Cooperative retransmission implementation in ns 2

Abstract

From the theoretical perspective cooperative communications are reasonably well understood. But in practical realizations of cooperative communication system are still quite limited, the articles in this special issue are devoted to implementation aspects related to cooperative retransmission implementation in ns 2.system..Cooperative retransmission in wireless networks has attracted many research attentions which is the basic idea when a receiver cannot decode a frame, the retransmission is handled not by its original source but rather by a neighbor that overheard the transmission successfully, in this situation may helper have a better channel to the destination and when it comes to this topic, three key issues need to be addressed, namely when to cooperate, whom to cooperate with and how to protect cooperative retransmission are addressed here. The fundamental of cooperative communications lie in the physical layer. However, the notation of cooperation is available in various forms at different protocol layer. To facilitate access to the physical layer information and adaptation to mobility, it is natural to introduce the notion of cooperation in the layer directly above the physical, namely, the medium access control MAC layer; we consider the case of multiple cooperating neighbors from a MAC-layer perspective and assume a receiver that can only decode one transmission at a time, while multiple retransmission by several neighbors that had heard the frame, will cause a collision, according to our protocol which we are particularly interested in MAC protocol design for cooperative communication based on 802.11 CSMA/CA, and a cooperation is initiated only if the direct transmission fails. An optimal relay node is selected in a distributed manner according to instantaneous relay channel conditions in the network.