Stochastic Behavior Study of Backoff Algorithms in Case of Hidden Terminals

In MANET, the hidden terminals problem is a common situation which leads to poor performances due to collisions and unfairness behavior of nodes. The use of RTS/CTS mechanism is helpful to improve the performances but not sufficient: it is important to design new backoff algorithms. But, before, it is necessary to understand how backoff algorithms deal with long-term and short-term unfairness and also with performances. In this paper, based on a stochastic process algebra, we provide a new study of the hidden terminals problem. The binary exponential backoff and the double increase double decrease backoff algorithms are studied in depth in this case. The state of the medium (idle, occupied by either collision or transmission) is computed and the probability of the different backoff´s stage is analysed. The short-term unfairness is clearly shown with a new metric. All results are given in both basic access and RTS/CTS one