Resource Optimization In Two-tier Femtocell Networks Based On Efficient Quality-of-service Support

Femtocell networks provide an effective solution to increase the system capacity and improve the coverage of cellular networks.As the advantages of low cost,low power consumption and easy deployment,femtocell base station meets the development requirements of mobile communication network.However,spectrum sharing as the network access technology in two-tier femtocell networks brings some technical difficulties,such as the co-channel interference from adjacent macrocell and femtocells will limit the system capacity.Power control is an important method for interference management because of its adjusting flexible and energy saving.With the development of mobile communication technology,more and more services are provided to customers.Different Quality-of-Service(QoS)indicators are devised by operators to meet different service requirements,for the purpose of improving the user experience and network performance.In addition,the actual wireless channel is often affected by climate,terrain,building shelter,and so on.Therefore it is necessary to design the power control scheme with the consideration of the uncertainty of channel gains.In this thesis,according to different wireless communication environments,different resource optimization problems are constructed to ensure different QoS requirements for macrocell and femtocells.And different robust power control schemes are proposed for interference management and network resource allocation.Firstly,considering the uncertainty of channel gains for communication links in fast fading environment,the channel gains are modeled subject to exponential distribution with unit mean.At the same time,considering the QoS requirements,i.e.,packet delivery rate,the objective function is constructed to maximize the net-benefits of macrocell user and femtocell users.A distributed robust power control algorithm is proposed to solve the optimization problem,and the optimal resource allocation scheme is obtained.Secondly,in order to construct the mathematical model of optimization problem for the two-tier femtocell network more reasonably,the Stackelberg game model is used to analyze the competition interaction between macrocell base station and femtocell users.Taking into account the communication requirements of users separately,the problem for macrocell is subject to the interference constraint,and the problem for femtocells is under the constraints of delay and packet delivery rate.Aiming at the uncertainty of channel gains for communication links of femtocells,the actual values of channel gains are formulated by its statistical characteristics.A power allocation and interference pricing algorithm is presented to deal with the optimization problem and improve the communication performance of the network system.Finally,considering the uncertainty of channel gains for communication links and interference links in slow fading environment,interval estimation is carried out to model the channel gains.In order to guarantee the transmission rate for macrocell user and the time delay for femtocell users,an optimization problem based on Stackelberg game is formulated,and the worst-case method is utilized to transform the uncertain problem into a deterministic one.In view of the dynamic characteristics that femtocell users access and leave femtocells,a dynamic power adjusting scheme is designed.By adjusting the transmission power of macrocell user,macrocell user cooperates flexibly with femtocell users for power allocation,and the utilization efficiency of system resources is maximized.