Phaser

Abstract

Signal processing on antenna arrays has received much recent attention in the mobile and wireless networking research communities, with array signal processing approaches addressing the problems of human movement detection, indoor mobile device localization, and wireless network security. However, there are two important challenges inherent in the design of these systems that must be overcome if they are to be of practical use on commodity hardware. First, phase differences between the radio oscillators behind each antenna can make readings unusable, and so must be corrected in order for most techniques to yield high-fidelity results. Second, while the number of antennas on commodity access points is usually limited, most array processing increases in fidelity with more antennas. These issues work in synergistic opposition to array processing: without phase offset correction, no phase-difference array processing is possible, and with fewer antennas, automatic correction of these phase offsets becomes even more challenging. We present Phaser, a system that solves these intertwined problems to make phased array signal processing truly practical on the many WiFi access points deployed in the real world. Our experimental results on three-and five-antenna 802.11-based hardware show that 802.11 NICs can be calibrated and synchronized to a 20 • median phase error, enabling inexpensive deployment of numerous phase-difference based spectral analysis techniques previously only available on costly, special-purpose hardware.

Human Activity Sensing with Wireless Signals: A Survey

“…It keeps stable without human existence. Previous research [37,117] show that the RF oscillator is frequency locked on a single commercial wireless NIC at startup. Therefore, there is no sampling frequency difference among the antennas on the same NIC.…”

“…Besides, the absolute phases differ because each radio chain connects to different RF oscillators. Phaser [117] proposes a phase autocalibration algorithm that corrects the phase offsets between the different radio oscillators at an AP.…”

Beam Search Strategy for MillimeterWave Networks with Out-of-Band Input Data

“…In case of mobile devices, energy and form factor constraints limit the number of antennas to one or two, even in mobile chipsets of the last generation [18]. Even if APs may be equipped with low-order MIMO transceivers in typical form factors, the median error in the angle estimation of 802.11 frames received by mobile devices with one antenna is about 20 degrees [19], [20], i.e., even in this case significant further refinement is necessary to ultimately align the antenna beams. This motivates trying alternative approaches that are less demanding in terms of hardware requirements.…”

“…In order to evaluate the link quality for different levels of misalignment between AP and UE antenna, we start from an ideal situation where the nodes are perfectly aligned and measure the RSS when adding different rotation drifts at steps of 7 ○ (corresponding to the antenna beamwidth). With the objective of better reproducing realistic scenarios, we randomly select the angle error between zero and 20 degrees as observed in past works that rely on one single antenna for sub-6 GHz legacy WiFi at the mobile device [19], [20]. In fact, in case of mobile devices, energy and form factor constraints limit the number of antennas to one or two, even in mobile chipsets of the last generation [10], [18].…”

A Multi-View Discriminant Learning Approach for Indoor Localization Using Amplitude and Phase Features of CSI

“…In order to utilize CSI phase, phase sanitization can be done by linear transformation of the phase values or by utilizing the phase difference between two antennas in 2.4 GHz band [39], [40]. Although CSI phase can be stabilized with the above methods, the average phase value obtained from these methods becomes different from the actual phase of the measured CSI due to the firmware problem in the 2.4 GHz band [36]. In order to avoid the problem of random phase error, we exploit the difference in phase values between two receiver antennas in 5GHz band.…”