TRIANGLE FRAME: Bluetooth Protocol (Part 1): Basics and Working

Handheld devices like a cell phone, palmtop and laptop were rapidly becoming an integral part of our daily lives. In most cases, these devices do not have compatible data communication interfaces, or, if they do, the interface requires cumbersome cable connections and configuration procedures.

Isn’t it absolutely fantastic to connect your PC to share music, data and calendar info without using any wires? Or to wirelessly access phone numbers on your PDA from your cell phone. Driving without holding the handset makes it dramatically safer and easier. Accessing the internet, print files from your computer and print photos taken from a digital camera without a single piece of wire lying in your office.

An obvious solution was to get rid of the cables and use short-range, wireless, inexpensive and universally adopted by device vendors to facilitate on-demand connectivity among devices .The marvel of engineering gave us the freedom of exchanging data without using yards of wires and popularly known as Bluetooth. It all started back in 1994 when Ericsson Mobile Communications began a utilitarian assessment on an inexpensive low-power radio solution between cell phones and phone accessories. The idea was to build a small radio both in cellular phones and laptop that would replace the cumbersome wires between them. Four years later Ericsson, along with Nokia, IBM, Toshiba and Intel formed the Bluetooth Special Interest Group (SIG). These were the leading companies in the field of mobiles, notebook computers and leaders in the digital market technology. With such big names of the field it immediately grabbed the media attention and there were very high expectations from the product. But a lot of complexities and problems were faced initially. Then in 1999 first Bluetooth spec 1.0 was launched and a year later spec 1.1. Today, the Bluetooth SIG has 3,400 companies.

Bluetooth is a wireless technology standard for connecting fixed or mobile devices using short radio link. It aims at providing wireless communication along with small size, minimal power consumption and low price. The technology was designed to be simple, and the target was to have it become standard in wireless connectivity. The name of Bluetooth has a very interesting story. The Bluetooth SIG adopted the code name as a tribute to the tenth-century Viking king Harald Blatand who peacefully united numerous small kingdoms under his region that were working under different rules same as done in Bluetooth technology. Harald liked to eat blueberries, which gave his teeth the coloration that lead to the nickname "Bluetooth."The symbol is also famous as its name and has a very interesting origin. The logo combines the representation of the Nordic runes Hagalaz (transcribed by 'H') and Berkana (transcribed by 'B') in the same symbol. This is, HB like Harald Blatand.

What makes Bluetooth special when wireless technologies like IrDA and Wi-Fi existed?

Pitting these technologies against each other would be unfair as each of them have their unique advantages and complement rather than compete with each other. Though IrDA supported wireless connectivity they needed optical contact that is direct line of sight and supported one to one data exchange using infra-red light. For example a remote control and television where we need to hold remote in line of sight of television. In the same way Wi-Fi offers a means to wirelessly connect one or more computers to each other and a router so that we can access the Internet. It uses longer distances and transfer data at faster rate as well but Bluetooth offers a means to link not just computers, but PDAs, headphones, headsets, printers and other technology with each other. The figure below represents the three networks.

“Wireless communication made easy” a tag line used to address Bluetooth but it is only for users not for the developers. The demands of creating Bluetooth-enabled products are very challenging. It should be flexible application topology so the exchange takes place between the required devices. Power required by Bluetooth should be low as no one wants a short battery life. Size is a important feature while designing. It should be small so adding Bluetooth capability to a device should not noticeably increase its size. A Quality of service is supported for voice and last but not the least Bluetooth cannot cost more than cables.

The promise of Bluetooth- What it can do!!

The promise of Bluetooth is extremely ambitious. Originally conceived as a low-power, short range technology to replace cables interconnecting devices such as printers, keyboards and mine. It has evolved its perceived potential to a much larger extent. It has given rise to Personal area network where everything is accessible within the Personal Operating Space that is related to communicating information both voice and data. There are various examples where Bluetooth model has been used.

As we can see initially Bluetooth was started in the area of mobile phone. Every manufacturer started implementing Bluetooth enabled devices in the phones. The reason behind this adoption was to use wireless headset with the phone which meant phone can be used even if it is in a briefcase or trunk. It was used to make a mobile phone or cordless modem to provide Dial –Up networking which allows connecting to internet without any physical phone line. Laptop can automatically utilize the users nearby cell phone to dial and connect to dial-up service. Peer to peer file exchange can be done without the presence of network infrastructure. For example a salesperson can share the contents of electronic slides with the audience. Bluetooth enables automatic detection of Bluetooth devices in the room enabling the transfer. Data synchronization between the devices is permitted by Bluetooth. For example a Bluetooth enabled desktop computer can wirelessly synchronize its contact list, task information, calendar to a user’s phone, PDA, or notebook. Nowadays, HP is making printers and notebooks with embedded Bluetooth technology so they can automatically detect Bluetooth –enabled printers in their area and wirelessly send documents to the printer without going through lengthy network and printing set-up process.

1. How does bluetooth work?

Bluetooth is a short range communication that is simple, secure and available everywhere. Billions of devices ranging from mobile phones and computers to medical devices and home entertainment products are enabled with Bluetooth devices.

In simple terms Bluetooth takes the information normally carried by wire and transmits it at a special frequency to another Bluetooth device. Both sending and receiving devices have same Bluetooth receiver chip, which translates data into wireless transmission and then back to normal again depending on the sender or receiver. Any Bluetooth device can be a master or slave depending on the application. Every device is equipped with a microchip (trans-receiver) that transmits and receives in the frequency of 2.4 GHz which is available to the whole world. Besides the information, there are three channels of voices available. The information can be exchanged at a speed up-to 1 megabit per second or 2 megabit for second in Second Generation of this Technology). Frequency hopping allows communicating inclusively without interferences. The transmitted data is divided into packets and each packet is transmitted on one of the 79 designated Bluetooth channels. Each channel has a bandwidth of 1 MHz’s. The first channel starts at 2402 MHz and continues up to 2480 MHz in 1 MHz steps. It usually performs 800 hops per second, with Adaptive Frequency-Hopping enabled. The master sets the hopping sequence, and the slaves synchronize to the Master. A cluster is formed by a master and up to seven active slaves known as Pico nets. The slaves in a Pico net only communicate with the master. A scatter net can be formed by linking two or more Pico nets. When a device is present in more than one Pico net, it must time-share and synchronize to the master of the Pico net with which it is currently communicating. Networks in Bluetooth are far more diverse and dynamic. As they are constantly formed and dissolved Bluetooth devices move in and out of range so there are limitless ways to connect them. The figure below summarizes the Bluetooth communication.

With the basic understanding of information exchange in Bluetooth system we now move ahead to specifications.

Frequency

The Bluetooth operates in the frequency range of 2.4 GHz. Though this band is available worldwide it may differ in some countries. This is the frequency band of scientific and medical industries 2.45 GHz (ISM*). The ISM* is opened for any system of radio and take care of the interferences of monitors, the controls for doors of garage, the wireless telephone and microwave oven. The ranges of the bandwidth in The United States and Europe are between 2.400 to 2.483,5 MHz and it covers part of France and Spain. The range of the bandwidth in Japan is between 2.471 to 2.497 MHz So the system can be used worldwide due to that transmitters of radio covers 2.400 and 2.500 MHz and makes it possible to select the appropriate frequency. ISM The industrial, scientific and medical (ISM) radio bands were originally reserved internationally for the use of RF electromagnetic fields for industrial, scientific and medical purposes other than communications. In general, communications equipment must accept any interference generated by ISM equipment.

Country	Frequency range	RF channels
Europe & USA	2400-2483.5 MHz	F =2402 + k MHz	k = 0,……..,78
Japan	2471-2497 MHz	F =2473+ k MHz	k=0,………22
Spain	2445-2475 MHz	F =2449+ k MHz	K=0,………22
France	2446.5-2483.5 MHz	F =2454+ k MHz	K=0,……..22

Table representing frequency band of various countries.

Power

According to the power of emission the equipments are qualified in 3 categories ranging from 1mW to 10mW. The recipient equipment must have at least 70dBm. The chips are incorporated in portable devices and powered by batteries and that’s why they should have minimum consumption of power up-to 97% less than a mobile phone so the battery of phone lasts longer. If Bluetooth devices do not exchange information then they establish the way of wait to save energy. The power of transmission that is used as specification is of 1 mW for a scope of 10 m, 100 mW for a scope of up to 100 m.

Device power class	Power Emitted	Range
Class 1	100mW	~ 100 m
Class 2	2.5mW	~10 m
Class 3	1mW	~1 m

Range

The connections have a maximum range of 10 meters, though using amplifiers it is possible to come up to 100 meters, but creating some distortion interferes. Maybe it doesn’t look too much, but it is necessary to remember that these devices were created by the intention of using them in closed environments and little distances.

2. Type of Data and Clients

It can carry both data and voice as an exchange. The different types of users of Bluetooth can be computers, PDA, mobile phone, etc. There are many other places Bluetooth is used. For example mobile phones, head set, stereo headphones, audio adapter, printer, keyboard, GPS system and many more.

Data Transfer Rate

It is one of the important features in Bluetooth device. Data transfer rate is defined as the speed at which data is transmitted from one device to another. It generally ranges from 1 mega -bite to 24 mega- bite depending on the type of Bluetooth device version as shown below.

Version	Data rate	Maximum output Application
Version 1.2	1Mbit/s	.7Mbits/s
Version 2.0	3 Mbit/s	2.1Mbits/s
Version 3.0	24Mbits/s	-

Frequency Hopping

It is method of transmitting radio signals by rapidly switching a carrier wave among many channels using a pseudorandom sequence known both to transmitter and receiver. It is useful to avoid collision where many devices use same frequency to send the signal and avoid interference.

Since the ISM band is open to anyone, radio systems operating in this band must cope with several unpredictable sources of interference, such as baby monitors, garage door openers, cordless phones and microwave ovens (the strongest source of interference). Interference can be avoided using an adaptive scheme that finds an unused part of the spectrum, or it can be suppressed by means of spectrum spreading. In the United States, radios operating in the 2.45-GHz ISM band are required to apply spectrum-spreading techniques if their transmitted power level exceeds 0 dBm [2]. Bluetooth radios use frequency-hop (FH) spread spectrum, since it better supports low-cost, low-power radio implementations. In addition, they better cope with near-far problems: a nearby jammer is effectively suppressed by the narrow channel filter as long as its jammer TX spectrum does not coincide with the selected hop channel. FH systems divide the frequency band into several hop channels. During a connection, radio transceivers hop from one channel to another in a pseudorandom fashion. The instantaneous (hop) bandwidth is small in FH radios, but spreading is obtained over the entire frequency band. This results in low-cost narrow-band transceivers with maximum immunity to interference.

Here we can see that channel time is divided into slots of 625uS. Each packet can occupy 1, 3 or 5 slots. The hopping frequency keeps constant within the packet. The master uses the odd number of slots to send the packets and slave uses even numbered.

3. Ad hoc Network

Ad hoc network is a decentralized wireless network where they do not rely on preexisting infrastructure such as routers instead each device participates in routing by routing data to the other nodes. An ad hoc network typically refers to any set of networks where all devices have equal status on a network and are free to associate with any other ad hoc network device in link range. Bluetooth also uses ad hop networking and is based on peer connectivity: a device carrying a Bluetooth radio can make a connection to any other device carrying a Bluetooth radio. There is no wired infrastructure with base stations or access points that can support the call setup or can provide low-power modes. In a Bluetooth system the master device can connect up-to seven other devices forming a network known as Pico net. For example a computer can connect to seven different Bluetooth enabled devices such as mouse, printer, CD-player, keyboard etc. The Pico net is a group of several devices that are in the same radio coverage where they share same channel that is constituted between two and eight other units. Two or more Bluetooth units that share a FH channel form a Pico net. To regulate traffic on the channel, one of the participating units becomes a master of the Pico net. However, users on the same channel must share capacity. Since the channel capacity is only 1 MHz, as more and more users are added, throughput per user quickly drops to less than some 10 kb/s. The spectral bandwidth available is 79 MHz, but cannot be used effectively when every unit must share the same 1-MHz hop channel. Therefore, another solution has been adopted. Units that share the same area and that are within range of one another can potentially establish ad hoc connections between themselves. However, solely units that truly want to exchange information share the same 1-MHz channel of a Pico net. This solution permits several Pico nets to be created with overlapping coverage areas. Each Pico net channel applies its own pseudorandom hopping sequence through the 79-MHz medium. The Pico nets are uncoordinated and hop independently. Within the Pico net, the participants have to share the 1 MHz, but multiple Pico nets share the entire 79 MHz, thus increasing the capacity. A collection of multiple Pico nets is called a scatter net. A maximum of 10 Pico nets can be connected to form a scatter net. A figure below shows how Pico net works.

A typical Ad hoc network.

Bluetooth Protocols

Bluetooth is not a single protocol but is made of different protocols seven to be exact. Each of these protocols work at different part of Bluetooth completing the Bluetooth configuration. Bluetooth hardware can be represented in a diagram with host, Bluetooth radio, link controller and link manager.