1 Introduction
Medium Access Control (MAC) protocols for wireless local area networks (WLANs) can be grouped into two broad categories, namely, reservation-based and contention-based MAC protocols. Time Division Multiple Access (TDMA) is a reservation-based conventional MAC protocol widely used in cellular wireless communication systems, such as Global System for Mobile Communications (GSMs) [1]. It provides collision-free access to the medium and has low delay and very small jitter. Because of these characteristics, TDMA is very suitable for real-time and deadline-sensitive traffic [2]. However, to ensure that nodes keep track of time frames and slots, TDMA protocols must maintain time synchronization among all nodes. More importantly, TDMA protocols have limited scalability and don't adapt well to changes in the number of nodes in a wireless network since the base station must adjust the frame length or slot allocation accordingly. In addition to these, it is difficult, due to the fixed length of the time slots, to efficiently utilize every time slot in a frame whenever the packet size varies.