A method and apparatus to improve the quality of control signaling based on signaling messages controlling speech or data transmission over an air interface between at least two Multi-User-Reusing-One-Slot/Voice Services Over Adaptive Multiuser Channels On One Slot (MUROS/VAMOS) capable wireless transmit/receive units (WTRUs). The WTRUs communicate with each other at the physical layer via signaling messages transmitted in control channels such as Slow Associated Control Channel (SACCH) and Fast Associated Control Channel (FACCH). Speech services are provided simultaneously over the same physical channel, and the Timing Advance (TA) and Power Command (PC) parameters of a WTRU are multiplexed in several occurrences of the SACCH or FACCH to increase the number of channel bits available for channel coding.