Faculty Profiles - TOMISATO Shigeru

A Study of Mobile Path Loss Estimation Models for a Sloping Terrain Area in Cellular Systems

Tomohiro Ohira, Takanori Hirai, Shigeru Tomisato, Masaharu Hata

18TH ASIA-PACIFIC CONFERENCE ON COMMUNICATIONS (APCC 2012): GREEN AND SMART COMMUNICATIONS FOR IT INNOVATION 472 - 477 2012

Language：English Publisher：IEEE

Mobile path loss estimation models for small cell area on a sloping terrain become important function in the radio link design of cellular systems. Okumura and Lee models are known for the sloping terrain path loss estimation, but the applicable cell size is lager than today's small cell area with less than 1.5km radius. Recently, a new estimation model called Fujitani model has been proposed for such a small cell including sloping terrain area. However, there were no comparison discussions about the estimation by the other models. In this paper, the path loss estimation comparisons by Okumura, Fujitani, and Lee models are discussed based on the same data measured in a typical short distance sloping terrain area. The result shows that Fujitani model is prospective for such sloping terrain path loss estimation in a small cell, but further measurement studies in various slope terrain areas and additional parameter considerations are needed to realize general applicability.

DOI： 10.1109/APCC.2012.6388183

Web of Science

An extension of clustering algorithm for smart-antenna use in wireless mesh networks

Shigeto Tajima, Nobuo Funabiki, Shigeru Tomisato, Masaharu Hata, Teruo Higashino

1st IEEE Global Conference on Consumer Electronics 2012, GCCE 2012 638 - 642 2012

Language：English

As a scalable cost-efficient Internet-access network, we have studied the Wireless Internet-access Mesh Network (WIMNET) that is composed of multiple access point (APs) connected through the Wireless Distribution System (WDS). Because all the traffics pass through an Internet Gateway (GW), the resolution of link congestions around the GW is very important. To solve this problem, we have proposed a clustering algorithm to partition the APs into a set of clusters where each cluster consists of the APs sharing the same GW. In addition, we have considered the use of a smart antenna at a special AP called a Smart AP (SAP). In this paper, we extend this clustering algorithm for smart antenna use at SAPs. Besides, we investigate the link activation strategy for the smart antenna, because it allows a variety of link activations for packet transmissions. We evaluate the effectiveness through simulations using the WIMNET simulator. © 2012 IEEE.

DOI： 10.1109/GCCE.2012.6379939

Scopus

Non-Linear Distortion Noise Control for Spectrum Sharing Systems

OKAMOTO Seiichiro, TOMISATO Shigeru, FUJII Hiromasa, HATA Masaharu, MIURA Shunji, KAYAMA Hidetoshi

Technical report of IEICE. RCS 111 ( 345 ) 165 - 170 2011.12

Language：Japanese Publisher：The Institute of Electronics, Information and Communication Engineers

Recently, a spectrum sharing method between wireless communication systems has been studied to use frequency resources with much higher efficiency. In general, different systems for spectrum sharing have different system bandwidths. Therefore, spectrum sharing systems such that a low-priority system has wider frequency bands than a high-priority system should be considered. In such spectrum sharing environments, reducing transmission power of the low-priority system in partial frequency bands overlapped with the high-priority system is considered to work effectively so as to avoid harmful interference to the high-priority system. This paper proposes a non-linear distortion noise control method based on a clipping and filtering method for the low-priority system to improve reception quality degradation which occurs in shared bands whose transmission power is reduced. The proposed method adaptively controls distortion noise power in shared bands with transmission power control according to the amount of the reduced power. In this paper, optimal clipping levels, required parameters in the proposed method, are investigated, and then the spectrum property and BER performance with the optimal clipping levels are evaluated by computer simulations. The results confirm that the proposed method can significantly improve reception quality of the low-priority system in shared bands with transmission power control.

A Clustering Algorithm for WDS Clusters with Two Access-Points Using Smart Antenna in Wireless Mesh Networks

TAJIMA Shigeto, FUNABIKI Nobuo, TOMISATO Shigeru, HATA Masaharu, HIGASHINO Teruo

Technical report of IEICE. RCS 111 ( 345 ) 81 - 86 2011.12

Language：Japanese Publisher：The Institute of Electronics, Information and Communication Engineers

As a scalable Internet access network, we have studied the Wireless Internet-access Mesh Network (WIMNET) that is composed of multiple access point (APs) connected through the Wireless Distribution System (WDS). For large scale WIMNET, because the traffic through the Internet gateway (GW) becomes very high, it is composed of multiple WDS clusters where one cluster consists of APs sharing the same GW. Even in this hierarchial WIMNET, links around the GW are still crowded in each WDS cluster and may become bottlenecks of whole communications. Hence, we have proposed the adoption of a Smart AP (SAP) using the smart antenna technology for bandwidth enhancements. In this paper, we propose an extension of our WDS clustering algorithm for WIMNET such that the GW and one adjacent AP are selected as SAPs in each WDS cluster. Through simulations using grid topology instances, we verify the effectiveness of our algorithm extension.

A WDS Clustering Algorithm for Wireless Mesh Network with Gateway using MIMO Channel

B-5-79 Inter-Sub-Carrier Interference Power Evaluated by Sub-Carrier Spacing of Spectrum Sharing Systems

SAEKI Takuya, TOMISATO Shigeru, FUJII Hiromasa, HATA Masaharu, MIURA Shunji, KAYAMA Hidetoshi

Proceedings of the Society Conference of IEICE 2011 ( 1 ) 458 - 458 2011.8

B-5-20 Non-Linear Distortion Noise Reduction for Spectrum Sharing Systems

OKAMOTO Seiichiro, TOMISATO Shigeru, FUJII Hiromasa, HATA Masaharu, MIURA Shunji, KAYAMA Hidetoshi

Proceedings of the Society Conference of IEICE 2011 ( 1 ) 399 - 399 2011.8

TAJIMA Shigeto, FUNABIKI Nobuo, TOMISATO Shigeru, HATA Masaharu, HIGASHINO Teruo

IEICE technical report 111 ( 8 ) 55 - 60 2011.4

Language：Japanese Publisher：The Institute of Electronics, Information and Communication Engineers

We have studied the Wireless Internet-access Mesh NETwork (WIMNET) as a scalable wireless local area network that is composed of multiple access points (APs) connected through the Wireless Distribution System (WDS). To avoid the performance degradation due to traffic overloads, the number of APs in a single WDS is limited. Hence, we have proposed a WDS clustering algorithm to partition a given set of APs into a disjoint set of WDS clusters where the APs in one WDS cluster shares a single gateway (GW) to the Internet and are connected by a single WDS. As all the traffics from/to the Internet pass through the GW in a WDS cluster, links incident to the GW can be bottlenecks of whole communications. In this paper, in order to increase the throughput there by adopting the MIMO channel at the GW, we propose an extension of the WDS clustering algorithm to the WIMNET with the MIMO channel GW. Through simulations using several instances, we verify the effectiveness of our algorithm extension.

B-5-105 Interference Power Regrowth of Spectrum Sharing Systems with Non-Linear Distortion

SAEKI Takuya, TOMISATO Shigeru, FUJII Hiromasa, HATA Masaharu, MIURA Shunji, KAYAMA Hidetoshi

Proceedings of the IEICE General Conference 2011 ( 1 ) 491 - 491 2011.2

An Iterative Peak Power Reduction Method with Adaptive Intermediary Over-Sampling for Wireless OFDMA Systems

Kazuhiko Fujimoto, Shigeru Tomisato, Masaharu Hata, Hiromasa Fujii

IEICE TRANSACTIONS ON COMMUNICATIONS E94B ( 2 ) 576 - 579 2011.2

Language：English Publisher：IEICE-INST ELECTRONICS INFORMATION COMMUNICATIONS ENG

This paper proposes an iterative peak power reduction method with adaptive intermediary over-sampling which uses the necessary minimum bandwidth according to iteration number for wireless OFDMA systems. The required bandwidth to each iteration number is evaluated by computer simulation, and over-sampling numbers in iterative processing are controlled by using the simulation results. The results show that the required bandwidth is 1.6, 2.0, and 2.7 times of the used signal bandwidth at the iteration number of 1, 2, and 3, respectively. The proposed adaptive over-sampling method can reduce its multiplication number by 13%.

DOI： 10.1587/transcom.E94.B.576

Web of Science

Sensor Collaborative Beam Forming with Low-Complexity Signal Processing

IEICE Transaction B J94-B ( 2 ) 137 - 146 2011

An extension of active access-point selection algorithm for throughput maximization in wireless mesh networks

Nobuo Funabiki, Junki Shimizu, Toru Nakanishi, Kan Watanabe, Shigeru Tomisato

Proceedings - 3rd IEEE International Conference on Intelligent Networking and Collaborative Systems, INCoS 2011 367 - 372 2011

Language：English

In order to offer an inexpensive, scalable Internetaccess wireless network, we have studied the architecture, protocols, and design optimizations of the wireless Internet-access mesh network (WIMNET) that adopts multiple access-points (APs) connected by wireless links. WIMNET can improve the dependability to failures of links and/or APs by allocating APs redundantly in the network field. Because redundant APs may increase the operational cost and degrade the throughput due to increasing radio interferences, only the necessary APs for the connectivity between the hosts and the Internet gateway should be activated in communications. Previously, we have defined the active AP selection problem of selecting the minimum number of active APs, and proposed its heuristic algorithm. However, the throughput should be maximized in WIMNET as a bandlimited wireless network, even if the number of active APs is slightly increased. In this paper, we propose the extension of the active AP selection algorithm for the throughput maximization using the average hop count. We confirm the effectiveness of our algorithm extension through simulations in three instances, where the throughput is improved by about 10% with 7-14 additional active APs on average. © 2011 IEEE.

DOI： 10.1109/INCoS.2011.50

Scopus

An active access-point selection approach for dependable wireless mesh networks

Nobuo Funabiki, Junki Shimizu, Masaharu Hata, Shigeru Tomisato, Toru Nakanishi, Kan Watanabe

Journal of Interconnection Networks 12 ( 3 ) 137 - 154 2011

Language：English Publisher：World Scientific Publishing Co. Pte Ltd

As an inexpensive, flexible, and scalable Internet-access wireless network, we have studied the architecture, protocols, and design optimizations of the Wireless Internet-access Mesh NETwork (WIMNET) that adopts multiple access-points (APs) connected through wireless links. WIMNET can improve the dependability to failures of APs and/or their links by allocating APs redundantly in the network field. Because redundant APs may increase the operational cost and degrade the throughput due to increasing radio interferences, only the necessary APs for connectivity between the hosts and the Internet gateway should be activated in communications. In this paper, we first define the active AP selection problem of selecting the minimum number of active APs, and prove the NP-completeness of its decision version through reduction from the known minimum set cover problem. Then, we propose an active AP selection algorithm of deactivating APs one by one until no more AP can be deactivated. Due to the limited transmission capacity in WIMNET, we further present an algorithm extension for throughput maximization. We verify the effectiveness of our proposal through simulations in three instances, where the number of active APs is reduced by more than 40% and the throughput is improved by more than 10% from the original in any instance. © 2011 World Scientific Publishing Company.

DOI： 10.1142/S0219265911002915

Scopus

Interference Properties of OFDMA Systems and under Spectrum Sharing Environment

A smart access-point selection algorithm for scalable wireless mesh networks

IAENG International Journal of Computer Science 38 ( 3 ) 260 - 267 2011

Interference power regrowth of spectrum sharing systems with non-linear distortion

The 7th IEEE VTS Asia Pacific Wireless Communication Symposium, APWCS 2011 MA1 1 - 5 2011

簡易な信号処理を用いるセンサ協調型ビーム形成法の検討

中野淳次郎, 駒田善紀, 冨里繁, 田野哲, 秦正治

電子情報通信学会論文誌B J94-B ( 2 ) 137 - 146 2011

A throughput evaluation of wireless Internet-access mesh network using MIMO and adaptive array antenna

Shigeto Tajima, Nobuo Funabiki, Shigeru Tomisato, Masaharu Hata, Teruo Higashino

The 2011 International Workshop on Smart Info-Media System in Asia (SISA 2011) 79 - 84 2011

FUKUDA Yuichiro, TOMISATO Shigeru, FUJII Hiromasa, HATA Masaharu, MIURA Shunji

IEICE technical report 110 ( 340 ) 233 - 238 2010.12

Language：Japanese Publisher：The Institute of Electronics, Information and Communication Engineers

This paper evaluates interference reduction effects by transmission power control (TPC) under spectrum sharing environment between different wireless systems in which an OFDMA system is assumed for the interfering system and the power density on a part of the interfering system band is reduced. The results of the computer simulations show that the undesired spectrum regrowth is caused by inter-sub-carrier interference, which results in degradation of interference reduction effects, and it is larger around the both ends of the TPC band. The spectrum regrowth on the TPC band is less than 1dB from the set transmission power density except 16 sub-carriers close to the band with default power density, when the transmission power density of the TPC band is 20 dB below the default density. On the other hand, the spectrum regrowth becomes more than 5 dB even around the center of the TPC band, when the transmission power density is reduced by -40 dB. Moreover, we also clarified the BER performance degradation on the victim system due to the spectrum regrowth.