Ph.D Thesis

Ph.D StudentKogan Alex
SubjectUtilizing Multiple Radio Interfaces in Wireless
DepartmentDepartment of Computer Science
Supervisor PROF. Roy Friedman
Full Thesis textFull thesis text - English Version


Contemporary mobile devices are equipped with multiple wireless interfaces, such as WiFi, Bluetooth, WiMax, ZigBee, NFC, etc. All these technologies differ dramatically one from another in their maximum transmission range, bandwidth and power demands. Among all subsystems operating inside mobile devices, wireless communication is known as being particularly power-hungry, accounting for as much as 50-70% of the total power consumption in small handheld devices, such as smartphones, and for 10% in laptops. Given the varying characteristics of different wireless technologies, an obvious question arises: Can we utilize the presence of multiple interfaces on contemporary mobile devices in order to improve their wireless networking capabilities in general and power efficiency in particular?

In this thesis we investigate this question from several perspectives: theoretical, more practical and fully experimental. The major body of this work considers the problem of energy consumption in multi-radio wireless networks. We formulate a novel optimization problem. A solution to this problem defines a network topology where some devices turn off their power-hungry interface while every device still remains connected to the rest of the network by at least one interface. Through theoretical analysis and simulations, we show that the proposed approach may achieve significant energy savings that increase with the density of the network. In the subsequent work, we develop a distributed middleware service that manages multiple wireless interfaces and heuristically approximates the optimal power-efficient topology of mobile and unreliable wireless networks.

We also make a contribution to general graph theory, showing how to improve state-of-the-art approximation solutions to the minimum dominating set problem in graphs where nodes have a bounded degree. Such graphs arise in many infrastructure-less network settings, such as ad-hoc networks, wireless sensor networks or peer-to-peer networks, where dominating sets play a crucial role.

In the experimental part of this thesis, we perform a combined power and throughput performance study of WiFi and Bluetooth in smartphones. In the process, we discover several interesting phenomena, some of which counter previous conventions, and draw some operative suggestions for researchers and smartphone developers.

Finally, we also consider the problem of reliable multicast. In our proposed approach, one radio interface is dedicated only for error recovery information transmissions, while other interfaces serve for transmitting the actual data. We demonstrate that with this approach each receiver needs to handle much fewer messages than in the common single radio approach, leading to better utilization of radio interfaces and energy conservation.