• Proceedings of the KAIS Fall Conference
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• 2010.11a
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• pp.225-227
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• 2010

본 논문은 OFDM 방식의 고속 광대역 모뎀의 주파수 오프셋을 추정하고 보상하는 알고리즘에 관한 것이다. 설계된 주파수 오프셋 추정 및 보상 알고리즘은 프리앰블 구간에서 초기 CFO(carrier frequency offset)를 추정 및 보상하고, 데이터 전송구간에도 잔류 CFO를 추정하고 보상하도록 동작한다. 초기 CFO보상은 시간축에서 동작하고, 잔류 CFO 보상은 FEQ 뒤에서 파일럿 캐리어의 정보를 이용하여 이루어진다. 잔류 주파수 오프셋을 보상할 때에는 ADC/DAC의 SFO(sampling frequency offset)도 추정하여 잔류 CFO와 동시에 보상하게 된다.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.10 no.5
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• pp.798-805
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• 2006

I evaluate the BER performance of downlink OFDMA systems in time variant Rayleigh Doppler fading channel, considering the carrier frequency offset and the nonlinear high power amplifier. I obtain the required output back-off of the nonlinear amplifier and value of frequency offset for good BER performance. And I also analyze the BER degradation upon Doppler fading channel.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.11 no.12
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• pp.2391-2397
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• 2007

I evaluate the BER performance of uplink OFDMA systems in time variant Rayleigh Doppler fading channel, considering the carrier frequency offset and the nonlinear high power amplifier. I obtain the required output back-off of the nonlinear amplifier and value of frequency offset for good BER performance. And I also analyze the BER degradation upon Doppler fading channel.

• Journal of IKEEE
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• v.3 no.1 s.4
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• pp.39-49
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• 1999

This paper describes a 1 GHz, low-phase-noise CMOS fractional-N frequency synthesizer with an integrated LC VCO. The proposed frequency synthesizer, which uses a high-order delta-sigma modulator to suppress the fractional spurious tones at all multiples of the fractional frequency resolution offset, has 64 programmable frequency channels with frequency resolution of $f_ref/64$. The measured phase noise is as low as -110 dBc/Hz at a 200 KHz offset frequency from a carrier frequency of 980 MHz. The reference sideband spurs are -73.5 dBc. The prototype is implemented in a $0.5{\mu}m$ CMOS process with triple metal layers. The active chip area is about $4mm^2$ and the prototype consumes 43 mW, including the VCO buffer power consumption, from a 3.3 V supply voltage.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.39C no.5
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• pp.413-417
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• 2014

In coherent superhigh speed optical transmission link, compensating the system impairments are critical issues. Among these issues, phase noise and carrier frequency offset are the most important impairments which interrupt the signal recovery. This paper suggests a algorithm of digital signal processing that compensates the phase noise and carrier frequency offset and verified its validity. The suggested digital signal processing algorithm has a lower computational complexity compared with the previous algorithms, so it can ease the burden of signal processing at the receiver to provide high speed optical transmission system.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.34 no.4C
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• pp.424-429
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• 2009

This paper suggests an autocorrelation function (AF) based carrier frequency offset (CFO) estimator based on a training sequence in flat fading channels. The proposed CFO estimator has the reduced computational burdens in the calculation of the AF when compared to AF-based conventional frequency estimators. The simulation results show that the proposed estimator achieves a better performance than the existing estimators. Furthermore, the performance of the proposed method has been observed to lie close to the Cramer-Rao lower bound (CRLB).

• The Journal of Korean Institute of Communications and Information Sciences
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• v.25 no.8B
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• pp.1436-1444
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• 2000

In this paper, we propose the joint carrier and symbol timing recovery algorithm using repetitive preamble and differential detection for burst modem. The proposed algorithm can estimate the frequency offset and the symbol timing error regardless of the amount of frequency offset, with a high accuracy, even using very short preamble and at low SNR values. The algorithms for continuous phase frequency shift keying (CPFSK) and phase shift keying (PSK) types are developed. Through computer simulations, we compare the proposed algorithm with the existing algorithms on the estimation accuracy in terms of the preamble length, and analyze those bit error rate(BER) performance.

• ETRI Journal
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• v.35 no.4
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• pp.706-709
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• 2013

As an alternative to the traditional pilot-aided orthogonal frequency division multiplexing (OFDM), the time-domain pseudonoise (PN)-padded OFDM provides a higher spectral efficiency. However, the carrier frequency offset (CFO) attenuates peaks of the conventional PN correlation output, which limits the CFO estimation range of the OFDM synchronizer. An improved correlation is proposed in this letter to remove the CFO-induced amplitude attenuation of correlation peaks. For a synchronizer adopting the designed correlator, a larger range of CFO acquisition is obtained through using wider correlation windows with a smaller interval between them. The proposed method of CFO acquisition is verified in a digital terrestrial multimedia broadcast receiver, in which the synchronizer is able to acquire CFOs up to ${\pm}320$ kHz in the DVB-T F1 channel. Furthermore, the acquisition range can be expanded in more favorable channels.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.29 no.1A
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• pp.18-30
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• 2004

In this paper, the calibration problem of an asynchronous CDMA-based antenna array is studied. A new iterative calibration algorithm for antenna array in the presence of frequency offset error is presented. The algorithm is applicable to a non-linear array and does not require a prior knowledge of the (direction of arrivals) DOAs of the signals of any user, and it only requires the code sequence of a reference user. The algorithm is based on the two step procedures, one for estimating both channel and frequency offset and the other for estimating the unknown array gain and phase. Consequently, estimates of the DOAs, the multi-path impulse response of the reference signal sources, and the carrier frequency offset as well as the calibration of antenna array are provided. The performance of the proposed algorithm is investigated by means of computer simulations and is verified by using field data measured through a custom-built W-CDMA test-bed.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.40 no.9
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• pp.1699-1709
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• 2015

Moving terminals like high-speed-train undergo high Doppler frequency shift, and this leads to carrier frequency offsets that have to be compensated to avoid degradation of communication performance. In multiple access mechanism like OFDMA, base-stations need complex hardware to compensate the uplink frequency offset. In this paper, we propose a method, which can reduce burden of the base-station and makes frequency offset estimation and compensation simple. This method contains transmitting new synchronization signal, estimating frequency offsets in base-station, transmitting feedback information to terminal, and compensating the offset in uplink transmission. Simulation results show the proposed method operates well in high Doppler frequency shift conditions of 500 km/h which is the requirements of 5G mobile communication.