The University of Minnesota is suing the nation's largest cell phone companies for patent infringement.

In four separate lawsuits, the university claims Sprint, Verizon, T-Mobile and AT&T are illegally using technology developed at the U of M.

General Counsel Bill Donohue said the litigation involves five separate wireless communications patents that engineering professor Georgios Giannakis developed.

Donohue contends the cell carriers are using the technology to improve the reliability of their 4G wireless data services without paying royalties to the U.

"Professor Giannakis has invented something here that's valuable and we want to protect it and make sure that we get an appropriate royalty for having done that."

Donohue said this particular research received funding from the U.S. Army and the National Science Foundation.

Giannakis is an internationally recognized expert in signal processing and networking, according to the university.

A University of Minnesota website says Giannakis holds an endowed chair in wireless telecommunications and is director of the Digital Technology Center.

He's worked at the University of Minnesota since 1999, and has received millions of dollars in public research funds.

All four companies declined comment.