No abstract

The growing ubiquity of cameras in hand-held

Cameras have become commonplace in phones, laptops, music-players and handheld games. Similarly, light emitting displays are prevalent in the form of electronic billboards, televisions, computer monitors, and hand-held devices. The prevalence of cameras and displays in our society creates a novel opportunity to build camera-based optical wireless communication systems based on a concept called visual MIMO. We extend the common term MIMO from the field of communications ("multiple-input multipleoutput") that is typically used to describe multiple antenna, multiple transmitter radio frequency communications channel. In the visual MIMO communications paradigm, the transmitters are light-emitting devices such as electronic displays and cameras are the receivers. In this paper we discuss and address several challenges in creating a visual MIMO channel. These challenges include: (1) electronic display detection, (2) embedding the transmission signal in the display video, and (3) system characterization for electronic display appearance.

Abstract-Mobile optical wireless has so far been limited to very short ranges for high data rate systems. It may be feasible to overcome the data rate limitations over large transmission range in optical wireless through camera receivers and light emitting transmitter arrays through a concept what we call "visual MIMO". In this concept multiple transmit elements of a light emitting array (LEA) are used as transmitters to communicate to the individual pixel elements of the camera which act as multiple receive elements to create the visual MIMO channel. Multiplexing information over parallel data channels albeit be very similar to RF MIMO in concept, the visual MIMO approach dramatically differs in its characterization. In visual MIMO since the received signal is essentially the image of the transmitting element, the perspective distortions in the visual channel dominate over some of the important properties of a RF wireless channel such as distance based attenuation and multipath fading. Some of the prominent perspective distortions include the reduction in the size of the image with distance and skew/rotation in the image due to angular view. Further lens blur (typically due to focus imperfection or jerks while capturing the image) can also significantly depreciate the image quality. In this paper we will detail how MIMO techniques such as multiplexing and diversity are characterized based on the effect of perspective distortions. Based our visual MIMO channel model we will derive the analytical channel capacity of the visual MIMO channel and using the same we illustrate the significance of parameters such as distance, viewing angle and blur in characterizing multiplexing and diversity in visual MIMO.

We investigate the linear transport properties of quantum point contacts (QPCs) whose symmetry is deliberately broken in a controlled manner. The devices that we study consist of a conventional split-gate QPC, which is modified by the inclusion of an additional perturbing gate that is used to modulate the electron density on one side of the device. As the voltage applied to this ‘finger gate’ is varied, we observe several reproducible features below the last integer plateau, as well as strong modifications of the integer-plateau staircase. Self-consistent calculations, performed for the exact device structure utilized in experiment, suggest that these features are related to the ability of the finger gate to strongly disrupt the symmetry of the QPC, reducing the electron density significantly on one side of the device. We discuss these results within the context of recent models for many-body electron transport in QPCs.