一种基于WLAN的OFDM频偏估计算法的FPGA实现

FPGA Realization of a Frequency Offset Estimation Algorithm for OFDM Systems Based on WLAN

频偏估计是正交频分复用 (OFDM)系统中的关键技术之一。文中分析了基于无线局域网 (WLAN)的OFDM系统载波频偏产生的原因 ,阐述了一种用时域自相关实现频偏估计的算法原理及可行性 ,提出了相应的FPGA实现方案 ,并对实现过程中需要注意的一些问题做了说明。该方案基于IEEE 80 2 .11a协议中的物理层帧结构 ,首先利用 5至 6个短符号进行复数自相关运算 ,然后将相关结果通过CORDIC算法求得它的幅角 ,最后换算成归一化频偏。

Frequency offset estimation is one of the key techniques in OFDM systems. The causes of the carrier frequency offset in OFDM systems based on WLAN are analyzed and principle and feasibility of the algorithm which estimates frequency offset by means of self-correlation in time domain are discussed, and the corresponding design realized in FPGA is presented. Furthermore, it explains some problems which are of concern during the design. Basing on the physical layer frame format defined in IEEE 802.11a protocol, this design firstly calculates the complex numbers’ self-correlation using 5 or 6 short symbols, then gets the argument of the result utilizing CORDIC algorithm, and finally converts it into normalized frequency offset.