Spectrum sharing analysis for unlicensed use in 6 GHz using Risk-Informed Interference Assessment

Abstract

In October of 2018, the FCC proposed new rules for opening 1.2 GHz of spectrum in the 6 GHz band, from 5925 to 7125 MHz, for unlicensed Wireless Local Area Networks (WLAN) devices. The objective is to allow WLAN in the 6 GHz band while sharing the spectrum with current incumbents. The traditional spectrum sharing approach relies on the worst-case scenario analysis of single events of severe consequences, regardless of their probability of occurrence, which leads to over-conservative use of the spectrum. Risk-Informed Interference Assessment (RIIA) is a quantitative approach that can be successfully applied for spectrum sharing analysis. Based on statistical analysis, RIIA estimates the probability and the consequence of interference. The objective is to allow flexible use of spectrum without being overprotective. It has been applied to a few coexistence studies in the last years and has shown great potential in providing informed insight to spectrum sharing analysis. To date, however, it has not been yet applied to coexistence studies in the 6 GHz band. In this work, we apply RIIA to analyze coexistence between WLAN and each type of incumbent service in this band and propose spectrum sharing mechanisms to reduce the probability of harmful interference. To facilitate sharing in the 6 GHz band, the FCC has divided it into four sub-bands, from U-NII-5 to U-NII-8, and proposed mitigation rules for each of them depending on the incumbents. This band is allocated to Broadcast Auxiliary Service (BAS) and Cable Television Relay Service (CARS) fixed and mobile links, Fixed Satellite Service (FSS) and fixed point-to-point links. These systems use narrow beamwidth antennas located at elevated heights, while WLANs employ low-power transmitters, mostly indoors, and, typically, omnidirectional antennas at few meters above the ground, which suggests the possibility that little energy from the incumbent links is perceptible on the ground and vice versa. To investigate this hypothesis, we apply RIIA to quantify the level of risk and its consequences to both, incumbent links and WLANs devices. Our analysis is based upon a four-step method. First, we make an inventory of all significant harmful interference hazards, in our case, 6 GHz Wi-Fi APs or incumbent links that could cause co-channel interference to the incumbents or Wi-Fi devices, respectively. Second, we define the interference protection criteria for each of them as consequence metrics to characterize the severity of hazards. Third, the likelihood and consequence of each hazard are analyzed. Using Monte Carlo simulations, we calculate the likelihood of downlink and aggregate interference from/to current incumbents to/from future WLANs and, using an interference protection criterion, determine if this interference can be tolerable. Finally, the likelihood-consequence results are aggregated and compared for different scenarios. This approach provides detailed coexistence analysis between WLAN and incumbent services in the 6 GHz band using the RIIA methodology. The results suggest that there is a low risk of harmful interference to terrestrial incumbent links in the U-NII-6 and U-NII-8 bands, which consider low-power indoor APs only. For the U-NII-5 and U-NII-7 bands, considering outdoor APs transmitting at full power, the probability of harmful interference ranges from low to high, depending on the scenario. To reduce this risk, it is suggested to implement a mitigation technique. In the case of a satellite incumbent, coexistence is possible without the need of mitigation techniques. Ultimately, this work will provide decision-makers with information regarding the risks associated with coexistence in the 6 GHz band.