An outer bound on secrecy achievable rate region for BCE

This paper considers the problems of the achievable rate regions on broadcast channel with the eavesdropper (BCE). Many articles have given the meaningful results, like the inner bound of this model. However, the specific analysis processes for this model have not been given by previous work, especially, the outer bound of BCE have not been given. So we focus on the study of the outer bound on the secrecy achievable rate regions of BCE and obtain a convincing result.