Research On LTE/LTE-A Coexistence With Wi-Fi In The 5 GHz Unlicensed Spectrum Band

With limited licensed spectrum and a significant increase in internet services,mostly video streaming,online gaming,traffic capacity become one of the most critical challenges in today networks.A practical approach for increasing network capacity is to use additional spectrum,LTE-A spectrum efficiency is already at its max level and provides excellent performance in dense network thanks to the air interface scheduling.Extending the advanced technologies such as LTE-A in the unlicensed spectrum is considered as a possible solution to fulfill these new internet service demands.However,mobile operators would need less modification for LTE-A to coexist with other radio access technologies in the unlicensed band such as Wi-Fi.These modifications may come from the air interface by changing the schedule channel technique or upgrade the core network.The second solution is less considered,the research community and standardization organizations are more focus on the air interface design than the core network modification to reduce the complexity of LTE-A deployment in the unlicensed spectrum.For unlicensed spectrum regulation entities impose some limitations depending on the country such as the transmission power,the channel access methods,the radar protection process,the spectrum aggregation,the channel occupation duration.If LTE-A needs to operate in the unlicensed band,it has to take consideration of all these aspects even if the regulation requirement can change from country to country.These requests come from the fact that the unlicensed band is a shared spectrum for different technologies;therefore operating in the unlicensed band required a mechanism that allows a fair coexistence with other technologies and also with other operators in the same spectrum·Network densification has already played a significant role to satisfy the high mobile data traffic with less spectrum needed.In release 13 the 3GPP extends LTE-A in the unlicensed band called License-Assisted Access(LAA)for downlink only to improve the user experiment with friendly coexistence with Wi-Fi.As a starting point of our work,we introduce the challenges and design requirements for LTE-A to operate in the unlicensed spectrum.Contrary to the licensed spectrum with dedicated resources,the unlicensed spectrum is a shared band where different technologies such as Wi-Fi and LTE-A itself from different network operators could coexist.Following the 3GPP standardization path,in this section,we present an overview of critical technologies that enable better performance of the coexisting network such as the channel occupancy time,the energy detection threshold,the power transmission,the QoS implementation.Finally,this section ends with the outline of our research project.·The deployment of LTE/LTE-A in the 5 GHz unlicensed spectrum is to improve the user experience with fair coexistence with the existing technologies in the same spectrum.In the second section,we evaluate the performance of LAA/Wi-Fi and LAA/LAA coexistence based on different scenarios,mechanism,and loads.In release 13 LBT category 4 was presented as a favorable coexistence mechanism that can achieve a fair coexistence with Wi-Fi.After showing the fair coexistence at low buffer traffic,we prove that the LBT category 4 presents some limitations at a full-buffer scenario.Therefore two variants of LBT-category 4 are presented,the first based on optimal contention windows and the second as a periodic access method.These mechanisms can improve coexistence performance and can even perform better in some cases compared to Wi-Fi/Wi-Fi coexistence.·With the uncertainty of the coexistence of LAA and Wi-Fi in any given area,the performance evaluation scenario oriented would not be very adequate to evaluate the impact of LAA on Wi-Fi or on LAA itself.Considering the randomness of these networks shape stochastic geometry approach is used to model the coexistence effect between these two technologies.However,the stochastic geometry method cannot capture the backoff procedure observed in DCF or LBT in case of successful or failed transmission.In the 3rd part of our work,we present the performance evaluation of LAA/Wi-Fi coexistence based on Markov chain and stochastic geometry tools.The proposed mathematical framework helps to model the spatiotemporal coexistence of LAA/WiFi coexistence with different metrics evaluation such as the medium access probability,SINR coverage probability,and the density of successful transmission in a random deployment scenario.·In release 14,the extension of LTE-A in the unlicensed spectrum is presented to enable uplink,and downlink transmission.Two mechanisms were proposed the cross-carrier and self-carrier scheduling.In cross-carrier scheduling,eNBs send the uplink grant signal to the UEs via the licensed spectrum while in self carrier-scheduling both uplink data and grant signals are sent through the unlicensed spectrum.However,with no guarantee to access the channel once a UE is scheduled,this problem becomes more critical in self-carrier scheduling where the double LBT mechanism makes the design more intricate and inefficient for resource management.Even if LTE-A would lose its high spectrum efficiency,the random access method proposed in the 4th section of this document offers better coexistence with other radio access terminals,including eLAA itself.Moreover,the control power function designed for LTE-A to combat the cell edge interference is also investigated.·To summarize this work,section 5th of this research project presents different coexistence mechanisms with pros and cons.The primary coexistence mechanism presented in release 13 with the 3 GPP evaluation parameter shows some drawbacks to meet the required fair coexistence from the 802.11 community.After proving the design issues in high load coexistence system,we proposed different analytical models for LAA-Wi-Fi coexistence from the downlink only to the uplink transmission.These models would also help to design a more friendly coexistence mechanism in the 5 GHz unlicensed spectrum and beyond.As the release 15 going for 5G standard,5GNR-U will also bring challenges on the coexistence between 5G networks and the next generation Wi-Fi in the 60 GHz band.