A method for exchanging data includes generating a usage indicator for an access window, the usage indicator including a first indication of if an allowed station in a list of allowed stations needs to receive information about its resource allocation and at least one of a second indication of a start time of the access window, and a third indication of the list of allowed stations, and broadcasting the usage indicator. The method also includes exchanging data with at least one of the allowed stations within the access window in accordance with the usage indicator.