• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.18 no.1 s.116
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• pp.53-61
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• 2007

This paper researches on the scheme superimposing the rotation phases over the pilot and data symbols in order to reduce the peak-to-average power ratio(PAPR) of the orthogonal frequency division multiplexing(OFDM) communication. The bandwidth and power efficiency are the main consideration. The phases of rotation vector are added to those of both pilot symbols and data symbols interlaying between any two pilot symbols in an OFDM block. Owing to this scheme the transmitter reduces the PAPR using the partial transmit sequences(PTS) and the receiver restores the data symbol utilizing the channel estimation of pilot symbols. Therefore, the bandwidth efficiency is accomplished by not using the further subcarriers for the reduction of PAPR and the enormous increase of bit error rate according to the receiving error of the side information, i.e. the phases of rotation vector, is prevented. In other words, both bandwidth-and power-efficiency and quality of communication performance can be improved.

• Journal of The Institute of Information and Telecommunication Facilities Engineering
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• v.4 no.1
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• pp.7-13
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• 2005

In this paper, we propose the time synchronization module on fiber optic repeater to use optic line delay for obtaining time synchronization between up-link and down-link, in the 2.3 GHz WiBro network using TDD/OFDM (Time Division Duplex/Orthogonal Frequency Division Multiplexing) Generally, when we use fiber optic repeater to remove the shade area, it occurs transmission delay which is caused by optic transmission between RAS (Radio Access Station) and fiber optic repeater and inner delay of fiber optic repeater. Because the WiBro system is adopting a TOO method and there exists the difference of switching time which is caused by these delay between up-link and down-link, it occurs ISI (Inter Symbol Interference), ICI (Inter Carrier Interference). These interference results in the reduction of the coverage. And the inconsistency between Up-Link and Down-Link switching time maybe gives rise to the interruption of communication. In order to prevent these cases, we propose synchronization module using analog optic line delay as the one of synchronizing up-link and down-link. And we propose the consideration factor for the designing time synchronization module and the feature of optic line of analog method. The measurement result of optic line time synchronization module of structure proposed is as follows, the delay error of $0.5{\mu}g$ and the insertion loss value below maximum 4.5dB in range of $0{\sim}40{\mu}s$. These results fully meet the specification of WiBro System.

• Journal of Korea Society of Industrial Information Systems
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• v.16 no.4
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• pp.27-35
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• 2011

Multicarrier-Direct Sequence/Code Division Multiple Access(MC-DS/ CDMA) which is a combination of Orthogonal Frequency Division Multiplexing(OFDM) and DS/CDMA has been of significant interest as a means to take such advantages as bandwidth efficiency, high bit rate and robustness against multipath fading. In this paper we study a reduced-complexity multiuser detection aided multirate MC-DS/CDMA with time(T)-domain and frequency(F)-domain spreading. The one- dimensional orthogonal variable spreading factor(1D OVSF) code extracted from 2D OVSF code are used as a spreading code in T/F-domain. The proposed system will use code grouping interference cancellation(CGIC) receiver to reduce Multiuser Interference(MUI). The CGIC receiver uses code grouping by the correlation properties of 1D OVSF code and dose not requires the code information and activity of other user. The multiuser detector with CGIC receiver will be analyzed in Time- and Frequency-domain separately(jointly). The system performance is analytically derived in Additive White Gaussian Noise(AWGN) channel and we also compare the system performance between proposed system and T/F spreaded single(multi) rate multiuser MC-DS/CDMA system. In the computer simulation results, the proposed receiver of demonstrated huge performance improvement over conventional matched filter receiver.

• Proceedings of the Korean Society of Broadcast Engineers Conference
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• 2010.11a
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• pp.63-66
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• 2010

본 논문은 차세데 3D-TV 방송을 위해 수정된 ATSC (Modified Advanced Television Systems Committee) 시스템 [1]에서 파일럿 (Pilot)을 이용한 채널 추정 대신, PN 시퀀스 (Pseudo-Noise Sequence)를 이용한 채널 추정 방식의 문제점에 대하여 2가지 방법으로 연구하였다. PN 시퀀스를 이용하여 채널을 추정하는 TDS-OFDM (Time Domain Synchronous - Orthogonal Frequency Division Multiplexing)시스템은 QAM (Quadrature Amplitude Modulation) 변조 방식을 사용하기 때문에 수신측 PN 시퀀스의 위상 변화가 일어나지 않는다. 하지만 수정된 ATSC 시스템에서 사용하는 VSB (Vestigial Side Band)변조 방식에서 직교위상 (Quadrature) 채널을 통해 전송되는 값은 동위상 (In-Phase) 채널을 통해 전송되는 값의 단순한 힐버트 변환 (Hilbert Transform)에 의해 생성되어 불규칙한 위상 변화가 발생한다. 따라서 수정된 ATSC 시스템에서 채널 추정을 위해 PN 시퀀스를 사용하게 된다면 상관 (Correlation) 특성을 잃어버릴 것이며 올바른 채널 임펄스 응답 (Channel Impulse Response)을 얻을 수 없다.

• Journal of Communications and Networks
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• v.10 no.3
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• pp.258-267
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• 2008

In this paper, we examine what changes the next-generation wireless communication systems will experience in terms of the technologies, services, and networks and, based on that, we investigate how the inter-cell interference management should evolve in various aspects. We identify that the main driving forces of the future changes involve the data-centric services, new dynamic service scenarios, all-IP core access networks, new physical-layer technologies, and heavy upload traffic. We establish that in order to cope with the changes, the next-generation inter-cell interference management should evolve to 1) set the objective of providing a maximal data rate, 2) take the form of joint management of power allocation and user scheduling, 3) operate in a fully distributed manner, 4) handle the time-varying channel conditions in mobile environment, 5) deal with the changes in interference mechanism triggered by the new physical-layer technologies, and 6) increase the spectral efficiency while avoiding centralized coordination of resource allocation of the users in the uplink channel.

• ETRI Journal
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• v.34 no.5
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• pp.655-665
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• 2012

Based on wideband precoding (WBP) in the multiple-input multiple-output orthogonal frequency division multiplexing system, an adaptive nonuniform codebook is presented in this paper. The relationship between the precoder distribution and spatial correlation is analyzed at first. A closed-form expression based on overlapped isosceles triangles is proposed as an approximation of the precoder distribution. Then, the adaptive codebook design is derived with the approximate distribution to minimize quantization errors. The capacity and bit error rate performance demonstrate that the adaptive codebook with WBP outperforms the conventional fixed uniform codebook.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.9 no.6
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• pp.2201-2216
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• 2015

Peak to average power ratio (PAPR) is one of the main imperfections in the broadband communication systems with multiple carriers. In this paper, a new crest factor reduction (CFR) scheme based on interleaved phase sequence called Dummy Sequence Insertion Enhanced Partial Transmit Sequence (DSI-EPTS) is proposed which effectively reduces the PAPR while at the same time keeps the total complexity low. Moreover, the prototype of the proposed scheme in field programmable gate array (FPGA) is demonstrated. In DSI-EPTS scheme, a new matrix of phase sequence is defined which leads to a significant reduction in hardware complexity due to its less searching operation to extract the optimum phase sequence. The obtained results show comparable performance with slight difference due to the FPGA constraints. The results show 5 dB reduction in PAPR by applying the DSI-EPTS scheme with low complexity and low power consumption.

• Proceedings of the Korean Information Science Society Conference
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• 2003.04d
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• pp.515-517
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• 2003

In this paper we examine the effects of the required portions of guard timing spaces in a MAC frame of ETSI BRAN HIPERLAN/2 system such as inter-mobile guard timing space in UL(Up Link) duration, inter-RCH(Random CHannel) guard timing space, sector switch guard timing space. In particular, we calculate the number of OFDM(Orthogonal Frequency Division Multiplexing) symbols required for these guard timing spaces in a MAC frame. We them evaluate the throughput of HIPERLAN/2 system as we vary parameter such as the guard time values defined in [2], the number of DLCCs(Data Link Control Connections), and the number of RCHs. Finally we show by numerical results that the portions for the 새심 summation of required guard timing spaces in a MAC frame are not negligible, and that they should be properly considered when trying to evaluate the performance of MAC protocol of HIPERLAN/2 system and also when determining the number of RCHs as well as the number of DLCCs in UL PDU trains at an AP/CC(Access Point/Central Controller).

• ETRI Journal
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• v.44 no.3
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• pp.400-412
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• 2022

In cognitive radio networks (CRNs), the computational complexity of resource allocation algorithms is a significant problem that must be addressed. However, the high computational complexity of the optimal solution for tackling resource allocation in CRNs makes it inappropriate for use in practical applications. Therefore, this study proposes a power-based pricing algorithm (PPA) primarily to reduce the computational complexity in downlink CRN scenarios while restricting the interference to primary users to permissible levels. A two-stage approach reduces the computational complexity of the proposed mathematical model. Stage 1 assigns subcarriers to the CRN's users, while the utility function in Stage 2 incorporates a pricing method to provide a power algorithm with enhanced reliability. The PPA's performance is simulated and tested for orthogonal frequency-division multiplexing-based CRNs. The results confirm that the proposed algorithm's performance is close to that of the optimal algorithm, albeit with lower computational complexity of O(M log(M)).

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.45 no.11
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• pp.1-8
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• 2008

In this paper, we analyze the symbol error rate (SER) performance of maximum likelihood (ML) joint detection in downlink multiple-input multiple-output (MIMO) multicarrier code division multiple access (MC-CDMA) systems by deriving a tight union bound on the symbol error rate (SER). The union bound for ML joint detection is utilized to demonstrate the performance of MIMO MC-CDMA systems quantitatively in multiuser and frequency selective Rayleigh fading environments. An analysis of the diversity order of the systems shows the effects of multiple users, spread subcarriers, and multiple antennas on the ML joint detection performance. Furthermore, the analysis shows that MIMO MC-CDMA systems without full loading can achieve more diversify than MIMO orthogonal frequency division multiplexing (OFDM) systems.