摘要
The rapid growth of mobile data traffic has caused great pressure on the limited spectrum resources,and there must be some better methods to deal with this problem.The innovative technology of Long-Term Evolution(LTE)using the unlicensed spectrum,known as LTE-Unlicensed(LTE-U),has been proposed to effectively alleviate the shortage of authorized band resources.LTE-U has explored a lot of potential capacity in mobile communication systems with limited authorized spectrum resources,and improved the spectrum utilization of unauthorized frequency bands.However,LTE-U is still facing challenges in its application.In this paper,we summarize the key features of LTE-U and the coex-istence of LTE-U with Wi-Fi in the unlicensed Spectrum.We analyze the key technologies(including carrier aggregation,HARQ,interference cancelation,and centralized scheduling),the operating modes and deployment scenarios(including carrier aggregation LTE-U,duty cycle LTE-U,and standalone LTE-U),and the advantages(including anchored LTE-U and Standalone LTE-U scenarios),as well as main technical challenges.We then address the different management mechanisms of LTE-U and Wi-Fi(including the differences between the MAC layer and physical layer),the types of coexistence technology classification(including channel separation and channel sharing technologies),and directions for future work.We hope that this comprehensive survey spurs further research in this promising area.
