Resource Allocation Schemes In OFDM-based Heterogeneous Cellular Networks

Recent investigations indicate that 50 percent of phone calls and 70 percent of wireless data services would take place in indoor environments in the coming decade.Instead of increasing macrocells of high deployment cost to meet the exponentially increasing data demands,user-installed femtocell access point with lower transmission power and lower cost which usually serves a registered group of subscribers is deemed as a promising solution to meeting the ever increasing wireless data requirement.Deploying femtocells underlaying macrocells is a promising way to improve the capacity and enhance the coverage of cellular systems.With the rapid development of mobile communications,radio spectrum resource is increasingly scarce and spectrum resource costs has become the operator burden.Cognitive radio is considered as an effective way to improve spectrum efficiency,which allows users to opportunistic access to spectrum without disturbing the primary users.Due to the inherent flexibility of OFDM technology,OFDM has paved its way for potential application in the physical layer of CR systems.In OFDM based wireless communication system,dynamic resource allocation can effectively use radio channel characteristics to maximize capacity of the system at a given bandwidth.This thesis is intended to provide comprehensive study of different dynamic resource allocation schemes in OFDM systems.By and large,the main contribution of this thesis can be summarized as follows.1.We build the general system model for adaptive resource allocation problem in OFDM wireless networks.In the model,we give full consideration to every power budget and the budgets of the bandwidth of the selected village,we also consider the disturbance to the primary user and the actual system elements,makes building model can depict the actual situation of the wireless network.2.In this paper,we formulated the clustering based subchannel and power allocation problem as an optimization problem.We try to maximize the sum throughput of all FUs while reducing the intra-tier interference and controlling the interference to the MU under its bearable threshold.It is divided into two procudures,the clustering and resource allocation.In the clustering,we proposed effective clustering a;gorithm to reduce intra-tier interference.We propose a two-step method to address the resource allocation problem:subchannel allocation and power distribution.The subchannel allocation procedure can roughly satisfy the rate requirements of all FUs and the power allocation algorithm can achieve a near optimal solution.3.We developed a general models to illustrate the resource allocation problems for heterogeneous cellular networks,in which the interference to the MUs under their bearable thresholds in the sense of probability due to imperfect CSI and the power budget and the bandwidth budget of each selected cell are both taken into consideration.We developed a three-stage method to deal with the subchannel and power allocation separately.By jointly considering the channel condition and interference level,an effective procedure of subchannel allocation is firstly performed.For the second step,the interference constraints are made tractable by Bernstein approximation.Finally,we propose a fast method by exploiting the structure of the problem,which is able to achieve the optimal power allocation and much more efficient than standard methods.Comparing to existing work in the literature,our models are more practical for heterogeneous cellular networks.In general,in terms of resource allocation problem in either dense or sparse Heterogeneous Cellular Networks,effective and efficient algorithms are proposed.Particularly,compared to other existing algorithms in literature,the significant lower complexity of our proposals will possibly enlighten the design of resource allocation strategy in the practical OFDM networks.