  This paper studies joint uplink (UL) and downlink (DL) resource allocation in
user-centric orthogonal frequency division multiple access (OFDMA) cloud radio
access network (CRAN), where the users select the distributed remote radio
heads (RRHs) to cooperatively serve their UL and DL transmissions over
different subcarriers (SCs). The goal of this paper is to maximize the system
throughput through jointly optimizing UL/DL scheduling, SC assignment, RRH
grouping/clustering and power allocation under the maximum power and fronthaul
capacity constraints. The problem is formulated as a mixed integer programming
problem which is non-convex and NP-hard. We propose an efficient algorithm
based on the Lagrange duality method to obtain an asymptotically optimal
solution for this problem. A heuristic algorithm is further proposed to reduce
the complexity. Simulation results illustrate that the proposed heuristic
algorithm also has a close-to-optimal performance, and the proposed algorithms
can considerably improve the system throughput compared to other benchmark
schemes.
