• Title/Summary/Keyword: Base Stations

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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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Efficient Resource Allocation Technique for LTE-Advanced based Interference Avoidance of Heterogeneous Network (LTE-Advanced 기반 이기종 네트워크 시스템의 간섭회피를 위한 효율적인 자원할당 기법)

  • Jang, Sung-Won;Seong, Hyeon-Kyeong
    • Journal of the Institute of Convergence Signal Processing
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    • v.17 no.1
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    • pp.46-52
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    • 2016
  • LTE-Advanced system consisting of the number of cells in the cellular environment because it is built to allow efficient use of limited frequency resources of adjacent cell interference avoidance should be considered. Transition services in accordance with the development of the mobile communication technology, wireless multimedia content from voice-centric mobile communications services and causing a lot of mobile data traffic, such as smart phones and tablet terminals spread of a data-driven surge in mobile data traffic base stations in urban areas by increasing became a reality that can not be prevented. In this paper, we propose a new Hybrid resource allocation technique for improving the performance of the cell boundary and analyzed the performance of the proposed new techniques to perform the simulation using LTE-Advanced system level simulator based on 19cell of cellular system model.

Development of the remote management and control system for wireless CATV network (무선 CATV망의 원격 관리 및 제어 시스템의 개발)

  • 송문규;이상설
    • The Journal of Korean Institute of Communications and Information Sciences
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    • v.23 no.4
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    • pp.1134-1147
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    • 1998
  • Remote management and control system for LMDS wireless CATV network which is being developed at SK Telecom is developed. This system is composed of central control division located at head center and remote units for remote transceivers equipped in base stations and repeaters. It monitors the state of the remote transceivers and controls the operations using PSTN for iterface. Remote transceivers whould be equipped in pairs, and the operations are exchanged automatically in case of emergency situations. the remote units are designed not only to perform commands form central control division, bet to inform emergency situations such as disorder and power failure. This system works well, which is established at Central research center in SK Telecom with remote units such as BTX, PPTX, and PPRX. This system could be utilized in other applications requiring remote control through sligh modifications.

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Effect of mobile terminal searcher on TDOA position location technique (TDOA 위치추정기법에서의 단말기 Searcher의 영향)

  • 김정태;서덕영
    • The Journal of Korean Institute of Communications and Information Sciences
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    • v.24 no.7A
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    • pp.1022-1027
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    • 1999
  • This paper proposes method that uses Time-Difference-of-Arrival(TDOA) of Forward Pilot signals from base stations(BS) arriving at a mobile station(MS) as a position location method of CDMA MS. MS searcher does acquisition of BS Pilot signals and measurement of TDOAs. In order to do it, its processing gain is very important. Proportional relationship of the gain to the signal coherent integration interval is theoretically derived and analyzed and field test is performed to show acquisition of weak Pilot signals and stable measurements of TDOA values by increasing the gain. Also, signal strength decrease exponentially by the distance it travels. Therefore, improvement of the searcher gain makes possible to acquire Pilot signals at a location far away from BS. Variation of possible position estimation area relative to the signal strength within a cell is simulated with computer. Neglecting shadow effect it indicated necessity of detecting signals below -35dB in order to cover over 90% of cell area. Thus, efforts to maximize searcher coherent integration interval in order to acquire weak Pilot signals are required for expansion of position estimation area and measurement of stable TDOA values.

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An Online Calibration Algorithm for Cellular CDMA Antenna Arrays (Cellular CDMA용 배열 안테나 오차 보정 알고리듬)

  • 석미경;조상우;전주환
    • The Journal of Korean Institute of Communications and Information Sciences
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    • v.29 no.2C
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    • pp.306-314
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    • 2004
  • Some receiver(and most transmit) beamforming algorithms with an array antenna at a cellular CDMA base stations require accurate internal and external calibrations. The external calibration, which usually needs to be done only once, determines the array manifolds, i.e. the complex response of each antenna as a function of DOA(Directions of Arrival). The internal calibrations are necessary because characteristics of RF/IF circuity of each receiver chain vary differently in response to temperature or humidity changes. We propose an iterative subspace-based calibration algorithm for an asynchronous CDMA-based antenna away in the presence of unknown gain and phase error is presented. We verify the subspace-based calibration algorithms by performing the experiment using measured data. Also, we propose an efficient algorithm using the simulated annealing technique. This algorithm overcomes the problem of the initial guessing in the subspace-based approach.

A standardization of AGNSS-Packet Timing Hybrid for a Synchronization of Femtocell (펨토셀 기지국 동기 획득을 위한 AGNSS-Packet Timing 하이브리드 표준화)

  • Kim, Jung-Hoon;Lee, Ji-Hun;Shin, Jun-Hyo;Jeong, Seok-Jong
    • The Journal of Korean Institute of Communications and Information Sciences
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    • v.36 no.12B
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    • pp.1611-1622
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    • 2011
  • The synchronization is one of the important issues for successful operation of femtocell. The synchronization of femtocell is distinctly different from that of larger wireless base stations in a number of important respects such as 1) The femtocell is located in indoor environment which may make it difficult to receive the adequate GNSS signals. 2) The backhaul of femtocell is connected to the public network which may have more PDV than private network. 3) The entire cost of femtocell needs to be very low. In our thesis, we investigate the candidate solutions including AGNSS (Assisted GNSS), NTP (Network Time Protocol), PTP (Precision Timing Protocol) and Cellular Network Listen for indoor timing solution. We propose the AGNSS-PTP Hybrid scheme which can improve time and frequency quality by selecting the better reference between AGNSS and PTP, and cover the standard status which are under discussion from IEEE, ITU-T, and IETF.

A Performance Enhancement Scheme for Heterogeneous Network Systems Utilizing Remote Radio Heads (원격송신국을 활용하는 이종 네트워크 시스템의 성능 개선 방안)

  • Yoo, Hyung-Gil;Sung, Won-Jin
    • The Journal of Korean Institute of Communications and Information Sciences
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    • v.37 no.1B
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    • pp.31-38
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    • 2012
  • In this paper, we propose a method to improve cell edge users' performance in HetNet (heterogeneous network) systems by cooperatively transmitting signals using remote radio heads (RRHs) located near coverage boundaries, referred to as edge RRHs. The proposed method locates the edge RRHs in specific locations of the cell boundary and provides an efficient operational strategy by adjusting the duty cycle of the edge RRHs and base stations. The effectiveness of the method is demonstrated by experimental performance based on the system model parameters of the CoMP (coordinated multi-point transmission and reception) scenario, which is discussed in LTE-Advanced (Long Term Evolution - Advanced) standard contributions. When compared with conventional methods, utilization of edge RRHs is especially advantageous for the performance improvement of lower percentile users in terms of average throughput and effectively improves the fairness among users.

Distributed Bit Loading and Power Control Algorithm to Increase System Throughput of Ad-hoc Network (Ad-hoc 네트워크의 Throughput 향상을 위한 적응적 MCS 레벨 기반의 분산형 전력 제어 알고리즘)

  • Kim, Young-Bum;Wang, Yu-Peng;Chang, Kyung-Hi;Yun, Chang-Ho;Park, Jong-Won;Lim, Yong-Kon
    • The Journal of Korean Institute of Communications and Information Sciences
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    • v.35 no.4A
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    • pp.315-321
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    • 2010
  • In Ad-hoc networks, centralized power control is not suitable due to the absence of base stations, which perform the power control operation in the network to optimize the system performance. Therefore, each node should perform power control algorithm distributedly instead of the centralized one. The conventional distributed power control algorithm does not consider the adaptive bit loading operation to change the MCS (modulation and coding scheme) according to the received SINR (signal to interference and noise ratio), which limits the system throughput. In this paper, we propose a novel distributed bit loading and power control algorithm, which considers the adaptive bit loading operation to increase total system throughput and decrease outage probability. Simulation results show that the proposed algorithm performs much better than the conventional algorithm.

An Improved Backoff Algorithm for the Random Access Protocol for the Ranging Subchannel of IEEE 802.16 Networks (IEEE 802.16 환경의 레인징 부채널에서 랜덤액세스 프로토콜의 Backoff 알고리즘 성능 향상 기법)

  • Kwon, Jeong-Min;Lee, Hyong-Woo;Cho, Choong-Ho
    • The Journal of Korean Institute of Communications and Information Sciences
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    • v.32 no.12A
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    • pp.1267-1275
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    • 2007
  • An improved backoff algorithm for retransmission randomization for OFDMA/CDMA/slotted ALOHA used in the ranging subchannel of IEEE 802.16 network is proposed. Exploiting the fact that a base station coordinates channel access using UL-/DL-MAP in the IEEE 802.16 networks, we propose a minor modification of the existing IEEE 802.16 in order to increase throughput, decrease delay variation and achieve a graceful performance degradation in case of overload channel condition of the random access protocol. The algorithm basically estimates the number of backlogged users and arrival rate using which, the BS calculates retransmission probability for the subscriber stations involved in a collision. Computer simulation is performed to demonstrate the effectiveness of the proposed algorithm and to compare the performance with existing binary exponential backoff algorithm.

Testing of Common Electromagnetic Environments for Risk of Interference with Cardiac Pacemaker Function

  • Tiikkaja, Maria;Aro, Aapo L.;Alanko, Tommi;Lindholm, Harri;Sistonen, Heli;Hartikainen, Juha E.K.;Toivonen, Lauri;Juutilainen, Jukka;Hietanen, Maila
    • Safety and Health at Work
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    • v.4 no.3
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    • pp.156-159
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    • 2013
  • Background: Cardiac pacemakers are known to be susceptible to strong electromagnetic fields (EMFs). This in vivo study investigated occurrence of electromagnetic interference with pacemakers caused by common environmental sources of EMFs. Methods: Eleven volunteers with a pacemaker were exposed to EMFs produced by two mobile phone base stations, an electrically powered commuter train, and an overhead high voltage transmission lines. All the pacemakers were programmed in normal clinically selected settings with bipolar sensing and pacing configurations. Results: None of the pacemakers experienced interference in any of these exposure situations. However, often it is not clear whether or not strong EMFs exist in various work environments, and hence an individual risk assessment is needed. Conclusions: Modern pacemakers are well shielded against external EMFs, and workers with a pacemaker can most often return to their previous work after having a pacemaker implanted. However, an appropriate risk assessment is still necessary after the implantation of a pacemaker, a change of its generator, or major modification of its programming settings.