Information Technology Reference
In-Depth Information
I
NTRODUCTION
Bluetooth is a low cost wireless radio technology designed to eliminate wires and cables
between mobile and fixed devices over short distances, allowing the formation of ad hoc
networks [1, 2, 3]. The lower layers of Bluetooth became the IEEE 802.15 standard for
wireless personal area networks (WPANs). It operates on the 2.4 GHz ISM (Industrial,
Scientific and Medical) band employing a frequency-hopping spread spectrum (FHSS)
technique. The transmission rate is up to 3 Mbps. The devices can communicate with each
other forming a network (called piconet) with up to eight nodes. Within a piconet, one device
is assigned as a master node and the others act as slave nodes. Devices in different piconets
can communicate using a structure called scatternet. The channel is divided in time slots of
625 us. A time-division duplex (TDD) scheme is used for full-duplex operation.
In order to improve the reliability of the data sent in the wireless channel, techniques such
as automatic repeat request (ARQ) and forward error correction (FEC) can be employed [8].
FEC employs error correcting codes to combat bit errors by adding redundancy (parity bits) to
information packets. The receiver uses the parity bits to detect and correct errors. FEC
techniques are associated with unnecessary overhead that increases energy consumption when
the channel is relatively error free. In ARQ techniques only error detection capability is
provided; the receiver requests to the transmitter the retransmission of the packets received in
error. Usually an ARQ scheme uses Cyclic Redundancy Check (CRC) codes for error
detection [8]. At the receiver, the CRC code verifies the packet. If it detects errors, the node
asks a retransmission for the transmitter (negative acknowledgement). If the reception is
correct, a positive acknowledgement is sent to the transmitter node. Hybrid ARQ schemes can
be developed using the combination of FEC and ARQ schemes. Some typical error control
techniques for wireless networks are discussed in [8].
Bluetooth v2.0 [2] with Enhanced Data Rate (EDR) specification offers three
transmission rates, which are basic rate of 1 Mbps (types of DHx and DMx), enhanced data
rates of 2 Mbps (EDR2, type of 2-DHx) and 3 Mbps (EDR3, type of 3-DHx). The basic rate
employs a binary Gaussian Frequency Shift Keying (GFSK) modulation, while EDR2 and
EDR3 increase data rates by using Differential encoded Phase Shift Keying (DPSK)
modulations, with a constellation of four symbols (
π/
4-DQPSK) and eight symbols (8DPSK),
respectively. In Bluetooth systems, there are many types of packets. These packets are chosen
according to channel conditions [7, 11, 15]. Using a long packet size will increase the
throughput of system. A long packet is used in the case of good channels. In the case of bad
channels, small packet size is used in transmission process. This will decrease the throughput
of system. In the Bluetooth system, there are several channel coding schemes that are
implemented. There are three type of error control coding which are used in Bluetooth
systems, 1/3 rate error control code, 2/3 rate error control code, and ARQ [1, 2, 3].
Researchers have agreed to the standardization of both access and header fields in Bluetooth.
Research concentrates on varying the method of coding the payload which means dividing the
payload between data and checksum [4,5,6,7,9,11,12,13,14,15,16,17,18,19].
