Improving LP-WAN performance in Dense Environments with Practical Directional Clients

Directional antennas are a promising solution for improving the range of client devices and capacity of wireless networks. Unfortunately, in LP-WAN systems directional antennas tend to be both large and expensive due to operating at sub-GHz frequencies. However, if a client device is willing to forgo improvements in antenna gain, it is possible to realize compact and low-cost antennas that provide spatial diversity control. In this paper, we show that by increasing spatial diversity in LP-WAN clients with limited (or no) client gain, we can dramatically increase overall network capacity and improve client battery life by avoiding re-transmissions. This type of directional control can also be used for hot-spot management by more effectively load balancing clients across gateways. We performed a sensitivity analysis using a combination of real hardware and simulation to explore the impact of various switchable antenna geometries on network capacity under a variety of deployment configurations. We then designed and evaluated three prototype multi-sector array clients: (1) a switchable patch antenna configuration, (2) a digital phase-shift nulling configuration, and (3) a low-cost switched PCB element phase-shift system. Each design explores a different hardware cost vs antenna beam performance operating point. We experimentally see that our real antenna beam patterns, captured in an anechoic chamber, perform in a similar manner to our simulated prediction models in terms of beam pattern and in simulation improve network capacity by up to 28% from interference isolation alone and up to 95% when offloading hot spots between four gateways. We also perform a small measurement study of how often our final design changes its configuration when deployed over multiple days on a campus testbed.