The important issue regarding ad hoc networks is to design suitable MAC protocols, which main purpose is to control the access to radio channel. The main challenge is to avoid collision in transmission and to effectively utilize radio channel. The MAC protocols can be classified into contention-free and contention based:
The most common access methods used in contemporary wireless networks such as WiFi are based on CSMA (Carrier Sensing Multiple Access). As the name suggests, the UE firstly “sense” the medium before data are sent. If the medium is for the time being used, the UE has to wait until the medium is released. If the medium is free, the UE sends its data immediately. To further minimize the probability of collision, other methods were introduced, such as CSMA-CD (CSMA with Collision Detection) or CSMA-CA (CSMA with collision avoidance).