Kan Watanabe

An Extension of Routing Tree Algorithm Considering Link Speed Change in IEEE 802.11n Protocol for Wireless Mesh Network

As an inexpensive, flexible, and scalable Internet-access network, we have studied architecture, protocols, and design optimizations of the Wireless Internet-access Mesh Network (WIMNET). WIMNET consists of multiple access-points (APs) as wireless routers that are connected through wireless links. One AP acts as a gateway (GW) to the Internet, where any host must reach there for the Internet access through multi-hop communications between APs. Because a lot of traffic must be handled by these links, the latest IEEE 802.11n protocol should be adopted to provide high-speed communications. In this paper, we first show that our throughput measurement results using commercial products implementing this protocol, reveal the quick drop of the throughput as the increase of the link distance. Then, we present extensions of our previously proposed routing tree algorithm for WIMNET and the WIMNET simulator in considering this link speed change by the distance. We verify the effectiveness of our proposals through simulations in four cases with different topologies.

A Proposal of an Active Access-Point Selection Algorithm in Wireless Mesh Networks

The wireless Internet-access mesh network (WIMNET) has been studied to offer an inexpensive, scalable Internet-access wireless network by adopting multiple access points (APs) connected by wireless links. WIMNET can improve the dependability to failures of links and/or APs by allocating APs redundantly in the network field. However, redundant APs may increase the operational cost and degrade the throughput due to increasing radio interferences. One solution to this problem is to activate only the necessary APs to provide the connectivity to the hosts while maximizing the throughput. In this paper, we first define this active AP selection problem of selecting the activated APs for communications, and propose its heuristic algorithm. The simulation results in three instances confirm the effectiveness of the proposed algorithm, and indicate the existence of an active AP selection that maximizes the throughput. Then, we present the average hop count and the traffic bias as the indices to seek the active AP selection with the maximal throughput, and the extension of our active AP selection algorithm using them.

An Online Fill-in-the-Blank Problem Function for Learning Reserved Words in Java Programming Education

The Java programming education to students has been held in a lot of universities and professional schools due to the reliability, portability, and easy learning. To assist this education, our group has developed a Java programming learning system based on the test-driven development method. However, this Web system targets students who have studied Java to some extent. In this paper, we propose a fill-in-the-blank problem function for this system to assist the learning of the Java reserved words by novice Java learners. Our function consists of a teacher service process and a student service process. By the former one, a teacher can generate a fill-in-the-blank problem easily by blanking the specified reserved words randomly from a sample Java code in the database. By the latter one, a student can repeatedly submit answers of a problem until all the questions are correctly solved for self-study. The function is implemented on an existing Web system and is applied to students who are currently learning Java. The questionnaire result confirms the effectiveness of our proposal.

An extension of fill-in-the-blank problem function in Java programming learning assistant system

Nowadays Java has been educated in many universities and professional schools as a reliable, portable, and practical programming language. To assist self-studies by students, we have developed a Web-based Java Programming Learning Assistant System (JPLAS). JPLAS has the two main functions of code writing problem and fill-in-the-blank problem to support studies at different levels. The former function intends that a student can write a whole code from scratch, where the submitted code is automatically tested on the server using the test-driven development (TDD) method. The latter function intends that a novice student can study Java reserved words, where a problem is generated by randomly removing the specified ones from a selected sample code and the removed one becomes the correct answer to each blank. In this paper, we extend this latter function for removing more general elements including variables and control symbols in problems. We analyze the conditions for selecting blanked elements with unique correct answers. For evaluations, we generated 100 problems with various levels using the extended function, and assigned them to students in the Java programming course in our department. Then, we gave a short test and a questionnaire with nine questions, where we found that students solving more problems achieved better scores in general, and their opinions support the effectiveness of our proposal.

AN ACTIVE ACCESS-POINT SELECTION APPROACH FOR DEPENDABLE WIRELESS MESH NETWORKS

As an inexpensive, flexible, and scalable Internet-access wireless network, we have studied the architecture, protocols, and design optimizations of the Wireless Internet-access Mesh NETwork (WIMNET) that adopts multiple access-points (APs) connected through wireless links. WIMNET can improve the dependability to failures of APs and/or their links by allocating APs redundantly in the network field. Because redundant APs may increase the operational cost and degrade the throughput due to increasing radio interferences, only the necessary APs for connectivity between the hosts and the Internet gateway should be activated in communications. In this paper, we first define the active AP selection problem of selecting the minimum number of active APs, and prove the NP-completeness of its decision version through reduction from the known minimum set cover problem. Then, we propose an active AP selection algorithm of deactivating APs one by one until no more AP can be deactivated. Due to the limited transmission capacity in WIMNET, we further present an algorithm extension for throughput maximization. We verify the effectiveness of our proposal through simulations in three instances, where the number of active APs is reduced by more than 40% and the throughput is improved by more than 10% from the original in any instance.

An application of cooking-step scheduling algorithm for homemade cooking and its extensions

Homemade cooking can have a key role for a healthy and cost-efficient life. To help this activity for busy people such as workers, students, and child-rearing families, we have proposed a cooking-step scheduling algorithm to suggest an optimal sequence of the cooking-steps when multiple dishes are cooked within a limited time. In this algorithm, the cooking procedure for each dish is divided into a set of cooking-steps, and the execution sequence of all the cooking-steps for the dishes is optimized such that the total cooking time is minimized. In this paper, we first show our application result of this algorithm in cooking five dishes and the arisen problems through this experiment. Then, we present four extensions of this algorithm to solve them. Through simulations and cooking experiments, we verify the effectiveness of the algorithm extensions.

Extensions of cooking guidance function on Android tablet for homemade cooking assistance system

Previously, we proposed a cooking-step scheduling algorithm to find a schedule of applying the cooking steps in the recipes for efficiently cooking multiple dishes simultaneously, to help healthy and cost-efficient lives for busy person. Then, we implemented a cooking guidance function on an Android tablet to navigate the cooking schedule in a kitchen. Although we confirmed the effectiveness through cooking experiments, we found three problems: 1) a user may click a starting button even if the previous required steps are not completed, 2) a user may miss the proper timing to stop a cooking-step, and 3) the duration time for a cooking-step may be varied by a user skill or a dish nature. In this paper, we extend the cooking guidance function by adding three features of starting condition checking, time-up alarming, and cooking rescheduling to solve these problems. We verify the effectiveness of the extended guidance function through experimentally cooking four dishes.

A Job Scheduling Method Based on Expected Probability of Completion of Voting in Volunteer Computing

This paper addresses the problem of job scheduling in volunteer computing (VC) systems where each computation job is replicated and distributed to multiple participants (workers) to remove incorrect results. In the job scheduling of VC, the number of assigned workers to complete a job is an important factor for the system performance, however, it cannot be fixed because some of the workers may not return results in real VC. We propose a job scheduling method which considers the expected probability of completion (EPC) for each job based on the workers history information. The key idea of the proposed method is to assign jobs so that EPC is always greater than a specified value (SPC). By setting SPC as a reasonable value, any job in the proposed method can be completed without excess allocations, which leads to the higher performance of VC systems. Simulation results show that the performance of the proposed method is up to 5 times higher than that of the conventional method, while keeping the error rate lower than a required value.

A modified routing tree algorithm considering link speed change in IEEE 802.11n for wireless mesh network

A Wireless Internet-access Mesh NETwork (WIMNET) can provide an expandable Internet-access network by adopting multiple Access-Points (APs) that have wireless connections with each other. Previously, we proposed a routing tree algorithm for generating an optimal routing path between the APs and the Internet Gate Way (GW) with a minimal transmission delay, assuming that every link has the same data transmission speed. However, our preliminary experiments found that the link speed using the IEEE802.11n as a new high-speed protocol for wireless communications, decreases drastically as the distance increases due to the lowered receiving signal quality. In this paper, we propose a modified routing tree algorithm to consider the large speed change in order to adopt the IEEE 802.11n in WIMNET effectively. In addition to links between APs, our modified algorithm selects the links between hosts and their associated APs. We verify the effectiveness of the modified algorithm through simulations in three topologies.

A Modified Active Access-Point Selection Algorithm Considering Link Speed Change in IEEE 802.11n for Wireless Mesh Networks

As an inexpensive, scalable Internet-access wireless network, we have studied the architecture, protocols, and design optimizations of the wireless Internet-access mesh network (WIMNET) that uses multiple access-points (APs) connected by wireless links. WIMNET can improve the dependability to failures of links and/or APs by allocating APs redundantly in the network field. Because redundant APs can increase the operational cost and degrade the performance due to increasing radio interferences, only the necessary APs for connections between the hosts and the Internet gateway should be activated at communications. Previously, we have defined the active AP selection problem of selecting the minimum number of active APs, and proposed its heuristic algorithm, assuming that every link has the same constant speed for simplicity. However, our preliminary experiments found that the link speed is greatly affected by the distance in the high-speed IEEE802.11n protocol that has recently become popular. In this paper, we propose a modification of the active AP selection algorithm to consider the link speed change, where we introduce a new design parameter for WIMNET to select links that have sufficient throughputs. We verify the effectiveness of our modified algorithm through simulations in four instances using the WIMNET simulator.