3 research outputs found
High-Accuracy Multi-Node Ranging For Coherent Distributed Antenna Arrays
The design and experimental implementation of a waveform for high-accuracy
inter-node ranging in a coherent distributed antenna array is presented. Based
on a spectrally-sparse high-accuracy ranging waveform, the presented
multi-frequency waveform enables high-accuracy ranging between multiple nodes
in an array simultaneously, without interference. The waveform is based on a
unique time-frequency duplexing approach combining a stepped-frequency waveform
with different step cycles per node pair. The waveform also inherently includes
beneficial disambiguation properties. The ambiguity function of the waveform is
derived, and theoretical bounds on the ranging accuracy are obtained.
Measurements were conducted in software-defined radio-based nodes in a
three-element distributed array, demonstrating high-accuracy unambiguous
ranging between two slave nodes and one master node.Comment: Submitted to IEEE Transactions on Aerospace and Electronic System
Open-Loop Distributed Beamforming Using Scalable High Accuracy Localization
We present a distributed antenna array supporting open-loop distributed
beamforming at 1.5 GHz. Based on a scalable, high-accuracy internode ranging
technique, we demonstrate open-loop beamforming experiments using three
transmitting nodes. To support distributed beamforming without feedback from
the destination, the relative positions of the nodes in the distributed array
must be known with accuracies below of the beamforming carrier
frequency to ensure that the array maintains at least 90\% coherent beamforming
gain at the receive location. For operations in the microwave range, this leads
to range estimation accuracies of centimeters or lower. We present a scalable,
high-accuracy waveform and new approaches to refine range measurements to
significantly improve the estimation accuracy. Using this waveform with a
three-node array, we demonstrate high-accuracy ranging simultaneously between
multiple nodes, from which phase corrections on two secondary nodes are
implemented to maintain beamforming with the primary node, thereby supporting
open-loop distributed beamforming. Upon movement of the nodes, the range
estimation is used to dynamically update the phase correction, maintaining
beamforming as the nodes move. We show the first open-loop distributed
beamforming at 1.5 GHz with two-node and three-node arrays, demonstrating the
ability to implement and maintain phase-based beamforming without feedback from
the destination.Comment: Submitted to IEEE Transactions on Wireless Communication
Adaptive Distributed Transceiver Synchronization Over a 90 Meter Microwave Wireless Link
We present an adaptive approach for synchronizing both the phase and
frequency of radio-frequency transceivers over long-range wireless links to
support distributed antenna array applications. To enable distributed
beamforming between separate wireless nodes, the oscillators in the
transceivers must operate at the same frequency, and their phases must be
appropriately aligned to support phase-coherent beamsteering. Based on a
spectrally-sparse waveform, a self-mixing circuit, and an adaptive control
loop, we present a system capable of synchronizing the RF oscillators in
separate transceivers over distances of nearly 100 m. The approach is based on
a spectrally-sparse waveform for joint inter-node ranging and frequency
transfer. A frequency reference is modulated onto one signal of a two-tone
waveform transmitted by the primary node which is demodulated and used to lock
the oscillator of the secondary node. The secondary node retransmits the
two-tone signal which the primary node uses for a high-accuracy range
measurement. From this range, the phase of the two transceivers can be aligned
to support beamforming. We furthermore implemented an adaptive phase control
approach to support high-accuracy phase coordination in changing environmental
conditions. We demonstrate continuous high accuracy links over a 90 m distance
in an outdoor environment for durations up to seven days, demonstrating
sufficient phase coordination in changing weather conditions to support
distributed beamforming at frequencies up to 3 GHz