BLUETOOTH INTERFACE
General Bluetooth Interface Characteristics:
• Operates in the 2.4 GHz band.
• Uses Frequence Hop (FH) spread spectrum, which divides the frequency band into a number of hop channels. During a connection, radio transceivers hop from one channel to another in a pseudo-random fashion.
• Supports up to 8 devices in a piconet (two or more Bluetooth units sharing a channel).
• Built-in security.
• Non line-of-sight transmission through walls and briefcases.
• Omni-directional.
• Supports both isochronous and asynchronous services; easy integration of TCP/IP for networking.
• Regulated by governments worldwide.
Bluetooth is intended to be a standard that works at two levels:
1.It provides agreement at the physical level — Bluetooth is a radio-frequency standard.
2.It also provides agreement at the next level up, where products have to agree on when bits are sent, how many will be sent at a time and how the parties in a conversation can be sure that the message received is the same as the message sent.
Bluetooth Frequency & Power:
Bluetooth interface communicates on a frequency of 2.45 gigahertz, which has been set aside by international agreement for the use of industrial, scientific and medical devices (ISM).
It radiates signal by sending out very weak signals of 1 milliwatt by this way Bluetooth devices avoid interfering with other systems . The low power limits the range of a Bluetooth device to about 10 meters .
Bluetooth working
Bluetooth uses a technique called spread-spectrum frequency hopping. In this technique, a device will use 79 individual, randomly chosen frequencies within a designated range, changing from one to another on a regular basis.
In the case of Bluetooth, the transmitters change frequencies 1,600 times every second, meaning that more devices can make full use of a limited slice of the radio spectrum. Since every Bluetooth transmitter uses spread-spectrum transmitting automatically, it’s unlikely that two transmitters will be on the same frequency at the same time. This same technique minimizes the risk that portable phones or baby monitors will disrupt Bluetooth devices, since any interference on a particular frequency will last only a tiny fraction of a second.
When Bluetooth-capable devices come within range of one another, an electronic conversation takes place to determine whether they have data to share or whether one needs to control the other. The user doesn’t have to press a button or give a command — the electronic conversation happens automatically. Once the conversation has occurred, the devices — whether they’re part of a computer system or a stereo — form a network.
Bluetooth systems create a personal-area network (PAN), or piconet, that may fill a room or may encompass no more distance than that between the cell phone on a belt-clip and the headset on your head. Once a piconet is established, the members randomly hop frequencies in unison so they stay in touch with one another and avoid other piconets that may be operating in the same room. Each piconet hops randomly through the available frequencies, so all of the piconets are completely separated from one another
Bluetooth Specifications:
• The devices in a piconet share a common communication data channel. The channel has a total capacity of 1 megabit per second (Mbps). Headers and handshaking information consume about 20 percent of this capacity.
• In the United States and Europe, the frequency range is 2,400 to 2,483.5 MHz, with 79 1-MHz radio frequency (RF) channels. In practice, the range is 2,402 MHz to 2,480 MHz. In Japan, the frequency range is 2,472 to 2,497 MHz with 23 1-MHz RF channels.
• A data channel hops randomly 1,600 times per second between the 79 (or 23) RF channels.
• Each channel is divided into time slots 625 microseconds long.
• A piconet has a master and up to seven slaves. The master transmits in even time slots, slaves in odd time slots.
• Packets can be up to five time slots wide.
• Data in a packet can be up to 2,745 bits in length
• There are currently two types of data transfer between devices: SCO (synchronous connection oriented) and ACL (asynchronous connectionless).
• In a piconet, there can be up to three SCO links of 64,000 bits per second each. To avoid timing and collision problems, the SCO links use reserved slots set up by the master.
• Masters can support up to three SCO links with one, two or three slaves.
• Slots not reserved for SCO links can be used for ACL links.
• One master and slave can have a single ACL link.
• ACL is either point-to-point (master to one slave) or broadcast to all the slaves.
• ACL slaves can only transmit when requested by the master
Advantages of Bluetooth Interface:
• Bluetooth provides flexible network that allows up to eight devices to share information.
• The network architecture allows one to add or remove nodes without additional infrastructure involved.
• The size of the implementation is small.
• Power consumption is small.
• It has the support of the security consideration like ‘Encryption’.
