Visible-light positioning (VLP) has been considered as a promising indoor positioning technology due to its high precision and low cost. However, current VLP techniques are greatly limited by the assumption that lights have to be turned on to emit shining light beams, which is not applicable to scenarios that do not need the illumination all the time. In this article, we design and implement a novel VLP system, DarkVLP, to achieve high-precision positioning when lights are “turned off.” The “turn off” state means lights emit the extremely low luminance that is imperceptible to human eyes. In order to realize such a system, we have to tackle nontrivial challenges in data encoding/decoding, modulation/demodulation, and positioning algorithm. Specifically, we propose the sliding rheostat-based modulation scheme to eliminate the need of a complex signal synchronization mechanism and landmark recognition algorithm at the receiver. We also propose the dual-photodiode-based positioning algorithm, which effectively mitigates effects of substantial signal strength fluctuation, to reliably achieve VLP. In the end, we design novel circuits and prototype our system DarkVLP on commercial off-the-shelf devices. The results of extensive experiments demonstrate that our DarkVLP system could achieve submeter precision under the extremely low luminance, which greatly broadens application scenarios of VLP.

Mobile messaging services like SMS, MMS and wireless instant messaging services have become the major revenue source of the wireless data services. Compared with the online web access model, messaging access is more preferred in the wireless environment because messaging systems work in an asynchronous way and can tolerate intermittent connectivity. Current mobile messaging focuses on consumer applications, e.g., person-to-person communication. To leverage mobile message usage in mobile enterprise applications, iMMS (Interactive Multimedia Messaging Service) is proposed in this paper, which adds interactive features into MMS standard to provide rich and friendly user interface, local interaction and offline operation. In this paper, a message package based programming model is introduced to support interactive messaging application development. A design of an iMMS framework based on this programming model is presented. The architecture of the framework is also discussed. Finally a mobile workflow solution is given to show the implementation of a mobile enterprise application on the framework.

Constructing indoor radio maps plays an important role in many services and applications, such as wireless base station planning. We propose a hybrid approach to constructing indoor radio maps by developing a novel indoor signal propagation model, called the hidden environment model (HEM). The model is hybrid because it combines on-site measurements with a number of different types of calculations. As part of this model, we introduce the idea of an environment factor matrix (EFM). The EFM represents a model of the environmental features that affect radio attenuation. We also develop a lazy sampling algorithm to help generate the EFM. The goal of the lazy sampling algorithm is to balance the number of measurements that need to be taken with our model's accuracy. The goal is to minimize the measurement workload while maintaining satisfactory accuracy. We evaluate our model by comparing the radio maps calculated from the model to a radio map obtained by exhaustive measurements. The results show that our hidden environment model achieves good accuracy.

An interactive multimedia messaging service platform and two demos are described in this paper.