dropped and damaged voice samples. Rising interference levels are experienced as increased background noise. Even up to a 4% bit-error rate, CVSD-coded voice is quite audible.
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