As video streaming services become more popular, users desire high perceived video quality, which has placed more stringent requirements on the quality of connection. Existing issues of cellular networks encourage users to seek alternative connections such as public Wi-Fi networks; however, expectations of both users and owners of Wi-Fi networks are not sufficiently satisfied and various concerns are yet to be addressed by a better Wi-Fi access system. Based on a go-as-you-pay scheme, we design and implement DiFi, a per-user-based system with dynamic resource allocation and pricing. DiFi offers data burst that accommodates user requirements on the burstiness of traffic, in addition to bandwidth. It better caters to the various individual requirements of users, and better utilizes the limited network resources for the owners. We leverage the blockchain-based smart contract to address realistic concerns on decentralized control, privacy and trustiness and our implementation is compatible with existing Wi-Fi infrastructures.

Due to the long-run and unpredictable nature of stream processing, any statically configuredexecution of stream jobs fails to process data in a timely and efficient manner. To achieve performance requirements, stream jobs need to be reconfigured dynamically. In this paper, we present Trisk, a control plane that support versatile reconfigurations while keeping high efficiency with easy-to-use programming APIs. Trisk enables versatile reconfigurations with usability based on a task-centric abstraction, and encapsulates primitive operations such that reconfigurations can be described by compositing the primitive operations on the abstraction. Trisk adopts a partial pause-and-resume design for efficiency, through which synchronization mechanisms in the native stream systems can further be leveraged. We implement Trisk on Apache Flink and demonstrate its usage and performance under realistic application scenarios. We show that Trisk executes reconfigurations with shorter completion time and comparable latency compared to a state-of-the-art fluid mechanism for state management.

Recent works have shown that acoustic signals can be leveraged to perform respiration monitoring with high accuracy and low energy consumption. Since smartphones, smart speakers, and many other IoT devices are already equipped with microphones and speakers, it is convenient to implement the acoustic sensing solutions on those devices. However, the existing technologies require the speaker to transmit certain ultrasonic signals to detect respiration. Although these signals are inaudible to adults, they are audible to children and pets and they may even have negative impacts on plants. In this article, instead of using ultrasonic signals, we are trying to leverage audible signals in daily lives, e.g., music or broadcasting audios, to detect human respiration. We design a respiration detection system which derives the respiration rate by continuously estimates the channel impulse response (CIR) using music and broadcast signals. We study the intersymbol interference (ISI) brought by the randomness of music and broadcast signal and give our strategy to minimize the interference. We also propose several techniques to resolve some practical issues, such as the multipath effect and sampling frequency offset between the speaker and the microphone. Extensive experiments are conducted to demonstrate the feasibility of our system. The result shows that our system can achieve high respiration detection accuracy with the mean error of less than 0.5 BPM when different audio signals are used.