Contacted by HR three months after applying via LinkedIn. Scheduled phone interview with manager. 1st phone screen: current project description. 2nd phone screen: Questions in mathematical optimization (how to minimize volume of ellipsoid, why is determinant a measure of volume of ellipsoid, etc). Next, two problems were sent to me to be solved in a week (one was a C programming problem- multipling two vectors- and the other an OFDM problem). One more phone screen with senior scientist- asked questions from resume, AdaBoost, etc. Finally, on-site interview: Started at 9 am, was asked to give an hour long presentation of two projects. Nine interviews throughout the day. All questions based on presentation, a lot of emphasis on linear algebra, optimization, adaptive filters and some Java. Very thorough interview process.