Kosei Kobayashi

Dynamic Neighbor Cell List Management for Handover Optimization in LTE

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.

UTRAN O&M support system with statistical fault identification and customizable rule sets

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.

Radio quality prediction based on user mobility and radio propagation analysis

The increasing number of wireless communications applications in mission critical tasks and lifeline areas demand increased wireless communications reliability. Radio quality prediction for mobile terminals will play a key role in enhancing this reliability. Time-series radio quality prediction (TSRP) methods, which predict future radio quality based on past radio quality measurements, have been proposed in the past. However, TSRP methods are difficult to apply to urban areas where fluctuations of radio quality are too large to make long-term predictions. On the other hand, movement of people is easier to predict because people tend to move toward certain destinations along streets. We propose a mobility-based radio quality prediction (MBRP) method that predicts future radio quality based on user mobility and radio propagation analysis. Evaluation results in single-hop and multi-hop wireless environments show that MBRP can achieve a prediction period more than two times longer than TSRP. We also introduce a prototype system that demonstrates the feasibility of MBRP.

A Radio Network Co-design System for Planning, Operation, and Customer Relations Divisions

Radio network planning after the initial rollout phase has a multitude of individual coverage and capacity problems. Such problems are often exposed by customer complaints or performance indicator degradations, so cooperation among network planning, operation, and customer relations divisions will help to more effectively improve network quality. In this paper, we propose to introduce radio network co-design by multiple divisions for sharing their issues and discussing possible solutions in the same place. To realize network co-design, we developed methods of 3D visualization of radio quality for enhancing comprehension of geographically dependent radio problems, high-speed prediction of radio propagation for interactive network planning, and estimation of radio resource usage for mutual understanding of the outcome of radio planning. Finally, we demonstrate an interactive wireless network design prototype system based on these methods.

Individually targeted radio network optimization

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%.