Non-orthogonal multiple access (NOMA) techniques have received considerable attention due to the increased multiuser access capability. The key advantage of NOMA is that of allowing multiple users to share the same frequency-, time- or code-resource. For users having better channel conditions, which are refereed to as strong users (SU)s, they can perform successive interference cancellation to decode the signal iteratively. For the users having poor channel conditions, which are refereed to as weak users (WU)s, they need to decode their own signal directly. Classic NOMA designs can be classified as non-cooperative systems, as there is no assistance between the SUs and WUs.