Explain what sdr (signal-to-data-ratio) and SNR (signal-to-noise-ratio) mean and how they can be used for evaluation. 解释什么是 sdr (信号数据比)和 SNR (信号噪声比) ? 他们是被如何用于评估的? Answer: sdr(signal-to-data ratio): a ratio of the number of signal elements to the number of data elements. If sdr > 1, a signal may contain self-synchronization information. SNR ( Signal-to-noise ratio ): a ratio of the average of signal power to the average of noise power. It is a measure to limit the theoretical bit rate.