• 전자공학회논문지 IE
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• v.47 no.3
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• pp.35-40
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• 2010

In this paper, we propose an algorithm to improve the precision of initial carrier-frequency offset estimation for multiband-OFDM (MB-OFDM) UWB system which is considering the quantization-noise effect. In the general OFDM system, the two adjacent and repeated preamble symbols are used for the initial carrier-frequency synchronization while the performance of the frequency-offset estimation is bounded by quantization effect generated from analog-to-digital conversion at the receiver. This paper proposes a method in which one-symbol interval between two adjacent preamble symbols for the initial frequency synchronization is extended to multiple-symbol interval between non-adjacent symbols in an extent that phase ambiguity does not occur. In this paper, we also present '6' as optimal multiple symbol interval for the MB-OFDM system with 30 preamble symbols on 3-band hopping and with 4-bit A/D conversion at the receiver. Under the channel environments for the MB-OFDM UWB system, the simulation results show that the proposed estimation algorithm can achieve the initial estimation in offset precision less than 5 ppm.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.16 no.3
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• pp.97-102
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• 2016

The UFMC(Universal Filtered Multi-Carrier) is one of multi-carrier transmission technique as a candidate of transmission method for the recent 5G communication system. The UFMC can be considered as the system which has both the advantages of OFDM(Orthogonal Frequency Division Multiplex) and the simplicity of FBMC(Filter Bank Multi-Carrier). CFO(Carrier Frequency Offset) causes the problem to lower the BER performance due to a mismatch between the sub-carriers in multi-carrier transmission scheme. The effect of CFO on UFMC is not greater than the OFDM. But it still degrades the system performance caused by interference between the sub-band. In this paper, we analyze the SNR degradation due to changes in the value of EsNo and CFO on UFMC system.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.12 no.3
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• pp.391-400
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• 2001

In this paper, the performance of a multicarrier CDMA system applying M-ary orthogonal signaling and adaptive subchannel allocation scheme is analyzed for forward links in Rayleigh fading channel. Also, the effect of error caused by subchannel allocation is analyzed. In the proposed system, each DS waveform is transmitted over the subchannel having the biggest fading among L subchannels. Considering M-ary orthogonal signaling and 4 subchannels, the BER of $10^{-3}$ is satisfied if SNRs are 7.33 dB, 5.33 dB, and 4.47 dB for k = 1, 2, and 3, respectively. Therefore, SNR is decreased as k is increased. If the error of subchannels exists, the BER of $10^{-3}$ is met if SNR is 8.18 dB in the absence of M-ary orthogonal signaling. So, a required SNR is declined about 0.85 dB. Adding the M-ary orthogonal signaling with k = 4, it is observed that the multicarrier CDMA system has performance improvement because a required SNR is 5.44 dB.

• 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.

• Proceedings of the IEEK Conference
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• 2000.09a
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• pp.55-58
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• 2000

본 논문에서는 제한된 통신 채널의 대역에서 주파수 효율이 높은 OFDM 시스템을 위한 반송파 주파수 동기 알고리즘을 제안한다. OFDM 시스템에서의 반송파 주파수 옵셋은 부반송파 간격의 정수배와 소수배로 나누어진다 소수배 주파수 옵셋이 ± 0.5 근처의 값을 가질 경우에는 정확한 정수배 주파수 옵셋 추정이 어렵고 반송파 동기 PLL이 소수배 주파수 옵셋을 추적하는데 많은 시간이 소요된다. 제안한 알고리즘은 정수배 주파수 옵셋을 제거하기 위해 2개의 심볼 만을 이용하고 다중경로 패널에서도 정확한 정수배 주파수 옵셋의 추정이 가능하다 또한, 소수배 주파수 옵셋이 ± 0.5 근처의 값을 가질 경우 적은 계산량으로 주파수 옵셋을 ± 0.1 이내로 보상할 수 있다.

• Bulletin of the Korean Space Science Society
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• 2004.04a
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• pp.43-43
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• 2004

국제적인 시각비교를 위해 GPS를 이용하고 있으나, GPS 신호에는 위성까지의 거리정보뿐 아니라 위성시계, 대류층, 이온층, 다중경로 오차 등이 포함되어 있다. 그 중 이온층 지연시간을 측정하기 위해서는 Ll과 L2 반송파 신호로부터 얻어지는 P코드와 위상정보를 이용할 수 있다. 반송파 위상 정보는 P코드보다 해상도가 좋기 때문에 위상정보를 이용하게 되면 고정밀도의 이온층 지연시간을 얻게 된다. 이온층 지연시간을 통해 총전자수를 나타내는 TEC 값을 얻을 수 있는데, 관측지점으로부터 시간에 따라 가장 높은 고도의 위성을 선택하여 P코드와 반송파 위상 정보를 통한 이온층 총전자수를 파악하고 정밀도를 비교분석 하였다. (중략)

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.34 no.11
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• pp.47-53
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• 2006

The power losses due to modulation index for multi-modulation scheme were analyzed under various transmission mode of satellite control and the necessary satellite link margin for transmission mode were proposed in this paper On the basis of the analyses for interference between the transmission signals and threshold of satellite control signal receiver, the optimal subcarrier signals were proposed for satellite range measurement methods, respectively. The subcarrier signal of 12 kHz or 14 kHz is proper for telecommand using the ESA method, and 16 kHz for telecommand signal using the GSTDN method. On the other hand, the telemetry subcarrier of 65.536 kHz is a proper in the viewpoint of receiver threshold value.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.24 no.6B
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• pp.1024-1031
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• 1999

In order to transmit high-speed wide band signals efficiently in multipath fading environments, M-ary QAM signalling combined with OFDM transmission technique is applied. In this paper, the effect of synchronization error caused by carrier frequency offset and SER(Symbol Error Rate) performance of OFDM-16QAM and OFDM-64QAM are theoretically analyzed. Our result shows that as the number of sub-carrier in OFDM system increases the frequency-offset caused inter-channel interference(ICI) increases significantly, and that an error floor occurs even at high SNR of OFDM system. For OFDM-64QAM, the error floor occurs at SER=1$\times$10-7 when a normalized frequency-offset is 0.001, in which the SNR degradation is much greater than that of OFDM-16QAM. From this study the maximum allowable frequency-offset of OFDM-16QAM and OFDM-64QAM systems can be determined to meet the specific SER requirement.

• 전자공학회논문지 IE
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• v.45 no.1
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• pp.24-30
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• 2008

In this paper, Digital MultiTone(DMT) is an emerging multi-carrier modulation scheme, which has been adopted for VDSL(Very high speed Digital Subscribe Line). A problem of DMT is its sensitivity to frequency offset between the transmitted and received carrier frequencies. This frequency offset introduces inter-carrier interference(ICI) in the DMT symbol. This paper is proposed an ICI cancelation scheme using Kalman Filtering. The performance of the proposed method is compared with conventional methods in terms of bit error rate performance, bandwidth efficiency, and computational complexity. Through simulations, it is shown that for high values of the frequency offset and for higher order modulation schemes, the EKF(Enhanced Kalman Filtering) method perform better than the others.

• Journal of Advanced Navigation Technology
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• v.14 no.5
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• pp.640-647
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• 2010

Many methods have been proposed to detect faults of carrier phase measurements, but there are no distinguished methods for land transportation systems. in this paper, the baseline constraints are used to detect faults in GPS carrier phase measurements with vehicle dynamic information. The faults include the multipath on GPS carrier measurements. Multiple antenna groups are used for this research. In the measurement domain the fault detection has been accomplished so that the implementation is easier than other methods.