Exploring transmit null forming in open-loop coherent distributed arrays

Mobile ad hoc networks (MANETs) consisting of nodes with single omnidirectional antennas and limited transmit power can support wireless connectivity over long distances through coherent operation. Although designed for short-range networked communication, the individual radio nodes in a MANET can be coordinated to form a sparse aperiodic array with a high power directional gain. By targeting a distant receiver with the array beam synthesized by a synchronized transmission, the MANET can ensure greater signal quality at the receiver. The sparse nature of the array coupled with the mobility-driven randomization of node positions makes the array gain somewhat uncontrollable outside of the main beam. Our work investigates methods of shaping the pattern of a coherent distributed transmit array using open-loop beamforming. A null-forming algorithm based on a partitioning of the network nodes into two sub-arrays is presented. Simulation results demonstrate the attenuation of the array factor in the desired null direction. A stochastic optimization step is also introduced.