• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.14 no.6
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• pp.567-574
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• 2003

It is important to design and evaluate the chip waveform with the minimum MAI under the bandwidth constraint in the interference-limited DS-CDMA system. In this paper, by approximation we present the analytical chip waveforms that are proposed and optimized in the reference. Their performances are compared with performances of three conventional chip waveforms: rectangular, half-sine and raised-cosine. Waveform 1 of the proposed chip waveform outperforms the conventional ones. BER and throughput performance are evaluated in the Rayleigh and Nakagami-m fading channels when DPSK modulation is used. When the required BER is 10$\^$-3/ in two fading channels, the capacity of the waveform 1 is improved about 20 % rather than raised-cosine one. When the offered traffic is 30 and the number of packet per bit(N$\sub$d/) is 14, maximum throughput of the waveform 1 is better than raised-cosine chip waveform about 18 % in two fading channels.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.10 no.8
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• pp.1502-1509
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• 2006

In this paper, we proposed reliability and capacity enhancement methods for IEEE 802.15.3 HDR-WPAN (High Data Rate-Wireless Personal Area Network) system which is currently getting an interest in home network technology adopting a MIMO technique. We also analyzed performance or the proposed system through a computer simulation. The HDR-WPAN system using V-BLAST algorithm, transmitting the different signal vector to each other's sub-channel, can get the transmission speed of more than 110Mbps using two Tx/Px antenna without bandwidth expansion in TCM-64QAM mode. Also the proposed system has reliability of 104 at $E_b/N_0=35dB$ under the Rayleigh fading channel in case of two Tx/Rx antenna with MMSE algorithm. The HDR-WPAN system adopting V-BLAST method has its drawback which is very complicated to determine the decision-ordering at the receiver. But, the proposed system enhances the transmission capacity and reliability without extra bandwidth expansion by sending data streams to multiple antennas.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.7 no.4
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• pp.652-657
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• 2003

In this paper, Adaptive Modulation and Coding (AMC) is combined with Multiple Input Multiple Output (MIMO) multiplexing to improve the throughput performance of AMC. In addition, a system that adopts Selection Transmit Diversity (STD) in the AMC-MIMO multiplexing system is proposed. The received SNR is improved by adopting STD techniques. And it increases probability of selecting MCS (Modulation and Coding Scheme) level that supports higher data rate. This leads to an increased throughput of the AMC-MIMO system. STD in our simulation selects 2 transmission antennas from 4 antennas and AMC-MIMO multiplexing process operates with the selected antennas. The computer simulation is performed in flat Rayleigh fading channel. The results show that the proposed system achieves a gain of 1Mbps over the AMC-MIMO multiplexing system with the same number of antennas at 15dB SNR.

• Journal of Advanced Navigation Technology
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• v.6 no.2
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• pp.158-167
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• 2002

In this paper, it is analyzed that WAP packet transmission time to improve performance of WAP using SAR-QT algorithm in Bluetooth channel. The order for SAR-QT algorithm to improve the transfer capability, it is fragmented in WTP total messages that are coming down from upper layer and then the packets are sent one at time in baseband. And it is studied that transmission time for WAP over Bluetooth according to DMI, DM3 or DM5 packet type using SAR-QT algorithm in Bluetooth piconet environment. This SAR-QT algorithm decreases WAP packet transmission time of L2CAP baseband packets by sending packet that are spanning multiple slots. From the results, in WAP over Bluetooth channels, it is found out that WTP packet size ought to be increased to decrease transmission time of WAP packet. In addition, considering BER in wireless channel, optimal WTP packet size is achieved for WAP over Bluetooth in a Rician fading environment.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.11 no.6
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• pp.2196-2201
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• 2010

The video transmission system using OFDM method at 18GHz frequency band was developed for wireless video transmission from subway to monitoring center when subway running. It is composed of digital modulation board and RF board. And it has a robust characteristics of multipath fading in subway tunnels at 18GHz. To verify the system, we used spectrum analyzer for analysing the output of transmission system and get the results that it has 350MHz frequency, 8MHz bandwidth and -19dBm channel power. Also we tested video receiving using MPEG-2 encoder and got good quality images.

• The KIPS Transactions:PartC
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• v.13C no.6 s.109
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• pp.677-684
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• 2006

This paper investigates the link margin of MB-OFDM UWB system quantitatively. Various simulations are performed considering the implementation loss by imperfect synchronization unit and the effect of multi-path fading channels. MB-OFDM UWB system uses ZP(Zero Padding) instead of CP(Cyclic Prefix) and supports two transmission modes; one is TFI(Time Frequency Interleaving) mode that transmits OFDM symbols using different carrier frequency from symbol to symbol according to Time Frequency(TF) codes, the other is FFI(Fixed Frequency Interleaving) mode that transmits OFDM symbols using a specific carrier frequency. The advantage of if and TFI is to be able to increase the transmitting power effectively compared to the existed OFDM systems that transmit the signal continuously at the same average transmitting power. From the analysis results of Ink margin, to guarantee the service range of 4m in 200Mbps mode, TFI mode must necessarily be implemented and the service range of 480Mbps mode is estimated about 1-2m in the line-of-sight multi-path channel (CMI).

• The Journal of Korean Institute of Communications and Information Sciences
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• v.28 no.5A
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• pp.267-275
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• 2003

In UMTS terminal modem uses 3 step search procedure for initial cell search, which comprises 1) slot synchronization, 2) code group identification and frame synchronization, and 3) scrambling-code identification. The performance of initial cell search procedure depends on search parameters like observation time and threshold. The purpose of this paper is to get the optimal observation time and threshold of each step for minimum mean acquisition time. In this paper we induce mean detection time of each step and mean acquisition timefrom the model of 3 step search procedure using state diagram. Also we propose initial cell search algorithm which utilize window search method against initial oscillator error, and select an appropriate observation time and threshold of each step by the analysis of simulation and induced result. It is shown that the mean acquisition time in multipath fading channel can be shorter than 500ms by using the determined observation time and threshold of each step.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.17 no.6
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• pp.89-95
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• 2017

UFMC is known as a candidate for the 5G wireless communication system because it is robust against ICI and better performs in asynchronous situation than OFDM. In the UFMC system, the filtering is performed for each subband so the performance of the filter is very important. The Dolph-Chebyshev filter has been used in conventional UFMC system because of its small out-of-band radiation. However it has distortion in the sub-band and skirt characteristics is not good enough. Therefore, it is necessary to study a new type of UFMC filter which reduces the distortion in the subband and has sharp skirt characteristics. In this paper we analyze the effect of filter frequency response in UFMC system and suggest the wavelet based type of filter that substitutes the Dolph-ChebyShev filter used in the conventional UFMC system. The simulation results show that wavelet filter has better BER performance in multipath fading channels than conventional filters.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.48 no.3
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• pp.13-18
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• 2011

Sphere Decoding (SD) is a decoding technique able to achieve the Maximum Likelihood (ML) performance in fading environments; nevertheless, the main disadvantage of this technique is its high complexity, especially in poor channel conditions. In this paper, we present an adaptive hybrid algorithm which reduces the conventional Sphere Decoder's complexity and keeps the ML performance. The system called Adaptive OSIC-SD modifies its operation based on Signal to Noise Ratio (SNR) information and achieves an optimal performance in terms of Bit Error Rate (BER) and complexity. Through simulations, we probe that the proposed system maintains almost the same bit error rate performance of the conventional SD, and exhibits a lower, quasi-constant complexity.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.10 no.5
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• pp.113-119
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• 2010

In this paper, the considered cognitive radio system has a pair of PT-PR and a pair of ST-SR. In first time slot(1 Phase), PT broadcast signal $x_p$ to PR, ST and SR. Then, each receivers(PR, ST, SR) decode received signal $x_p$. In second time slot(2 Phase), ST combine decoded signal ${x_p}^{\prime}$ and signal $x_s$, and it broadcast combined signal to PR and SR. PR and SR decode combined signal. At this time, PR can achieve diversity gain, due to using MRC, it combine 'received and decoded signal ${x_p}^{\prime}$ at 1 phase' and 'detected signal $x_p$ at 2 phase'. SR use linear combining technique and it can obtain $x_s$.