Interference Management For LTE In Unlicensed Bands

With the exponential growth of wireless data traffic and the increasing scarcity of licensed spectrum,mobile network operators intend to use the unlicensed spectrum,such as the ISM bands and TV white space,to offload their traffic.In the future,it is very likely that two of the most prominent wireless technologies,LTE and WiFi,will coexist on the same unlicensed bands.Existing simulation results show that LTE is slightly impacted by such coexistence while WiFi is severely hampered by LTE transmissions.Hence,smart modifications to the resource management functionalities are indispensable on both LTE and WiFi sides to achieve harmonious coexistence.In this thesis,we firstly study two channel sensing schemes for LTE in unlicensed bands,i.e.,periodic sensing and persistent sensing.For the periodic sensing scheme,LTE nodes sense the channel for a fraction of time within each subframe and determine whether to transmit during the remaining fraction of time within the subframe.This process repeats for every subframe.For the persistent sensing scheme,LTE nodes keep sensing the channel during one whole subframe until the channel is free and then transmit during the following several subframes.Simulation results verify the proposed sensing schemes by comparing it with the no-sensing case in the studied scenarios.Secondly,we propose and evaluate an adaptive p-persistent CSMA scheme for LTE in unlicensed bands,which ensures a dynamic tradeoff between LTE and WiFi by adjusting the probability of LTE accessing the unlicensed channels according to the interference level.Concretely,we consider three mapping relations to realize this method.Since the only required interference measurement is performed by LTE base stations,our approach does not require communication among different technologies.Simulation results show that the proposed LTE adaptive p-persistent CSMA scheme can provide a flexible tradeoff between LTE and WiFi when they coexist with each other.Finally,we conclude the thesis and discuss some future research directions that may lead to successful joint deployment of LTE and WiFi in the same unlicensed bands.