Research On The TOA Estimation Techniques In OFDM Wireless Systems

Orthogonal frequency division multiplexing (OFDM) has been applied into many wireless systems, such as the communication systems in the space, the wireless local area networks, the wireless metropolitan area networks, and the wireless cellular networks. The time-of-arrival (TOA) estimation techniques for the OFDM signals are researched and applied in the OFDM systems because of the increasing requirements for the services of ranging, localization, navigation, remote sensing, and so on. The available researches and applications include the TOA localization applications in the Wi-Fi networks, the positioning and ranging applications in the WiMAX networks, the positioning applications in the 3GPP LTE systems, and the applications in the wireless systems in the space. Although there have been so many researches, the TOA estimation techniques for the OFDM signals are not developed perfectly. The dissertation investigates the TOA estimation techniques for the OFDM wireless signals in the additive white Guassian noise (AWGN) channels, the TOA estimation techniques in the Multipath channels for the OFDM wireless signals where all the sub-bands are available to a single user, and the TOA estimation techniques for the orthogonal frequency division multiple access (OFDMA) wireless signals where all the sub-bands are not available to a single user. The main research works and innovation points are listed as follow:1. In the TOA estimation for the OFDM wireless signals in the AWGN channels, the traditional TOA estimation algorithms based on the pseudorandom noise (PN) sequences and the phases of continuous waves are studied. And a TOA estimation algorithm based on the correlation property and phase differences between the sub-carriers in the OFDM symbol is proposed. An iterative TOA estimation algorithm based on maximum-likelihood (ML) is proposed according to the properties of the cost function in the ML TOA estimation algorithm for the OFDM signals in the AWGN channels. The proposed sub-carrier phase difference based TOA estimation algorithm consists of a TOA coarse estimation based on sequence correlation and a TOA fine estimation based on the phase differences between the sub-carriers. The algorithm is of a larger non-fuzzy TOA estimation range and higher estimation accuracy, compared with the traditional algorithms. The proposed iterative TOA estimation algorithm is of lower complexity compared with the ML algorithm with exhaustive search, and higher accuracy compared with the proposed sub-carrier phase difference based algorithm. 2. In the TOA estimation for the OFDM wireless signals in the multipath channels, the cell search scheme and TOA estimation algorithm for the OFDM signals in the multipath channels are investigated for the TOA estimation procedure. A novel cell search signal and cell search scheme based on sequence and sign detection are proposed for the problems of the interference between sectors, multipath fading, frequency offset, and timing offset. The problems of multipath effect and resolution are analyzed for the available sequence correlation based OFDM TOA estimation algorithm, and the problem of high complexity is analyzed for the super-resolution algorithms. Based on the analysis, a novel TOA estimation algorithm is proposed for the OFDM TOA estimation in the multipath channels. In the proposed algorithm, the coarse TOA estimation is achieved with leading edge search. Then the effect of the fractional TOA on the cost function of the coarse estimation is investigated, and the Fine TOA estimation is achieved by defining a spreading function. The simulation results show that the proposed cell search scheme is of low complexity and high efficiency. The proposed OFDM TOA estimation algorithm is of high ability of anti-multipath, and the TOA estimation resolution is not limited by the sampling rate. Although, compared with the ML algorithm, the proposed algorithm is of a lower accuracy, the complexity is much lower than that of the ML algorithm.3. In the TOA estimation for the OFDMA wireless signals, the frequency offset estimation algorithm for signal preprocessing and OFDMA TOA estimation algorithm are investigated. A training sequence is designed for the frequency offset estimation, and a frequency offset estimation algorithm is proposed for the OFDMA sub-band based subcarrier assignment. The algorithm is based on the phase difference between the subcarriers in the neighboring symbols. In the OFDMA TOA estimation, the available training sequence and TOA estimation algorithms are analyzed. The available training sequence is improved for the full use of frequency resources. According to the improved sequence, a novel TOA estimation algorithm is proposed. In the proposed TOA estimation algorithm, the coarse estimation is achieved with the differential correlation between the subsequences at the odd sub-carriers and the even sub-carriers and the peak searching on the channel impulse response. And the fine TOA estimation is achieved based on the variation of the channel impulse response for the compensation of the fractional TOA. The Simulation results show that the proposed frequency offset estimation algorithm is of higher accuracy compared with the CP based algorithm. The resolution of the proposed OFDMA TOA estimation algorithm is not limited by the sampling rate, and the accuracy is higher compared with the LS algorithm.