Design and implementation in USRP of a preamble-based synchronizer for OFDM systems

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.