Nowadays, vehicles have been increasingly adopted in many spatial crowdsourcing (SC) applications. Similar to other SC applications, location privacy is of great concern to vehicle workers as they are required to disclose their own location to servers to facilitate the service utilities. Traditional location privacy protection mechanisms cannot be applied to vehicle-based SC since they assume workers mobility on a 2-dimensional plane without considering the network-constrained mobility features of vehicles. Accordingly, in this paper, we aim at addressing issues related to Vehicle-based spatial crowdsourcing Location Privacy (VLP) over road networks. Our objective is to design a location obfuscation strategy to minimize the quality loss due to obfuscation with geo-indistinguishability satisfied. Considering the computational complexity of VLP, by resorting to discretization, we first approximate VLP to a linear programming problem that can be solved by well-developed approaches. To further improve the time efficiency, we conduct constraint reduction for VLP by exploiting key features of geo-indistinguishability in road networks and problem decomposition based on VLPs constraint structure. Finally, we carry out both trace-driven simulation and real-world experiments, where our experimental results demonstrate the superiority of our approach over a known state-of-the-art location obfuscation strategy in terms of both QoS and privacy.

We are witnessing a rising concern over communication security and privacy. Conventional cryptography techniques encrypt data into unreadable codes, but still expose the existence of communications through metadata information (e.g., packet timing and size). In contrast, we propose a steganographic communication scheme adopting a novel combination of the intrinsic optical noise and a unique signal spreading technique to hide the existence of optical communications, i.e., optical steganography. We experimentally implement a prototype steganographic communication system, which requires zero cover-signal overhead to enable a stealth communication channel over the existing communication infrastructure. Both the frequency and time domain characterizations of our prototype implementation verify the feasibility of our approach. We also demonstrate the first practical steganographic communication that provides reliable communication performances between real computers at the application layer (200-300 Mbps file transfer rate and 25-30 Mbps Internet data rate) over long-distance optic-fibers (25-50 km). Additional bit-error-rate measurements illustrate negligible channel interference between the public and stealth communications (less than 1 dB power penalty). We further quantitatively demonstrate that the eavesdropper's chance of matching system parameters to effectively recover the stealth signal is $2^{-10}$ by random guessing, and that the eavesdropper's ability of detecting the stealth signal hidden in the transmission channel is strictly limited close to a random guess. Our steganographic communication scheme provides an attractive foundation for mitigating eavesdropping at the link-level, thus paving the way for future privacy-enhancing technologies using the physical layer characteristics of communication links.

Serious games (SGs) are a practice of growing importance due to their high potential as an educational tool for augmented learning. However, little effort has been devoted to address student learning optimization in an SG from a systematic point of view. This article tackles this challenge by developing a learning-embedded attribute Petri net (LAPN) model to represent game flow and student learning decision-makings. The dynamics of learner behaviors in game are then addressed through the incorporation of learning mechanisms (i.e., reinforcement learning (RL) and random forest classification) into the Petri net model for knowledge reasoning and learning. Finally, an algorithm based on LAPN is proposed, aiming to guide learners to achieve a faster and better solution to problem-solving in game. The benefit of the proposed model and algorithm is then demonstrated in the SG Gridlock.

We propose and experimentally demonstrate a hybrid free space optical (FSO) communication and radio frequency (RF) multiple-input and multiple-output (MIMO) system for interference separation. The system switches between FSO and RF MIMO modes and makes use of the complementary advantages of the two modes. The MIMO receiver separates signal of interest from in-band interference with blind source separation (BSS), while the separation ratio is limited by the physical dimensions of the MIMO antenna array. With FSO channel, the system achieves over 30dB signal to interference plus noise ratio, so the wireless system can transmit signals with high orders of modulation. When the FSO channel is blocked and line-of-sight transmission condition is not satisfied, the system switches to the RF MIMO mode for interference cancellation. The wireless system maintains continuous transmission at a lower bit rate. Both the FSO mode and the RF MIMO mode can be seamless integrated with photonic signal processing system for wideband and real-time interference cancellation.

In this paper, we propose and experimentally demonstrate a three-dimensional (3D) microscopic system that reconstructs a 3D image based on structured light illumination. The spatial pattern of the structured light changes according to the profile of the object, and by measuring the change, a 3D image of the object is reconstructed. The structured light is generated with a digital micro-mirror device (DMD), which controls the structured light pattern to change in a kHz rate and enables the system to record the 3D information in real time. The working distance of the imaging system is 9 cm at a resolution of 20 μm. The resolution, working distance, and real-time 3D imaging enable the system to be applied in bridge and road crack examinations, and structure fault detection of transportation infrastructures.

The threat and defend model of optical steganography based on amplified spontaneous emission noise is experimentally demonstrated. Although the optical delays in a steganography system generate large key space to hide and recover the stealth signals, delays in interferometer introduce spectral fringes that can be identified by the coherent detection attack and thus expose the stealth channel. To defend such attacks, the spectral fringes are removed by with stealth data rate that is beyond the response speed of the coherent detection. Experimental results show that the spectral signatures can be protected by both wideband property of spontaneous emission noise and setting up the optical delays and data rate within the secure range. Such defending method can guide the design of a secure optical steganography system.