Zhou et al. describe the use of multiple frequencies for parallel communication over the regular sensor devices that provide limited bandwidth in single channels. Using multiple frequencies in wireless sensor networks (WSNs) helps achieve improved network throughput. The paper explains the need for this protocol, showing why the already-existing multifrequency media access control (MAC) protocols are not suitable for typical WSN applications.

The authors summarize the major contributions of their work as being: a novel multifrequency MAC protocol specifically designed for WSNs; a comprehensive presentation of the tradeoffs among physical frequency requirements; a presentation of new toggle transmission and snooping techniques that enable single radio transceivers in sensor devices to achieve scalable performance; and the implementation of an optimal nonuniform back-off algorithm in multifrequency MAC networks.

The motivation for this work, according to the authors, was an endeavor “to obtain a better understanding of the cost that [request to send/clear to send (RTS/CTS)] control packets incur [in] multifrequency protocols in general wireless ad hoc networks, [as compared to] WSNs.” The authors also present the design details of the multifrequency MAC protocol for WSNs, describe the frequency assignments and the media access methodologies, and discuss their subtleties. Six groups of experiments were used to evaluate the performance of the protocol and to compare it with the carrier sense multiple access (CSMA) protocol. Tables and figures are appropriately used to explain the experimental results.

The paper is well written and very well organized (if the reader will excuse the inadvertent repetition of nine whole lines in the introduction). I highly recommend it to all professionals interested in WSNs.