Estimate And Correction Of CFOs For OFDM Baseband System

Along with high-speed development of multimedia technique and mobile communication,demand for information transmission velocity is increasingly increased, and required code transmitted velocity is increasingly improved. Nowadays transmission velocity of a path of information is required up to several Mb/s. Moreover, transfers channel are mostly multipath decline or frequency selectivity decline. In order to overcome channel decline, OFDM (Orthogonal Frequency Division Multiplexing) is attached importance.OFDM is a parallel modulation system using multicarrier, which means that the data are multiplexed onto and transmitted over multiple carrier frequencies called subcarriers. The subcarrier spectra overlap in OFDM which improve frequency availability, and the subcarriers are strictly mutually orthogonal,which make Interference among overlapping spectra, or intercarrier interference (ICI) be avoided. At the same time, receiver can completely separate every path of modulation signal. Further, any path of subcarrier could adopt M-system modulation and modulation mode may be different, which can self-adaptively alter to adapt channel variety.However, if orthogonality is destroyed, ICI can cause severe performance degradation. Thus, it is critical that orthogonality be maintained among the different subcarriers, and primary source for ICI is Carrier Frequency Offset (CFO).In order to maintain orthogonality among subcarriers, a CFOs step-size estimation model based on cyclic prefix (CP) is established to avoid severe performance degradation caused by ICI, and some are investigated that includes selection of step-size parameter, performance of correction coefficient, control of variable step-size, the error of CFOs estimation, algorithmic stability and typical steady-state performance and etc.First, OFDM is presented, including basic signification, development actuality and primary applications.Then, principle and realization of OFDM are described. After an averaging window algorithm is introduced, the mathematic model of step-size algorithm of CFOs estimation is obtained through step-size parameter.Third, design idea for hardware is explained, as well as various part in system and VHDL implementation process of baseband operation. Furthermore, comparing with VSB and LMR, step-size algorithm performance is under typical steady-state. Based on the results of simulation referred to MATLAB, stability, coefficients, in- and variable step-size are verified.Finally, executable program of step-size algorithm is designed, control for variable step-size is stressed, and experimental results are listed and discussed.Experimental results indicate that self-designed programs can be accurately performed on circuit board. Maximal error of CFOs estimate is 0.0987 in±3σvariance interval, when mobile velocity are 400 km/h, according with verdicted principle that in order for the ICI effects to be negligible, the error of CFOs estimation must be accurate within 1-2% of the subcarrier spacing. At the same time, setup time and steady time are decreased to improve code transmission velocity. Additionally, store resource consumed by CP is 20% of other algorithms’to reduce loss of information velocity.