Optimal Transmission Strategy and Explicit Capacity Region for Broadcast   Z Channels
  This paper provides an explicit expression for the capacity region of the two-user broadcast Z channel and proves that the optimal boundary can be achieved by independent encoding of each user. Specifically, the information messages corresponding to each user are encoded independently and the OR of these two encoded streams is transmitted. Nonlinear turbo codes that provide a controlled distribution of ones and zeros are used to demonstrate a low-complexity scheme that operates close to the optimal boundary. 
Bike Xie, Miguel Griot, Andres I. Vila Casado, and Richard D. Wesel