  This paper deals with distributed beamforming techniques for wireless
networks with half-duplex amplify-and-forward relays. Existing schemes optimize
the beamforming weights based on the assumption that channel state information
(CSI) is available at the relays. We propose to use adaptive beamforming based
on deterministic perturbations and limited feedback (1-bit) from the
destination to the relays in order to avoid CSI at the relays. Two scalable
perturbation schemes are considered and practical implementation aspects are
addressed. Simulation results confirm that the proposed techniques closely
approach optimum performance and have satisfactory tracking properties in
time-varying environments.
