Fast open-loop synchronization for distributed downlink beamforming

Distributed beamforming has recently been proposed as an energy-improved wireless communication technique, whereas the overhead of carrier synchronization will reduce its performance gain. In this paper we propose a fast open-loop carrier synchronization protocol by fully exploiting the broadcast nature of the wireless links. In comparison with the conventional open-loop synchronization protocols, the proposed one reduces obviously the number of times-lots required by a certain precision of carrier synchronization, especially for a large scale base stations case. The general expressions under any number of base stations is presented. An analysis of the statistical properties of the estimation errors and the resulting power gain of the distributed downlink beamforming is provided. The numerical results demonstrate that a near-ideal distributed downlink beamforming performance can be achieved by the proposed protocol but with low synchronization overhead.