USRP系统中基于序列的同步器的设计与实现
Design and implementation in USRP of a preamble-based synchronizer for OFDM systems
摘要：
正交频分复用（Orthogonal Frequency Division Multiplexing，OFDM）由于其高传输速率和对符号间干扰（Intersymbol Interference，ISI）的鲁棒性而成为诸如Wi-Fi和LTE的无线技术中最广泛采用的方案之一。然而，OFDM对同步误差高度敏感，这影响了载波的正交性。通过在通用软件无线电外围设备（USRP）的软件定义无线电（SDR）中的实现，分析了几种基于前导码符号相关性的同步算法。这种实现分三个阶段执行：帧检测，比较自相关输出和接收信号的平均功率;时间同步，其中实现基于短前导码符号和长前导码符号的互相关;以及频率同步，其中检测并校正由信道添加的载波频率偏移（CFO）。同步器的性能通过USRP的实施进行了验证。结果为选择最佳同步方案提供了实际指导，并显示了USRP有效实现数字通信系统的通用性。
英文摘要：
The Orthogonal Frequency Division Multiplexing (OFDM) is one of the most widely adopted schemes in wireless technologies such as Wi-Fi and LTE due to its high transmission rates, and the robustness against Intersymbol Interference (ISI). However, OFDM is highly sensitive to synchronism errors, which affects the orthogonality of the carriers. We analyzed several synchronization algorithms based on the correlation of the preamble symbols through the implementation in Software-Defined Radio (SDR) using the Universal Software Radio Peripheral (USRP). Such an implementation was performed in three stages: frame detection, comparing the autocorrelation output and the average power of the received signal; time synchronism, where the cross-correlation based on the short and long preamble symbols was implemented; and the frequency synchronism, where the Carrier Frequency Offset (CFO) added by the channel was detected and corrected. The synchronizer performance was verified through the USRP implementation. The results serve as a practical guide to selecting the optimal synchronism scheme and show the versatility of the USRP to implement digital communication systems efficiently.
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