Network localization for distributed transmit beam forming with mobile radios

This paper describes open-loop and reference-aided methods to localize and synchronize a network of mobile radios to perform distributed transmit beamforming. To steer beams to a desired location, the radios must (a) synchronize their independent clocks, (b) estimate their positions relative to each other, and (c) estimate the relative angular orientation of their constellation to the steering direction. To estimate (a) and (b), messages containing transmission and reception time stamps are transmitted between the beamforming radios in a round-robin fashion. Inter-radio ranges and clock offsets are estimated from these measurements. To estimate (c), we can use GPS measurements alone to direct the beam to a known location (open-loop operation), or we can use GPS and transmissions from the intended recipient at a known location to aid beam-steering (reference-aided operation). In both cases, a Kalman filter is used to blend the measurements and propagate the node states through the beamforming process.