Resource Allocation In Wireless Heterogeneous Networks Under Imperfect Channel State Information

As the foundation of 5G,wireless heterogeneous networks has the advantages of enhancing coverage area,reducing blind area(especially indoor area),increasing network transmission capacity,enhancing the reliability of networks,improving the utilization of spectrum resources,energy saving and so on.Femtocell networks are the typical example of two-layer heterogeneous networks.However,the introduction of femtocell networks brings a lot of new problems and challenges for mobile networks.Since femtocell networks share spectrum resources with macrocell networks,it definitely results in co-channel interferences,including inner-tier interference and cross-tier interferences.Due to the complexity and dynamics of real mobile networks,especially with the larger and denser deployment for the networks in the future,the instantaneous channel gains in two-tier heterogeneous networks become more complicated and changeable.Moreover,the access mode of heterogeneous networks becomes more flexible and open in the future,which leads to serious information transmission security.Therefore,Considering the uncertainties of channel gains in the two-tier heterogeneous networks,robust interference management scheme and secure transmission scheme are designed.First,considering the uplink interference management problem under flat fading environment,we simultaneously investigate the uncertainties in both signal links and interference links.The uncertainties are,respectively,modeled as ellipsoid uncertainty and Gaussian uncertainty.Under the present of the both flat fading channels,two robust interference management scheme are proposed for the wireless heterogeneous networks.Then,considering fast fading environment with channel gains change quickly,the interference management problem is usually hard to solve due to the fast changing of channel gains.Aiming at dealing with the problem,we propose two interference management schemes for the heterogeneous networks.The first scheme based on statistical characteristics converts probability constraint into deterministic constraints.The other utilizes the channel gains samples to guarantee the QoS of users,which largely enhance its applicability in practical systems.Finally,a joint subchannel and power allocation secure transmission scheme is proposed for the downlink transmission security problem in the two-tier heterogeneous networks to enhance the secure performance.In the scheme,ubiquitous interferences in the heterogeneous networks are exploited to degrade the eavesdropper's performance and then the secure transmission performance is improved without consuming extra energy.Moreover,a switch-function-based frame is established to model the different requirements in the secure transmission problem.