This article has been accepted for inclusion in a future issue of this journal. Content is final as presented, with the exception of pagination. IEEE/ACM TRANSACTIONS ON NETWORKING 1 AirSync: Enabling Distributed Multiuser MIMO With Full Spatial Multiplex

Abstract—The enormous success of advanced wireless devices is pushing the demand for higher wireless data rates. Denser spec-trum reuse through the deployment of more access points (APs) per squaremile has the potential to successfullymeet such demand. In principle, distributedmultiusermultiple-input–multiple-output (MU-MIMO) provides the best approach to infrastructure den-sity increase since several access points are connected to a cen-tral server and operate as a large distributed multiantenna access point. This ensures that all transmitted signal power serves the purpose of data transmission, rather than creating interference. In practice, however, a number of implementation difficulties must be addressed, the most significant of which is aligning the phases of all jointly coordinated APs. In this paper, we propose AirSync, a novel scheme that provides timing and phase synchronization ac-curate enough to enable distributed MU-MIMO. AirSync detect