  This paper presents a hierarchical approach to resource allocation in
open-access femtocell networks. The major challenge in femtocell networks is
interference management which in our system, based on the Long Term Evolution
(LTE) standard, translates to which user should be allocated which physical
resource block (or fraction thereof) from which femtocell access point (FAP).
The globally optimal solution requires integer programming and is
mathematically intractable. We propose a hierarchical three-stage solution:
first, the load of each FAP is estimated considering the number of users
connected to the FAP, their average channel gain and required data rates.
Second, based on each FAP's load, the physical resource blocks (PRBs) are
allocated to FAPs in a manner that minimizes the interference by coloring the
modified interference graph. Finally, the resource allocation is performed at
each FAP considering users' instantaneous channel gain. The two major
advantages of this suboptimal approach are the significantly reduced
computation complexity and the fact that the proposed algorithm only uses
information that is already likely to be available at the nodes executing the
relevant optimization step. The performance of the proposed solution is
evaluated in networks based on the LTE standard.
