• Journal of Magnetics
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• v.21 no.3
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• pp.330-339
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• 2016

A magnetic field sensing system with a single primary sensor and multiple reference sensors deployed locally and orthogonally, was proposed for downlink signal reception and interference cancelling for Through-the-Earth Communication (TEC). This paper mathematically analyzes a design optimization process for a search coil magnetometer (SCM), and applies that process to minimize the bandwidth of the primary SCM for TEC signal reception and the volume of reference SCMs for multiple distributions. The primary SCM achieves a 3-dB bandwidth of 7 Hz, a sensitivity threshold of 120 fT/${\surd}$Hz, and a volume of $2.32{\times}10^{-4}m^3$. The entire sensing system volume is as small as $10^{-2}m^3$. Experiments with interference from industrial frequency harmonics demonstrated an average of 36 dB and 18 dB improvements in signal-to-interference ratio and signal-to-interference plus noise ratio, respectively, using multichannel recursive-least-squares algorithm. Thus, the proposed sensing system can reduce the interference effectively and allows reliable downlink signal reception.

• Journal of electromagnetic engineering and science
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• v.4 no.4
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• pp.183-189
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• 2004

In this paper, the Eigen-RAKE receiver in wideband direct sequence code-division multiple access(DS-CDMA) systems with downlink smart antenna is analyzed for different spreading bandwidths(1.25 MHz, 5 MHz, 10 MHz) and different channel environments(macro, micro). The realistic spatio-temporal wideband multipath channel is assumed, one of which is standardized multiple-input single-output(MISO) radio channel model for WCDMA link-level simulations proposed by $3^{rd}$ generation partnership project(3GPP) contributions. We assumed spatial scattering phenomenon in which many unresolvable path signals within a limited range of spatial angle simultaneously contribute to the signals received at the receiver. Several multipaths within one chip are distinguished into each one and the first multipath components are selected as the desired signal and the others are considered self-interference. Downlink DS-CDMA system with eigenbeamformer using wider bandwidth present better performance than that using narrow bandwidth system by employing Eigen-RAKE receiver of many number of branches. It is shown that the downlink eigenbeamformer is more effective in typical urban macro cellular environments when using Eigen-RAKE receiver.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.7 no.11
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• pp.2597-2615
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• 2013

This paper proposes a dynamic downlink load control scheme that jointly employs dynamic load threshold management and virtual coverage management schemes to reduce the degree of performance degradation due to traffic overload in two-tier femtocell networks. With the proposed scheme, the downlink load in a serving macrocell is controlled with a load threshold which is adjusted dynamically depending on the varying downlink load conditions of neighboring macrocells. In addition, traffic overloading is alleviated by virtually adjusting the coverage of the overloaded serving macrocell, based on the adjusted load threshold of the serving macrocell. Simulation results show that the proposed scheme improves the performance of two-tier femtocell networks in terms of the outage probability and sum throughput. This improvement is significantly increased with appropriate values of load thresholds and with an intermediate-level adjustment of the virtual coverage area (i.e., handover hysteresis margin: HOM). Furthermore, the proposed scheme outperforms both a previously proposed load control scheme with a static load threshold and the LTE system without a HOM adjustment.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.31 no.5A
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• pp.451-458
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• 2006

In this paper, we propose a novel scheduling algorithm for downlink transmission which utilizes scarce wireless resource efficiently in an Orthogonal Frequency Division Multiple Access/Time Division Duplex system. Scheduling schemes which exploit channel information between a Base Station and terminals have been proposed recently for improved performance. Time series analysis is used to estimate the channel state of mobile terminals. The predicted information is then used for prioritized scheduling of downlink transmissions for improved throughput, delay and jitter performance. Through simulation, we show that the total throughput and mean delay of the proposed scheduling algorithm are improved compared with those of the Proportional Fairness and Maximum Carrier to Interference Ratio schemes.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.41 no.10
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• pp.53-59
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• 2004

A new downlink beamforming method is proposed for coherent detection of Cellular systems with BPSK modulation where there exists only common pilot channel. To solve phase mismatch between traffic and pilot signals at desired mobile and to reduce interference to other mobiles, the proposed downlink beamforming method considers a cost function of signal to interference ratio criteria and gives a solution for the cost function. The computer simulation showed that the proposed method can solve the phase mismatch problem and give improved BER performance in time-varying channels.

• Aerospace Engineering and Technology
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• v.1 no.2
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• pp.45-50
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• 2002

A conceptual design on the link budget of TC&R RF subsystem which transfers command and telemetry data as RF signal between the ground system and the 2005SAT spacecraft is presented in this paper. In order to perform the analysis of the link budget, we divided the analysis process into two processes, i.e., uplink and downlink process. For the uplink the power flux density at the spacecraft and the margin of the command receiver are calculated. In the case of the downlink the downlink EIRP and the margin of C/ No and Eb / No at the ground station are calculated. Through the uplink performance analysis, the power at the command receiver has well efficient margin, and the margin of C/ No and Eb / No is also fully proper for the downlink case.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.33 no.5A
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• pp.542-548
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• 2008

This paper proposes a handover scheme using uplink and downlink signals in IEEE 802.16e systems. Exploiting the channel reciprocity in TDD systems, the proposed scheme triggers handover initiation process using uplink signal. In addition, it exploits the uplink and downlink hysteresis to determine the handover direction. Simulation results show that the proposed algorithm with joint hysteresis reduces the outage probability by about 10% compared with the mobile assisted handover in IEEE 802.16e.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.20 no.4
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• pp.396-405
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• 2009

This paper describes playback downlink and telecommand uplink channel design performed for a transportable small-sized KOMPSAT(Korea Multi-Purpose Satellite) ground station. As a result of downlink channel design, required receiving performance was calculated from the threshold signal-to-noise ratio of playback signal and it was revealed that this performance can be guaranteed in 1.5 m ground station with 6.5 dB/K of G/T. For the uplink channel design, 40 dBW of EIRP was derived from the threshold signal-to-noise ratio of telecommand signal received at on-board receiver. The implemented small-sized ground station based on design was evaluated to be fully acceptable for KOMPSAT TT&C(Telemetry, Tracking and Command) system and playback downlink design without taking account of additional 3 dB system link margin was shown to be effective because it had provided constantly initial channel performance without any remarkable degradation over several years of tests with KOMPSAT and KOMPSAT-2, for both uplink and playback downlink in the elevation angle above $10^{\circ}$.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.36 no.12C
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• pp.764-773
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• 2011

Despite enormous performance gain with multi-antenna transmission in the single cell environment, its gain diminishes out in the multi-cell environment due to interference. It is also very hard to solve the efficient downlink beamforming with low complexity in multi-cell environment. First, this paper shows that the asymptotically sum rate optimal downlink beamformings at low and high SNR are maximum ratio transmit (MRT) and zero forcing (ZF) beamforming in the multi-cell system, respectively. Secondly, exploiting the asymptotically optimal downlink beamforming, we develop simple two types of near optimal downlink beamforming schemes having the form of minimum mean squared error (MMSE) beamforming obtained from the dual uplink problem. For each type, three different subclasses are also considered depending on the computational complexity. The simulation results show that the proposed near optimum algorithms provide the trade-off between the complexity and the performance.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.31 no.3A
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• pp.291-303
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• 2006

In this paper, we analyze functional requirements of the IEEE 802.22 WRAN, and propose a downlink 프레임 structure satisfying the requirements. The proposed downlink 프레임 structure maximizes e transmission efficiency by adopting the cognative radio to assign the sub-channel by reflecting the channel environment of WRAN. We also calculate the signalling overhead for both downlink and uplink, and analyze the performances of time synchronization, frequency synchronization and cell identification based on the 프리앰블 in downlink and suggest the channel estimation method tough 프리앰블 or pilot. As a final result, e stationary beamforming (SBF) algorithm with dynamic channel allocation(DCA) is proposed. The proposed OFDMA downlink 프레임 structure with channel adaptive sub-channel allocation for cognitive radio applications is verified to meet the requirements of IEEE 802.22 WRAN, by computer simulations.