Consistently High MIMO Rates via Switched-Beam Antennas

The demand for wireless bandwidth is rising to unprecedented levels. The industry has responded with the inclusion of advanced PHY techniques, most notably multi-user (MU) MIMO, in the most recent Wi-Fi and LTE standards. However, despite the theoretical promise for large multiplexing gains, in practice the rate gains are modest due to a combination of large overhead to collect channel state information and not-so-well-conditioned channel matrices. In this paper, we propose to replace omni-directional antennas with inexpensive switched-beam antennas to produce well-conditioned channel matrices for MU-MIMO purposes with very low overhead. Remarkably, the experimental results with both software-defined radios and commercial Wi-Fi chipsets show that, when appropriate antenna modes are used, this leads to a 3.5\times-5\times average throughput improvement in indoor environments. What is more, our backward compatible protocol extension coupled with an efficient algorithm to select appropriate antenna modes, achieve the aforementioned gains with almost zero overhead.