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 (NOMA)
and wireless backhaul via beamforming is a promising way for downlink
user-centric ultra-dense networks (UDNs) to improve system performance.
However, the ultra-dense deployment of radio access points in macrocell
and the 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 the sum-of-ratios
decoupling and successive convex approximation methods, we transform the
original problem into a series of convex optimization subproblems.
Furthermore, we solve each subproblem through the 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.