The Research On Carrier Frequency Offset Estimation Algorithms For OFDM System With Multiple Antennas

Orthogonal Frequency Division Multiplexing (OFDM) is a new technology in the90s.OFDM isdeveloped from multi-carrier modulation technique, whose distinguished feature is that the varioussub-carriers are orthogonal to each other. OFDM has many outstanding advantages, such as highbandwidth efficiency and strong ability to suppress Inter-Symbol Interference (ISI); and meanwhileOFDM also naturally has the capacity of anti-frequency selective fading. Carrier Frequency Offset(CFO) mainly comes from the frequency deviation between the transmitter and local oscillator of thereceiver and Doppler shift is also a source of it in the mobile channel environment. Not only it causesthe phase rotation of the demodulated constellation points, which will affect symbol decision, but alsothe more serious thing is that the orthogonal between the subcarriers of the system will be destroyedby it, which will result in the interference between the subcarriers, and make the performance of thesystem declining. Compared with the single carrier, the multi-carrier transmission system such asOFDM is more sensitive to the impact of the CFO. In this paper, we research the algorithm of theblind CFO estimation in the OFDM system with multiple antennas. The main work can besummarized as follows:For the Single Input Multiple Output OFDM (SIMO-OFDM) system, we first develop thealgorithms of the CFO estimation based on Multi-Invariance Estimation of Signal Parameters viaRotational Invariance Techniques (MI-ESPRIT) and Multi-invariance Multiple Signal Classification(MI-MUSIC). The simulation results show that the performances of the two algorithms are better thansome conventional CFO estimation algorithm, such as the CFO estimation algorithms based onESPRIT and cyclic prefix, etc. And the CFO estimation algorithm based on MI-MUSIC has betterperformance.In addition, the CFO estimation algorithm based on MI-MUSIC can still work withoutconstant module property or stationary property, and both the integer CFO and the fractional CFO canbe estimated effectively.Then, we propose an algorithm of the CFO estimation based on the trilinear decomposition. Thealgorithm uses trilinear model, and then reconstructs the received signal in the SIMO-OFDM system.Finally it uses the least squares (LS) method to estimate the CFO. The simulation results show that thealgorithm can still work without constant module property or stationary property, and it’s even stillable to work without the virtual carriers.For the Multiple Input Multiple Output OFDM (MIMO-OFDM) system, we propose two algorithms of the CFO estimation based on MI-ESPRIT and MI-MUSIC respectively. Both of the twoalgorithms reconstruct the received signal which will make the received signal have the property ofmulti-invariance, and then use the MI-ESPRIT algorithm and the MI-MUSIC algorithm to estimatethe CFO respectively. The simulation results show the effectiveness of the two algorithms, and thealgorithm based on MI-MUSIC has the more outstanding performance. Meanwhile, the algorithmbased on MI-MUSIC can estimate both the integer CFO and the fractional CFO, which can still workwithout constant module property or stationary property and even without the virtual carriers.