A COTS based asynchronous distributed array processor utilizing reduced-rank STAP

Distributed array processing has been a topic of interest due to its added advantage of sensor placement and processing gain for leveraging transmit/receive beamforming configurations. However, having independent local oscillators at each sensor presents a synchronization challenge for a distributed array. We explore the use of reduced-rank signal processing and Signals-of-Opportunity (SOOs) to maintain better-distributed sensor coherency while performing Space-time Adaptive Processing (STAP) when GPS is unavailable for local sensor oscillator synchronization. Reduced-rank signal processing requires fewer samples for STAP convergence, thereby allowing less stringent coherency constraints on the distributed array processor. Less stringent coherency constraints enables the use of SOOs as timing reference beacons in the field of view, thereby eliminating the need to have a dedicated transmitter for sensor synchronization. We explore these concepts utilizing COTS Software Defined Radios (SDRs) providing data to an asynchronous distributed array processor (ADAP). The SDRs are setup to simultaneously sample the SOO and the Signal-of-Interest (SOI) to enable the distributed array processor to achieve both sensor synchronization and reduced-rank STAP on the SOI. Results are presented utilizing FM HD radio towers as both SOOs and SOIs, but our approach can easily be extended to a variety of other signals such as TV, cellular tower, and satellite signals just to name a few.