Research On Small Cell Discovery,On/Off Switching And Radio Interface Synchronization For Dense Hetnet

As one of the key enabling technologies for the fifth generation(5G)mobile communication,dense heterogeneous network(HetNet)can effectively improve network capacity and data transmission rate.However,with a large number of small cell base stations(SBSs)densely deployed,in order to fully exploit the advantages of dense HetNet,various technical challenges must be overcome,such as energy consumption of SBSs,small cell discovery,and collaborative operation in the network.Therefore,this thesis mainly studies the following aspects:In the scenario of dense HetNet,problems of high energy consumption of user equipment(UE)within the small cell discovery process and severe co-channel interference of synchronization reference signals(PSS/SSS)among small cells are given full concern,and a small cell discovery scheme based on the time of arrival(TOA)fingerprint database and flexible transmission of PSS/SSS is proposed.In the proposed scheme,a fingerprint database is constructed by measuring the TOA of macro-cells' cell-specific reference signals(CRS).Before establishing an effective connection with the small cells,UE periodically reports the TOA fingerprint information of its current location.The network controller initiates the fingerprint matching process with the fingerprint database to control the UEs' inter-frequency scanning(IFS)operation and the PSS/SSS configuration and transmission of SBSs.The proposed small cell discovery mechanism can thus significantly reduce the IFS energy consumption of the UEs,effectively alleviate the co-interference of PSS/SSS among small cells and improves the effective detection rate of small cells.In the 5G dense HetNet,the energy consumption of SBSs and the interference among small cells are particularly prominent.Therefore,a small cell on/off switching control algorithm based on the interference contribution ratio(ICR)is proposed.In order to avoid a large amount of the information feedback and measurement process of the UEs,a network adjacency matrix is proposed and designed on the basis of the ICR definition.The network can obtain the ICR values of the small cells quickly and effectively by using the network adjacency matrix and the number of UEs served by each small cell in the current switching on/off cycle.In addition,the dynamic ICR threshold and iteration decision mechanism of switching on/off are designed to effectively adjudicate small cell on/off status.Simulations illustrate that the proposed algorithm can significantly increase the energy efficiency of SBSs and reduce the interference among small cells.Meanwhile,the traffic load loss in small cell caused by the small cell on/off switching mechanism is maintained at a low level.As far as the deficiency of the traditional network synchronization technology in dense HetNet is concerned,where it is necessary to expand the scale and accuracy of the radio-interface based synchronization(RIBS)for small cells,a multi-hop RIBS scheme based on radio-interface synchronization signal(RISS)propagation delay compensation is proposed.By comparing the time-frequency detection performance of existing different reference signals,positioning reference signals(PRS)is adopted as the RISS.The RISS transmission is operating with a frame shift mechanism to reduce the RISS interference among different source cells.With the RISS propagation delay compensation,the proposed scheme can effectively compensate the propagation delay between the source cell and the target small cell,and improves the timing synchronization precision in each synchronization stratum.The simulation verifies that the proposed scheme can effectively enhance the synchronization precision of each synchronization stratum and expand the synchronization range of the RIBS.