Abstract-Crowd counting, which count or accurately estimate the number of human beings within a region, is critical in many applications, such as guided tour and crowd control. A crowd counting solution should be scalable and be minimally intrusive (i.e., device-free) to users. Image-based solutions are device-free, but cannot work well in a dim or dark environment. Non-image based solutions usually require every human being carrying device, and are inaccurate and unreliable in practice. In this paper, we present FCC, a device-Free Crowd Counting approach based on Channel State Information (CSI). Our design is motivated by our observation that CSI is highly sensitive to environment variation, like a frog eye. We theoretically discuss the relationship between the number of moving people and the variation of wireless channel state. A major challenge in our design of FCC is to find a stable monotonic function to characterize the relationship between the crowd number and various features of CSI. To this end, we propose a metric, the Percentage of nonzero Elements (PEM), in the dilated CSI Matrix. The monotonic relationship can be explicitly formulated by the Grey Verhulst Model, which is used for crowd counting without a labor-intensive site survey. We implement FCC using off-theshelf IEEE 802.11n devices and evaluate its performance via extensive experiments in typical real-world scenarios. Our results demonstrate that FCC outperforms the state-of-art approaches with much better accuracy, scalability and reliability.

Using a linearly chirped optical probe pulse in free-space electro-optic measurements, a temporal wave form of a co-propagating THz field is linearly encoded onto the frequency spectrum of the optical probe pulse, and then decoded by dispersing the probe beam from a grating to a detector array. We achieve acquisition of picosecond THz field pulses without using mechanical time-delay device. We also demonstrate a single-shot electro-optic measurement of the temporal wave form of a THz pulse.

By introduction of an optical gating beam on a semiconductor wafer, near-field terahertz (THz) imaging with a dynamic aperture has been realized. The spatial resolution is determined by the focus size of the optical gating bean and the near-field diffraction effect. THz imaging with subwavelength spatial resolution (better than 50mum) is demonstrated.

No abstract

Using an optically chirped pulse in an electro-optic detection system, we image the spatiotemporal distribution of a terahertz (THz) pulse. We demonstrate single-shot THz field imaging of photoconductive emitters.