Research On User Association And Base Station Operation In Green Hetnets

To support the massive growth of mobile data,the heterogeneous cellular network is a crucial technology to achieve spectrum and energy efficiency,which densely deploys various low power base stations within a macro-cellular region.Energy harvesting is an emerging green technology,which can harvest renewable energy from the environment to reduce the on-grid energy consumption.Considering the low transmit power of the base station,heterogeneous cellular networks provide a good scenario for the energy harvesting technology.Hence,green heterogeneous cellular networks have a great prospective.This work is supported by Beijing Natural Science Foundation"Research on Energy Efficient Heterogeneous Cellular Networking for Small Cell Cooperation".User association associates users with the serving base stations properly,which could enhance the system performance.Considering the constant energy consumption,the base stations with low traffic load should be turned off to reduce the overall energy consumption.In heterogeneous cellular networks with hybrid energy sources,we should take users' requests,channel quality,base stations' load and renewable energy distribution into account.Therefore,it is very important to study the user association and base station operation problem.An iterative user association algorithm and a Lagrange threshold based base station operation algorithm are proposed in heterogeneous cellular networks with hybrid energy sources.This thesis investigates the user association problem.The Cobb-Douglas production function is first introduced to formulate a user association problem under a flow-level traffic model.Then a low complexity algorithm implemented by user and base station side is proposed,which can converge to the global optimal solution.Simulation results demonstrate that the proposed algorithm can utilize the renewable energy efficiently,and enable flexible tradeoffs by adjusting the weight value.This thesis formulates the base station operation problem.The combinatorial optimization problem is decomposed into two subproblems based on the time scale separation.For the user association problem,an iterative algorithm implemented by the user and base station side is proposed to achieve load balancing.For the base station choosing problem,a simple algorithm is designed to determine the active base stations using a Lagrange multiplier as the threshold.Simulation results demonstrate that the proposed algorithm can reduce energy consumption,and enable flexible tradeoffs between energy consumption and load balancing.