Resource Allocation for Energy Efficient User Association in
User-Centric Ultra-Dense Networks Integrating NOMA and Beamforming,
Abstract
A coupling of wireless access via non-orthogonal multiple access and
wireless backhaul via beamforming is a promising way for downlink
user-centric ultra-dense networks (UDNs) to improve system performance.
However, ultra-dense deployment of radio access points in macrocell and
user-centric view of network design in UDNs raise important concerns
about resource allocation and user association, among which notably is
energy efficiency (EE) balance. To overcome this challenge, we develop a
framework to investigate the resource allocation problem for energy
efficient user association in such a scenario. The joint optimization
framework aiming at the system EE maximization is formulated as a
large-scale non-convex mixed-integer nonlinear programming problem,
which is NP-hard to solve directly with lower complexity. Alternatively,
taking advantages of sum-of-ratios decoupling and successive convex
approximation methods, we transform the original problem into a series
of convex optimization subproblems. Then we solve each subproblem
through Lagrangian dual decomposition, and design an iterative algorithm
in a distributed way that realizes the joint optimization of power
allocation, sub-channel assignment, and user association simultaneously.
Simulation results demonstrate the effectiveness and practicality of our
proposed framework, which achieves the rapid convergence speed and
ensures a beneficial improvement of system-wide EE.