• Title/Summary/Keyword: cell load balancing

Search Result 41, Processing Time 0.037 seconds

Adaptive Periodic MLB Algorithm for LTE Femtocell Networks (LTE 펨토셀 네트워크를 위한 적응적 주기의 MLB 알고리즘)

  • Kim, Woojoong;Lee, Jeong-Yoon;Suh, Young-Joo
    • The Journal of Korean Institute of Communications and Information Sciences
    • /
    • v.38C no.9
    • /
    • pp.764-774
    • /
    • 2013
  • The number of users and data packets has increased in 4G cellular networks. Therefore, 4G cellular network providers suffer from the network capacity problem. In order to solve this problem, femtocell concept is suggested. It can reduce the coverage hole and enhance the QoS. However, only small number of femtocells experience the large amount of loads. To solve this problem, Mobility Load Balancing (MLB) algorithm is suggested, which is a kind of load balancing algorithm. To distribute the traffic load, MLB algorithm modifies the handover region. If the handover region is reduced by MLB algorithm, some cell edge users are compulsively handed over to neighbor femtocell. In this paper, we analyze the relation between MLB performing period and performance indicators. For example throughput and blocking probability is reduced, if period is decreased. On the contrast, if period is increased, the number of handover frequency is decreased. Using this relation, we suggest the adaptive periodic MLB algorithm. This algorithm includes the advantage of both long period and short period MLB algorithm, such as high throughput, the small number of handover frequency, and low blocking probability.

Traffic Asymmetry Balancing in OFDMA-TDD Cellular Networks

  • Foutekova, Ellina;Sinanovic, Sinan;Haas, Harald
    • Journal of Communications and Networks
    • /
    • v.10 no.2
    • /
    • pp.137-147
    • /
    • 2008
  • This paper proposes a novel approach to interference avoidance via inter-cell relaying in cellular OFDMA-TDD (orthogonal frequency division multiple access - time division duplex) systems. The proposed scheme, termed asymmetry balancing, is targeted towards next-generation cellular wireless systems which are envisaged to have ad hoc and multi-hop capabilities. Asymmetry balancing resolves the detrimental base station (BS)-to-BS interference problem inherent to TDD networks by synchronizing the TDD switching points (SPs) across cells. In order to maintain the flexibility of TDD in serving the asymmetry demands of individual cells, inter-cell relaying is employed. Mobile stations (MSs) in a cell which has a shortage of uplink (UL) resources and spare downlink (DL) resources use free DL resources to off-load UL traffic to cooperating MSs in a neighboring cell using ad hoc communication. In an analogous fashion DL traffic can be balanced. The purpose of this paper is to introduce the asymmetry balancing concept by considering a seven-cell cluster and a single overloaded cell in the center. A mathematical model is developed to quantify the envisaged gains in using asymmetry balancing and is verified via Monte Carlo simulations. It is demonstrated that asymmetry balancing offers great flexibility in UL-DL resource allocation. In addition, results show that a spectral efficiency improvement of more than 100% can be obtained with respect to a case where the TDD SPs are adapted to the cell-specific demands.

Development of a hard bearing type balancing machine (강성 베어링형 밸런실 장치의 개발)

  • 권이석;이동환;박중윤;홍성욱
    • Proceedings of the Korean Society of Precision Engineering Conference
    • /
    • 1994.10a
    • /
    • pp.773-777
    • /
    • 1994
  • This paper is devoted to the development and performance evaluation of a hard bearing type balancing machine for rigid rotors. The pedestals of the balancing machine are designed to be rigid to be rigid enough to enable the balancing to operate far below the fundamental critical speed. The force measuring method is implemented to the balancing machine. The forces due to unbalance are measured through load cell that are attached to the pedestals. A helical coupling is used for transmitting the driving force from an AC servo motor to the rotor to be balanced. The experimental results show that the current hard bearing type balancing machine can indicate the presence of unbalance beyond 1 .mu. m in specific unbalance unit. The limitation of the current balancing machine is due to the coupling that is likely to make inconsistent offset errors everytime the rotor is connected to the machine.

  • PDF

An Efficient Load-Balancing Algorithm based on Bandwidth Reservation Scheme in Wireless Multimedia Networks (무선 멀티미디어 망에서 대역폭 예약을 이용한 효율적인 부하 균형 알고리즘)

  • 정영석;우매리;김종근
    • Journal of Korea Multimedia Society
    • /
    • v.5 no.4
    • /
    • pp.441-449
    • /
    • 2002
  • For multimedia traffics to be supported successfully in wireless network environment, it is necessary to provide Qualify-of-Service(QoS) guarantees among mobile hosts(clients). In order to guarantee the QoS, we have to keep the call blocking probability below a target value during hand-off session. However, the QoS negotiated between the client and the network may not be guaranteed due to lack of available channels for traffic of a new cell, since on service mobile clients should be able to continue their sessions. In this paper, we propose an efficient load-balancing algorithm based on the adaptive bandwidth reservation scheme for enlarging available channels in a cell. Proposed algorithm predicts the direction of clients in a cell and adjusts the amount of the channel to be reserved according to the load status of the cell. This method is used to reserve a part of bandwidths of a cell for hand-off calls to its adjacent cells and this reserved bandwidth can be used for hand-off call prior to new connection requests. If the number of free channels is also under a low threshold value, our scheme use a load-balancing algorithm with an adaptive bandwidth reservation. In order to evaluate the performance of our algorithm, we measure metrics such as the blocking probability of new calls and dropping probability of hand-off calls, and compare with those of existing schemes.

  • PDF

Adaptive Online Load Balancing Algorithm for Multimedia Service in Cellular Networks (셀룰러 네트워크 상에서 멀티미디어 서비스 제공을 위한 효율적인 온라인 부하분산 기법에 대한 연구)

  • Kim, Sung-Wook
    • The Journal of Korean Institute of Communications and Information Sciences
    • /
    • v.30 no.12B
    • /
    • pp.811-817
    • /
    • 2005
  • Efficient bandwidth management is necessary in order to provide high quality service to users in a multimedia wireless/mobile network. In this paper, I propose an on-line load balancing algorithm with preemption. This technique is able to balance the traffic load among cells accommodating heterogeneous multimedia services while ensuring efficient bandwidth utilization. The most important features of my algorithm are its adaptability, flexibility and responsiveness to current network conditions. In addition, my online scheme to control bandwidth adaptively is a cell-oriented approach. This approach has low complexity making it practical for real cellular networks. Simulation results indicate the superior performance of my algorithm.

Enhancement of Cell Voltage Balancing Control by Zero Sequence Current Injection in a Cascaded H-Bridge STATCOM (STATCOM에서 영상분 전류주입에 의한 셀간 전압평형화 제어의 향상)

  • Kwon, Byung-Ki;Jung, Seung-Ki;Kim, Tae-Hyeong
    • The Transactions of the Korean Institute of Power Electronics
    • /
    • v.20 no.4
    • /
    • pp.321-329
    • /
    • 2015
  • The static synchronous compensator (STATCOM) of cascaded H-bridge configuration accompanying multiple separate DC sides is inherently subject to the problem of uneven DC voltages. These DC voltages in one leg can be controlled by adjusting the AC-side output voltage of each cell inverter, which is proportional to the active power. However, when the phase current is extremely small, large AC-side voltage is required to generate the active power to balance the cell voltages. In this study, an alternative zero-sequence current injection method is proposed, which facilitates effective cell balancing controllers at no load, and has no effect on the power grid because the injected zero sequence current only flows within the STATCOM delta circuit. The performance of the proposed method is verified through simulation and experiments.

MADF: Mobile-Assisted Data Forwarding for Wireless Data Networks

  • Xiaoxin;Gary, Shueng-Han;Biswanath;Bharat
    • Journal of Communications and Networks
    • /
    • v.6 no.3
    • /
    • pp.216-225
    • /
    • 2004
  • In a cellular network, if there are too many data users in a cell, data may suffer long delay, and system's quality-of-service (QoS) will degrade. Some traditional schemes such as dynamic channel-allocation scheme (DCA) will assign more channels to hot (or overloaded) cells through a central control system (CC) and the throughput increase will be upper bounded by the number of new channels assigned to the cell. In mobile-assisted data forwarding (MADF), we add an ad-hoc overlay to the fixed cellular infrastructure and special channels-called forwarding channels- are used to connect mobile units in a hot cell and its surrounding cold cells without going through the hot cell's base station. Thus, mobile units in a hot cell can forward data to other cold cells to achieve load balancing. Most of the forwarding-channel management work in MADF is done by mobile units themselves in order to relieve the load from the CC. The traffic increase in a certain cell will not be upper bounded by the number of forwarding channels. It can be more if the users in hot cell are significantly far away from one another and these users can use the same forwarding channels to forward data to different cold neighboring cells without interference. We find that, in a system using MADF, under a certain delay requirement, the throughput in a certain cell or for the whole net-work can be greatly improved.

Individual DC Voltage Balancing Method at Zero Current Mode for Cascaded H-bridge Based Static Synchronous Compensator

  • Yang, Zezhou;Sun, Jianjun;Li, Shangsheng;Liao, Zhiqiang;Zha, Xiaoming
    • Journal of Electrical Engineering and Technology
    • /
    • v.13 no.1
    • /
    • pp.240-249
    • /
    • 2018
  • Individual DC voltage balance problem is an inherent issue for cascaded H-bridge (CHB) based converter. When the CHB-based static synchronous compensator (STATCOM) is operating at zero current mode, the software-based individual DC voltage balancing control techniques may not work because of the infinitesimal output current. However, the different power losses of each cell would lead to the individual DC voltages unbalance. The uneven power losses on the local supplied cell-controllers (including the control circuit and drive circuit) would especially cause the divergence of individual DC voltages, due to their characteristic as constant power loads. To solve this problem, this paper proposes an adaptive voltage balancing module which is designed in the cell-controller board with small size and low cost circuits. It is controlled to make the power loss of the cell a constant resistance load, thus the DC voltages are balanced in zero current mode. Field test in a 10kV STATCOM confirms the performance of the proposed method.

DC Voltage Balancing Control for Multilevel H-Bridge STATCOM (다단 인버터 STATCOM의 직류전압 평형 제어)

  • Kim, Kyoung-Jin;Song, Seong Ho;Jeong, Seung-Gi
    • Proceedings of the KIPE Conference
    • /
    • 2010.11a
    • /
    • pp.234-237
    • /
    • 2010
  • This paper proposes a balancing control of DC-link voltages of a H-bridge multilevel inverter for STATCOM application. Individual DC link voltage is controlled by simply adjusting the d-q voltage reference through a PI controller in each cell while the main controller carries out the reactive power control. The correctness and effectiveness of the method are validated by PSIM simulation with unbalanced load condition data taken from a typical arc furnace load, showing the adverse effects of load unbalance to DC link voltage significantly suppressed.

  • PDF

Power Balancing Strategy in the Microgrid During Transient (마이크로그리드 과도상태 시 전력 수급 균형 전략)

  • Seo, Jae-Jin;Lee, Hak-Ju;Jung, Won-Wook;Won, Dong-Jun
    • The Transactions of The Korean Institute of Electrical Engineers
    • /
    • v.59 no.4
    • /
    • pp.707-714
    • /
    • 2010
  • When problems such as line fault, breakdown of a substation or a generator, etc. arise on the grid, the Microgrid is designed to be separated or isolated from the grid. Most existing DGs(Distributed Generators) in distribution system use rotating machine. However, new DGs such as micro gas turbine, fuel cell, photo voltaic, wind turbine, etc. will be interfaced with the Microgrid through an inverter. So the Microgrid may have very lower inertia than the conventional distribution system. By the way, the rate of change of frequency depends on the inertia of the power system. Moreover, frequency has a strong coupling with active power in power system. Because the frequency of the Microgrid may change rapidly and largely during transient, appropriate and fast control strategy is needed for stable operation of the Microgrid. Therefore, this paper presents a power balancing strategy in Microgrid during transient. Despite of strong power or frequency excursions, power balancing in the Microgrid can be maintained.