• Journal of Communications and Networks
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• v.14 no.6
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• pp.619-628
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• 2012

The ZigBee network has been considered to monitor electricity usage of home appliances in the smart grid network. ZigBee, however, may suffer from a coexistence problem with wireless local area network (WLAN). In this paper, to resolve the coexistence problem between ZigBee network and WLAN, we propose a new protocol constructing a cognitive smart grid network for supporting monitoring of home appliances. In the proposed protocol, home appliances first estimates the transmission timing and channel information of WLAN by reading request to send/clear to send (RTS/CTS) frames of WLAN. Next, based on the estimated information, home appliances transmit a data at the same time as WLAN transmission. To manage the interference between WLAN and smart grid network, we propose a cognitive beamforming algorithm. The beamforming algorithm is designed to guaranteeing zero interference to WLAN while satisfying a required rate for smart metering. We also propose an energy efficient rate adaptation algorithm. By slowing down the transmission rate while satisfying an imperceptible impact of quality of service (QoS) of the receiver, the home appliance can significantly save transmit power. Numerical results show that the proposed multiple antenna technique provides reliable communications for smart metering with reduced power comparing to the simple transmission technique.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.35 no.4A
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• pp.386-393
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• 2010

In this paper, we analyse HARQ scheme that utilizes symbol mapping diversity (SMD) techniques such as MDSM and CORE. The exploitation feasibility of MDSM and CORE is evaluated in the perspective of system complexity and storage capacity as we consider a BICM system based on 3GPP LTE standards and multipath fading channels. Also, a simple method which obtains SMD effects by circularly shifting bit-block in a codeword is proposed. The experimental results performed in BICM-OFDM systems with single antenna as well as multiple antennas show that frame error rate of the proposed method is close to that of CORE while having lower complexity.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.32 no.7C
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• pp.644-651
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• 2007

In multiple antenna systems, vertical Bell Labs Layered Space-Time (V-BLAST) systems enable very high throughput by nulling and cancelling at each layer detection. In this paper, we propose a V-BLAST system which combines with signal space diversity technique. The benefit of the signal space diversity is that we can obtain an additional gain without extra bandwidth and power expansion by applying inphase/quadrature interleaving and the constellation rotation. Through simulation results, it is shown that the performance of the proposed system is less than 0.5dB away from the ideal upper bound.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.18 no.12
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• pp.1352-1358
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• 2007

This paper address the statistical charateristics of MUSIC algorithm which is suggested as satellite direction finding algorithm. If the MUSIC algorithm is adopted as a satellite direction detection method in mobile TT&C system, then the statistical performance of the MUSIC algorithm will be closely related with the overall performance of the system. So statistical characteristics of the parameter in the respect of SNR and data length are addressed and then analyse the final effects to the satellite direction finding.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.14 no.11
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• pp.1113-1120
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• 2003

It is expected in the future that the demand of optical subcarrier multiplexing system, in which a number of small size base stations with only antenna and RF transmission are connected to central station using optical fiber, will be increased in the CDMA digital cellular mobile communication network. In this paper, in order to analysis the performance of optical SCM system fur CDMA RF signal transmission, MZ modulator is modelled as a non-linear transfer function with cubic operation. The performance degradation due to multipath signals and other user signals through MB modulator is analyzed and the performance is improved using the Rake receiver.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.14 no.12
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• pp.2649-2656
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• 2010

MC-DS-CDMA is technique where a single data symbol is transmitted at multiple subcarriers which are orthogonal to each other. With this technique, frequency diversity can be achieved. The performance of uplink MC-DS-CDMA systems with the application of MRRC antenna diversity over time variant channels is analyzed. Time variant channels lead to interchannel interference which increases the bit error rate in the receiver. The BER performance of this system over multipath fading environment is evaluated, considering the channel estimation error, carrier frequency offset, and the nonlinear high power amplifier.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.29 no.4A
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• pp.423-428
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• 2004

High-data rate and high speed communication techniques are required for wireless mobile communication systems to provide multimedia services. A multiple antenna technology may be used to meet this demand. In this paper, a method for performance improvement of a WCDMA downlink system using space time block coding is proposed in quasi-static Rayleigh fading channels. The proposed receiver uses the cross correlation matrix obtained by each finger corresponding to multi paths. To obtain maximum diversity gain, the inverse of cross correlation matrix and the Hermitian matrix of the channel matrix for each path arc computed, and then applied to received signals. Various simulation results show that the proposed receiver outperforms a conventional receiver in Rayleigh fading channels.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.37A no.9
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• pp.753-761
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• 2012

In this paper, we study a power allocation technique for Tomlinson-Harashima precoding (THP) in multi-user multiple input single output (MISO) downlink systems. In contrast to previous approaches, a mutual information based method is exploited for maximizing the sum rate of zero-forcing THP systems. Then, we propose a simple power allocation algorithm which assigns proper power level for modulo operated users. Simulation results show that the proposed scheme outperforms a conventional water-filling method, and it provides similar performance with near optimal method with much reduced complexity.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.33 no.2A
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• pp.130-138
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• 2008

In this paper, we propose a user selection method to maximize the sum-rate of downlink over opportunistic beamforming. The throughput of an opportunistic beamforming with non-uniformly distributed or a small number of users can decrease. In order to improve the throughput, we propose a scheduling method that does not use SINR or SNR but uses the effective channel gain of each user obtained from the SINR or SNR feedback. The proposed method makes it possible to select users flexibly according to the distribution of users. In numerical results, we show that the proposed methods improve the average sum-rate about 60% when users are distributed non uniformly.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.45 no.12
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• pp.1-6
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• 2008

In this paper, bias control circuit structure have been employed to improve the power added efficiency of the CMOS class-E power amplifier on low input power level. The gate and drain bias voltage has been controlled with the envelope of the input RF signal. The proposed CMOS class-E power amplifier using bias controlled circuit has been improved the PAE on low output power level. The operating frequency is 2.14GHz and the output power is 22dBm to 25dBm. In addition to, it has been evident that the designed the structure has showed more than a 80% increase in PAE for flatness over all input power level, respectively.