  Heterogeneous cloud radio access networks (HCRANs) are potential solutions to
improve both spectral and energy efficiencies by embedding cloud computing into
heterogeneous networks (HetNets). The interference among remote radio heads
(RRHs) can be suppressed with centralized cooperative processing in the base
band unit (BBU) pool, while the intertier interference between RRHs and macro
base stations (MBSs) is still challenging in H-CRANs. In this paper, to
mitigate this inter-tier interference, a contract-based interference
coordination framework is proposed, where three scheduling schemes are
involved, and the downlink transmission interval is divided into three phases
accordingly. The core idea of the proposed framework is that the BBU pool
covering all RRHs is selected as the principal that would offer a contract to
the MBS, and the MBS as the agent decides whether to accept the contract or not
according to an individual rational constraint. An optimal contract design that
maximizes the rate-based utility is derived when perfect channel state
information (CSI) is acquired at both principal and agent. Furthermore,
contract optimization under the situation where only the partial CSI can be
obtained from practical channel estimation is addressed as well. Monte Carlo
simulations are provided to confirm the analysis, and simulation results show
that the proposed framework can significantly increase the transmission data
rates over baselines, thus demonstrating the effectiveness of the proposed
contract-based solution.
