• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.33 no.7A
• /
• pp.702-709
• /
• 2008

This paper presents a frequency offset estimation scheme which can be used for packet based OFDM communication systems. The proposed scheme detects the failure of performing coarse frequency offset estimation and compensates the error of estimated coarse frequency offset. The preamble structure considered in this paper is based on the preamble specified in IEEE802.11a and IEEE802.11p standards. We performed simulation to compare the performance according to the different number of reference packets used to detect the failure of performing coarse frequency offset estimation. The simulation results show that the proposed scheme has better performance than the conventional scheme in the low SNR(below 2dB) environment.

• Journal of the Institute of Electronics Engineers of Korea TC
• /
• v.41 no.9
• /
• pp.47-54
• /
• 2004

The previous works for WLAN system based on OFDM is mainly individual study for independent frequency offset or symbol synchronization. In this paper, the performance of IEEE 802.11a WLAN(Wireless Local Area Network) system in the realistic indoor multipath channel models is analyzed with frequency offset compensation and channel estimation methods. For the performance analysis of the WLAN system indoor Rayleigh multipath channels are adopted, and the BER(Bit Error Rate) of WLAN system is calculated with y2 code-rate 16-QAM based on standard specification. From the simulation results, the difference of required Eb/No for BER of 10-3 is 1-2dB between the channel estimation and frequency offset compensation, and perfect channel estimation and no frequency offset.

• Journal of Positioning, Navigation, and Timing
• /
• v.11 no.3
• /
• pp.191-198
• /
• 2022

In order to increase the practical use and navigational application performance of the Korean Positioning System (KPS), it is required to provide interoperability with other Global Navigation Satellite System (GNSS). This kind of interoperability can be obtained by broadcasting the time offset between KPS and GNSS using a KPS navigation message. With the assumption that KPS Time (KPST) will be generated by the similar method and equipment of UTC(KRIS), the overall behavior of KPST will be close to that of UTC(KRIS). Therefore, the time offset between KPST and GPS Time (GPST) is estimated by using UTC(KRIS) instead of KPST because KPST can not available at the present time. In this paper, we describe the estimation results of the KPS to GPS Time Offset (KGTO) obtained by using a GNSS time transfer receiver which reference inputs are fed from UTC(KRIS). The estimated KGTO performance is compared to the time offset between UTC(KRIS) and UTC(USNO) which is used to generate GPST and considered as the real GPST. The time offset between UTC(KRIS) and UTC(USNO) is obtained by using the Bureau International des Poids et Mesures (BIPM) Circular T report. From the results, it is observed that KGTO can be estimated under 10 ns with the assumption that KPST will be generated by a similar method of UTC(KRIS) generation.

• Proceedings of the IEEK Conference
• /
• 2008.06a
• /
• pp.239-240
• /
• 2008

A new frequency offset estimator using low cross-property of PN sequences is proposed in the orthogonal frequency division multiple access (OFDMA) uplink systems. Simulation results show that the proposed estimator improves the mean square error (MSE) performance compared to conventional estimator [2] where each user have both different timing offset and different frequency offset. In addition, the MSE performance is improved as the length of PN sequence increases.

• Proceedings of the IEEK Conference
• /
• 1999.11a
• /
• pp.51-54
• /
• 1999

It is well known that the OFDM transmission is weak against the frequency offset. We evaluate the BER performance of the OFDM system with guard interval and simple one-tap equalizer bank. For the small frequency offset, the loss in $E_{b}$ $N_{o}$ is about 1㏈ at required BER = 10$^{-5}$ , when the mean value of the second-ray's attenuation coefficient is 0.25 and the normalized frequency offset, which is normalized about OFDM symbol time, is 5%.%.%.

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

• Journal of the Korea Institute of Information and Communication Engineering
• /
• v.12 no.5
• /
• pp.906-911
• /
• 2008

This paper designed Simulik Model to cancel the carrier frequency offset in OFDM using CORDIC Algorithm and evaluated its performance. And Simulink Model compared with Xilinx System Generator Model for FPGA implementation. As a result of simulation, we confirmed that both model is error free by CORDIC when offset frequency is lower than $10^5MHz$. Also, we verified the performance through Hardware Co-simulation with Xilinx Spartan3 xc3s1000 fg676-4 Target Device, and timing analysis and resource estimation.

• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.24 no.9B
• /
• pp.1624-1630
• /
• 1999

Code division multiple access (CDMA) is a promising air interface technique for cellular systems. When an MS (Mobile Station) moves to an adjacent cell, the handoff between the serving cell and the target cell is needed. Compared with the hard handoffs, the soft handoffs between two CDMA channels with the identical frequency assignments and frame offsets can provide a better quality of service by minimizing the undesirable ping pong phenomenon of back-and forth handoffs between two adjacent cells in conventional hard handoffs. For the soft handoff of a call to an adjacent cell to be successful, the adjacent cell should assign to the call the same frame offset as that being used in the original cell by the call. In this paper, considering the assignment states of the frame offsets of the adjacent cells, a frame offset assignment algorithm for the originated call is proposed. And analytic method for the handoff blocking probability due to the lack of the frame offset capacity is also presented to show the advantage of the proposed algorithm with respect to the soft handoff blocking probability.

• The Journal of the Institute of Internet, Broadcasting and Communication
• /
• v.18 no.1
• /
• pp.97-103
• /
• 2018

In satellite communication, modulated beacon signal is spreaded by gold sequence and the modulated beacon is transmitted via linear phase modulation. Due to the difference in characteristics of the satellite and the receiver on the ground, frequency offset (FO) occurs. An existing modulated beacon receiver is a method of synchronizing the frequency of a modulated beacon signal using FFT(Fast Fourier Transform), which not only increases the delay and complexity in terms of system implementation but also has a separate circuit for compensating the phase difference due to FO and phase offset from FFT points. In order to overcome this problem, this paper proposes and analyzes a scheme for compensating and demodulating the coarse FO and phase offset at one time using the 2-phase shaped characteristics of the modulated beacon signal. Also, through the simulation, the modulation index suitable for the proposed method is analyzed and the appropriate cumulative number is also analyzed.

• Journal of the Korea Institute of Information and Communication Engineering
• /
• v.9 no.3
• /
• pp.638-646
• /
• 2005

In recent wireless communications, direct conversion transceiver or If sampling SDR-based receivers have being designed as an alternative to conventional transceiver topologies. In direct conversion receiver a.chitectu.e, the 1.equency/phase offset between the RF input signal and the local oscillator signal is a major impairment factor even though the conventional AFC/APC compensates the service deterioration due to the offset. To rover the limited tracking range of the conventional method and effectively aid compensation scheme in terms of I/Q channel imbalances, the frequency/phase offset compensation in RF-front end signal stage is proposed in this paper. In RF-front end, the varying phase offset besides the fixed large frequency/phase offset are corrected by using early-late phase compensator. A more simple frequency and phase tacking function in digital signal processing stage of direct conversion receiver is effectively available by an ingenious frequency/phase offset tracking method in RF front-end stage.