Research On Robust Power Control Algorithmin Two-tier Femtocell Networks With Imperfect CSI

In recent years,it is becoming more and more important to improve indoor wireless coverage.One solution is to introduce the femtocell into the macrocell.However,the introduction of femtocell brings the interference problem,which will reduce the system performance.Thus,how to maximize the throughput and energy efficiency of the network while suppressing the interference has become a hot research in the two-tier femtocell network.And power control is an important method of interference suppression.In the existing,the majority are based resulting in the power control to be a research focus in the two-tier femtocell networks.In the existing power control alrorithms,the majority are based on the assumption that channel state information(CSI)is perfect,which is inconsistent with the imperfect CSI in practical two-tier femtocell networks.Therefore,robust power control algorithms in two-tier femtocell networks with imperfect CSI are researched in the paper and the main contents are as follows:1.Considering femtocells are sparsely deployed scenario and densely deployed scenario respectively in two-tier femtocell networks with imperfect CSI,the paper studies the robust optimization problem for maximizing the throughput of femtocell networks,while satisfying the quality of service(QoS)of the macrocell user equipment(MUE).Firstly,using the additive uncertainty description method,the imperfect CSI model is established.Secondly,based on the worst-case robust optimization,the original problem is transformed into a deterministic convex optimization problem.Based on the equivalent problem,the closed-form expression of robust power control is obtained.What's more,a robust power control algorithm aimed for maximizing the throughput is designed,which has a low computation complexity.Simulation results show that the proposed algorithm can strictly guarantee the QoS of the MUE,which is suitable for the practical two-tier femtocell networks.2.In sparsely deployed scenario,the robust EE maximization problem is investigated when both the femtocell channel and the cross-layer interference channel have channel gain estimation errors.Firstly,the worst-case robust optimization is used to ensure the QoS of MUE and femtocell user equipments(FUEs).The above problem is modeled as a max-min optimization problem with infinite constraints,which is a NP-hard problem.Thus,according to the nonlinear fractional programming,the non-convex optimization problem is transformed into a convex optimization problem.At last,the closed-form expression of the robust power control is given,and a robust algorithm for maximizing the EE is proposed,which introduces an admission control based on channel gain.Simulation results demonstrate that the proposed algorithm has a slight loss in EE,but it can strictly guarantee the QoS of MUE and FUEs.