An efficient and fair polling scheme for Bluetooth

Bluetooth is a universal radio interface in the 2.45 GHz frequency band, which will enable users to connect a range of small electronic devices. Any two or more Bluetooth-enabled devices that come within range of each other can set up an ad hoc connection, called a piconet. Within a piconet, the unit that establishes the piconet becomes the master and the rest of the units act as slaves. The master sends a data or POLL packet to poll a slave and the slave responds with a packet in the next time slot. The manner in which the master polls the slaves has a significant impact on the system performance. We first discuss previously proposed polling schemes for Bluetooth. We then propose a new polling scheme called Pseudo-Random Cyclic Limited slot-Weighted Round Robin (PLsWRR) that builds on the Limited Weighted Round Robin (LWRR) scheme presented by Capone, Kapoor and Gerla (see IEEE ICC 01, Finland, June, 2001). The PLsWRR scheme has the following two important properties: (i) as in LWRR, it tries to distinguish between slaves on the basis of their "activeness", i.e., according to the traffic history. LsWRR reduces the rate of polling to less active slaves by not polling them for a certain number of slots (as opposed to cycles). This keeps the maximum time that a slave may not be polled bounded. (ii) The order in which slaves are polled in each cycle is determined in a pseudo-random manner. We show that it is very important to use a pseudo-randon ordering of slaves in a cycle and that a polling scheme that does not employ a pseudo-random ordering can easily lead to unfairness among TCP connections. We also show by means of simulations that the PLsWRR scheme performs consistently well on scenarios with different traffic sources like TCP and CBR and achieves high throughput and fairness.