| With the rapid development of mobile communications,wireless data traffic has experienced explosive growth and continues to challenge the limits of network capacity.In order to improve network capacity,mobile operators have introduced new technologies such as large-scale antennas,full-duplex and ultra-dense networking to further increase spectrum utilization,and on the other hand,continue to exploit new available spectrum resources.The spectrum resources available to operators are limited.Although the use of spectrum resources in the low-frequency band is already relatively saturated,the unlicensed spectrum in the 5G Hz band is still worth exploring.To be able to use unlicensed spectrum,3 GPP Release 13 proposes a licensed as-sisted access(LAA)technology that uses carrier aggregation to combine 5G Hz unlicensed LTE and licensed LTE to achieve faster data rates,more sensitive responsiveness and better user experience.LAA provides a uni-versal unified network that exceeds the enhanced capacity and coverage of Wi-Fi,simplifies management,and provides a high-density,future-oriented,self-organizing network,which will significantly save operators’ deployment and operating costs.This paper mainly considers LAA networking scenarios,and studies key issues such as LBT mechanism design and uplink scheduling transmission.The goal is to make full use of unlicensed spectrum resources to increase capacity while reducing the impact on existing access systems such as Wi-Fi.The main research content and innovation points are summarized as follows.(1)For the problem of spectrum leakage of adjacent channels exist-ing in LAA access,this paper proposes a LAA access technology based on multi-carrier LBT mechanism to increase the transmission rate by dynami-cally aggregating more available unlicensed band carriers.First,the trans-mission process between the LAA node and the Wi-Fi node is modeled as a Markov chain model,and the transmission probability and collision proba-bility of the node in a steady state are deduced,and the saturation through-put of the node is obtained.The simulation results show that the proposed multi-carrier LAA access method significantly improves the system through-put,and also has less influence for existing Wi-Fi networks.(2)For the UE in the uplink resource scheduling request,due to the un-certainty of the unlicensed band,the efficiency of both sides of the interaction is low and prolonged.This paper proposes a scheduling method to reduce the response delay.It is mainly the three sequential processes of SR,UL grant and BSR required for uplink transmission under the licensed frequency band,which are adjusted to use the BSR to request uplink transmission resources directly under the unlicensed frequency band,to avoid excessive LBT de-tection,and to simplify UE-side operations.Therefore,the interaction effi-ciency between the base station side and the UE side and the response speed of the base station are improved.Simulation results show the effectiveness and feasibility of the proposed method.(3)For NR and future LAA in the standalone scenario,how the RMSI indicates the actual transmission location of the SSB,this paper studies the effective transmission of RMSI in unlicensed bands.Since unlicensed bands cannot guarantee reliable periodic transmission of RMSI,special mecha-nisms are needed to ensure that RMSI is correctly received by the UE.In this paper,a new NR unlicensed-band system information transmission method is designed to achieve the communication between the UE side and the NR network side under the condition that the NR network side can not provide the UE with the licensed spectrum access anchor.This method can effectively improve the success probability of RMSI transmission under standalone sce-narios.At the end of the paper,the content of the research is summarized,and relevant analysis and summary are made in the future direction for further research. |
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