Complexity of Bradley-Manna-Sipma Lexicographic Ranking Functions

In this paper we turn the spotlight on a class of lexicographic ranking functions introduced by Bradley, Manna and Sipma in a seminal CAV 2005 paper, and establish for the first time the complexity of some problems involving the inference of such functions for linear-constraint loops (without precondition). We show that finding such a function, if one exists, can be done in polynomial time in a way which is sound and complete when the variables range over the rationals (or reals). We show that when variables range over the integers, the problem is harder -- deciding the existence of a ranking function is coNP-complete. Next, we study the problem of minimizing the number of components in the ranking function (a.k.a. the dimension). This number is interesting in contexts like computing iteration bounds and loop parallelization. Surprisingly, and unlike the situation for some other classes of lexicographic ranking functions, we find that even deciding whether a two-component ranking function exists is harder than the unrestricted problem: NP-complete over the rationals and $\Sigma^P_2$-complete over the integers.Comment: Technical report for a corresponding CAV'15 pape

Energy-efficient broadcasting with cooperative transmissions in wireless sensor networks

[[abstract]]Broadcasting is a method that allows the distributed nodes in a wireless sensor network to share its data efficiently among each other. Due to the limited energy supplies of a sensor node, energy efficiency has become a crucial issue in the design of broadcasting protocols. In this paper, we analyze the energy savings provided by a cooperative form of broadcast, called the Opportunistic Large Arrays (OLA), and compare it to the performance of conventional multi-hop networks where no cooperation is utilized for transmission. The cooperation in OLA allows the receivers to utilize for detection the accumulation of signal energy provided by the transmitters that are relaying the same symbol. In this work, we derive the optimal energy allocation policy that minimizes the total energy cost of the OLA network subject to the SNR (or BER) requirements at all receivers. Even though the cooperative broadcast protocol provides significant energy savings, we prove that the optimum assignment for cooperative networks is an NP-complete problem and, thus, requires high computational complexity in general. We then introduce several suboptimal yet scalable solutions and show the significant energy-savings that one can obtain even with the approximate solutions.[[fileno]]2030137030017[[department]]電機工程學

Machine Learning for Cyber Physical Systems

This open access proceedings presents new approaches to Machine Learning for Cyber Physical Systems, experiences and visions. It contains selected papers from the fifth international Conference ML4CPS – Machine Learning for Cyber Physical Systems, which was held in Berlin, March 12-13, 2020. Cyber Physical Systems are characterized by their ability to adapt and to learn: They analyze their environment and, based on observations, they learn patterns, correlations and predictive models. Typical applications are condition monitoring, predictive maintenance, image processing and diagnosis. Machine Learning is the key technology for these developments

REASONING OVER STRINGS AND OTHER UNBOUNDED DATA STRUCTURES

Ph.DDOCTOR OF PHILOSOPH

Tools and Algorithms for the Construction and Analysis of Systems

This open access two-volume set constitutes the proceedings of the 27th International Conference on Tools and Algorithms for the Construction and Analysis of Systems, TACAS 2021, which was held during March 27 – April 1, 2021, as part of the European Joint Conferences on Theory and Practice of Software, ETAPS 2021. The conference was planned to take place in Luxembourg and changed to an online format due to the COVID-19 pandemic. The total of 41 full papers presented in the proceedings was carefully reviewed and selected from 141 submissions. The volume also contains 7 tool papers; 6 Tool Demo papers, 9 SV-Comp Competition Papers. The papers are organized in topical sections as follows: Part I: Game Theory; SMT Verification; Probabilities; Timed Systems; Neural Networks; Analysis of Network Communication. Part II: Verification Techniques (not SMT); Case Studies; Proof Generation/Validation; Tool Papers; Tool Demo Papers; SV-Comp Tool Competition Papers

Traffic-Aware Deployment of Interdependent NFV Middleboxes in Software-Defined Networks

Middleboxes, such as firewalls, Network Address Translators (NATs), Wide Area Network (WAN) optimizers, or Deep Packet Inspector (DPIs), are widely deployed in modern networks to improve network security and performance. Traditional middleboxes are typically hardware based, which are expensive and closed systems with little extensibility. Furthermore, they are developed by different vendors and deployed as standalone devices with little scalability. As the development of networks in scale, the limitations of traditional middleboxes bring great challenges in middlebox deployments. Network Function Virtualization (NFV) technology provides a promising alternative, which enables flexible deployment of middleboxes, as virtual machines (VMs) running on standard servers. However, the flexibility also creates a challenge for efficiently placing such middleboxes, due to the availability of multiple hosting servers, capabilities of middleboxes to change traffic volumes, and dependency between middleboxes. In our first two work, we addressed the optimal placement challenge of NFV middleboxes by considering middlebox traffic changing effects and dependency relations. Since each VM has only a limited processing capacity restricted by its available resources, multiple instances of the same function are necessary in an NFV network. Thus, routing in an NFV network is also a challenge to determine not only via a path from the source to destination but also the service (middlebox) locations. Furthermore, the challenge is complicated by the traffic changing effects of NFV services and dependency relations between them. In our third work, we studied how to efficiently route a flow to receive services in an NFV network. We conducted large-scale simulations to evaluate our proposed solutions, and also implemented a Software-Defined Networking (SDN) based prototype to validate the solutions in realistic environments. Extensive simulation and experiment results have been fully demonstrated the effectiveness of our design