A base station (11) of a wireless cellular communication network operating in unlicensed spectrum adjusts (118) the robustness of a downlink transmission in response to the power level of any interference encountered in the channel and the source of the interference. The base station (11) estimates (110) whether the source of interference encountered is a eLAA or WLAN network (110). An offset to a transmission format—a measure of transmission robustness to noise and interference—is calculated (112) in response to the interference power level and the source of the interference. An initial transmission format is adjusted (118) by the offset, and data are transmitted (120) to a UE using the adjusted transmission format. In other embodiments, the base station (11) may compare its interference to that detected by the target UE, to ascertain whether the two likely have the same source. Similarly, in some embodiments the base station may perform a spatial analysis such as angle of arrival to ascertain whether the source of interference is physically close to the target UE. In these embodiments, the base station may further adjust the transmission format in response to information gleaned about the source of interference.