Channel or path diversity is known to improve performance in physical layer designs, channel access strategies, path switching mechanisms, etc. In this paper, we focus on "user-level" mechanisms that operate simply by distributing packet transmissions across multiple channels. We seek to understand when, why, and to what extent this can be of benefit, and equally important, whether these benefits can be realized with as little of an added cost as possible. In that context, our main contribution is not so much in identifying optimal policies for leveraging channel diversity, but in introducing the concept of channel "equivalence" and demonstrating that channel diversity yields substantial benefits mostly when channels are approximately equivalent. We build on this finding to investigate the robustness of these improvements against errors in the characterization of the available channels or changes in their characteristics. We also explore the sensitivity of the results as the number of available channels varies. The findings of the paper demonstrate that by allowing packet transmissions from multiple users to intelligently share channels, it is possible to improve overall performance and robustness through simple and portable user-level mechanisms.
We investigate issues that Bluetooth may face in evolving from a simple wire replacement to a large-scale ad hoc networking technology. We do so by examining the efficacy of Bluetooth in establishing a connected topology, which is a basic requirement of any networking technology. We demonstrate that Bluetooth experiences some fundamental algorithmic challenges in accomplishing this seemingly simple task. Specifically, deciding whether there exists at least one connected topology that satisfies the Bluetooth constraints is NP-hard. Several implementation problems also arise due to the internal structure of the Bluetooth protocol stack. All these together degrade the performance of the network, or increase the complexity of operation. Given the availability of efficient substitute technologies, Bluetooth's use may end up being limited to small ad hoc networks. KeywordsBluetooth, performance, scatternets, topology formation, wireless ad hoc networks This material is posted here with permission of the IEEE. Such permission of the IEEE does not in any way imply IEEE endorsement of any of the University of Pennsylvania's products or services. Internal or personal use of this material is permitted. However, permission to reprint/republish this material for advertising or promotional purposes or for creating new collective works for resale or redistribution must be obtained from the IEEE by writing to pubs-permissions@ieee.org. By choosing to view this document, you agree to all provisions of the copyright laws protecting it. Abstract-We investigate issues that Bluetooth may face in evolving from a simple wire replacement to a large-scale ad hoc networking technology. We do so by examining the efficacy of Bluetooth in establishing a connected topology, which is a basic requirement of any networking technology. We demonstrate that Bluetooth experiences some fundamental algorithmic challenges in accomplishing this seemingly simple task. Specifically, deciding whether there exists at least one connected topology that satisfies the Bluetooth constraints is NP-hard. Several implementation problems also arise due to the internal structure of the Bluetooth protocol stack. All these together degrade the performance of the network, or increase the complexity of operation. Given the availability of efficient substitute technologies, Bluetooth's use may end up being limited to small ad hoc networks.
This paper represents a first step in exploring the formation of connected topologies in ad-hoc networks built on the Bluetooth technology. Connectivity is the most basic requirement for any system aimed at allowing devices to communicate with each other and in this paper we illustrate that this seemingly innocuous goal gives rise to many significant challenges in the context of the Bluetooth technology. We start with a brief overview of Bluetooth and its operation and then identify some of the major problems the technology faces when used to build ad-hoc networks. The paper's contributions are in introducing basic algorithmic problems associated with building connected Bluetooth networks and in developing several possible solutions capable of generating "good" connected topologies.
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