Recent years have witnessed the conceptualization and development of light-to-camera communication (LCC). Various innovative modulation schemes are designed for throughput improvement. Nevertheless, the fundamental limits of LCC itself are still unknown from a theoretical perspective. In this paper, we present the LCC channel model to shed light on a question: how to improve the system performance under identical conditions of transmitting/receiving device and modulation scheme. We reveal the channel parameters of LCC that affect the formation of the signal layer and provide a design guideline for increasing the symbol rate. Moreover, we improve the demodulation performance by sampling judging points from the separated signal layer instead of detecting the widths of bands in capture images. To enhance the signalto-noise ratio, we propose a short-time linear regression algorithm to filter out the noise from the signal layer. We build a hardware prototype with the simple ON-OFF keying to demonstrate the proposed channel model under various experiment settings. The results show that the system throughput reaches 8.2 kbps with a symbol rate of 25 kBd. We believe our techniques for symbol rate increasing and demodulation improvement can help other LCC systems improve their performance. INDEX TERMS Visible light communication, channel model, mobile computing, ON-OFF keying.
The last two decades have witnessed significant advances in the field of indoor positioning systems, which have led to technologies with high location precision. However, there still lacks robust meter-level indoor positioning approaches which only rely on in-building communication infrastructures and smartphones. We present STARLIT, a system that enables a single LED beacon to localize smartphones to within sub-meter. As the smartphone camera contains millions of pixels, we create a virtual sensor array with the camera to measure the received signal strength (RSS) of the LED beacon. Different from the existing camera-based approaches, which need to capture images of the LED within a short light-to-camera distance, we utilize the reflection light from the floor. By exploiting the rolling shutter mechanism in the smartphone cameras, we propose a solution to separate the signal layer from the image background and noise. Given the measured RSSs, we establish an equation set with the Lambertian model and the camera projection model to solve the location of the smartphone. We have implemented STARLIT and evaluated its performance in an office room. Our experiments demonstrate that the STARLIT can achieve a median error of 23cm and an 80-percentile error of 55cm.
Under the trend of communication network gradually flattening, media has become the condition of democratic politics operating and builder of political discourses. From the relationship of media and politics, based on some classical theories such as ears and eyes, agenda setting, supervision by public opinion, guidance of public opinion, it can be found that in the construction of benign political ecology, political open has become premise by ear and eye, political participation play as approach because of agenda setting, political repair considers itself as safeguard under supervision of public opinion, political coordination serve as means with guidance of public opinion. The processes of benign political ecology construction can't do without the constructive role of media. Political open, political participation, political repair and political coordination are the main dimensions of building benign political ecology, which is also a course of government, society and public open information, participate decision, coordinate direction, repair divergence with the help of media.
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