协作异构网络中的用户接入与功率控制联合优化

本文研究协作异构网络下行传输中的用户接入和功率控制问题。考虑多基站采用协作传输来回避小区间干扰，在满足用户数据率需求、单基站功率约束、以及给定每个用户最多接入基站个数的限制下，最小化所有基站的总发射功率。该问题属于包含0/1变量和连续变量的组合优化问题，其全局最优解可以通过遍历搜索得到，但会导致很高的计算复杂度。为了降低复杂度，本文提出了一种基于几何规划的用户接入和功率控制联合优化方法。所提出的方法首先将问题中的0/1变量表示为连续函数，进而将得到的优化问题转化为几何规划问题并进行求解。仿真结果表明，相比于现有的用户接入最近基站方法、用户接入信号最强基站方法、以及偏移接收能量最大方法，所提出的方法能够有效地平衡网络中各小区负载，因而可以支持更高的用户数据率需求，在相同的用户数据率需求下能够大幅降低系统的总发射功率。 

Joint Optimization of User Access and Power Control in Cooperative Heterogeneous Networks

This paper studies joint optimization of user access and power control in downlink cooperative heterogeneous networks. Given coordinated transmission among base stations (BSs) to suppress the inter-cell interference, the user access and power control policies are jointly optimized, aimed at minimizing the total transmit power of all BSs, subject to per-user rate requirement, per-BS power constraint, and the restriction on the maximal number of BSs accessed by each user. This problem is a combinatorial optimization problem involving both 0/1 variables and continuous variables, where exhaustive searching is required to obtain globally optimal solution at the expense of very high computation complexity. To reduce the complexity, an efficient joint optimization method for user access and power control based on geometric programming is proposed, which first approximates the involved 0/1 variables as continuous functions, then transforms the resultant optimization problem into a standard geometric programming problem that can be solved efficiently. Simulation results show that, compared to the existing accessing nearest BS policy, accessing receive-power-maximal BS policy, and accessing biased-receive-power-maximal BS policy, the proposed method can effectively balance the traffic load of cells, and thus can support much higher data rate requirements of users and can also largely reduce the total transmit power under the same users’ data rate requirement.