Philipp Blum

Trace-based evaluation of clock synchronization algorithms for wireless loudspeakers

We present an evaluation strategy for clock synchronization algorithms. It is based on a combination of measured traces, which provide for realistic performance estimation, and of simulation, which guarantees repeatability. The evaluation strategy includes parameter-optimization to allow for a fair comparison of algorithms; a general-purpose evolutionary optimizer is used for this purpose. The strategy is applied in a case study, evaluating the performance of four clock synchronization algorithms in the wireless loudspeakers application. We find that the phase-locked loop algorithm, as well as the linear-regression and the gradient algorithm achieve sufficient synchronization in a lightly loaded network. Only the local selection algorithm is able to maintain sufficient synchronization under heavy network load, as generated for example by concurrent audio or video streaming.

Interval-based clock synchronization is resilient to mobility

Clock synchronization is a crucial basic service in ad-hoc sensor networks. Most proposed algorithms employ hierarchical communication structures that may be expensive to maintain when nodes are mobile and network topologies are dynamic. Interval-based synchronization has been proposed as particularly suited for sensor networks, as it does not require any particular communication pattern. In this paper, we show that node mobility puts no burden on interval-based synchronization, but actually helps it. This is not the case for time-estimate-based approaches that rely on specific communication patterns. Mobility resilience therefore further strengthens the case of interval-based clock synchronization for ad-hoc sensor networks