Research On Cross-tier Interference Management Based On Power Control Game

With the development of wireless communication technology, a wide range of network coverage has been resolved. A large number of voice and high-speed data services have taken place in the room, thus improving the quality of service and indoor coverage has become a hot topic of current research in the field of wireless communications. In order to solve the above problems, femtocell technology is introduced. And the two-tier femtocell networks are formed by macrocell and femtocells. However, femtocells will bring the cross-tier interference to the macrocell network, which affects the performance of the entire system network. Power control is an effective means for interference management. And game theory is an effective means to research policymakers’multi-objective optimization problem, which combined power control can control the cross-tier interference effectively in the two-tier femtocell networks. Cross-tier interference management in the two-tier femtocell networks must meet:(1) the transmission performance of macrocell can’t be affected by femtocells; and (2) when the performance of macrocell is guaranteed, femtocells should improve their performance possibly.For the two cross-tier interference problems, this paper uses the non-cooperative power control game scheme firstly. In order to meet the macrocell’s QoS requirements and decrease cross-tier interference, the existing literature has proposed the distributed utility-based SINR adaption algorithm. In the algorithm, macrocell user and femtocell users participate in a non-cooperative game to compete for power resources so that they can maximize their utility functions. However, due to the reward coefficients and penalty coefficients of the proposed algorithm are fixed, the SINR performance of FBSs is limited. Analysis showed that two kinds of coefficients have a greater impact on the Nash equilibrium. To improve the FBSs’ SINRs, we propose an utility coefficients optimizing scheme. Firstly we study how the coefficients to work on the FBSs’ SINR performance. Through further analysis, we find that more power is reduced, the greater outage probability. We set the minimum outage probability threshold and gain optimal reward coefficients and penalty coefficients by iterating. So under the condition of satisfying the MBS’s QoS requirements, the FBSs’ SINRs improve greatly. The simulation results show the effectiveness of the proposed utility coefficients optimal scheme.However, due to each user selfishly maximizes their utility in the non-cooperative power control game, it will lead to more interference and a dilemma Nash equilibrium. So the overall performance of the network will extremely deteriorate. Hence we use Stackelberg game to control the femtocells’ power. In the existing reference, the network power controller (NPC) is the leader, and FBSs are the followers. Each FBS needs to meet the conditions of total interference to MUE and the data rate. NPC sets the same price for per unit power consumption of each FBS, which will lead the deep fading femtocells not to meet the condition of data rate and cause unfair distribution of data rate. So the deep fading femtocells will be removed and become non-active FBSs. In order to increase the number of active FBSs and a fairer distribution of data rate, we propose a non-uniform pricing scheme, which considers not only the condition of the total interference to MUE but also the condition of interference caused by each FBS to MUE. Hence NPC makes different prices to different FBSs. We use the new price and power update algorithm so that prices get convergence, which results Stackelberg equilibrium. Finally, comparing the simulation results of the Stackelberg game with non-uniform pricing scheme, uniform pricing scheme, and non-cooperative game, we can know that the non-uniform pricing scheme is effective.