• Title/Summary/Keyword: Mobile Stations

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Identifying the Location of a Mobile Object in Real-time using PID-controlled Moving Objects Spatio-Temporal Model

  • Zhi, Wang;Sung, Kil-Young;Lee, Kyou-Ho
    • Journal of information and communication convergence engineering
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    • v.9 no.5
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    • pp.545-550
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    • 2011
  • Trilateration is a typical method to locate an object, which requires inherently at least three prerecognized reference points. In some cases, owing to out of reachability to communication facilities the target node cannot be reachable always to three base stations. This paper presents a predictive method, which can identify the location of a moving target node in real time even though the target node could not get in touch with all three base stations. The method is based on the PIDcontrolled Moving Objects Spatio-Temporal Model Algorithm. Simulation results verify that this method can predict the moving direction of a moving target, and then combine with its past position information to judge accurately the location.

Supporting Real-Time Multimedia Traffic in a Wireless LANs

  • Shin, Myung-Sik;Yang, Hae-Sool
    • Journal of The Institute of Information and Telecommunication Facilities Engineering
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    • v.8 no.1
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    • pp.6-11
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    • 2009
  • This paper presents a new dynamically adaptable polling scheme for efficient support of real-time traffic over an IEEE 802.11 wireless LAN network. The poll scheduling plays an important role in IEEE 802.11 PCF. However, the current version of the polling list management scheme proposed in the IEEE 802.11 standard is inefficient when a variable number of mobile stations have variable packets to transmit. If Point Coordinator has an exact information on the station status, it is possible to efficiently perform polling. In this paper, we suggest an adaptable polling scheme to meet requirements of the stations. In our scheme, each station transmits packets including a piggyback information to inform that it wants to receive a poll in the next polling duration. Simulation results indicate that our scheme may reduces the packet discard ratio and real-time packet transfer delay.

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Performance Improvement of Wireless Uplink Channels Using Packet Diversity (패킷 다이버시티를 이용한 무선 상향 링크의 성능 개선)

  • Lee, Goo-Yeon;Kim, Hwa-Jong;Jeong, Choong-Kyo;Lee, Yong
    • Journal of Industrial Technology
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    • v.24 no.B
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    • pp.187-192
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    • 2004
  • In this paper, we introduce a packet diversity scheme to increase uplink channel utilization in a wireless network where forward error correction is used. The packet diversity allows neighbor base stations to receive uplink packets from a mobile terminal in order to increase the utilization of the uplink channel. By allowing multiple base stations to receive the same packets, we can improve the error correction capability in an uplink channel. By incorporating the packet diversity we can reduce the parity overhead of each packet for a given tolerable loss probability, which improves the link efficiency.

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Up/Downlink Hybrid Inter-Cell Coordination Patterns of the TDD/MC-CDMA System, TDD/MC-CDMA

  • Han, Sang-Jin;Lee, Sung-Jin;Lee, Sang-Hoon;Gil, Gye-Tae
    • The Journal of Korean Institute of Communications and Information Sciences
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    • v.34 no.5A
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    • pp.421-428
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    • 2009
  • Inter-cell coordination has been an emerging issue for mitigating inter-cell interference in broadband wireless access networks such as IEEE802.16 and 3GPP LTE (Long Term Evolution). This paper proposes uplink/downlink hybrid inter-cell coordination patterns for a TDD (Time Division Duplex)/MC-CDMA (Multi-Carrier Code Division Multiple Access) system. For the performance analysis, closed forms of inter-cell interferences are derived when uplink and downlink transmissions coexist over a multi-cell environment. In the analysis, we find an optimal ratio of downlink transmit powers of BSs (Base Stations) based on the target outage probability and the performance according to ratios of uplink/downlink transmit powers of MSs (Mobile Stations)/BSs is explored. Our numerical results show that interference mitigation utilizing the characteristics of the uplink and downlink power ratio is very effective in improving system performance in terms of QoS.

Vector Channel Modeling & Position Estimation using Direction Finding Methods for CDMA Mobile Wireless Systems (CDMA 환경에서 위치추정을 위한 벡터채널 모델링과 Direction Finding을 이용한 위치 추정)

  • 김장섭;이용우;정우곤
    • Proceedings of the IEEK Conference
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    • 1999.11a
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    • pp.27-30
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    • 1999
  • A spatio-temporal vector channel model is introduced for the position location (PL) estimation problem for CDMA cellular system environment. Two common ways for the PL make use of the AOA (Angle Of Arrival) and TDOA (Time Difference Of Arrival) from a subscriber to the multiple sensors (base stations). In this paper, we applied the derived vector channel to simulate the multipath channel for the angle of the signal arrival in CDMA systems. Cross-correlation method is a good candidate among other direction finding algorithms available in literature, especially in wideband modulation as in the CDMA system. The PL estimation errors are evaluated for different channels, which are obtained as a parameter of scattering radius of the suggested model. We noted that the number of sensors (base-stations) are related to the PL errors in favor of the available data.

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Transmission Diversity Scheme Using Antenna Array of Small Cell (소형 기지국의 안테나 배열을 이용한 전송 다이버시티 기법)

  • Paik, Jong-Ho
    • The Journal of Korean Institute of Communications and Information Sciences
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    • v.41 no.3
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    • pp.301-303
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    • 2016
  • This paper proposes a method providing diversity gain using small base stations in a cell coverage in order to improve diversity gain. The small base stations and the conventional base station consist a virtual MIMO array by using the cooperative communication scheme. Also, transmission diversity scheme is applied. A mobile user can receive the signals having the improved reliability by the applied transmission diversity scheme and the cooperative communication scheme.

Cooperative MAC Protocol Using Active Relays for Multi-Rate WLANs

  • Oh, Chang-Yeong;Lee, Tae-Jin
    • Journal of Communications and Networks
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    • v.13 no.5
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    • pp.463-471
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    • 2011
  • Cooperative communications using relays in wireless networks have similar effects of multiple-input and multiple-output without the need of multiple antennas at each node. To implement cooperation into a system, efficient protocols are desired. In IEEE 802.11 families such as a/b/g, mobile stations can automatically adjust transmission rates according to channel conditions. However throughput performance degradation is observed by low-rate stations in multi-rate circumstances resulting in so-called performance anomaly. In this paper, we propose active relay-based cooperative medium access control (AR-CMAC) protocol, in which active relays desiring to transmit their own data for cooperation participate in relaying, and it is designed to increase throughput as a solution to performance anomaly. We have analyzed the performance of the simplified AR-CMAC using an embedded Markov chain model to demonstrate the gain of AR-CMAC and to verify it with our simulations. Simulations in an infrastructure network with an IEEE 802.11b/g access point show noticeable improvement than the legacy schemes.

Supporting Real-Time Multimedia Traffic in a wireless LANs

  • Shin, Myung-Sik;Yang, Hae-Sool
    • 한국정보통신설비학회:학술대회논문집
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    • 2008.08a
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    • pp.249-252
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    • 2008
  • This paper presents a new dynamically adaptable polling scheme for efficient support of real-time traffic over an IEEE 802.11 wireless LAN network. The poll scheduling plays an important role in IEEE 802.11 PCF. However, the current version of the polling list management scheme proposed in the IEEE802.11 standard is inefficient when a variable number of mobile stations have variable packets to transmit. If Point Coordinator has an exact information on the station status, it is possible to efficiently perform polling. In this thesis, we suggest an adaptable polling scheme to meet requirements of the stations. In our scheme, each station transmits packets including a piggyback information to inform that it wants to receive a poll in the next polling duration. Simulation results indicate that our scheme may reduces the packet discard ratio and real-time packet transfer delay.

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The Measurement of Fading Characteristics of The Beamforming on Mobile ad-hoc Channel Environments (이동 ad-hoc채널에서 빔 형성 방식의 페이딩 특성 측정)

  • Ko, Hak-Lim;Park, Byeong-Hoon
    • Journal of the Institute of Convergence Signal Processing
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    • v.8 no.4
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    • pp.266-271
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    • 2007
  • In mobile channel environments, the effect of the multi-path fading reduces the performance of the mobile communication severely. Previous studies on the effect of the multi-path fading show that, only the channel between fixed base stations and mobile terminals are considered. However, the future mobile communication service such as telematics may use the communication between moving mobile terminals, so called mobile ad-hoc communication, the studies on the channel is required for such situations. In this paper we have measured the mobile channel and analyzed the fading characteristics when using the linear array antennas. In the data measurements, we sent the QPSK modulated signal with carrier frequency of 2GHz band and received the signal using the array antennas equipped on moving vehicles. We have analyzed the fading characteristics and the effects of the fading reduction using the CDF of fading depth using data collected from two moving vehicles. The simulation results show that the beamforming technique adds 6 or 7dB to the fading margin than that of the selection diversity depending on channel environments.

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Analysis of Usefulness of Domain-Based Network Caching in Mobile Environment (이동 환경에서 영역기반의 네트워크 캐슁 효용성 분석)

  • 이화세;이승원;박성호;정기동
    • Journal of Korea Multimedia Society
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    • v.7 no.5
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    • pp.668-679
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    • 2004
  • When users of mobile environments move fast or slow into a number of base stations(BS) and request the services of continuous media data such as video or audio, this study examines what the caching has the usefulness in mobile environments. Namely, to reduce packet disconnections and network overheads in mobile environments and minimize transmission delay time, we propose domain-based hierarchical caching structure and study whether application of caching has the usefulness. So we have a model based on user environments and hierarchical network structure to process continuous media services, and analyze the usefulness of caching which depends on the mobile patterns of user and the locations of caching nodes. And then, we research whether caching offers the usefulness in mobile environments. As the result, we are able to see that an adaptable application of caching is needed because the hit ratio and the number of replacement vary in large according to mobile patterns of user and locations of caching.

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