Practical synchronization techniques for multi-channel MAC

Researchers have proposed many wireless MAC protocols such as [20], [8], [25], [24], [6], and [17] which exploit frequency-agile radios and multiple available channels to increase network through-put. These protocols usually only require each node to have one radio. By carefully coordinating the frequency hopping of different nodes, different node pairs can use multiple channels simultaneously. In [17], Mo et al classified these protocols into four generalized categories and compared their performances through both analysis and simulation. They found that the Parallel Rendezvous family of protocols has the best overall performance by removing the bottleneck of a single control channel. These protocols show good promise for use with multi-hop networks because these networks suffer from self-interference and traditional MAC protocols using only one channel often fail to provide satisfactory throughput. However, we are not aware of any implemented Parallel Rendezvous multi-channel MAC protocols. We argue one major reason is that existing proposals such as McMAC[17] and SSCH[6] have not thoroughly considered a practical aspect of the design essential for a working implementation, namely: synchronization. Through an exploration including an implementation exercise on hardware, we show that synchronization for multi-channel MAC protocols is a non-trivial problem. We designed and implemented a synchronization mechanism specifically for this purpose and show that it has tackled the problem of synchronizing one-hop neighbor pairs effectively, thereby paving the way for efficient multi-channel MAC protocols.