Asynchronously Coordinated Multi-Timescale Beamforming Architecture for Multi-Cell Networks

Modern wireless devices such as smartphones are pushing the demand for higher wireless data rates. The ensuing increase in wireless traffic demand can be met by a denser deployment of access points, coupled with a coordinated deployment of advanced physical layer techniques to reduce inter-cell interference. Unfortunately, advanced physical layer techniques, e.g., multi-user (MU) MIMO found in 802.11ac and LTE-advanced, are not designed to operate efficiently in a coordinated fashion across multiple densely deployed transmitters. In this paper, we introduce a new coordination architecture, which can achieve high performance gains without the high overhead and deployment cost that usually comes with coordination, thus making the vision of high capacity wireless access via densely deployed transmitters practical. The basic idea is to loosely coordinate nearby transmitters using slow varying channel statistics, while keeping all the functionality which depends on fast varying channel state information and has tight time deadlines locally. We achieve this via a smart combination of analog and digital beamforming using inexpensive front ends, a provably efficient algorithm to select compatible users and analog beams across all transmitters, and backward compatible protocol extensions. Our performance results, which include analysis, simulations, and experiments with software defined radios and directional antennas, show that our approach can achieve the $10\times $ gains of the theoretically optimal coordinated MU-MIMO approach, without the need to either tightly coordinate the clocks of the remote transmitters or meet tight delay constraints.