A first radio has duplex communication with a second radio and a third radio, without using a base station by using a multiple-access protocol system. The first radio is configured to switch back and forth between being a master radio and a slave radio in the multiple-access protocol system. In some embodiments, time-division multiplexing is used as the multiple-access protocol system for the first radio, the second radio, and the third radio to communicate. In some embodiments, the master radio provides timing synchronization and/or assigns transmission slots for radios in the multiple-access protocol system.