Priority-Based Scheduling Algorithm With QoS Support In Bluetooth Piconet

Bluetooth is a global open standard for wireless data and voice transmission. As a low cost and short-range wireless communication technology, Bluetooth provides a special way to connect and exchange information between land and mobile equipments. The foundation of it is to build general wireless air interface and the control software. So the communications and computer technology can be integrated and the electronic devices produced by different companies are allowed to work with each other in a short distance without wire connections.A Bluetooth device with the role of"Master"can communicate with up to 7 enabled devices with the role of"Slave". This network of"group of up to 8 devices (1 master+7slaves)"is so called a piconet. A Scatternet is composed of 2 or more piconets. The overall transmission performance of the piconet is mostly depended on the adopted polling scheduling algorithm. It is a specific method by which the master can access and serve the slaves.At present, there are two types of scheduling algorithm for Bluetooth piconet , One type is the Non-Preview Scheduling algorithm including PRR(Pure Round Robin),ERR(Exhaustive Round Robin),GRR(Gated Round Robin),EPM (Exhaustive Pseudo-Cyclic Master Queue Length) and so on, The other type includes PP(Priority Policy), KFP(K-Fairness Policy),etc.., namely the Preview Scheduling algorithm.It is very important for practical application to study the scheduling algorithm from theory. PRR, ERR, GRR Scheduling algorithms can be implemented easily with the low cost hardware, and it is widely used by the current Bluetooth products. In this paper, a scheduling model of Bluetooth piconet was set up, and the mechanism of gated polling scheduling was analyzed. According to Pseudo-conservation theorem, the exact expression of the mean waiting time was derived theoretically, which can be used for half-symmetrical traffic modes. Moreover, the exact expression of the mean waiting time in general traffic modeswas presented, based on the decomposition theorem suggested by Cooper, etc... and analytical approaches of M/G/1 queues with vacations. The numeral and simulation results show that the proposed expressions are relatively exact estimate. Furthermore, the channel utilization ratio, fairness and throughput of the piconet with gated polling are also defined and analyzed.Comparing with Non-Preview Scheduling technique, Preview Scheduling technique can achieve better performance, but it also added complex; what's more, the most argument of Preview Scheduling is preview method which mater attain state of slave queue, Bluetooth didn't provide the preview mechanism.Current existing MAC (Medium Access Control) scheduling schemes (including Non-Preview scheduling and Preview scheduling) only provide best-effort services for all master-slave connections, It is very challenging to provide QoS (Quality of Service) support for different connections. With the fast development of Bluetooth technique, it will be used to connect internet, transmit images and the signals of audio /video. Therefore, it is very important to design a new scheduling algorithm to provide different QoS requirements.The Paper recommends the core criteria of Bluetooth protocol and emphasizes the base band criteria which affects MAC scheduling, including ACL (Asynchronous Connection-Less) connections and SCO (Synchronous Connection-Oriented) connections and their data packet formats. Then the paper gives transmission mechanism of Bluetooth packet, the special which determines that Bluetooth piconet scheduling be different from others.A Priority-Based Scheduling Algorithm with QoS Support in Bluetooth Piconet-QTBS is proposed as to improve current scheduling scheme's deficiencies and provide QoS supports for all master-slave connections. The paper adds 2bit HOL (head-of-the-line) in packet head of Bluetooth by studying the piggyback of TCP packet, HOL can be registered next packet size of every slave queue to carry out function of mater preview; meanwhile, the paper adopts SJF(Shortest Job First) algorithm to diminish packet delay, SJF could get minimum mean waiting time in all polling schemes.QTBS considers both delay and throughput performance on each Master-Slave pair in scheduling decisions, and thus, attempts to maximize overall performance by the equation P =αT + (1 ?α)D. Where T is the priority value based queue state to improve delay and throughput performance, D is the number of yielding or yielded service maintained by each Master-Slave pair to consider fairness performance, it can adjust the polling chance of every Master-Slave pair to prevent low priority pair from starvation.αis the weight parameter for system performance between delay (or throughput) and fairness.The paper build a test platform using BTPS system in order to validate the performance of the QTBS, BTPS is designed by MATLAB. The paper simulates three experimental environments by BTPS, the first one and the second one are based"best-effort"services, the third one includes QoS requirement in Bluetooth. Compared with ERR and PP scheduling, QTBS can attain the best network performances which include packet delay and channel utilization radio and fairness when all Master-Slave pairs are"best-effort"services; In addition, there is QoS requirement (for example, CBR) in Bluetooth, QTBS could get minimum delay and the steadiest delay jitter, it can gratify QoS requirement.Therefore, QTBS comes true the purpose that the paper proposed at first.