A station for facilitating communication in a wireless network for multi-user transmission, the station comprising: one or more memories; and one or more processors coupled to the one or more memories, the one or more processors configured to cause: processing a first trigger frame (1302, 1402) received from an access point, wherein the first trigger frame (1302, 1402) schedules a first uplink multi-user transmission and indicates a plurality of resources for indicating existence of data to be sent to the access point, transmitting, during the first uplink multi-user transmission to the access point and in response to the first trigger frame (1302, 1402), a first uplink frame (1304, 1404) that has no data field and that has a signal indicating existence of data to be sent from the station to the access point, wherein the transmitting comprises transmitting the signal on a first resource of the plurality of resources, and wherein the one or more processors are configured to cause: selecting the first resource of the plurality of resources, and generating the first uplink frame (1304, 1404) based on the selected first resource, characterized in that the one or more processors are further configured to cause: identifying based on the first trigger frame mapping information between the plurality of resources and a plurality of stations, wherein selecting the first resource comprises selecting the first resource among the plurality of resources based on the mapping information, and/or wherein the mapping information uniquely assigns the first resource to the station. one or more memories; and one or more processors coupled to the one or more memories, the one or more processors configured to cause: processing a first trigger frame (1302, 1402) received from an access point, wherein the first trigger frame (1302, 1402) schedules a first uplink multi-user transmission and indicates a plurality of resources for indicating existence of data to be sent to the access point, transmitting, during the first uplink multi-user transmission to the access point and in response to the first trigger frame (1302, 1402), a first uplink frame (1304, 1404) that has no data field and that has a signal indicating existence of data to be sent from the station to the access point, wherein the transmitting comprises transmitting the signal on a first resource of the plurality of resources, and wherein the one or more processors are configured to cause: selecting the first resource of the plurality of resources, and generating the first uplink frame (1304, 1404) based on the selected first resource, characterized in that the one or more processors are further configured to cause: identifying based on the first trigger frame mapping information between the plurality of resources and a plurality of stations, wherein selecting the first resource comprises selecting the first resource among the plurality of resources based on the mapping information, and/or wherein the mapping information uniquely assigns the first resource to the station. processing a first trigger frame (1302, 1402) received from an access point, wherein the first trigger frame (1302, 1402) schedules a first uplink multi-user transmission and indicates a plurality of resources for indicating existence of data to be sent to the access point, transmitting, during the first uplink multi-user transmission to the access point and in response to the first trigger frame (1302, 1402), a first uplink frame (1304, 1404) that has no data field and that has a signal indicating existence of data to be sent from the station to the access point, wherein the transmitting comprises transmitting the signal on a first resource of the plurality of resources, and wherein the one or more processors are configured to cause: selecting the first resource of the plurality of resources, and generating the first uplink frame (1304, 1404) based on the selected first resource, characterized in that the one or more processors are further configured to cause: identifying based on the first trigger frame mapping information between the plurality of resources and a plurality of stations, selecting the first resource of the plurality of resources, and generating the first uplink frame (1304, 1404) based on the selected first resource, characterized in that the one or more processors are further configured to cause: identifying based on the first trigger frame mapping information between the plurality of resources and a plurality of stations, wherein selecting the first resource comprises selecting the first resource among the plurality of resources based on the mapping information, and/or wherein the mapping information uniquely assigns the first resource to the station.