Reducing Inter-piconet Delay for Large-Scale Bluetooth Scatternets

When more than seven devices to be connected in a Bluetooth scatternet, bridge devices are used to connect two piconets into a scatternet. To deal with possible data transmissions between different piconets, the bridge device must switch to different masters frequently. Suppose that a bridge is serving a piconet and the master in another piconet is calling it at the same time, the calling master has to wait until the bridge completes the previous service. Such transmission delay may accumulate in a long period and the performance of the whole Bluetooth network will degrade significantly. This work tries to smooth the kind of transmission delay in Bluetooth network. This work proposes two new scheduling protocols: the static schedule and the hybrid schedule. This static schedule deals with this kind of coordination among piconets distributedly by applying edge coloring technique. In case of heavy traffic load, the static schedule is expected to perform well. On the other hand, in case of light traffic load, the static schedule may results in long and unavoidable routing delay even there is no transmission between piconets; thus a naive random round-robin schedule in each piconet becomes more appropriate in case of light traffic load. Thus, in the hybrid schedule, each master in its piconet runs round-robin scheme initially; when the traffic load is heavier than a predefined threshold value, it turn to run the static schedule. Also, a new graph model, delay graphs, is proposed to model and estimate the delay time required for the proposed scheduling schemes theoretically. Finally, we conduct simulations by using ns-2 simulator and Bluehoc to demonstrate the efficiency and effectiveness of the proposed scheduling protocols.