This talk will present a new method to estimate the bearing of a radiotransmitter with a mobile, single-antenna receiver, and its implementation ona software-defined radio (SDR) testbed. The bearing estimation method relieson the following principle: by considering the signal received at severalpoints along its trajectory, the receiver implicitly creates a virtual multi-antenna array (similarly to synthetic aperture radar systems) that can be usedto estimate the bearing of the radio transmitter. Virtual multi-antenna arrayshave two major differences with conventional multi-antenna arrays: 1) theposition and orientation of each antenna in the virtual array depends on themovement of the receiver and must be estimated; and 2) the local oscillator(LO) offset between transmitter and receiver adds a phase offset to the signalreceived by each “virtual” antenna, which must be estimated and compensatedfor. The first problem is solved by using an inertial measurement unit (IMU),which can provide the relative position and orientation of the receiver forshort time periods. The second problem is solved by expanding the signal modelthat is used in bearing estimation algorithms (such as MUSIC) to account forLO offset. The proposed system is implemented on a USRP-N210 SDR with anexternal high-end IMU and tested in an anechoic chamber. The SDRimplementation is a mixture of FPGA and software development, while some partsof the data are processed off-line. The results show that our method is indeedfeasible, with bearing estimation errors of only a few degrees. We thenpresent the first efforts of an implementation on a USRP-E310 SDR which has anintegrated, lower-quality IMU.