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Bluetooth

 

 

Bluetooth

The Concept

Bluetooth is a specification to standardize on a low-cost, low-power RF (Radio Frequency) solution for wireless transmission between a wide variety of devices such as PCs, keyboards, cordless telephones, cell phones, headsets, printers, monitors, LCD projectors, and PDAs (Personal Digital Assistants).

Initially developed by Ericsson, the specification was furthered by the Bluetooth SIG (Special Interest Group) consortium (April, 1998) of Ericsson, IBM, Intel, Nokia and Toshiba. At some point during this process, the code name Bluetooth was attached, after Harald Blaatand, the 10th century Danish king who unified Denmark and conquered Norway. (I'm betting that the Vikings at Ericsson had a good deal to do with the name selection.)

Bluetooth was intended to create a single digital wireless protocol to address end-user problems arising from the proliferation of various mobile devices that need to keep data synchronized (i.e., consistent from one device to another).

Bluetooth operates on both a point-to-point and a point-to-multipoint basis. Although it primarily is promoted as a means of eliminating cables between devices such as keyboards, computers, headsets, cellular phones, and so on, Bluetooth also has limited LAN potential in the form of a PAN (Personal Area Network).

Current standards allow as many as eight devices to be linked together in a piconet, or very small network, with as many as seven devices slaved to a single master. In a true WLAN application, Bluetooth is overshadowed by 802.11b (Wi-Fi) and other more robust standards.

Bluetooth operates in the 2.4 GHz band and makes use of the Gaussian Frequency Shift Keying (GFSK) modulation scheme and FHSS (Frequency Hopping Spread Spectrum). The nominal link range is as much as 100 meters, although most devices will be limited to 10 meters, and the theoretical gross data rate is up to 1 Mbps, under optimal conditions.

Device Classes

Bluetooth radios are divided into classes, each of which specifies a transmission power level. The higher the transmission power, of course, the greater the range over which the signal can be transmitted successfully, i.e., at an acceptable error rate. And each of the three classes is targeted at certain applications.

Class

Power Output

Approximate Range

Applications

1 100 mW 100 meters Access Points
2 2.5 mW 10 meters PCMCIA Cards for PCs, Printers, Scanners, Copiers, Fax Machines, LCD Projectors
3 1 mW 6 meters Cell Phones*, PDAs, Cordless Phones, CD Players, Digital Cameras, Headsets, Keyboards

*Note: While most Class 3 devices will be Bluetooth-equipped at the time of manufacture, there are adapters in the form of Bluetooth-equipped battery packs for some older cell phones.

At 100 meters, Class 1 has about the same coverage as 802.11b, the prevalent WLAN standard. Since it is highly unlikely that Bluetooth can compete effectively in this space, most devices will fall into Class 2 or Class 3, with Bluetooth largely serving as a replacement for short cables to connect peripherals to devices. Examples include connecting a keyboard and mouse to a PC, or a headset to a cell phone or CD player.

Frequency Band

The 2.4 GHz range is part of the ISM (Industrial, Scientific and Medical) band. The great thing about this unlicensed band is that it is freely available for use by just about anyone and anything, although there are regulatory limitations on power levels in order to reduce the potential for interference between devices in proximity.

In this day and age of expensive licensed RF spectrum, there is a lot of pressure on the 2.4 GHz ISM band. This is the same range in which 802.11b runs, for example.

HomeRF, a competing non-standard PAN solution, runs in this band, as well. It's also the same range used by RF bar code scanners, microwave ovens, garage door openers, some cordless phones, numerous devices used in the hospital and clinic applications, and a whole bunch of other stuff.

So, the problem with the ISM band is that somebody can fire up an 802.11b WLAN and knock your Bluetooth network down, and vice versa. Or you can initiate a file transfer and cause garage doors to go up and down all over the neighborhood.

As you might well imagine, the competition in this band becomes a real issue when you try to combine the two interfaces in a single device, like a PCMCIA card in a laptop. While several manufacturers have announced products that would resolve these problems and allow the two solutions to coexist on the same device, I'm not aware of any that have shipped. I suppose that's not such a big issue at the moment, but it will be once Bluetooth becomes more prevalent.

I'll share a story with you now. It's one of those little bits of anecdotal evidence that underscores the importance of frequency allocation and management.

According to a consultant friend of mine, he was called into Singapore about a year ago on an emergency basis to troubleshoot and resolve a problem with the wireless ATM (Automatic Teller Machine) network. It seems that the network had begun to suffer frequent, unexplainable link failures.

As the story goes, the network was running in the 2.4 GHz range. The source of the difficulty was (you guessed it) isolated to Bluetooth, which had only recently been approved for use in Singapore. My friend tells me that he isolated, diagnosed and resolved the problem in pretty short order. I suspect that his fee was pretty healthy.

While I don't expect my ATM network to fail when some jogger runs by the bank while listening to music on a Bluetooth-equipped CD player and headset combination, I do worry about interference with my Wi-Fi network if someone walks into the office with a Bluetooth-equipped cell phone and headset.

 

The Bluetooth wireless technology specification connects all your mobile devices, such as laptops, mobile phones, portable handheld devices and the Internet. But how does it work and do we really need to be so connected?

 

The Bluetooth SIG is working with the newly formed IEEE 802.15 Working Group on the development of consensus standards for Wireless Personal Area Networks (WPANs). There's no indication as to when standards are expected to be released, but at least someone's working on the problem.

Spread Spectrum

Bluetooth makes use of spread spectrum transmission. Specifically the technique is FHSS (Frequency Hopping Spread Spectrum), which involves the transmission of short bursts of packets over a range of frequency channels within the wideband carrier.

The transmitter and receiver hop from one frequency channel to another in a carefully choreographed hop sequence determined by the master. In the case of Bluetooth, the hop sequence involves 79 channels with spacing of approximately 1 MHz.

All 79 channels must be hopped through in a continuous cycle at the rate of 1600 hops per second. That creates a bit of a problem, as the devices hop through even the noisy channels, which virtually ensures that some packets will be dropped, which requires retransmissions, which negatively affects throughput.

Note: France, Japan, Spain and some other countries also use portions of the 2.4 GHz band for military communications and other non-commercial purposes. The Bluetooth standard was modified for use in those countries through the definition of a 23-hop sequence that avoided those channels.

Bandwidth and Throughput

Bluetooth gross bandwidth is rated at a theoretical 1 Mbps under optimal conditions. Optimal means that the signal is at the maximum allowable strength, that the airwaves are clear of EMI (ElectroMagnetic Interference) and RFI (Radio Frequency Interference), that the distance between transmitter and receiver is within the allowable limits, that clear line-of-sight is established, and I suppose that you've got your nose twitched just right. Since optimal never happens, throughput is always considerably less.

Bluetooth technology supports both SCO (Synchronous Connection Oriented) links for voice and ACLs (Asynchronous Connectionless Links) for packet data. Bluetooth supports an asynchronous data channel in asymmetric mode of up to 721 Kbps in either direction and 57.6 Kbps in the reverse direction. Alternatively, the data channel can be supported in symmetric mode of up to 432.6 Kbps.

As yet another alternative, Bluetooth supports up to three simultaneous synchronous packet voice channels, or a channel that simultaneously supports both asynchronous data and synchronous voice. Communications are in full-duplex (FDX) using TDD (Time Division Duplex) as the access technique. Voice coding is accomplished using the CVSD (Continuously Variable Slope Delta) modulation technique.

The best case is that you can expect bandwidth of about 700 Kbps, although actual throughput is considerably less once you factor in things like overhead and error control. Now, that's plenty of bandwidth for headset-to-cell phone or PC-to-printer connectivity, but it's not even close to the gross bandwidth of 11 Mbps delivered by 802.11b under optimal conditions.

Security

Wireless security is something of an oxymoron, at least in the RF space. After all, the signal is radiated, and any knucklehead with an RF receiver tuned to the right frequency can pick it up.

With a high-gain antenna, he (most knuckleheads are guys) can even be well beyond your anticipated range and still pick up an intelligible signal. FHSS makes signal interception a bit more complicated, but not impossible.

Bluetooth security is device-based rather than user-based. There are three security levels:

  • Level 1: No Security
  • Level 2: Service-level-enforced security, which is established after channel negotiation
  • Level 3: Link-level-enforced security, which is established prior to channel negotiation.

Level 2 generally is recommended unless security is really important to you, as Level 3 gets a bit involved. One of the purported advantages of Bluetooth is its simplicity, which fades pretty quickly at Level 3.

Encryption is built in through an algorithm known as Eo, which uses randomly selected 128-bit keys, which is generally considered to be a pretty secure approach.

The real problem is with the authentication mechanism, which uses a PIN (Personal Identification Number) up to 128 bits that can be shared automatically. If the user sets the PIN to 0 (Zero), any other device can establish a connection at will.

Depending on the application, of course, the best solution probably is an external encryption program such as SSL (Secure Socket Layer) or VPN (Virtual Private Network) software. That would make you feel a whole lot better if you're moving sensitive files back and forth between laptops, notebooks or PDAs.

Further, each equipped device periodically transmits a device identifier known as a Bluetooth Device Address (BDA), and does so in the clear, i.e., unencrypted, much like a cell phone. So, anyone with a high-gain antenna can track a given device... and, therefore, the person associated with it. Beware, you privacy advocates!

Networking

There are several possible Bluetooth networking scenarios: piconets and scatternets. Piconets are very small networks.

At the simplest level, a piconet can be a point-to-point connection set up to connect a device to a peripheral (e.g., a cell phone or CD player to a headset), or perhaps to connect two laptop computers for a file transfer. Piconets can get more complex, with as many as seven devices slaved to a single master.

Scatternets are formed when multiple piconets are in range, i.e., when multiple masters are in proximity. In a scatternet scenario, a given device could assume multiple roles, serving as a master of one piconet and a slave on another.

Applications

Bluetooth breaks out a number of applications standards, known as profiles. Profiles include cell phones, cordless phones, voice communications directly between Bluetooth devices, serial port emulation, headsets, computer and fax modems, and LAN access points. Let's put some of these profiles to work in some gizmos.

First, you establish an ad hoc network during a meeting in a client's conference room in order to synch up Outlook calendars, exchange electronic business cards (vCards), or swap files. You do this after you've all disabled your security mechanisms, of course. (Don't forget to re-enable them after the meeting.)

During the meeting, you take notes with your Bluetooth-equipped pen. It recognizes what you are writing, and forwards it to your PC or PDA. (Several companies have developed these things. I kid you not.)

 

When you get back to the office, you synch up your PDA to your desktop or laptop without using a special cradle, and from a distance of 30 feet with no line-of-sight requirement. Then, you connect your laptop to the Internet via a Bluetooth access gateway built into a DSL router so that you can transmit your meeting notes to your colleagues at broadband speed while you're printing the documents via a Bluetooth link to your serial printer.

While driving home after a successful day's work, you put on your Bluetooth headset that connects to your cell phone, which is in your briefcase, which is in the back seat of your car, so that you can tell your boss how great you are.

Better yet, you talk to your rear view mirror. Chrysler recently (January 2002) announced a really cool Bluetooth implementation. U-Connect will soon let motorists make hands-free, voice-activated calls from Bluetooth-equipped cell phones. You'll be able to activate the system by touching a button on the rear-view mirror.

Into a microphone in the mirror, you then recite the telephone number you wish to dial. Once the voice-activated call is connected, your hands-free transmission is through the mirror mic and your reception is through the car speaker system. Your cell call overrides the radio. No docking system is required for the cell phone.

In my humble opinion, the pen gizmo is pretty silly. (Some engineer has too much time on his hands, and his company has too many yen to worry about it.) The rest of it's pretty cool. U-Connect is awesome.

There are more examples, some of which seem pretty silly, and others of which seem pretty cool. One thought is that inexpensive (waterproof) Bluetooth chips embedded in your clothes will transmit washing instructions to your clothes washer. Your clothes washer will alert you via your Bluetooth watch when the cycle is complete.

Who knows, you may even get a synthesized voice alert from your Bluetooth washer through your Bluetooth DSL router access point over the Internet via your Bluetooth cell phone that connects to your Bluetooth headset through your Chrysler PT Dream Cruiser U-Connect audio system. "Dude, Your laundry's done." I hope I never live to see the day we're that well connected.

Prognosis

The original members of the Bluetooth SIG were Ericsson, IBM, Intel, Nokia and Toshiba, as I previously noted. The group has now expanded to include 3Com, Agere Systems, Microsoft and Motorola, and hundreds of Associate and Adopter companies.

Even after the formation of the Bluetooth SIG in 1998, Bluetooth stalled for several years in the face of competition from the emerging 802.11b and the general decline in the economy. Microsoft gave Bluetooth a big boost when it joined the SIG in December 1999 and particularly when it announced Bluetooth support for Windows XP.

Microsoft just recently (October 2002) announced the Microsoft Wireless Optical Desktop for Bluetooth, which is the industry's first Bluetooth compatible keyboard, mouse and transceiver combination. In conjunction with that announcement, Michael W. Foley, chairman of the Bluetooth SIG at Microsoft, stated that "Bluetooth is poised to be the cable replacement technology of choice."

I'm sure that you have your own opinion about Microsoft and it may not agree with mine (I like 'em.), but I'm sure that we can agree on one point: When Microsoft supports a technology (or anything else), it's a good bet that it's a winner. Bluetooth now fits into that category.

It doesn't hurt that Apple also announced Bluetooth support for Mac OS X 10.2. Now, I no longer put much faith in industry forecasts these days, but it's worth noting that IDC expects Bluetooth semiconductor revenues to increase from $76 million in 2001 to $2.6 billion in 2006.

 

 

 

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