There is much interest in integrating millimeter wave radios (mmWave) into wireless LANs and 5G cellular networks to benefit from their multi-GHz of available spectrum. Yet, unlike existing technologies, e.g., WiFi, mmWave radios require highly directional antennas. Since the antennas have pencil-beams, the transmitter and receiver need to align their beams before they can communicate. Existing systems scan the space to find the best alignment. Such a process has been shown to introduce up to seconds of delay, and is unsuitable for wireless networks where an access point has to quickly switch between users and accommodate mobile clients.

Recent years have seen a lot of work in moving distributed MIMO from theory to practice. While this prior work demonstrates the feasibility of synchronizing multiple transmitters in time, frequency, and phase, none of them deliver a full-fledged PHY capable of supporting distributed MIMO in real-time. Further, none of them can address dynamic environments or mobile clients. Addressing these challenges, requires new solutions for low-overhead and fast tracking of wireless channels, which are the key parameters of any distributed MIMO system. It also requires a software-hardware architecture that can deliver a distributed MIMO within a full-fledged 802.11 PHY, while still meeting the tight timing constraints of the 802.11 protocol. This architecture also needs to perform coordinated power control across distributed MIMO nodes, as opposed to simply letting each node perform power control as if it were operating alone. This paper describes the design and implementation of MegaMIMO 2.0, a system that achieves these goals and delivers the first real-time fully distributed 802.11 MIMO system.

We present a demonstration of a real-time distributed MIMO system, DMIMO. DMIMO synchronizes transmissions from 4 distributed MIMO transmitters in time, frequency and phase, and performs distributed multi-user beamforming to independent clients. DMIMO is built on top of a Zynq hardware platform integrated with an FMCOMMS2 RF front end. The platform implements a custom 802.11n compatible MIMO PHY layer which is augmented with a lightweight distributed synchronization engine. The demonstration shows the received constellation points, channels, and effective data throughput at each client. It also shows how these vary as a function of interference, the timeliness of channel feedback, and the transmission rates used by the different transmitters.