As the location-based service (LBS) plays an increasingly important role in real life, the topic of positioning attracts more and more attention. Under different environments and principles, researchers have proposed a series of positioning schemes and implemented many positioning systems. With widely deployed networks and massive devices, wireless fidelity (Wi-Fi) technology is promising in the field of indoor positioning. In this paper, we survey the authoritative or latest positioning schemes for Wi-Fi-assisted indoor positioning. To this end, we describe the problem and corresponding applications, as well as an overview of the alternative methods. Then, we classify and analyze Wi-Fi-assisted indoor positioning schemes in detail, as well as review related work. Furthermore, we point out open challenges and forecast promising directions for future work.

This paper considers the problem of how to reduce the I/O overhead of data update operations in erasure coding based storage systems. To this end, we first analyze the I/O overhead of update operations with current update approaches.We find the key to reduce such I/O overhead is designing a scheduling algorithm to construct the sequence of update operations. Such an algorithm needs to execute with a time limit, since update requests work under a stringent latency constraint. To quickly schedule the order of update operations, we propose an efficient algorithm, namely UCODR. Our theoretical analysis verifies that UCODR can effectively reduce the I/O overhead of update operations when multiple blocks are updated. To further confirm its effectiveness, we implement a prototype storage system to deploy UCODR with different erasure codes. Extensive experiments are conducted on the prototype storage system with real-world traces. The experimental results show that UCODR can reduce the time of update operations by up to 35% and improve the throughput of the storage system by up to 67%, compared with the state-of-the-art update approaches.

Multi-cloud storage is recently a viable approach to solve the vendor lock-in, reliability, and security issues in cloud storage systems. As a key concern, data placement influences the cost and performance of storage services. Yet, in practice it remains challenging to address the huge solution space. Previous studies typically focus on constructing efficient data placement schemes based on the predicted pattern of workloads or assuming fully a-priori known network conditions. They cannot be easily applied in multi-cloud storage scenarios, which typically involve dynamic network conditions and time-varying workloads. To this end, we formulate the data placement optimization in a combinatorial multi-arm bandit (CMAB) perspective and solve it by learning placement strategy online. In contrast to a stationary setting where reward distributions are unknown but identical over time, we consider a realistic multi-cloud environment with non-stationary conditions, i.e. , reward distributions change over time. To swiftly accommodate this, we propose an adaptive window combinatorial upper confidence bound based data placement (AW-CUCB-DP) scheme to reduce latency and cost. In AW-CUCB-DP, a simple and efficient change detector, i.e., Page-Hinkley test with forgetting mechanism (FM-PHT), is employed to enable variable-size sliding windows to handle both gradual and abrupt variations in network conditions or workloads. We establish that AW-CUCB-DP is asymptotically optimal in the non-stationary multi-cloud environment. Trace-driven experiments further verify that our scheme outperforms alternatives, especially in highly dynamic environments.

Cloud-of-clouds storage can enhance the data security and reliability of online applications by encrypting, encoding, and distributing user data across multiple clouds. Fast transferring large volumes of data through networks with limited bandwidths remains a practical challenge, especially in the event of disaster backup. To address this, we model a data storage process using an information flow graph and estimate inter-cloud traffic. We propose a new Network Coding-based Cloud-of-Clouds Backup (NC3B) framework, which enables collaborative encoding and data exchange among backup clouds to utilize inter-cloud bandwidth efficiently. We analytically corroborate that NC3B effectively reduces write operation latency. We also demonstrate the NC3B framework by incorporating two cutting-edge Reed-Solomon (RS) based data storage techniques, namely All-Or-Nothing Transform-RS (AONT-RS) and Converge AONT-RS (CAONT-RS), referred to as Network coding-based Backup AONT-RS (NBAONT-RS) and Network coding-based Backup CAONT-RS (NBCAONT-RS), respectively. To validate our approach, we deploy a real-world prototype storage system on Amazon EC2 using a cluster trace set, and underscore the effectiveness of NC3B, showcasing reductions in latency of up to 50% compared to state-of-the-art approaches, alongside throughput improvements of up to 98%. These findings underscore the benefits of NC3B in real-world storage scenarios.

Cloud-of-clouds storage systems are widely used in online applications, where user data are encrypted, encoded, and stored in multiple clouds. When some cloud nodes fail, the storage systems can reconstruct the lost data and store it in the substitute nodes. It is a challenge to reduce the latency of data recovery to ensure data reliability. In this paper, we adopt a Reinforcement Learning-based Data Recovery (RLDR) approach to reduce the regeneration time. By employing the Monte-Carlo method, our approach can construct the tree-topology-based regeneration process, a.k.a. regeneration tree, to effectively reduce the regeneration time. Through rigorous analysis, we apply the information flow graph to optimize the inter-cloud traffic for a given regeneration tree. To verify the merit of RLDR, We conduct extensive experiments on real-world traces. Experiments demonstrate that RLDR can significantly accelerate the regeneration process. Specifically, RLDR can reduce the regeneration time by up to 92% and increase the throughput by up to twelve-fold, compared to the prior art.