Coexistence Gaps in Space via Interference Nulling for LTE-U/WiFi Coexistence

To avoid the foreseeable spectrum crunch, LTE operators have started to explore the option to directly use the underutilized unlicensed spectrum in 5GHz UNII bands being mainly used by IEEE 802.11 (WiFi). However, as LTE is not designed with shared spectrum access in mind, it has a potential to seriously harm Wi-Fi. Currently suggested solutions focus on forcing LTE-U to introduce coexistence gaps in either frequency, time, or space domain, and are addressing the coexistence only indirectly due to the lack of coordination among the coexisting WiFi and LTE-U networks. Contrary to these schemes, our proposal introduces explicit cooperation between neighboring LTE-U and WiFi networks. We suggest that LTE-U BSs equipped with multiple antennas can create coexistence gaps in space domain in addition to the time domain gaps by means of cross-technology interference nulling towards WiFi nodes in the interference range. In return, LTE-U can increase its own airtime utilization while trading off slightly its antenna diversity. We demonstrate that such cooperation offers benefits to both WiFi and LTE-U in terms of improved throughput and decreased channel access delay. More specifically, system-level simulations reveal a throughput gain up to 221% for LTE-U network and up to 44% for WiFi network depending on the setting, e.g., distance between the two cells, number of LTE antennas, and WiFi nodes in the LTE-U BS neighborhood. Our approach provides significant benefits especially for moderate separation distances between LTE-U/WiFi cells where interference from a neighboring network might be severe due to the hidden network problem.