Research On Carrier Synchronization Algorithm In OFDM System

Orthogonal frequency-division multiplexing(OFDM) technology is a special kind of multi carrier transmission scheme, which is one of the core technologies of the fourth generation mobile communication system(4G). In recent years, OFDM technology has been concerned, mainly because it has a lot of advantages, one of the most important is that it can be very good to fight against narrow band interference and frequency selective fading.In the OFDM system, the power spectrum of the sub channels is overlapped, so the orthogonality between the sub carriers is more stringent. Carrier frequency offset(CFO) will break the orthogonality between the sub carriers, introduce Inter-symbol interference(ISI) and Inter carrier interference(ICI), then resulting in the loss of the OFDM system. Therefore, effective measures must be taken to compensate the deviation of the carrier frequency.In this paper, we study the synchronization techniques in OFDM system, especially the system of carrier synchronization algorithm. These algorithms can be divided into two categories: non data aided and data assistant. The non-data aided algorithms are mainly based on the structure characteristics of OFDM system. Because this kind of algorithm does not rely on auxiliary signal, so the spectrum efficiency is higher. And the data aided method need to insert the loop sequence into the signal.Although it can reduce the data transmission efficiency, it can capture the speed of and the accuracy of estimation and is suitable for data communication. In this paper, we give some specific algorithms for these two kinds of algorithms, including ML algorithm, LS algorithm, Moose algorithm and SC algorithm. Firstly, the basic idea of these algorithms is studied, and then the simulation results of the algorithm are realized. Finally, the simulation results and the performance of the algorithm are analyzed.In the second part of this paper, the advantages and disadvantages of the carrier synchronization algorithm are deeply studied, and the improved algorithm is proposed. Firstly, the disadvantages of ML algorithm are analyzed, and the improved algorithm based on multi-symbol and CP is proposed. Secondly, the least square carrier synchronization algorithm based on LS algorithm is proposed. The new algorithm introducesself-cancellation technology, which reduces the interference of the sub carrier, and makes the received signal more pure, so that the new algorithm has better performance. Then, a cosine function algorithm is proposed by the research of Moose algorithm. The algorithm is the same as the Moose algorithm, which sending two complete OFDM training before sending data symbols, and the algorithm is carried out by using the correlation matrix between the two symbols. Through simulation analysis, it can be seen that the algorithm has a better performance than the Moose algorithm. Finally, a new algorithm is proposed for SC algorithm. The new algorithm makes the symbol timing synchronization and integer frequency offset estimation more accurate. In the time of the fractional frequency multiplication estimation, the algorithm has better performance due to the introduction of the iterative algorithm.