Youxi Tang

A novel frequency offset estimation method for OFDM systems with large estimation range

In this paper, we proposed a novel frequency synchronization method which has larger estimation range than conventional method proposed by Tufvesson. A two steps frequency offset estimation method is performed in the new method. In the first step the received signal is correlated with local training sequence to eliminate the influence of training sequence which makes the estimation range of frequency offset is independent of period of the repeated data in the training sequence. The received signal is correlated with its delay in the second step to obtain the fine estimation of frequency offset. Precise estimation can be achieved in the proposed method than Tufvessons method. The period of the repeated data in the training sequence determines the estimation range of the frequency offset in the conventional method, while in the new method they are irrelevant. Tens of subcarriers spacing can be estimated by the new method. The new method can be used in other cases as long as a known sequence is transmitted, which will introduce valuable flexibility in training sequence design. The validity of the algorithm is verified in AWGN channel and multipath fading channel.

Clipping noise mitigation for channel estimation in OFDM systems

This letter provides a new technique to mitigate the clipping noise on pilot symbols in clipped and pilot-aided orthogonal frequency division multiplexing (OFDM) systems. The basic principle is to directly filter the clipping noise on the positions of pilots in the frequency domain before the insertion of pilots. Simulation results show that the new technique can effectively improve channel estimation and system performance

A minimum clipping power loss scheme for mitigating the clipping noise in OFDM

The paper proposes a new method, minimum clipping power loss scheme (MCPLS), to control the clipping noise based on the relationship between the power of clipped portion and the clipping noise power of OFDM signals. First, the transmitter generates multi-route signals that carry the same information then estimates the clipping noise power of every route under the same clipping threshold. The transmitter then selects the signal with the lowest clipping noise power to clip and transmits the signal. The simulation results proved that this method can mitigate clipping noise and improve the performance of the system. The signal-to-noise ratio is gained 8 dB to achieve 10/sub -3/ symbol-error-rate when the number of subcarriers is 256, the modulation mode is 16-QAM, the clipping threshold is 1.5 and the redundancy of system is 0.59%. The floor of symbol-error-rate is reduced from 10/sub -3/ to 3/spl middot/10/sub -5/. The arithmetic achieves better effect if the threshold is lower.

OFDM synchronization using PN sequence and performance

In this paper, we propose a novel method for orthogonal frequency-division multiplexing (OFDM) time and frequency synchronization by using PN sequence and barker code, time synchronization performance is improved by barker code, and we also propose a simple but effective method by setting the threshold during time synchronization. Improved frequency synchronization algorithm is presented in this paper too. The idea of multipath utilizing is the core of the frequency synchronization algorithm. The performance of the synchronization proposed here is better than that of conventional methods. Estimation precision is boosted from 10/sup -3/ to 10/sup -4/ for moderate SNR. The requirements of time and frequency synchronization for beyond 3G system based on OFDM can be well satisfied while using the proposed method.

Frequency synchronization in MIMO OFDM system

The paper proposes a frequency offset method in multi-input multi-output (MIMO) orthogonal frequency division multiplexing (OFDM) systems; it is an improvement of the method of T.C.W. Schenk and A. van Zelst (see Proc. IEEE Vehicular Tech. Conf., Fall 2003). A two-step strategy is adopted. First, a small correlation span is used to get a large estimation range. After the estimated frequency offset is compensated, a large correlation span is used to make the estimation more precise. Simulations in AWGN and Rayleigh channels verified the validity of the proposed algorithm.

A precise frequency offset estimator for OFDM system

In this paper, we proposed a new frequency synchronization method for orthogonal frequency division multiplexing (OFDM) system by using PN sequences. It is an improvement of Tufvessons method. In the new method the frequency offset is estimated in two steps. First a small step (span of the correlation) is used for estimation of frequency offset which will result in a larger estimation range but is less precise. After the frequency offset has been compensated, the second estimation is conducted which is a large step. The new algorithm has large estimation range and the estimation is more precise. Performance of the new estimator is improved drastically compared to that of the old one. In AWGN channels, the Cramer-Rao bound of the new method is achieved and it coincides with the Cramer-Rao bound of Schmidls method.

OFDM clipping noise mitigation by a novel minimum clipping power loss scheme

The performance of a new method, minimum clipping power loss scheme, which is based on the relationship between the powers of clipped portion and the clipping noise power of OFDM signals is analyzed in this paper. The effect of different power allocation schemes on the side-information is given. The simulation results prove this method can mitigate clipping noise and improve the performance of system. The performance of the arithmetic is better than that of using the partial transmit sequences to mitigate the clipping noise. The floor of symbol-error-rate is reduced. The arithmetic achieves the better effect if the threshold is lower. While the number of subcarriers is large enough, the performance of system can be close to the theory value.

Effect of channel estimation error onto the BER performance of PSAM-OFDM in Rayleigh fading

In this paper, the current analysis focuses on the influence of BER performance in Rayleigh fading propagation environments, which results from the channel estimation error of pilot symbol assisted modulation (PSAM) in orthogonal frequency division multiplexing (OFDM) systems. This paper first characterizes the distribution of the amplitude and phase estimates using PSAM, and the formula for BER as a function of channel correlation and interpolation filter in time and frequency is given. Also interchannel interference due to Doppler effects is taken into account. Theoretical and simulation results show that channel estimation error leads to a 1-dB degradation in average signal-to-noise ratio for the parameters considered.

Optimum partial interference canceling factor in pilot assistant coherent OFDM system with power training sequence synchronization

Correct time and frequency synchronization is important for the performance of orthogonal frequency-division multiplexing (OFDM) system. While using the partial power training sequences to synchronize in orthogonal frequency-division multiplexing (OFDM) system, the received data signals will be interfered by the training sequences. In this paper, we give a method for suppressing the interference caused by the training sequence, and introduce an optimized formula for the partial interference canceling factor of partial power training sequence. The above technique is evaluated by means of pilot assistant coherent OFDM system under time-varying multipath Rayleigh fading channels, and the linear interpolation channel estimator is employed to exploit the frequency domain correlation. Especially we focus on only one OFDM symbol in a packet transmission, that is, both the OFDM data and the training sequences are included in one OFDM symbol, and there are no other symbols before or after it. Both theoretical and simulated results of the above technique are presented. It has been shown that the better BER performance can be achieved as compared with no separation, and only the one OFDM symbol can accomplish user data communication assignment.

A high performance frequency offset estimation method for OFDM systems

In this paper, we proposed a new frequency synchronization method for an orthogonal frequency division multiplexing (OFDM) system by using training sequences. In the conventional method, the estimation range of the frequency offset is determined by the period of the repeated sequences which compose the training sequence. But in the new method it is independent of period of the repeated sequences. The proposed method can estimate frequency offset over ten times the subcarrier separation. So we can choose a longer period of repeated sequence for time synchronization, which means much better performance can be achieved. Also the method can be extended to any other methods for frequency synchronization as long as a known training sequence is used.