arXiv subjects

Kiichi Tokuyama

Publications and source records attributed to Kiichi Tokuyama.

4 recordsLinked to original sources

arXiv2026

Dynamic Modeling of Target Cell Location for Mobility Robustness Analysis in Cellular Networks: Technical Report

Mobility robustness optimization (MRO) requires an appropriate selection of handover (HO) parameters such as the time-to-trigger (TTT) and offset margin to balance HO failures and ping-pong HOs. Existing stochastic geometry-based analyses for MRO have treated the angular position of the target base station (BS) as uniformly distributed over a feasible region. However, this treatment does not explicitly capture the spatial distribution of the target BS dynamically selected as a user equipment (UE) moves through the network. In this paper, we develop a stochastic geometry-based analytical framework for MRO in sub-6 GHz cellular networks. We derive the distribution of the HO triggering time and the spatial distribution of the dynamically selected target BS under straight-line UE mobility. Based on these distributions, we formulate too-late HO and ping-pong HO events as mutually exclusive events and analytically derive their probabilities. Numerical results validate the analysis, demonstrate improved accuracy over the conventional uniform-angle model, and reveal the tradeoff between the two HO events and the dependence of the optimal TTT on BS density.

cs.NI↗

arXiv2023

Periodic handover skipping in cellular networks: Spatially stochastic modeling and analysis

Handover (HO) management is one of the most crucial tasks in dense cellular networks with mobile users. A problem in the HO management is to deal with increasing HOs due to network densification in the 5G evolution and various HO skipping techniques have so far been studied in the literature to suppress excessive HOs. In this paper, we propose yet another HO skipping scheme, called periodic HO skipping. The proposed scheme prohibits the HOs of a mobile user equipment (UE) for a certain period of time, referred to as skipping period, thereby enabling flexible operation of the HO skipping by adjusting the length of the skipping period. We investigate the performance of the proposed scheme on the basis of stochastic geometry. Specifically, we derive analytical expressions of two performance metrics -- the HO rate and the expected downlink data rate -- when a UE adopts the periodic HO skipping. Numerical results based on the analysis demonstrate that the periodic HO skipping scenario can outperform the scenario without any HO skipping in terms of a certain utility metric representing the trade-off between the HO rate and the expected downlink data rate, in particular when the UE moves fast. Furthermore, we numerically show that there can exist an optimal length of the skipping period, which locally maximizes the utility metric, and approximately provide the optimal skipping period in a simple form. Numerical comparison with some other HO skipping techniques is also conducted.

cs.IT↗

arXiv2020

Correlation Coefficient Analysis of the Age of Information in Multi-Source Systems

This paper studies the age of information (AoI) on an information updating system such that multiple sources share one server to process packets of updated information. In such systems, packets from different sources compete for the server, and thus they may suffer from being interrupted, being backlogged, and becoming stale. Therefore, in order to grasp structures of such systems, it is crucially important to study a metric indicating a correlation of different sources. In this paper, we aim to analyze the correlation of AoIs on a single-server queueing system with multiple sources. As our contribution, we provide the closed-form expression of the correlation coefficient of the AoIs. To this end, we first derive the Laplace-Stieltjes transform of the stationary distribution of each AoI for the multiple sources. Some nontrivial properties on the systems are revealed from our analysis results.

cs.PF↗

arXiv2020

Time-based Handover Skipping in Cellular Networks: Spatially Stochastic Modeling and Analysis

Handover (HO) management has attracted attention of research in the context of wireless cellular communication networks. One crucial problem of HO management is to deal with increasing HOs experienced by a mobile user. To address this problem, HO skipping techniques have been studied in recent years. In this paper, we propose a novel HO skipping scheme, namely, time-based HO skipping. In the proposed scheme, HOs of a user are controlled by a certain fixed period of time, which we call skipping time. The skipping time can be managed as a system parameter, thereby enabling flexible operation of HO skipping. We analyze the transmission performance of the proposed scheme on the basis of a stochastic geometry approach. In the scenario where a user performs the time-based HO skipping, we derive the analytical expressions for two performance metrics: the HO rate and the expected data rate. The analysis results demonstrate that the scenario with the time-based HO skipping outperforms the scenario without HO skipping particularly when the user moves fast. Furthermore, we reveal that there is a unique optimal skipping time maximizing the transmission performance, which we obtain approximately.

cs.NI↗