A Spectrum Etiquette Protocol and Interference Coordination for LTE in Unlicensed Bands (LTE-U)

LTE in unlicensed bands (LTE-U) holds the promise of alleviating the licensed spectra scarcity and enhancing capacity by utilizing the unlicensed spectra. However, once LTE-U accesses an unlicensed band, there is almost no any opportunity for unlicensed systems (e.g. 802.11 WLAN) with inferior control abilities and CSMA/CA, to access that any more. In order to solve this unfair coexistence problem, we propose a spectrum etiquette protocol that restricts the priority of LTE-U and balances the extreme unfair competition. Besides, for engineering implementation of the proposed spectrum etiquette, an LTE-802.11 fusion protocol stack is designed for LTE-U. However, the restrictions of the spectrum etiquette would degrade the throughput of LTE-U on unlicensed spectra. Therefore, successive interference cancellation (SIC) is adopted to perform interference coordination for LTE-U. Moreover, we also study the problem of deriving the optimal lower power and the time length of each normal power transmission allocation strategy that maximizes the ergodic capacity of LTE-U under the proposed spectrum etiquette. The simulation study shows that the improved ergodic throughput of LTE-U can be achieved by our proposed interference coordination and the traffic need of 802.11 WLAN can be satisfied as much as possible under the proposed spectrum etiquette.