This paper considers the problem of secret communication over a two-receiver
multiple-input multiple-output (MIMO) Gaussian broadcast channel. The
transmitter has two independent, confidential messages and a common message.
Each of the confidential messages is intended for one of the receivers but
needs to be kept perfectly secret from the other, and the common message is
intended for both receivers. It is shown that a natural scheme that combines
secret dirty-paper coding with Gaussian superposition coding achieves the
secrecy capacity region. To prove this result, a channel-enhancement approach
and an extremal entropy inequality of Weingarten et al. are used.Comment: Submitted to 2010 IEEE International Symposium on Information Theory,
Austin, Texa