A transmission apparatus comprises an assignment information generator which, in operation, assigns resources on a resource unit (RU) basis to one or more terminal stations (STAs) and generates assignment information that specifies RUs allocated to the one or more STAs; a transmission signal generator which, in operation, generates a transmission signal that includes a legacy preamble, a non-legacy preamble and a data field, wherein the non-legacy preamble comprises a first signal field and a second signal field that carry a set ID and the assignment information, and wherein the set ID identifies one assignment set comprising the one or more STAs and a plurality of assignment indices, and wherein the assignment information comprises a resource assignment indication for each of a plurality of assignment which are referenced by the plurality of assignment indices; and a transmitter which, in operation, transmits the generated transmission signal.