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On the Impact of Inter-Piconet Scheduling in Bluetooth Scatternets


The current Bluetooth specification defines the notion of interconnected piconets, called scatternets, but does not define the actual mechanisms and algorithms necessary to set up and maintain them. A scatternet will typically be set up in an ad-hoc fashion to interconnect piconets. For instance, a typical personal area network (PAN) would comprise of a user’s wearable and portable electronic devices in a piconet formation, while scatterneting enables networking between many PANs. A PAN interconnect will serve its own traffic as well as traffic from the Internet. The inter-piconet Bluetooth units, i.e. the gateways interconnecting the piconets in a scatternet, need to time-division multiplex their presence in each of their piconets. The time division in gateways effectively limits the network capacity and may introduce bottleneck points in the network. Therefore an inter-piconet scheduling (IPS) algorithm is required in order to efficiently coordinate the inter-piconet Bluetooth units and maximize the network capacity. This may be achieved, for example, by using rendezvous points –pre-negotiated slots that a piconet master agrees to poll the gateway, and the gateway agrees to have switched to that master’s frequency hopping sequence and accept the poll. The impact of the rendezvous IPS algorithm to the overall scatternet is studied in this paper. We consider this an important question because the inter-piconet scheduling functions may require support from low layers usually implemented in silicon [2]. We assume a distributed approach is required and evaluate performance of a range of different proposed rendezvous scheduling algorithm. The difference of our approach to existing work is that our algorithms are based on more information exchange between nodes. While this creates higher traffic and memory overhead it allows for more efficient scheduling of the scarce bandwidth. On one extreme we have a minimum intelligence/silicon space totally random assignment and on the other a maxmin optimum forwarding throughput assignment. While we are convinced that random assignments have scalability advantages, crucial for some applications esp. those of embedded systems, we study more silicon-intelligent approaches that may prove necessary for multimedia applications over Bluetooth links. Audio and video streaming is bandwidth consuming, usually spans considerable time lengths, and generally requires a steady network response due to its real time nature. The maxmin optimum algorithm is shown by simulation experiments to have a total network throughput of more than a 30% than simpler non-random solutions and without creating bottleneck gateways, and at least 2 times better than random schemes. This improvement may be considered important to some applications, especially considering the Internet typical client data rates, but comes at the cost of a higher design complexity/cost.

Paper: PDF file of paper

Information & Date

IC'02, Las Vegas, NV, June. 2002


Manthos Kazantzidis
Mario Gerla