A method for establishing an uplink transmission. A recipient station receives a trigger frame. The trigger frame including at least one per user info field. Each of the at least one per user info field comprising at least a user identifier field identifying a STA to be allocated a resource unit, a resource unit allocation field for allocating a resource unit for the identified STA, and a spatial stream allocation field identifying a number of streams to be allocated for the identified STA. The recipient STA evaluating an order of the at least one per user info fields to determine a sequence of the allocated streams that matches the order of the at least one per user info fields. The recipient STA comparing the values from each of the resource unit allocation fields and grouping corresponding at least one per user info fields with matching values to identify members of a set STAs allocated to MU-MIMO. In some aspects, the spatial stream allocation field of the per user info fields comprises three bits.