A hybrid MAC protocol based on ADAPT with modified back-off mechanism

Media Access Control (MAC) plays an important role in coordinating channel access among the nodes. This is especially important for Mobile Ad-hoc Networks (MANETs), where all mobile nodes use the same frequency spectrum for transmission. In this paper, a hybrid MAC protocol ADAPT-CND (ADAPT Considering Node Degree) is proposed, which is based on ADAPT. In ADAPT, back-off mechanism similar to Binary Exponential Back-off (BEB) is adopted to regulate the contention probability, while in ADAPT-CND, a modified BEB is proposed. In the modified back-off mechanism, each node regulates its contention window with varied step length, the step length is set according to each node´s degree. By doing this, the modified back-off mechanism enables each node to regulate its contention probability adaptively with the aggravating competition, thereby obtain satisfied throughput even under the existing of large quantities of competition nodes. In this way, ADAPT-CND enables each node to self-adjust its behavior based on both traffic loads and its own node degree. From simulation results, we see evident improvement of throughput performance with respect to packet arrival rate and node density relative to ADAPT.