What did the dentist say to the man with green teeth? “My advice to you sir is to wear a brown or yellow tie.” Apologies, I couldn't resist this old joke that kept popping up into my mind as I started to look into the details of Bluetooth technology. While that old joke is incredibly bad, just as incredible is that Bluetooth technology has already been around more than 10 years!Bluetooth is pretty cool as it's one of those technologies that work right out of the box with no or minimal setup. This edition of IT World takes our usual exploration of technology to see what makes it tick and to build a fundamental understanding of the topic at hand. This time the topic is Bluetooth.Bluetooth's plug and play has a lot of communication setup and protocol details as explained in the 1,400-page specification. Although I guess “plug and play” is not appropriate for Bluetooth as you're really not plugging anything in—a main feature! In this installment of IT World we'll be covering all the basics—saving most of the detailed analysis for Part II. This time (Part I) we'll examine a little background, spread spectrum techniques used by Bluetooth, and basic connections and communications. In addition, an overview of other wireless communication protocols is provided. Part II will dive into the transport architecture and hierarchy in more detail as well as Bluetooth packet structure and a look at what the future holds for Bluetooth.The initial effort in April 1998 was a consortium of manufacturers and vendors of personal technology. Ericsson, IBM, Intel, Microsoft, Nokia, Toshiba, and Puma Technology were all involved early on. The project was code named Bluetooth after Harald I Bluetooth Gormson, the 10th-century Danish king who unified Denmark. Interesting, but I am unsure why they picked this king and name in particular. How do these kinds of things work? I can imagine representatives from all those companies sitting around a large conference room, “What should we call this thing?” Would you have said, “How about Bluetooth? You know he united Denmark in much the same way we're uniting around a small personal wireless network to do away with cables surrounding a personal PC.”The Bluetooth Special Interest Group (SIG) was established a few months later in September 1998. The general definition is that it's a specification to standardize wireless transmission between a wide variety of devices. Originally the focus was personal data assistants (PDAs), cordless telephones, cordless headsets, PCs, and printers, to name a few.I think of Bluetooth as a sort of virtual cable. I've seen Bluetooth wireless mice, for example. Maybe I could also take advantage of Bluetooth connectivity so my laptop can sync e-mail with my mobile phone? Or maybe it would allow me to connect my PDA to send data to a fax machine? Maybe for a cordless headset for my cell phone that secretly attaches to my ear so people passing me on the highway think I'm talking to myself?Bluetooth operates in a picocell topology in the 2.45GHz range of the ISM band. The Industrial, Scientific, and Medical spectrum has several small frequency bands that are not strictly regulated by the Federal Communications Commission (FCC). They are 902–928MHz, 2.4–2.483GHz, and 5.725–5.850GHz. These ISM bands are unlicensed in that there are no requirements to register with the FCC—or need their permission in any way (although there are some power and range limitations). The open and unlicensed aspect is why cordless phones use these bands. Magnetrons in your microwave oven irradiate your food at 2.45GHz and are terrific noise sources in the ISM band. Bluetooth uses a frequency hopping spread spectrum technique, also common in WiFi, to operate in such a noisy environment.Spread spectrum techniques are used to prevent the effects of interference since these bands are open for use without much regulation. Unlicensed devices are required to be tolerant of other ISM emissions in these bands. Typically unlicensed low-power uses are able to operate in these bands without causing problems for other ISM users. However, according to 47 CFR Part 15.5, low-power communication devices must accept interference from licensed users of that frequency band. In addition the rules say that the unlicensed device must not cause interference to licensed users.As with any radio—the farther you get from the broadcasting source, the weaker the signal. As the signal weakens it gets less distinguishable from the general RF noise floor. Mentioned above, in the ISM band, you are required to be tolerant of the noise. Though in our case, this problem is somewhat lessened with the short distances typical in Bluetooth network areas or picocells (very small RF cells or radius of use). Spread spectrum techniques use many frequencies to transmit data instead of a single carrier frequency. Maybe your cubicle is next to the office kitchenette with the antique microwave oven and your wireless mouse doesn't seem to function properly around lunchtime. Frequency Hopping Spread Spectrum (FHSS) implies that you “hop around” from one carrier frequency to another. In this way if one carrier frequency is swamped out by some kind of noise, the neighbor or other carriers may not. Of course it helps the intended receiver to know what your hopping pattern is and hence one of the parts of the Bluetooth protocol.With the FHSS technique, each bit of data or information is transmitted a number of times. The “chip” time is the length of time at each frequency or channel. The chip times are much smaller than the “symbol” times, as shown in Figure 1. The 2.4GHz ISM band has an available bandwidth of about 84MHz. This spectrum is broken into 1MHz wide channels. FHSS uses 79 of the available channels. The Bluetooth specification says devices must change frequency (hop) at 625μS intervals among the 79 1Mhz wide channels.Bluetooth has two general data transmission speeds. The Basic Rate has a symbol time of 1 Mega-symbol per second (Ms/s) supporting a bit rate of 1 Megabit per second (Mb/s). The Enhanced Data Rate (EDR) has a gross air bit rate of 2 or 3Mb/s.Typical Bluetooth operation utilizes a physical radio channel that is shared by a group of Bluetooth devices synchronized to a common clock and frequency hopping pattern. One of the Bluetooth communication nodes supplies this synchronization reference and is known as the master. All other Bluetooth gadgets in that picocell become slave devices. A group of devices synchronized and communicating in this fashion form a piconet. This is the fundamental form of communication in the Bluetooth wireless technology. The picocell is the physical area within which the piconet must operate.Each device can communicate with up to seven other devices within a single piconet. In addition, each device can belong to several piconets simultaneously. Unlike most other wireless standards, Bluetooth provides developers the definition for application and link layers so they can support data and voice applications.Devices in a piconet use a specific frequency hopping pattern, which is algorithmically determined by certain fields in the Bluetooth address and clock of the master. The basic hopping pattern is a pseudo-random ordering of the 79 channels in the ISM band. What's cool is that the hopping pattern can be adapted to exclude a portion of the frequencies that are used by interfering devices. This reminds me, I wish my stomp box that's supposed to squelch feedback frequencies from my amped acoustic guitar actually worked. It would be even nicer if it worked automatically as advertised. With Bluetooth, however, it is automatic: the adaptive hopping technique helps the picocells and piconets tolerate other static (non-hopping) or noisy elements located in or passing through the ISM band.There are a variety of different wireless communication technologies and protocols available today. Some like WiFi (IEEE 802.11x) are designed to communicate with computer networks. These include WiMAX (Worldwide Interoperability for Microwave Access) and IEEE 802.16 that are mainly intended as MANs (Metropolitan Area Networks). MANs in that range are typically on the order of 50km (~30 miles). Requiring line of sight connections, WiMAX operates in the 10 to 66GHz frequency bands. Each one of the various IEEE 802.16x standards vary in carrier frequencies, ranges, and data speeds but again, are generally intended for MANs, rural, or other hard-to-wire locations.Also upcoming (currently prevalent in South Korea) is WiBro (Wireless Broadband). WiBro is intended for high data rates and mobile environments, keeping you connected up to about 40 mph. The other up and coming technology defined by IEEE 802.20 keeps you connected up to more than 150 mph! That means there's connectivity hope for drivers in Illinois, Florida, and New Jersey. In California WiBro would be sufficient as it seems you're confined to slower speeds due to either traffic or mountainous curvy and steep roads. Unless you're born and raised in Mendocino and know every nook, cranny, and curve (and speed trap) when racing through the hills near there.Wireless communications that have much smaller coverage areas are standards like ZigBee (IEEE 802.15.4). This is yet another group effort of nine companies promoting ZigBee. Operating at different frequencies within the ISM bands, the range is up to 100m and originally intended for use in industrial remote control systems. The focus for ZigBee is low power, low cost, and ease of use.There are smaller field wireless connectivity mechanisms like IrDA, NFC, and RFID. They typically operate over just a few feet, intended for things like bar code replacement, security tags, or synchronizing PDAs with each other. IrDA (Infra Red Data Association) does not pass through solid objects and so is relegated to such implementations as PDAs, printers, and laptops. Low power and short distances are key. Near Field Communication (NFC) keeps communication distances down to just under eight inches and is used in ticketing, payment (credit cards), and gaming. RFID (covered previously in IT World March/April 2005: An Introduction to RFID) is the most prevalent. With more than 140 standards for RFID use, it offers a broad range of applications. Tracking and counting of inventory mark RFID's biggest user base. Powered tag RFID applications allow a bit farther range and can be used in places like the toll way, bridges, or tunnels to automatically charge you for access via your RFID tag as you go whizzing by. Exxon/Mobil can tag your car and use the information to enable the gas pump, charging your account as you fill up. Marathon runners can wear ankle bracelets with RFID marking their progress and finish place ranking. Small powerless RFID tags get their electrical supply power from the RFID scanner, enabling the tiniest of chips to be imbedded into currency, making counterfeiting nearly impossible. Powered RFID tags offer greater communication distances but then require things like battery management and environmental considerations.Finally, the most specialized wireless communication we'll mention is Near-Field Magnetic Communication, requiring only an amazing 100 nanowatts of electrical power. Developed, patented, and licensed by Aura Communications, it is currently used only in telephone wireless headsets.The Bluetooth specification is large and detailed as it tries to accommodate many kinds of devices and how they prefer to communicate. The bottom line is that in a Bluetooth piconet there will be master and slave devices. There will be between two and eight devices communicating at any one time in a Bluetooth piconet. Each piconet will have just one master—all other devices in that piconet will be slaves. However, a device may belong to two piconets at any one time, as shown in Figure 2. A Bluetooth device can be a master in one piconet and a slave in another. When a device connects piconets in this way the combined piconet is known as a scatternet.Piconets can be static or dynamic if devices come and go or stop and start communicating, as when moving in and out of radio proximity. The master has the clock that the slaves must synchronize with. The master device also determines the FHSS patterns or algorithms that all connecting devices will use.The Bluetooth specification focuses on the communication connection levels and therefore is only described at the lower levels of the OSI Reference Model. Layer 1 of the OSI Reference Model is the physical layer and maps to the Bluetooth Physical Layer, also called the RF and Baseband layers. In the OSI Reference Model the Data Link Layer (Layer 2) is broken into two sublayers known as the Media Access Control (MAC layer) and the Logical Link Control. For Bluetooth, the spec defines linking and link management at the MAC layer as shown in Figure 3.In the next installment of IT World we'll continue the Bluetooth analysis picking up the story at this point. Part II will cover the transport architecture and hierarchy, the rest of the communication protocol, and Bluetooth packet structure and use. We'll also look into what the future might have in store for Bluetooth and Bluetooth enabled devices.