The dynamic channel selection mechanism used in existing multi-channel MAC protocols selects an idle data channel based on channel usage information from one-hop neighbor nodes. However, this method can cause multi-channel hidden node problem in multi-hop wireless networks. This letter proposes a new approach to channel selection. Nodes snoop data channels during idle times and then select an idle data channel within the carrier sensing range using both the snooping results and the channel usage information. Our simulation results verify that the proposed channel selection approach can effectively avoid the multi-channel hidden node problem and improve the networkwide performance.

We expect that most cellular phones and notebook computers will have Bluetooth in the near future. Many convenient applications will flourish. An example is exchanging multi-media electronic name cards using cellular phones. Today, most people carry a cellular phone. If the user interface can be made as simple as handing out a printed business card, the electronic cards exchanged over Bluetooth would make printed ones obsolete. However the current Bluetooth specification is not adquate to support short peer-to-peer transactions requiring symmectric user interface and fast response time. Connection establishment can take more than 10 s and two devices must start in an asymmetric manner. In this paper, we propose a random inquiry procedure tailored for name card exchange. It allows a symmectric user interface, and device discovery completes within 280 ms with probability 0.999. With this performance, it then becomes practical to provide a hot button on cellular phones that users will simply press to exchange electronic name cards.