Study On Scheduling Algorithm Of Bluetooth Piconet

Bluetooth has been a practical global standard for short-range wireless data and voice communication. Bluetooth enables various personal data devices to have wireless communication function easily because it has many intriguing characteristics, such as low cost, low power, small size, and free spectrum. With the development and popularization of Bluetooth, there is increasing interest in wireless ad hoc networks built from portable devices equipped with Bluetooth. However, after piconet constructed by Bluetooth devices, which scheduling scheme could make the best use of the network resource and handle QoS requests is the most important issue for Bluetooth piconet.The ad hoc wireless mobile network based on Bluetooth is self-constructive, self-organizable, and self-manageable wireless mobile network without additional network devices. The Bluetooth network is contributed by piconets, each piconet is distinguished by its own hoping frequency sequence. A Bluetooth device in network could be either a master or a slave, each piconet is constructed by one master and up to 7 active slaves. The communication between nodes strictly complies with the master-slave mode, that slaves can't send data to master forwardly or another slave. Only after data transmission from master to slave, could the slave send back data in the next time. Bluetooth node applies Time-Division Duplex transmission mode, the Bluetooth protocol divided each second into 1600 portion, one portion is called a slot, which is the basic time unit of Bluetooth communication. The data sent by Bluetooth device applies baseband packet mode, one baseband packet could be divided into 3 parts: Access Code, Header and Payload. Payload is used for take data that the node transmits. Bluetooth baseband packets have several types, they cost 1 up to 5 odd slots, accordingly their Payload are different.After construction of Bluetooth piconet, master polls slave one by one according to scheduling algorithm. Polling is the main method the master applies,how to fairly and efficiently serve slaves is the key of scheduling algorithm. So impartiality and efficiency are the focus, impartiality means that each slave in the piconet should obtain similar poll times while their data stream are similar, efficiency means how to use network resource best to improve network throughout based on impartiality. Thus it can be seen that impartiality and efficiency are a couple of contradictions. How to work out this pair of contradictions, and find a optimized scheme is the main concept of designing a scheduling algorithm for Bluetooth.Along with the research of scheduling algorithms for Bluetooth piconet by worldwide scholars, the scheduling algorithms are more and more perfect in theory. So people turn to focus on the designing scheduling algorithms for applications. Scheduling algorithms handling QoS(Quality of Service) begin to be lodged by some scholars. QoS is a muster of some technologies for acquiring expectant service level on throughout, delay dithering, delay, the rate of missing packets and so on. In Bluetooth piconets, the main targets of QoS are flow rate and maximum delay.First, this paper simply introduces Bluetooth technology, including actuality of Bluetooth, construction of Bluetooth protocol, communication mode of Bluetooth and its other characteristics. By compared with other wireless local networks, it concludes that Bluetooth is one of the most potential wireless Ad Hoc technologies. Then, the paper exactly introduces every subsistent polling scheme, according to their characteristics, the author divides them into two kinds: traditional polling schemes and self-adaptable schemes. Traditional polling schemes all adopt simple polling theory, that the master serves the slaves based on fixed sequence, how to serve chosen slave distinguish each scheme from others. Self-adaptable schemes are advanced from Traditional polling schemes, for these schemes, the concept priority is important. The master sets a priority for each slave, the slave with highest priority can be served first. The author concludes that there are two steps to optimize scheduling scheme: how to choose slave and how to serve chosen slave. According to this, the author proposes his own algorithm—The polling scheme according to demand. On choosing slave, the algorithm adopts the concept ofpriority from self-adaptable schemes, by computing probability of having data in the connection and the interval from last null packet, it gives out each active slave's priority. In this progress, the algorithm handles FR(Flow Rate) and MD(Maximum Delay) requests of QoS. On serving the chosen slave, after comparing traditional polling schemes, the algorithm adopts limited Round Robin(LRR) to set each active slave's service gate.Last, the author simulates the proposed algorithm and compares it with other representative schemes. For comparing algorithm's total performance, the author proposes a approximate mathematic expressions. The result of simulation show that this algorithm harmonizes the impartiality and efficiency of Bluetooth piconet and handle QoS requests, it can be used for the schedule of Bluetooth piconets.