"Signals and Systems" of Shanghai Jiaotong University seems to be a course for on-the-job graduate students. Very easy to understand, pay attention to principles. Teachers have a great grasp of the course and have their own opinions and styles. But now that I have read it again, it seems that the miles are gone. I remember there were a lot of broadcasts. Secondly, Tsinghua University's Signals and Systems does not pay attention to the content, which is enlightening and vivid. After reading it, it can help you to establish your own knowledge system and the relationship between chapters.
Zheng version of the signal and system, institutional courses, to explain the practical problems of Beijing Post is good, can be used for reference, but the content is less, very detailed. Signal and Linear System Analysis by Li Xuewu Wuda of Xidian is genuine. According to the test center, it is aimed at Xidian. If you just want to listen to the textbook, it is not recommended.
Ma Hongyu's Zheng Signal and System is very detailed, most of which are based on PPT. Teachers' internal thinking and experience are relatively poor. If you can't understand a place at all, you can consider watching a class at her place, but it is not recommended to watch more. At present, the pressure of postgraduate entrance examination is still quite great, and the competition is fierce. Most people will choose a reliable postgraduate training institution for targeted counseling, focusing on teaching quality, landing rate and cost performance. It is important to find the right method with the right teacher.