Akira Fukuda

Performance analysis of flexible hierarchical cellular systems with a bandwidth-efficient handoff scheme

In this paper, a bandwidth-efficient handoff strategy is proposed and analyzed for hierarchical cellular systems. Mobile subscribers are divided into two classes, i.e., low- and high-mobility subscribers. In our bandwidth-efficient handoff strategy, each of the originating and handoff calls of both slow and fast mobile subscribers first tries to get a channel in a microcell. Macrocells are overlaid over the microcells to handle overflowed calls. A call overflowed into a macrocell requests a take-back to the new microcell at each border crossing of the microcells. The request will be accommodated by the target microcell if there is any idle traffic channel in the cell. An analytical model is developed, and the most important performance measures such as the blocking probability of originating calls and the forced termination probability of calls are evaluated. It is shown through extensive comparisons with other candidate handoff strategies that if the total traffic load of the system is not very heavy, our scheme has the best bandwidth efficiency and can provide better quality of service for mobile subscribers without bringing too much processing expense to the system.

Efficient Survey Database Construction Using Location Fingerprinting Interpolation

A critical problem with location fingerprinting is the considerable time and effort spent measuring received signal strengths at all location candidates to create the survey database. To reduce this cost, existing methods use a signal path loss model to interpolate part of the survey database from data actually measured at location candidates. However, the positioning accuracy can become degraded, especially in an indoor area delimited by walls. In this paper, we confirm the degradation in accuracy of the existing method through a preliminary experiment, and propose an accurate interpolation method for survey databases. In the proposed method, part of the survey data is interpolated using a path loss model containing wall attenuation. Furthermore, to confirm the effectiveness of the proposed method, we evaluate the location estimation performance with the interpolated survey database and also verify the interpolated data. The proposed method improves the positioning accuracy by 25% over that of the existing method.

Network-Based Context-Aware Input Method Editor

In this paper, we propose a context-aware Input Method Editor (IME) as a ubiquitous service for improving the input of text on mobile devices. In our proposed IME, it estimates the context of users according to position information from GPS (Global Positioning System) sensor or a presence information from the Internet. Simultaneously, it generates a personal context-aware dictionary dynamically from the keywords gotten via some APIs in the Internet. Currently, the information of user’s context is also provided by NGN. In this paper, we explain the overview of our proposal and prototype implementation in Japanese.

Formal Verification of Software Designs in Hierarchical State Transition Matrix with SMT-based Bounded Model Checking

Hierarchical State Transition Matrix (HSTM) is a table-based modeling language for developing designs of software systems. Although widely used and adopted by (particularly Japanese) software industry, there is still lack of mechanized formal verification supports for conducting rigorous and automatic analysis to improve reliability of HSTM designs. In this paper, we first present a formalization of HSTM designs as state transition systems. Consequentially, based on this formalization, we propose a symbolic encoding approach, through which correctness of a HSTM design with respect to LTL properties could be represented as Bounded Model Checking (BMC) problems that could be determined by Satisfiability Modulo Theories (SMT) solving. We have implemented our encoding approach in a tool called Garakabu2 with the state-of-the-art SMT solver CVC3 as its back-ended solver. Furthermore, in our preliminary experiments, a conceptually simple but steadily effective way of accelerating SMT solving for HSTM designs is investigated and reported.

An SMT-Based Approach to Bounded Model Checking of Designs in Communicating State Transition Matrix

State Transition Matrix (STM) is a table-based modeling language for developing designs of software systems. Although widely accepted and used in software industry, there is lack of formal verification supports for conducting rigorous analysis to improve reliability of STM designs. In this paper, we present a symbolic encoding approach for STM designs that employ message passing as the means of communication, through which correctness of a STM design with respect to invariant properties could be Bounded Model Checked (BMC) by using Satisfiability Modulo Theories (SMT) solving techniques. We have built a prototype implementation of the proposed encoding and the state-of-the-art SMT solver -- Yices, is used in our experiments as a back-end tool to evaluate the effectiveness of our approach. In addition, two approaches for accelerating SMT solving by introducing additional knowledge are proposed and their effectiveness is shown by our preliminary experimental results.

A Multilateration-based Localization Scheme for Adhoc Wireless Positioning Networks Used in Information-oriented Construction

We have developed an adhoc wireless positioning network (AWPN) scheme for information-oriented construction that can temporarily and easily provide a positioning area in both indoor and outdoor environments. The particular requirements of AWPNs are easy deployment and easy configuration because the network should be removed on completion of construction and must frequently accompany the active construction section as it shifts from area to area. In this paper, we propose a localization scheme based on the multilateration method to fulfill the requirements of such AWPNs. The proposed scheme locally and dynamically calibrates the attenuation coefficient defined in the path loss model for radio wave propagation in order to reflect local, fresh propagation characteristics. The results of evaluations conducted on the efficacy of our proposed scheme indicate that it reduces the average error by 30% relative to the conventional approach.

On Accelerating SMT-based Bounded Model Checking of HSTM Designs

Hierarchical State Transition Matrix (HSTM) is a table-based modeling language for developing designs of software systems. We have proposed a Satisfiability Modulo Theory (SMT) based Bounded Model Checking (BMC) approach in [1] to provide formal verification supports for conducting rigorous and automatic analysis to improve reliability of HSTM designs. In this paper, we continue that work by developing and evaluating approaches to accelerating BMC of HSTM designs. The approaches center around an unrolled Bounded Reach ability Tree (BRT) of a HSTM design that is built with stateless explicit state exploration. Specifically, reach ability of invalid cells (representing undesired states) of a HSTM design, which occurs within the bound concerned, could be discovered during construction of the BRT, and furthermore, if no such occurrence, the constructed BRT could be utilized to rule out unnecessary subformulas of a BMC instance for verification of LTL properties. We have implemented these approaches in a tool called Garakabu2 with the state-of-the-art SMT solver CVC3 as its back-ended solver. Our preliminary experiments show that verification could be accelerated substantially.

Highly efficient multipoint relay selections in link state QoS routing protocol for multi-hop wireless networks

In this paper, we propose three heuristics for highefficiency selections of MPRs (multipoint relays) in link state QoS routing protocol: MIMS (maximizing integration metric selection), MQES (maximizing QoS-efficiency selection), and MCIS (minimizing cost-inefficiency selection). The basic approach of these selections is to determine a smaller set of MPRs that provide better QoS paths between any two nodes. The main objective in doing so is to maximize the QoS (quality of service) effect while limiting routing overhead for flooding control traffic. In addition, we evaluate the performance of the routing protocols with the proposed selections by simulation. The results indicate that the proposed methods achieve high-efficiency selection; as compared to an existing MPR selection taking into account the QoS requirements, MIMS reduces the maintenance cost by 30%, while the throughput of the resultant path is decreased by 13%, and MCIS reduces the cost by 21% without any decrease in the throughput.

WiFi AP-RSS Monitoring Using Sensor Nodes toward Anchor-Free Sensor Localization

Sensor localization is one of the big problems when building large scale indoor sensor networks since GPS is unavailable in indoor environments. Many indoor localization systems have been proposed to tackle the sensor localization problem, yet user cooperation or many anchor nodes are required. In this paper, we propose a sensor localization system using WiFi APs as anchors. WiFi APs are largely installed in indoor environments and are managed by a network system manager. Using WiFi APs as anchors, we can localize sensor nodes without newly deployed anchor nodes. As a first step of our sensor localization system, this paper presents a WiFi AP-RSS monitoring system using sensor nodes. Sensor nodes are equipped with IEEE802.15.4 (ZigBee) modules, which cannot demodulate WiFi (IEEE802.11) signals. We therefore developed a cross-technology signal extraction scheme on sensor nodes. We herein describe the design and implementation of our AP-RSS monitoring system. The experimental evaluations show that our AP-RSS monitoring system successfully retrieves AP-RSS with an average error of 1.26dB.

AP-assisted CTS-blocking for WiFi-ZigBee Coexistence

WiFi interference is one of the big problems in ZigBee-based sensor networks. In this paper, we present a new WiFi-ZigBee coexistence scheme named AP-assisted CTS-blocking (AA CTS-blocking). The AA CTS-blocking uses an RTS/CTS (request to send, clear to send) mechanism to prevent WiFi transmissions during ZigBee communications. An RTS/CTS mechanism is defined in the IEEE 802.11 standard and is supported by off-the-shelf WiFi devices. We present the design and implementation of AA CTS-blocking utilizing an off-the-shelf WiFi device as it is. The experimental evaluations revealed that AA CTS-blocking reduced frame error rate (FER) by approximately 5% compared to an existing WiFi-ZigBee coexistence scheme.