Cost-Efficient Resource Allocation in Cloud Radio Access Networks With Heterogeneous Fronthaul Expenditures

As an advanced paradigm, the cloud radio access network (C-RAN) promises high spectral efficiency (SE) and energy efficiency (EE). However, the capacity-constrained front-haul has become a key performance bottleneck in C-RANs. Besides SE and EE metrics, the cost related to different kinds of fronthaul is another major concern for operators. In this paper, an economical SE (ESE) metric is proposed to jointly take traditional EE and the impact of wired/wireless fronthaul cost into account. Aiming to maximize ESE, a non-convex beamformer design problem with fronthaul capacity and transmit power constraints is formulated, and an algorithm containing outer and inner loops is proposed to deal with this non-convexity. In particular, in the outer loop, the bisection search method is adopted to transform the primal problem into an equivalent subproblem; while in the inner loop, owing to the equivalence between the subproblem and the weighted sum rate, the subproblem is solved by the weighted minimum mean square error approach. Simulation results demonstrate that the proposed ESE is more reasonable than SE and EE for the fronthaul-constrained C-RAN. Furthermore, the proposed optimization solution can significantly improve ESE, in which the impact of fronthaul cost on ESE is evaluated.