Research On Energy Efficiency Optimization In Dense Small Cell Networks

In order to deal with the explosive growth of wireless traffic,the architecture of small cell networks(SCN)has been proposed in the 3rd Generation Partnership Project(3GPP)Release 12.A small cell is a kind of base station with low energy consumption and low cost,whose main application scenarios are outdoor and indoor hot spots.Small cells can be easily deployed and largely increase the system capacity,which makes it one of the important research directions in the future fifth generation(5G)mobile system.Moreover,dense deployment of small cells can guarantee high-speed data services in hotspots and becomes the inevitable trend of SCN.Due to the smaller coverage and less number of users per small cell,the traffic fluctuation may be large.So,the small cells with light traffic load for a long time may cause a waste of energy.Since the potential number of small cells may be huge in dense deployment,the energy consumption problem or energy efficiency optimization problem in SCN have drew wide attention.Therefore,the energy efficiency optimization becomes one of the key optimization directions for SCN,and high energy efficiency is also an important target of 5G mobile system.Among the technologies for energy efficiency optimization,small cell on/off(also known as small cell switch or sleep)technology,which has an excellent energy saving performance,is widely studied.3 GPP also incorporated this technology into the standard and proposed some assistive technologies to promote its development.Therefore,this thesis studies the optimization strategies of energy efficiency for SCN on the basis of small cell switch technology.The following works are covered in this thesis:First,a small cell cluster model is constructed as the research scenario.Then,the power consumption model of a small cell BS is introduced.The energy consumption minimization problem is built based on service quality requirement of user equipment(UE)to improve the system energy efficiency.By analyzing the problem,both the access and scheduling operation and the small cell sleep operation greatly influence the system energy efficiency,which makes the problem complex.So a sub-optimal solution is proposed by decomposing the formulated problem into two sub-problems:UE access and scheduling problem and small cell sleep problemAs to the first problem,the UE access and scheduling problem is modeled as a many-to-many matching problem.An Energy-saving-based Access and Scheduling strategy is proposed to solve this problem.Simulation results show that this strategy can reduce the load of the BS and power consumption of BS,but this strategy has a very limited energy saving performance.As to the small cell sleep problem,in view of the small cell cluster scenario,the concept of Diluted Load is introduced as a sleep indicator.Then,a Diluted Load-based sleep strategy is proposed to solve the problem,and the solution for the overall energy consumption minimization problem needs iterations of the UE access and scheduling strategy and small cell sleep strategy.Simulation results show that the proposed strategy significantly reduces power consumption of the small cell BS and the actual UE block ratio.Finally in the research of small cell activation strategy,to ensure the UE service quality when load fluctuation is relatively large,three schemes are proposed:sleep strategy redo scheme,small cell random activation scheme and Discovery Reference Signal-based activation scheme.Then,the advantages and disadvantages of these schemes are analyzed,so that the appropriate scheme can be selected for practical use according to their respective features.