• Proceedings of the Korean Institute of Communication Sciences Conference
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• 1998.10a
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• pp.1009-1013
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• 1998

• The Journal of Korean Institute of Communications and Information Sciences
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• v.36 no.5A
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• pp.432-440
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• 2011

For the 4th generation mobile communication, LTE-advanced system needs the broad frequency band up to 100MHz for providing the data rate of maximum 1Gpbs. However, it is very difficult to secure the broad frequency band in the current frequency allocation situation. So, carrier aggregation was proposed as the solution, in which several fragmented frequency bands are used at the same time. Basically, multiple parallel receivers are required to get the information data from the different frequency bands but this conventional multi-chain receiver system is very inefficient. Therefore, in this paper, we like to study the single chain system that is able to receive the multi-band signals in a single receiver based on the time division multiplexing (TDM) reception method. This proposed TDM receiver efficiently manage to receive the multi-band signals in time domain and handle the baseband signals with one DSP board. However, the serious distortion could be generated by the sampling timing offset (STO) in the TDM-based system. Therefore, we like to analyze STO effects in the TDM-based system and propose a compensation method using estimated STO. Finally, it is shown by simulation that the proposed method is appropriate for the single chain receiver and show good compensation performance.

• The Journal of the Acoustical Society of Korea
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• v.28 no.5
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• pp.432-440
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• 2009

Recently, the necessity of underwater acoustic communication and demand for transmitting and receiving various data such as voice or high resolution image data are increasing as well. The performance of underwater acoustic communication system is influenced by underwater channel characteristic. Especially, a delay spread caused by reverberation and multi-path induces the ISI (Inter-Symbol-Interference) and reduces the communication performance. In this paper, we study the OFDM (Orthogonal Frequency Division Multiplexing) technique for robust the delay spread in underwater channel. We also use the clipping method to overcome the performance degradation in high PAPR (Peak-to-Average Power Ratio). We confirm the performances of underwater communication system by the underwater channel model simulation model and experiment in small water tank. As a result, the multi-carrier modulation with clipping method presented low BER and the previous single carrier modulation had high BER.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.11 no.6
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• pp.1150-1155
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• 2007

Orthogonal Frequency Division Multiplexing (OFDM) is an emerging multi-carrier modulation scheme, which has been adopted for several wireless standards such as IEEE 802.11a and HiperLAN2. A well-known problem of OFDM is its sensitivity to frequency offset between the transmitted and received carrier frequencies. This frequency offset introduces inter-carrier interference (ICI) in the OFDM symbol. This paper investigates three methods for combating the effects of ICI: ICI self-cancellation (SC), maximum likelihood (ML) estimation, and extended Kalman filter (EKF) method. These three methods are compared in terms of bit error rate performance.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.4 no.5
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• pp.691-708
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• 2010

An important issue of supporting multi-users with diverse quality-of-service (QoS) requirements over wireless networks is how to optimize the systematic scheduling by intelligently utilizing the available network resource while, at the same time, to meet each communication service QoS requirement. In this work, we study the problem of a variety of communication services over multi-media heterogeneous cognitive OFDM system. We first divide the communication services into two parts. Multimedia applications such as broadband voice transmission and real-time video streaming are very delay-sensitive (DS) and need guaranteed throughput. On the other side, services like file transmission and email service are relatively delay tolerant (DT) so varying-rate transmission is acceptable. Then, we formulate the scheduling as a convex optimization problem, and propose low complexity distributed solutions by jointly considering channel assignment, bit allocation, and power allocation. Unlike prior works that do not care computational complexity. Furthermore, we propose the FAASA (Fairness Assured Adaptive Sub-carrier Allocation) algorithm for both DS and DT users, which is a dynamic sub-carrier allocation algorithm in order to maximize throughput while taking into account fairness. We provide extensive simulation results which demonstrate the effectiveness of our proposed schemes.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.14 no.1
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• pp.54-61
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• 2003

This paper shows the results of emissive electromagnetic field characteristics on medium voltage power line(22.9 kV). The measurements were taken when communications signals were coupled into the 22.9 kV main wire of medium voltage power-line in a frequency range of 9 kHz to 30 MHz. The results of the measurement are as follows-emissive electromagnetic Held characteristics from multi carrier signals were superior to a single carrier signal. And we confirmed the PLC transmission distance was 1.8 km when multi-carrier transmission power was 20 dBm. Electric field strength was under the 40 dBuV/m at 30 MHz when 10 m method was measured.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.13 no.4
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• pp.285-301
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• 1988

The symbol error rate equations of multi-level quadrature PRS(QPRS) system have been derived in the individual and composite environment of Gaussian/impulsive noise, cochannel CW interference, carrier offset, phase jitter and fading. And using the derived error rate equations, the probability of error has been evaluated and shown in graphs as functions of carrier to noise power ratio, carrier to interference power ratio, phase error, impulsive index, the ration of Gaussian noise to impulsive noise power component, signal to noise power ration in phase locked loop(PLL), and fading figures. The rseults show that the error rate performances are generally more more degraded by impulsive noise than by Gaussian noise. But on the contrary the erors occurred more frequently by Gaussian noise than impulsive noise in a fading environment.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.5 no.4
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• pp.621-629
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• 2001

In this thesis a wireless data transmission system has been proposed and analysed that uses the multi-carrier technique with the adaptive modulation scheme. In general, the OFDM(Orthogonal Frequency Division Multiplexing) system is assigning a same amount of information to all sub-carriers in a wireless data transmission. In the proposed system, the different amount of information is assigned to each sub-carrier depending on the state of channel and the target probability of error of system. With the proposed scheme, the transmission rate can be maximized with the fixed power and the required power to transmit the information can be minimized with the target probability of error of system.

• Electronics and Telecommunications Trends
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• v.11 no.4 s.42
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• pp.13-25
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• 1996

본 고에서는 ADSL(Asymmetric Digital Subscriber Lines) 서비스를 DMT(Digital Multichannel Transmitter) 시스템 모델에 관하여 고찰한다. CSA(Carrier Service Area) 구역에서 6Mb/s급의 다중반송파변조방식(multi-carrier modulation)을 전송방식으로 하는 ADSL-3급 서비스가 가능한 가입자 루프 및 전송신호 특성을 고려한 설계 요구 조건을 살펴보고, 이를 만족하는 DMT ADSL 시스템 모델, 등화기 구조 및 DMT ADSL시스템의 성능예측방법을 고찰함으로써 보다 나은 성능의 ADSL시스템 구현을 위한 설계방향을 제시하고자 한다.

• ETRI Journal
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• v.37 no.2
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• pp.338-347
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• 2015

The multi-carrier transmission signal in Multi-Carrier Code Division Multiple Access (MC-CDMA) has a high peak-to-average power ratio (PAPR), which results in nonlinear distortion and deteriorative system performance. An n-tuple selective mapping method is proposed to reduce the PAPR, in this paper. This method generates $2^n$ sequences of an original data sequence by adding n-tuple of n PAPR control bits to it followed by an interleaver and error-control code (ECC) to reduce its PAPR. The convolutional, Golay, and Hamming codes are used as ECCs in the proposed scheme. The proposed method uses different numbers of the n PAPR control bits to accomplish a noteworthy PAPR reduction and also avoids the need for a side-information transmission. The simulation results authenticate the effectiveness of the proposed method.