Takayuki Warabino

Broadcast methods for inter-vehicle communications system

This paper presents novel broadcast methods for an inter-vehicle communications system for ITS. During inter-vehicle communications, it is essential that emergency information be broadcast to surrounding vehicles. Emergency information such as emergency-vehicle-approach information and traffic accident information are needed by vehicles in a particular area. By limiting the broadcast direction, the proposed methods can provide broadcasts to a particular area and avoid mistakenly notifying other areas where the information is not needed. We developed a simulation and experimental system for the proposed method and confirmed that the information is broadcast to the desired area.

BBU-RRH switching schemes for centralized RAN

Mobile data traffic has been increasing at a rapid pace over the past few years due to the rise of both smartphones and tablets. Small cell deployments are one of the most effective ways to increase system capacity by improving the spatial reuse of radio resources for the explosive increase in traffic loads. However, it leads to be a large cost impact for operators. Centralized RAN (C-RAN) has been proposed, which has the potential ability to reduce network costs due to reductions in civil work and/or electricity costs at local base station sites by centralizing baseband units to the center side. Moreover, C-RAN can be expected to further reduce network costs using baseband unit (BBU) pooling functions in which the centralized BBU resources can be dynamically allocated to remote radio heads (RRHs) depending on traffic load. This paper proposes semi-static and adaptive BBU-RRH switching schemes for C-RAN and evaluates their effectiveness through simulations. Under conditions of 100 RRHs, here, a RRH is comparable to a cell, and traffic distribution with a typical traffic profile in office (business) area, we confirmed that the number of BBUs can be reduced by 26% and 47% for semi-static and adaptive schemes, respectively, compared with conventional cell deployment.

Device Authentication and Registration Method Assisted by a Cellular System for User-Driven Service Creation Architecture

Personal devices and access systems have recently become more diversified, and there is a need for technology that enables users to flexibly and securely create their own private services in a user-driven manner, utilizing the presently available access systems and devices. To this end, the authors have designed User-driven Service Creation Architecture (USCA). It enables users to create a secure private network as a substrate for such services. This network is called a Personal Network (PN) and is an extension of the concept of Personal Area Network (PAN). It is organized by the personal devices related to services that users wish to enjoy or offer. This paper focuses on the security issue of USCA: how to certify the eligibility of users or devices wishing to join a PN. It proposes a device authentication and registration method, with the assistance of cellular systems, IMS/MMD (IP Multimedia System/ MultiMedia Domain). By means of this method, users can bind the correctness of devices to their cellular phone, and can thus create secure PNs only with solicited devices.

Advanced load balancing in LTE/LTE-A cellular network

Due to the nature of mobile communications, traffic load is not equal throughout the cellular network. While much traffic is concentrated on a specific cell (i.e., called a hotspot cell), the traffic load on adjacent cells is often low. To efficiently accommodate the imbalance in traffic, load balancing (LB) between base stations has attracted attention in recent years. This paper proposes an advanced LB method for LTE/LTE-A cellular networks which utilizes exiting mechanisms such as handover parameter control (HPC) and cell coverage control (CCC). Since the two mechanisms have advantages and disadvantages, the proposed method selects the appropriate LB method according to the situation. The paper presents overall procedures and a detailed selection algorithm to maximize the offloading effect on the hotspot cell with avoidance of interference on surrounding cells. In addition, through a simulation, we confirmed that 1) the proposed method could achieve higher offloading effect than the native HPC by 20% of cell capacity and that 2) it could avoid interfering with the surrounding cells compared to CCC when the traffic load on the hotspot cell is relatively low.

Secure Data Sharing in Mobile Environments

This paper proposes an approach for secure data sharing on mobile terminals with members of a particular group. To avoid the data being compromised due to loss or theft, this approach prevents data leakage, while allowing the correct members to recover the data to a new mobile terminal thanks to cooperation between a mobile terminal and a network server. The fundamental concept used to achieve data security involves applying data encryption and secret sharing of the encryption key. In addition, this approach newly introduces a key encapsulation mechanism (KEM) and threshold cryptography. The approach also combines the use of a data protection approach, based on a secret sharing scheme, in order to achieve an efficient data reading process. Once one of the members reads the data, he/she need not use threshold cryptography to reconstruct the encrypted key, but instead uses a secret sharing scheme. This paper confirms the potential of this approach via the prototype implementation onto a mobile phone.

Adaptive media switching for future vehicle-to-vehicle communication

Vehicle-to-vehicle (peer-to-peer) communication is expected to play an important role in ITS (intelligent transport systems). This paper proposes an adaptive media switching method for future vehicle-to-vehicle communication. Our method adopts an approach to select the most suitable radio communication media from several possible types based on the vehicle locations, available media and communication quality. Before the network configuration of inter-vehicle and roadside-vehicle communication changes, the vehicle detects it and then initiates the media reselection. During such media switching, our proposed HTTP-based session layer mobility avoids any interruption of communication. We conducted field tests using several experimental vehicles. The results verify that our proposed method is effective in selecting the most suitable media, and disconnection of communication during the media switching is also avoided

Basic Design of a User-Driven Service Creation Platform Assisted by Cellular Systems

In spite of recent advances of personal communication devices and access network technology, users are still facing the issues such as high device maintenance costs, complication of inter-device cooperation, illegal access to devices, and leakage of personal information. Consequently, it is difficult for users to securely construct a network with local as well as remote personal devices. We propose a User-driven Service Creation Platform (USCP), which enables users to construct a secure private network in a simple and intuitive way, making the most of the authentication mechanism in cellular networks. USCP separates signaling and data paths in a flat structure of a virtual network topology. In this paper, we describe the basic design of USCP.

Load sharing of location-based routing in overlay networks

This paper proposes a load sharing method of location-based routing in overlay networks. In previous works, the authors have proposed location-based routing, in which a sender designates the destination location (e.g. latitude and longitude) in packets and the overlay network delivers the packets to receivers residing in the designated location. While overlay network technologies facilitate the network deployment of robust distributed systems, proprietary identifier composition achieves high performances in an overlay server. This paper focuses on a load sharing method to enhance the scalability of previous works. With this method, when the number of receivers registering a single service exceeds a certain threshold, the server delegates the handling of a portion of receivers to other servers. This paper defines the design policies and also shows their applicable protocol sequence. For example, while tree-based identifier partitioning ensures compatibility with existing mechanisms, the selection method applied to the designated servers avoids a long detour for packet transmission etc. This paper also discusses performance evaluations on a developed test-bed system. Evaluations confirm that the proposed method improves system throughput and eases processing burden in an overlay server for large-scale information delivery.

A Lightweight Approach to Protect Mobile Data

This paper proposes a lightweight approach for protecting data on mobile terminals by improving our former approach [Warabino et al., 2006]. In order for the data not to be compromised due to loss or theft, our approach prevents data leaks and allows the correct user to recover the data to a new mobile terminal thanks to cooperation between a mobile terminal and a network server. The fundamental concept used to achieve data security involves applying data encryption and secret sharing of the encryption key. The master share is newly introduced to generate all the encryption keys for data on a mobile terminal. A user simply need reconstruct the master share onto a new mobile terminal to recover the environment of that lost. We confirmed the effectiveness of our approach through the implementation of both approaches onto a mobile phone.

Proposal of ID Composition for Fast Location Lookup in Overlay Nodes

This paper proposes an ID composition for fast location lookup in overlay nodes. In the paper, we assume a location-based routing system constructed on an overlay network. While the overlay approach facilitates network deployment, recent DHT (Distributed Hash Table) technologies allow us to construct robust and high-scalable distributed systems. The point of our proposal is how to map physical location with ID space in DHT. The proposed ID composition realizes fast location lookup only by bit comparisons of IDs. Performance evaluations show that the processing time of location lookup is less than 5 microseconds, even when the number of registered locations is 1 million. The ID composition also allows unicast and multicast transport operations to support both service discovery and information delivery. In addition, this paper discusses how to effectively conduct information delivery within a circular area. Two rules, such as the 4-packet rule and rectangle rule, reduce communication traffic between overlay nodes and receivers to be one third of the simplest method.