Simultaneous Transmission Opportunities for LTE-LAA Co existing with WiFi in Unlicensed Spectrum from Exploiting Spatial Domain

In this thesis, we first give an intensive review on the background of LTE-LAA technology, the research status of LTE-LAA and WiFi co-existence mechanisms and 3GPP Rel. 13 standardization on LTELAA. The existing co-existence designs focus on the time-domain, frequency-domain and power-domain to achieve fairness between two systems. Simultaneous transmissions are avoided to reduce collision probability. However, by exploiting the spatial domain, we discover the possibility of simultaneous LTE-LAA/WiFi transmission opportunities as long as the interference received at the WiFi receiver is well managed. We first show the feasibility of such simultaneous transmission opportunities considering AP/UE location diversity and various coverage overlap situations between LTE-LAA small cell and WiFi AP. Then, by utilizing multi-antenna beamforming capability, we propose a more practical co-existence scheme combing DoA estimation and null steering technologies. As the lack of direct communication link between LTE-LAA and WiFi systems, we also give our design of information exchange that requires minimal modifications on current WiFi standards and with little to none extra overhead. From the discussions and simulation results, we prove the existence of such simultaneous transmission opportunities that do not bring extra impact on WiFi networks. The channel occupancy time of LTE-LAA can be greatly improved. However, problems and challenges are also identified that require future investigations.