A Pseudo Random Coordinated Scheduling Algorithm for Bluetooth Scatternets MobiHoc 2001 Outline Abstract Introduction Overview of the PCSS algorithm Operation of PCSS Reference algorithm Simulation results Conclusions Abstract To schedule communication with bridging nodes one must take into account their availability in the different piconets. This algorithm assign meeting points with their peers such that the sequence of meeting points. Introduction Two important phenomena that can reduce the efficiency of the polling based communication. Slaves that have no data to transmit. At the time of an expected poll one of the nodes of a master-slave node pair may not be present in the piconet. Introduction Hard coordination Eliminates ambiguity with regards to a node s presence in piconets, but it implies a complex, scatternet wide coordination problem. Introduction Soft coordination Nodes decide their presence in piconets based on local information. Introduction Two key component of this algorithm Checkpoints Serve as regular meeting points for neighboring nodes when they can exchange packets. Dynamic adjustment of checking intensity Bandwidth can be allocated and deallocated to a particular link. Overview of the PCSS algorithm A node remains active on the current link until there is user data in both directions or until it has to leave for a next checkpoint. A pseudo random sequence that is generated based on Bluetooth clock of the master MAC address of the slave Overview of the PCSS algorithm Current base checking interval Operation of PCSS Initialization Communication Increasing and Decreasing Checking Intensity Initialization A master slave node pair share the same master s clock and slave s MAC address information Guaranteed that the same pseudo random sequence will be produced at each node. Communication A node remains active on the current link until there is user data in both directions or until it has to leave for a next checkpoint. During the communication any of the nodes can leave in order to attend a coming checkpoint on one of its other links. Communication After passing a checkpoint the variable t (i) check is updated to the next checkpoint by pseudo random generator(PseudoChkGen). t (i) check =PseudoChkGen(T (i) check, A (i) slave,t (i) ) There is a maximum and minimum checking interval T max =2 f max and 2 f min. Increasing & decreasing checking intensity To measure the utilization of checkpoints (i) on t the i th link of the node. If the checkpoint has been utilized the variable (i) is updated as (i) =q uti * (i) + (1-q uti ) * 1 0