A wireless network is provided that includes a base station and subscriber stations that communicate with the base station using radio frequency (RF) time division duplex (TDD) signaling. The base station may establish medium access control (MAC) connections with each station. The base station monitors communications with the stations and, in accordance, assigns stations or MAC connections to modulation groups. The base station transmits signals on MAC connections or to stations in a modulation group in adjacent TDD slots within a TDD frame. The base station may receive access requests from the stations, evaluate traffic requirements for the stations, and determine a longest downlink portion for the stations. The base station then allocates downlink and uplink portions of a TDD frame according to the length of the longest downlink portion.