Shaoqian Li

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.

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.

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.

OFDM frequency offset estimator using PN sequences and its improvement

We propose two new frequency synchronization methods for the orthogonal frequency division multiplexing (OFDM) system. They have a large estimation range and acceptable precision in the Rayleigh channel. One of the methods does not waste system bandwidth because the training sequence is superimposed on the data of the OFDM symbol. The performance of the two methods is better than that of the method proposed by F. Tufvesson et al. (see Proc. IEEE Vehicular Technology Conf. VTC 1999-Fall, p.2203-7, 1999).

Adaptive admission control strategy for multiple services in WCDMA system

The third generation mobile communication systems are expected to offer a large variety of services and calls for more flexible and efficient admission control strategy. This paper presents an adaptive admission control strategy for uplink transmission in WCDMA systems. The adaptive strategy gives priority to handoff calls and dynamically adjusts the number of guard channels according to the failure rates of the handoff calls. Simulation results demonstrate that the proposed strategy is more robust than fixed strategy under different mobility environment.

Comparison of the BER performance of symbol-by-symbol and multiple-symbol differential detection OFDM system in multipath fading channels

In multipath channels, for orthogonal frequency division multiplexing (OFDM) system, the bit error rate (BER) of symbol-by-symbol differential detection (SSDD) is analyzed, the comparison of BER performance of SSDD and multi-symbol differential detection (MSDD) is obtained by simulation, the results indicate that when the whole bandwidth of the symbols used to MSDD is much less than the coherent bandwidth of the channel, the BER performance of MSDD is better than that of SSDD; when the whole bandwidth of the symbols used to the MSDD is closed to the coherent bandwidth of the channel, the BER performance of SSDD is better than that of MSDD.

NEW FREQUENCY SYNCHRONIZATION ESTIMATOR FOR OFDM BY USING PN SEQUENCES AND CYCLIC PREFIX

A new frequency synchronization method is proposed in this paper. It uses PN (pseudo-noise) sequences and cyclic prefix for synchronization in OFDM (orthogonal frequency division multiplexing) system. Several subcarriers estimation range can be reached using the new method. When cyclic prefix is used in fine frequency synchronization, the MSE (mean square error) of the proposed method is less than the method only used PN sequences for the span of the correlated data is large. This has been verified by simulations in AWGN channel and Rayleigh channel.

New packet scheduling algorithm in wireless CDMA data networks

The future 3G/4G wireless communication systems will provide internet access for mobile users. Packet scheduling algorithms are essential for QoS of diversified data traffics and efficient utilization of radio spectrum.This paper firstly presents a new packet scheduling algorithm DSTTF under the assumption of continuous transmission rates and scheduling intervals for CDMA data networks . Then considering the constraints of discrete transmission rates and fixed scheduling intervals imposed by the practical system, P-DSTTF, a modified version of DSTTF, is brought forward. Both scheduling algorithms take into consideration of channel condition, packet size and traffic delay bounds. The extensive simulation results demonstrate that the proposed scheduling algorithms are superior to some typical ones in current research. In addition, both static and dynamic wireless channel model of multi-level link capacity are established. These channel models sketch better the characterizations of wireless channel than two state Markov model widely adopted by the current literature.