Phaser: Enabling Phased Array Signal Processing on Commodity Wi-Fi Access Points

Abstract

i n recent years, there has been renewed interest within the mobile and wireless networking communities in addressing problems related to the sensing of signals using multi-antenna radios, such as MIMO Wi-Fi access points. Recent examples include systems that localize RFID tags [8] and Wi-Fi devices [6, 9], enhance Wi-Fi security [10], and passive radar systems that pinpoint human movements [1, 2, 4]. These systems, and others, share an important common thread: they all rely on phased array signal processing; a set of techniques that makes various comparisons between the radio signals received from each of the antennas of a radio. Phased array processing has been applied in weather and military radar, seismology, and astronomy to great benefit, but its application to indoor and outdoor wireless and mobile communications presents new challenges and opportunities for novel system designs, as the above work demonstrates. While the aforementioned work demonstrates useful applications of phased array signal processing in mobile wireless local-area network designs, many of these systems rely on expensive, specialized hardware, which prohibits wide-scale deployment. Meanwhile, Wi-Fi is becoming ubiquitous, with many Wi-Fi access points (APs) being equipped with multiple network interface cards (NICs), each with multiple antennas [11]. If these widely deployed APs could be converted into miniature phased array receivers, signal processing systems could be run truly