On uncertainty principles for linear canonical transform of complex signals via operator methods

The linear canonical transform (LCT) has been shown to be a useful and powerful analyzing tool in optics and signal processing. Many results of this transform are already known, including its uncertainty principles (UPs). The existing UPs of the LCT for complex signals can only provide sharp bounds with LCT parameters satisfying $$a_1/b_1\ne a_2/b_2$$. However, in most cases, we strive to find a lower bound, but not a sharper bound, since a lower bound often leads to optimization problems in signal processing applications. In this paper, we first present a much briefer and more transparent derivation to obtain a general uncertainty principle of the LCT for arbitrary signals via operator methods. Then, we derive lower bounds of three UPs of the LCT for complex signals, which are tighter lower bounds than the existing ones. We also prove that the derived results hold for arbitrary LCT parameters.