On dimension scarcity for user admission in MIMO interference aligned networks

This work focuses on the admission of new (secondary) users in a network where existing (primary) users are interference aligned. One of the challenges in this scenario is to achieve the promised degrees of freedom for the secondary users with limited available dimensions. We design a secondary admission network to achieve interference alignment as in equivalent general peer-peer networks, even when the secondary nodes are configured with limited antenna/spatial dimensions, along with a very strict zero-interference constraint from the primary network. To provide enough dimensions for secondary users to achieve interference alignment, we utilize three effective methods: a) time extension structure; b) adaptivity to network partial connectivity; c) partial interference alignment. The presented analysis shows how the degrees of freedom (DoF) can be achieved for the secondary network in both the constant and time-variant channels.