By Colleen Kearney Rich
Have you ever been on your cellular phone and heard the echo of the conversation you are having? That may be a result of the so-called “ping-pong effect,” and Mason electrical engineer Brian Mark has two patents that would help make this problem less likely to happen.
With that echo, you are listening to your call ping-ponging between two base towers. When you use a mobile phone, you are not really connecting directly to the person you are calling, you are connecting to a base tower that then relays your call to the phone of the person you are calling.
“The phone will pick up the strongest signal [from a base tower],” says Mark. If you are moving, the phone will connect or reconnect to whichever signal is stronger. Sometimes the “handoff” between towers isn’t as smooth as it should be. The result: the ping-pong effect, dropped calls, and data transmission delays.
“We wanted to design a handoff mechanism to enable a smoother transition,” says Mark, who directs the Network Architecture and Performance Lab at Mason and teaches in the Volgenau School of Engineering.
Mark shares the patents, Cellular Network Handoff Decision Mechanism and Cellular Network Handoff Modeling, with his former PhD student Alexe Leu, who completed his doctoral degree in 2004.
Based on work supported by Samsung, Mark also has two patents related to the efficient routing of data in an ad hoc network. Ad hoc networks differ from cellular networks in that the data are relayed among mobile devices without base towers. His most recent work and patent, invented with former PhD student Ahmed Nasif, both have to do with cognitive radio, sometimes called frequency, or spectrum-agile radio.
“With cognitive radios, a block of wireless spectrum can be shared dynamically by unlicensed users,” says Mark. The transceiver “senses” when a part of the spectrum isn’t being used and can change its operating frequency to make use of it—all while avoiding harmful interference to the licensed users of the spectrum.
“Cognitive radio has emerged as an active research area in the past several years because of its potential to allow us to keep pace with the increasing demand for more wireless capacity,” he says.