A wireless communications system with a transmission speed of 18 Mbit/s is presented using the 2.4 GHz ISM band. This system employs the Carrier Frequency Offset-Spread Spectrum (CFO-SS) scheme and the Dual-Polarization Staggered Transmission (DPST) scheme. The 18 Mbit/s CFO-SS system (named CFO-SS18) was developed and its performance evaluated in fields. In this paper, the detailed operating principle of CFO-SS and DPST schemes, together with the specifications and structures of CFO-SS18, are presented. Results of indoor and field tests obtained by using CFO-SS18 are also presented.

This paper presents experimental results of a future road-to-vehicle communications system with handover function. The proposed handover scheme, based on the current Dedicated Short Range Communication System (DSRC) standard (ARIB STD-T75) in Japan, maintains the continuity of data transmissions over multiple radio zones by transferring received and remaining data between base stations located along the roadside. Moreover, a link connection/disconnection method is newly proposed to avoid repetition of link connection and disconnections around the cell entrance and to actualize smooth handover between cells. The proposed method determines the link connection and disconnection timing by measuring the received signal strength and observing the results of CRC (Cyclic Redundancy Code) error checks of the control channel. By applying the proposed method to mobile stations (MS) in the DSRC system, the communication link between the MS and the base station (BS) can be smoothly connected. Field experiments were conducted to evaluate the performance and validity of the proposed methods using actual equipment. Experimental results show that the proposed methods perform a smooth link connection between cells and achieve a very short handover processing delay of less than 42 milliseconds.

The authors propose a user-centric seamless handover (HO) scheme, which is a kind of a vertical HO from a new perspective, toward a next generation network where heterogeneous access networks converge. The users' experience-oriented scheme allows users to enjoy the optimal service quality for real-time applications in respective access networks. In addition, the scheme sustains on-going sessions during the vertical HO. The proposed scheme consists of two methods -- the bicasting of Different Quality-level Streams (DiffQS) and the Delay Difference Absorption (DDA) method. Initially, the authors propose two plausible methods for the SIP-based bicasting of DiffQS. This document introduces a SIP-capable network element named the HO Assistive Server (HOAS). HOAS controls bicasting of DiffQS and provides users with the optimal service quality for real-time applications via respective access networks as well as avoiding packet loss during HO. The DDA method is also proposed to prevent a service interruption and smoothly continue a real-time service during HO. Evaluation results show that the scheme achieves the seamless service continuity from the users' perspective for HO between cellular and high-speed wireless access via the implementation of a prototype system.

CR (Cognitive Radio) is a technology that can realize more intensive and efficient spectrum use through spatial and temporal utilization. In the context of mesh networks where each base station consists of heterogeneous multi-radio interfaces, packet switch in L2/L3 of each base station selects each radio interface and channel adaptively in order to take full advantage of all multiple heterogeneous interfaces. At first, this paper examines the achievable performance of the new packet switch schemes in mesh topology. Secondly, we investigate the potentiality of dynamic base station relocation approach in order to cope with the change of terminal traffic distribution, and show the impact of packet switch policy on dynamic base station relocation.

In OSI management, we utilize a scope parameter in Common Management Information Service (CMIS) that enables us to operate multiple Managed Objects (MOs) at one CMIS operation, so that we may reduce the number of communications between a manager and an agent. The more the number of MOs increases, the harder it is to find optimal combinations of scopes. In an existing approximation algorithm for finding optimal combinations of scopes, there are restrictions on the structure of a naming tree for the algorithm to work efficiently and the lower bound of its approximation ratio, n/4, grows in proportion to the number of MOs, n. This paper proposes a new approximation algorithm that removes the restriction on the structure of a naming tree and significantly improves the approximation ratio to (1 + ln n) in the upper bound, by keeping the same time complexity as the existing algorithm.

Network monitoring is one of the most significant functions in network management to understand the state of a network in real-time. In SNMP (Simple Network Management Protocol), polling is used for this purpose. If the time interval for two consecutive polling requests is too long, then we cannot understand the state of the network in real-time. Conversely, if it is too short, then the polling message traffic increases and imposes a heavy load on the network. Many dynamic polling algorithms have been proposed for controlling the increase in the polling message traffic. However, they cannot keep track of the time variations of management information values, since their main objectives are to check whether or not a network node is active and the next polling interval is determined being independent of the time variations of the values. The existing polling algorithms are thereby not applicable to the case where monitoring the time variation of management information values is critical. This paper proposes a new dynamic polling algorithm which, by making use of Discrete Fourier Transformation, enables not only to control the increase in the polling message traffic but also to keep track of the time variations of network management information values. We show the availability of the proposed algorithm by evaluating it through both simulations and experiments in actual network environment.

This paper discusses a design and an implementation of a MIB tester, a conformance test tool of Management Information Base (MIB) for TMN. A remote test method is used as a practical test configuration. We classify test purposes into three; basic interconnection test, capability test and behaviour test. Test items for the capability test are defined according to Managed Object Conformance Statement (MOCS) and Managed Relationship Conformance Statement (MRCS). Test items for the behaviour test is defined according to GDMO BEHAVIOUR clause. The MIB tester automatically generates test scenarios for capability tests, which are also used as those for the basic interconnection test, and supports the scenario creation of the behaviour test in an user-friendly manner. We evaluate the implemented MIB tester through its application to the actual TMN agents.

For backup of failed VPs (Virtual Paths) in ATM (Asynchronous Transfer Mode) networks, many self-healing algorithms have already been proposed. However, since the existing algorithms recover each failed VP with a single backup VP, a problem arises in that those algorithms cannot necessarily provide a failed VP having a higher recovery priority with a larger recovery ratio, which is the ratio of the bandwidth of a backup VP to that of a failed VP. For a solution to the problem, this paper proposes a new self-healing algorithm which recovers each failed VP with one or more backup VPs. We also evaluate its availability by comparing with an existing algorithm through simulations.