1. Academic: The topic of the paper must have academic value and make a certain contribution to the development of communication engineering. This may involve new theories, methods, technologies or applications.

2. Feasibility: The topic of the paper must be feasible, that is, researchers need to have enough resources and ability to complete the research. This may include time, funds, equipment, data, etc.

3. Innovation: The topic of the paper needs to be innovative, and the existing research cannot be simply repeated. This may involve putting forward new problems, new methods and new theories.

4. Relevance: The topic of the paper needs to be related to the field of communication engineering and cannot deviate from the theme. This may involve wireless communication, optical communication, network security, signal processing, information theory and other sub-fields.

5. Tutor's professional background and research direction: The topic selection of master's thesis usually needs the support and guidance of the tutor, so the topic selection needs to conform to the tutor's professional background and research direction.

6. Research direction and policy of the school: Different schools may have different research directions and policies, which will also have an impact on the topic selection of the thesis.

7. Social demand and development trend: The topic of this paper also needs to consider the social demand and development trend in the field of communication engineering, so that the research results can be applied to practice and recognized by the society.

Generally speaking, the topic selection of communication engineering master's thesis needs to meet the above restrictions, and at the same time, give full play to one's professional expertise and interest as much as possible to achieve the best research results.