Algorithm Of OFDM Frequency Offset

In recent years, communication technology reached its peak during the rapid development, but the limited spectrum resources limited the development of communication technology.When sub-carrier spectrum of orthogonal frequency division multiplexing (OFDM) technology is orthogonal, spectrum resources can derive better use and have a strong ability to robust anti-multipath interference, which make OFDM technology become mainstream technology of contemporary wireless communications technologies. However, the higher resource utilization of OFDM technology is based on the orthogonality of each sub-carrier spectrum. Once the orthogonality between each sub-carrier is destructed, inter-carrier interference (ICI) is generated, which will result in great reduction in the performance of the received signals and can not reflect the advantages of OFDM technology. This paper studies the carrier frequency offset estimation algorithm for OFDM systems, and focus on seeking low complexity and relatively good performance of the carrier frequency offset estimation algorithm.In this paper we pay more attention to the carrier frequency offset estimation algorithm for OFDM systems. Frequency offset estimation algorithms based on cyclic prefix, time-domain pilot sequence and pseudo-random (PN) sequence are studies in detail from both theoretical analysis and simulation. Firstly, the paper systematically introduces OFDM technologies, including the basic principles of OFDM technology, history, advantages and disadvantages of the OFDM systems and its application in the field of wireless communications. Secondly, based on the research status of carrier frequency offset estimation algorithm of OFDM systems at home and abroad, causes of frequency offset and the methods to estimate the frequency offset value, a scheme to optimize the system performance is proposed in the paper. Thirdly, this paper studies the carrier frequency offset estimation algorithm for OFDM systems from both theoretical analysis and simulation. Fourthly, an improved algorithm of carrier frequency offset estimation algorithms is proposed based on the studying of various algorithms. The main contents of this paper are as follows.1、The frequency offset for the OFDM system, particularly the carrier frequency offset is studied. The main factors causing the carrier frequency offset, the impact on system performance for frequency offset and research status of carrier frequency offset estimation algorithm at home and abroad are analyzed.2、This paper studies the carrier frequency offset estimation algorithm for OFDM systems from both theoretical analysis and simulation. There are four main algorithms in our research, namely, estimation algorithm based on cyclic prefix, estimation algorithm based on symbol retransmission, estimation algorithm based on the time domain pilot, estimation algorithm based on pseudo-random (PN) sequence.3、Two improved algorithms based on the cyclic prefix frequency offset estimation algorithm are proposed in this paper. Firstly, an improved algorithm of frequency offset estimation algorithm based on cyclic prefix non-correlation is proposed. The main ideas of the algorithm are that the cyclic prefix and the redundant part are averagely divided into two small sequences, and respectively average operations are carried. Obtain the correlation of corresponding partial and derive the values of the frequency offset estimation. The average value which is the final estimate value of the values derived is calculated. Secondly, an improved algorithm of frequency offset estimation algorithm based on cyclic prefix correlation is proposed. The main idea of the algorithm is that a novel frequency offset estimation algorithm based on cyclic prefix is formed combining frequency offset estimation algorithms based on cyclic prefix non-correlation with frequency offset estimation algorithms based on cyclic prefix correlation. The basic principle of the algorithm is that the cyclic prefix and the redundant part are averagely divided into two small sequences, respectively. The corresponding former part conducts correlation operation, and the corresponding latter part conducts correlation operation after calculating the mean. According to the correlation, respectively calculate the frequency offset estimation values. Finally the mean value of the estimate values is derived, which is the value of the frequency offset estimation algorithm of the improved algorithm.4、In view of the frequency offset estimation algorithm based on pilot, this paper presents a decimal times frequency offset estimation algorithm based on pilot. In frequency offset estimation algorithm based on pilot frequency, the frequency offset estimation process is divided into two processes, namely, decimal times frequency offset estimation process and integer times frequency shift estimation process. This paper proposes an improved algorithm of decimal times frequency shift estimation algorithm. The main principle of the improved algorithm is that the pilot symbols is fractionized into four small sequences, or four same short sequences can be directly inserted, and use the correlation between the short sequences to obtain the value of frequency offset estimation.