Séminaire des équipes de recherche
Harmonious Coexistence Between Wi-Fi and LTE Systems in the 5 GHz Bands: Challenges and Solutions
- Date : 13/07/2017
- Place : Inria de Paris, Bâtiment C, C334 - 14h00
- Guest(s) : Marwan Krunz (University of Arizona)
Enabling harmonious coexistence between heterogeneous wireless systems is a challenging problem, but one that needs to be urgently addressed in order to quell the exploding demand for more spectrum. In this talk, we focus on coexistence between Wi-Fi and LTE systems in the unlicensed 5 GHz U-NII band, as an anecdote of heterogeneous coexistence over shared spectrum. Recently, the FCC allowed wireless operators to extend their LTE services to the unlicensed 5 GHz band. This gave rise to various flavors of LTE-unlicensed (LTE-U) technologies, including CSAT, LAA, MulteFire, etc. Yet, strong concerns were raised regarding LTE-U’s impact on the performance of other incumbents of the unlicensed band, especially Wi-Fi. These concerns center on LTE’s aggressive, schedule-based channel access approach, relative to the more benign contention-based access of Wi-Fi. It is also generally believed that interference-mitigation mechanisms suggested for fair coexistence in the 5 GHz band do not properly capture the complex interactions between various incumbents of this band. In this talk, we present novel techniques for LTE interference mitigation, exploiting the full-duplex (FD) capabilities of future Wi-Fi systems. Specifically, we propose a modified Wi-Fi operation mode in which Wi-Fi stations exploit FD communications to enable simultaneous transmission and sensing (TS) so as to reduce the time required to detect collision with LTE signals. To identify LTE-U interference, we develop a simple detector that takes advantage of the cyclic prefix in LTE waveforms to achieve high detection accuracy. We then consider the problem of selecting the clear channel assessment (CCA) threshold for LTE signals. IEEE 802.11 standards follow an overly conservative approach in this regard, relying on energy detection to identify non-Wi-Fi interference. Instead, we derive an optimally fair CCA threshold that Wi-Fi systems can use when coexisting with a duty-cycled LTE-U system. Another aspect of our work focuses on jointly adapting the transmission rate and duplex mode of a Wi-Fi device in an LTE/Wi-Fi coexistence scenario. Using a partially observable Markov decision process (POMDP), we solve this problem and show how adaptation can significantly improve the performance for both systems. Finally, we turn our attention to competition/cooperation among multiple LTE operators in the unlicensed 5 GHz band. We first demonstrate the detrimental performance impact of non-cooperation among operators. Subsequently, we introduce a framework, called MatchMaker, which incentivizes coordination among operators and at the same time balances the performance of both LTE and Wi-Fi to achieve harmonious coexistence of the two systems. Our simulation results show that MatchMaker has the potential to almost double the throughput of an LTE system and triple the throughput of a Wi-Fi system, compared to a non-coordinated operation.