Bluetooth Presentation by Dr. S. Radha, HOD/ ECE SSN College of Engineering
Objective • The main objective of this session is to make the students, • Understand the Bluetooth which is a wireless LAN technology, its architecture, layers and frame formats.
BLUETOOTH Bluetooth is a wireless LAN technology designed to connect devices of different functions such as telephones, notebooks, computers, cameras, printers, coffee makers, and so on. A Bluetooth LAN is an ad hoc network, which means that the network is formed spontaneously. Topics discussed in this section ArchitectureBluetooth LayersBaseband Layer L2CAP
Bluetooth - Architecture Bluetooth defines two types of networks: piconet and scatternet. Piconet Small net Can have up to eight stations One of the stations is called primary (master) and the rest are secondaries (slave). One to one and one to many communication. Along with seven secondaries, additional eight secondaries can be in the parked state.
Bluetooth - Architecture Scatternet Piconets are combined to form scatternets. A station can be a member of two piconets. A secondary station in one piconet can be a primary in other piconet. Bluetooth devices built-in short range radio transmitter. Data rate is 1 Mbps. 2.4GHz bandwidth.
Bluetooth - Layers Bluetooth uses several layers that do not exactly match with those of the Internet model. Radio layer Roughly equivalent to the physical layer of the Internet model. Range is limited to 10m and they are low power devices. Band Uses 2.4GHz ISM band divided into 79 channels of 1MHz each.
Bluetooth - Layers FHSS Bluetooth uses the frequency hopping spread spectrum method to avoid interference from other networks. 1600 hops per second. A device uses a frequency for only 625 s. Modulation GFSK modulation GFSK uses a carrier frequency. Bit 1 is represented by a deviation above the carrier and Bit 0 is represented by a frequency below the carrier.
Bluetooth - Layers Modulation These frequencies are defined according to the formula for each channel as, fc = 2402 + n, n = 0,1,2………….78 Baseband layer Roughly equivalent to the MAC sublayer in LANs. Access method is TDMA (using time slots). Length of the time slot is equal to the dwell time (625s). During the time one frequency is used, a sender sends a frame to the receiver.
Bluetooth - Layers TDMA Bluetooth uses TDD-TDMA, which is a kind of half duplex communication. Communication for each direction uses different hops. If a piconet has a single secondary, TDMA operation is simple. Time is divided into 625s slots. Primary communicate in even numbered slots and secondary in odd numbered slots.
Bluetooth - Layers Physical links Two types of links can be created between primary and secondary namely, SCO links and ACL links. SCO Synchronous connection oriented link. Used when avoiding latency is more important than integrity Physical link is created between primary and secondary by reserving specific slots at regular intervals. No retransmission in case of packet damage. Used for real time audio
Bluetooth - Layers ACL Asynchronous connectionless link. Used when data integrity is more important than delay. Retransmission takes place in case of corrupted package. Maximum data rate is 721 kbps.
Bluetooth - Layers Frame format Three types : one-slot, three-slot and five-slot. A slot is 625 s. In that, 259 s is needed for hopping and control mechanisms. Then one-slot frame lasts only for 366 s. With 1MHz Bandwidth and 1 bit/Hz, the size of a one-slot frame is 366 bits. Size of a three-slot frame is 1616 bits. Size of a five-slot frame is 2866 bits.
Bluetooth - Layers Access code 72 bit field, contains synchronization bits and the identifier of the primary to distinguish the frame of one piconet from another. Header Address : three bit subfield can define upto seven secondaries. Bits 000 indicates broadcast. Type : defines the type of data coming from the upper layers. F : 1 bit subfield for flow control. When set to 1, it indicates that the device is unable to receive more frames (buffer is full).
Bluetooth - Layers Header A : 1 bit subfield used for acknowledgement. Bluetooth uses stop and wait ARQ. S : 1 bit subfield holds a sequence number. HEC : 8 bit header error correction is a checksum to detect errors in each 18 bit header section. Payload : data from upper layers.
Bluetooth - Layers L2CAP Logical Link Control and Adaptation Protocol is roughly equivalent to LLC sublayer in LANs. Used for data exchange on an ACL link. L2CAP frame contains a 16 bit length field which defines the size of the data coming from the upper layer, a channel ID field which defines a unique identifier for the virtual channel created at this level and the payload. The functions of L2CAP include multiplexing, segmentation and reassembly, QoS and group management.
Summary Bluetooth is a wireless LAN technology that connects devices (called gadgets) in a small area. A Bluetooth network is called a piconet. Multiple piconets form a scatternet. A Bluetooth network consists of one primary and up to seven secondaries. Bluetooth layers are radio layer, baseband layer, L2CAP layer and upper layers. Bluetooth used FHSS and GFSK modulation. Access method is TDD – TDMA. Phsyical links can be SCO or ACL links.