The use of mobile data is rapidly increasing along with the popularity of smartphones and tablets. The use of indoor data, especially, is expected to be further increased. Indoor cell evolved Node Bs (eNBs) are being installed and they are expected to increase the areas overlaid by indoor and outdoor cells to offload indoor mobile data. We confirmed increases in the handover (HO) failure rates from our analysis of field measurements due to rapid drops in communication quality when user equipment (UE) moved through the doors of a building. If HO failure occurred, the quality of experience (QoE) for real-time applications, e.g., voice over Internet protocol (VoIP) and streaming, degraded due to service interruptions and rebuffering. Thus, it was important to reduce the HO failure rates and disconnection times due to HO failure. We propose a scheme of dual HO triggers that improves the performance of HO from/to an indoor cell while maintaining that of HO between outdoor cells. The proposed scheme introduces events to UE measurement reports to detect rapid drops in communication quality in addition to conventional events that are optimized to the HO between outdoor cells. LTE simulations confirmed that the new HO trigger prevented UE from going out-of-synchronization before the completion of the HO process. The simulation results indicated that the proposed scheme improved indoor-cell-related QoE. More specifically, the number of dropped calls reduced by 87%, the number of service interruptions for VoIP reduced by 92%, and the HO failure rate reduced by 23 points. Moreover, the proposed scheme also improved outdoor-cell-related QoE. In short, it significantly improved QoE by reducing HO failure rates in indoor and outdoor cell environments.

Mobility Robustness Optimization (MRO), i.e. self-optimization of handover (HO) parameters, is a key driver for expanding Heterogeneous Networks (HetNet) while suppressing the need for drive tests. 3GPP Long Term Evolution (LTE) has introduced a scheme for MRO that enables the eNB, i.e. a base station, to detect HO failures while coordinating with other eNBs via the X2-interface (X2-Intf). However, neighboring eNBs do not always have X2-Intf because of technical constraints. In this paper, we propose an inter-eNB coordination-free algorithm for MRO. The algorithm adjusts the Cell Individual Offset (CIO) on the basis of ping-pong HOs and HO failures that are detected by monitoring HO related signaling via interfaces other than X2-Intf. LTE HetNet simulations confirmed that the algorithm was resistant to the detection error of HO failures and its HO performance was comparable to that of an algorithm using X2-Intf. Moreover, the proposed algorithm reduced the total number of HO failures from pico cells by 33% while keeping the ping-pong HO rate at an acceptable level, even with quasi-optimal default settings. The HO performance from the macro cells always had good quality, irrespective of whether the proposed algorithm was used or not.

Self-optimization of the neighbor cell list (NCL) is expected to improve handover performance and reduce the need for site surveys. 3GPP Long Term Evolution (LTE) has introduced automatic neighbor relation (ANR), which enables a base station to manage neighbor cells on the basis of measurements made by mobiles. Because the radio coverage changes during network operations, it is essential to immediately update the NCL to improve handover performance, especially when the number of measured neighbor cells exceeds the upper limit of NCL size. In this paper, we propose a dynamic NCL management scheme to enhance NCL convergence and alleviate missing neighbor problems. The proposed scheme gives higher priority to newly detected neighbor cells over existing cells and ensures fast and accurate NCL updates after radio coverage changes. According to the LTE network simulations, the proposed scheme provides 70% faster recovery of the average radio link failure rate due to the missing neighbors compared with the non-prioritized scheme. It was also confirmed that the duration of missing neighbors is reduced by 39% on average.

Sporadic network quality problems in a cellular network become prevalent after the initial rollout phase. Such problems occur in limited area of the service coverage and they are often revealed only by on-site measurement or customer feedback. Therefore, their quantitative analysis is difficult. They must therefore be solved individually under time and cost restrictions. We propose a simulation-based framework for solving these problems efficiently. A prototype system based on this framework was developed that supports fast simulation and three-dimensional visualization of radio quality and coordinated analysis of radio quality data and operational statistics. Using our system, we devised and implemented countermeasures (neighbor cell list optimization and antenna tilt tuning) for sporadic network quality problems in part of a commercial 3G cellular network in Hong Kong. The countermeasures mitigated these problems and improved the related key network indicators by as much as 60%.

With the proliferation of mobile-network services, mobile networks have become one of the core social infrastructures and are therefore required to operate stably. Conventional mobile-network-management systems can detect and recover from faults according to previously formulated rules. However, such semi-static rules are vulnerable to large variation in quality of networks and to sudden increases in traffic, which are inherent to radio access networks. Maintenance personnel often had to perform case-by-case analyses for the vast numbers of abnormal cases and such analyses and creation of rules may have taken more time when new faults appeared. In addition, providing network elements timely is essential to maintaining network quality but it is becoming more difficult as mobile networks become larger and more complicated. To overcome these problems, we have developed a system that enhances the conventional UMTS Terrestrial Radio Access Network (UTRAN) management system of mobile networks and improves stability during network operation. In this paper, we present main features of the system and its fundamental technologies: fault detection based on statistical reliability, root-cause analysis of the fault, a rule editor easy to create and modify fault-analysis rules for maintenance personnel, and guidance on expansion based on long-term analysis of trends. We tested this system then confirmed it could reduce fault-detection errors in a conventional management system through theoretical calculations and trials in a cellular mobile network.

With the increase in cell-phone business communications, SLA-based contracts with cellular network operators assure the consumer of better quality communications. However, today's cellular networks can only differentiate the service quality amongst user groups in emergency situations. This paper presents a mobile SLA framework that provides a service quality guarantee for corporate cellular phone users. We propose a multi-stage dynamic partitioning (MSDP) call admission control scheme to allocate radio resources efficiently amongst the different users and service types. The simulation results demonstrate that MSDP can maintain the service quality at the level required in a typical SLA cycle, and that service is always available for all user types.

We have experimentally demonstrated two- dimensional (2-D) photonic crystal (PC) waveguides (WGs) such as straight, bent, Y-branch, directional coupler (DC), and quantum dots (QDs)-based nonlinear optical (NLO) WGs using a GaAs air-bridge membrane with triangular-lattice line-defect WGs. These WGs are necessary for a 2-D PC-based symmetric Mach-Zehnder (PC-SMZ) type ultrafast all-optical switch. Experimental results on the clear observation of the optical interference at the Y-junction DC, nonlinearity-induced phase shift at the NLO waveguide, and transmission spectra in the total PC-SMZ WG configuration will be addressed, as well as measured results on each WG element.

A scalable MPEG-4 video codec architecture is proposed to achieve low power consumption and high cost-effectiveness for IMT-2000 multimedia applications. The MPEG-4 video codec consists of a 16-bit multimedia-extended RISC processor and dedicated hardware accelerators, which bring about both low power consumption and programmability. The proposed architecture is extended and applied for the development of two MPEG-4 LSIs. One is an MPEG-4 video codec LSI, which performs an MPEG-4 video encoding and decoding at 15 frames per second with quarter common intermediate format. The other is an MPEG-4 audiovisual LSI, containing three 16-bit RISC processors and a 16-Mbit embedded DRAM, executes the major functions of 3GPP 3G-324M video telephony for IMT-2000 applications. By introducing the optimization of the embedded DRAM configuration, clock gating technique, and low power motion estimation, the MPEG-4 audiovisual LSI consumes only 240 mW when it activates MPEG-4 video SP@L1 codec, the AMR speech codec, and the H.223 annex B multiplex at 60 MHz clock rate.

A high-speed workstation network system which interconnects distributed workstations and servers through a 100 Mbps optical LAN employing the OSI protocol is developed. The network throughput is maximized by employing a newly developed intelligent high-speed network controller consisted of a 100 Mbps token-ring processor(TRP) and 32-bit MPU which executes all the 7-layered OSI protocol. The remote retrieval capability of database of the system is theoretically confirmed and is experimentally proved.>