2 research outputs found
A scalable architecture for distributed receive beamforming: analysis and experimental demonstration
We propose, analyze and demonstrate an architecture for scalable cooperative
reception. In a cluster of N + 1 receive nodes, one node is designated as the
final receiver, and the N other nodes act as amplify-and-forward relays which
adapt their phases such that the relayed signals add up constructively at the
designated receiver. This yields received SNR scaling linearly with N, while
avoiding the linear increase in overhead incurred by a direct approach in which
received signals are separately quantized and transmitted for centralized
processing. By transforming the task of long-distance distributed receive
beamforming into one of local distributed transmit beamforming, we can leverage
a scalable one-bit feedback algorithm for phase synchronization. We show that
time division between the long-distance and local links eliminates the need for
explicit frequency synchronization. We provide an analytical framework, whose
results closely match Monte Carlo simulations, to evaluate the impact of phase
noise due to relaying delay on the performance of the one-bit feedback
algorithm. Experimental results from our prototype implementation on
software-defined radios demonstrate the expected gains in received signal
strength despite significant oscillator drift, and are consistent with results
from our analytical framework.Comment: submitted to IEEE Transactions on Wireless Communication
Some aspects of physical prototyping in Pervasive Computing
This document summarises the results of several research campaigns over the
past seven years. The main connecting theme is the physical layer of widely
deployed sensors in Pervasive Computing domains. In particular, we have focused
on the RF-channel or on ambient audio.
The initial problem from which we started this work was that of distributed
adaptive transmit beamforming. We have been looking for a simple method to
align the phases of jointly transmitting nodes (e.g. sensor or IoT nodes). The
algorithmic solution to this problem was to implement a distributed random
optimisation method on the participating nodes in which the transmitters and
the receiver follow an iterative question-and-answer scheme. We have been able
to derive sharp asymptotic bounds on the expected optimisation time of an
evolutionary random optimiser and presented an asymptotically optimal approach.
One thing that we have learned from the work on these physical layer
algorithms was that the signals we work on are fragile and perceptive to
physical environmental changes. These could be obstacles such as furniture,
opened or closed windows or doors as well as movement of individuals. This
observation motivated us to view the wireless interface as a sensor for
environmental changes in Pervasive Computing environments.
Another use of physical layer RF-signals is for security applications.
We are currently working to further push these mentioned directions and novel
fields of physical prototyping. In particular, the calculation of mathematical
operations on the wireless channel at the time of transmission appears to
contain good potential for gains in efficiency for communication and
computation in Pervasive Computing domains