sum frequency的用法和樣例：
例句
- It realizes graphics protraction of time and frequency domain in every time period.
它實現了各個信號的時域和頻域的圖形的繪製。 - The simulation for QPSK shows that the algorithm can estimate the carrier phase and frequency offset accurately and reduce the system BER effectively.
結果表明，用該演算法可以精確估計載波相位和頻差，有效地降低系統的誤碼率。
