| The 3GPP has been playing a pivotal role in the development of mobile communication and the LTE-A,which is standardized and promoted by 3GPP,has already become the most widely deployed fourth generation mobile communication network in the world.However,with the increasing data traffic of indoor and hot spot areas,LTE-A system is facing new challenges.In this regard,3GPP proposes small cell enhancement for indoor and hot spot areas in Release 12.At the same time the domestic operators and some equipment manufacturers are coincidentally developing the LTE-Hi(LTE-Hotspot/indoor)technology for the same purpose.LTE-Hi solves the problem of dramatic increase in data traffic in the indoor and hot spot areas by intensive deployment of small cells operating in higher frequency band than that of the macro cells.This kind of deployment further enhances the system capacity and offloads traffic of the macro cell to the small cells.While bringing lots of benefits,the LTE-Hi system has some urgent problems to be solved.Therefore,this thesis mainly studies the following aspects:1.Aiming to solve the problem of high energy consumption in the process of small cell discovery(SCD),a reference signal arrival time estimation based fingerprint database and a dual frequency small cell deployment scheme are proposed as two SCD solutions for the LTE-Hi system,respectively.The former method constructs the fingerprint database by measuring the time delays that the macro cell reference signals propagate from the macro cells to the target user equipment(UE)and the corresponding macro cell IDs.The fingerprint obtained by the UE with intra-frequency measurement will be used to scan the whole fingerprint database.Only when a fingerprint-match match occurs,will the UE initiates the following procedure of inter-frequency measurement(IFM).Simulation results show that the proposed fingerprint database scheme can significantly save the UE energy consumption in the SCD procedure,compared with the traditional periodic inter-frequency measurement scheme.As for the dual frequency bands SCD deployment scheme,it is mainly proposed to perform the SCD operation for the UEs located at the macro cell edge area.In this scheme,the small cells are assumed to be simultaneously deployed in the low and high frequency band.Whether or not a UE is in the vicinity of small cells is estimated by the homogeneous interference intensity generated by small cell signal to the macro cell signal.Simulation results illustrates that the proposed scheme also tremendously saves energy consumption UEs in the SCD process while ensuring the QoS of them.2.The dense deployment of the LTE-Hi small cells makes the overall network energy consumption significantly increased.For this problem,a traffic load evaluation based small cell on/off switching scheme is proposed.In the scenario of low traffic load,the small cells with relatively traffic load are selected by the traffic load threshold,and then the selected small cells are divided into two sets with different average traffic levels by using the iterative threshold test algorithm.The small cells in the low-traffic-level set will be switched off if it does not result in degradation of the system QoS.Simulation results show that the proposed scheme significantly reduces the energy consumption of the system and greatly improves the energy efficiency. |
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