Interference Mitigation Via Cross-Tier Cooperation in Heterogeneous Cloud Radio Access Networks

In this paper, a cross-tier cooperation framework in H-CRAN is proposed to mitigate inter-tier interference. Specifically, a small cell remote radio head (S-RRH) acts as the relay for multiple macrocell users (MUEs), and obtains a fraction of time slot from multiple MUEs as a reward. Through the cooperation, the S-RRHs can obtain extra spectrum resource for serving small cell users (SUEs) which are secondary users, while the MUEs which are primary users can improve their data transmission utility. The cooperation problem is formulated as a mixed integer programming, which is NP-hard. To solve this problem, we transform the cooperation problem into a joint cooperation time and power allocation problem and a cooperator selection problem. First, we solve the joint cooperation time and power allocation problem to obtain the maximum cooperation utility of all the possible cooperating pairs. We derive the closed-form solution for the allocation problem by using linear independence constraint qualification and Karush-Kuhn-Tucker conditions. Then, we solve the cooperator selection problem by a two-sided matching algorithm. Extensive simulation results show that the utility of macrocell networks and small cell networks can be improved by adopting the proposed cooperation framework, and the cooperator selection result is stable and close-to-optimal.