With the turn of new decade, wireless communications face a major challenge on connecting many more new users and devices, at the same time being energy efficient and minimizing its carbon footprint. However, the current approaches to address the growing number of users and spectrum demands, like Massive MIMO, demand exorbitant energy consumption. The reason is that traditionally Massive MIMO requires a digital beamforming architecture that needs a separate RF chain per antenna, so the power consumption scales with number of antennas. Instead, GreenMO creates a new Massive MIMO architecture with just a single physically laid RF chain, shared by all the antennas and introduces for the first time, the concept of virtualizing the RF chain hardware. That is, GreenMO creates an optimal number of virtual RF chains to serve a given number of spatial streams, depending on channel conditions and network load. Due to efficient, softwarized control over the number of virtual RF chains, GreenMO paves the way for green and flexible massive MIMO. We prototype GreenMO on a PCB with eight antennas and evaluate it with a WARPv3 SDR platform in an office environment. The results demonstrate that GreenMO is 3× more power-efficient than traditional Massive MIMO and 4× more spectrum-efficient than traditional OFDMA systems, while multiplexing 4 spatial streams, and can save upto 50% power in modern 5G NR base stations.

Millimeter wave (mmWave) sensing has recently gained attention for its robustness in challenging environments. When visual sensors such as cameras fail to perform, mmWave radars can be used to provide reliable performance. However, the poor scattering performance and lack of texture in millimeter waves can make it difficult for radars to identify objects in some situations precisely. In this paper, we take insight from camera fiducials which are very easily identifiable by a camera, and present R-fiducial tags, which smartly augment the current infrastructure to enable myriad applications with mmwave radars. R-fiducial acts as fiducials for mmwave sensing, similar to camera fiducials, and can be reliably identified by a mmwave radar. We identify a set of requirements for millimeter wave fiducials and show how R-fiducial meets them all. R-fiducial uses a novel spread-spectrum modulation technique to provide low latency with high reliability. Our evaluations show that R-fiducial can be reliably detected with a 100% detection rate up to 25 meters with a 120-degree field of view and a few milliseconds of latency. We also conduct experiments and case studies in adverse and low visibility conditions to demonstrate the potential of R-fiducial in a variety of applications.

In the last decade, the bandwidth expansion and MIMO spatial multiplexing have promised to increase data throughput by orders of magnitude. However, we are yet to enjoy such improvement in real-world environments, as they lack rich scattering and preclude effective MIMO spatial multiplexing. In this paper, we present ScatterMIMO, which uses smart surface to increase the scattering in the environment, to provide MIMO spatial multiplexing gain. Specifically, smart surface pairs up with a wireless transmitter device say an active AP and re-radiates the same amount of power as any active access point (AP), thereby creating virtual passive APs. ScatterMIMO avoids the synchronization, interference, and power requirements of conventional distributed MIMO systems by leveraging virtual passive APs, allowing its smart surface to provide spatial multiplexing gain, which can be deployed at a very low cost. We show that with optimal placement, these virtual APs can provide signals to their clients with power comparable to real active APs, and can increase the coverage of an AP. Furthermore, we design algorithms to optimize ScatterMIMO's smart surface for each client with minimal measurement overhead and to overcome random per-packet phase offsets during the measurement. Our evaluations show that with commercial off-the-shelf MIMO WiFi (11ac) AP and unmodified clients, ScatterMIMO provides a median throughput improvement of 2 X over the active AP alone.