Cognitive Tcp In Wireless Network Technology Research

Cognitive radio is one of the most popular and cutting-edge research field inwireless communications. At the same time, the cognitive radio networks based oncognitive radio is getting more and more attentions. However, researches on TCPtechnology for cognitive radio networks are rare.Based on wired networks, the traditional TCP technology will face enormouschallenges in cognitive radio networks. Firstly, because of not knowing the status of thelink layer, traditional TCP will take unnecessary congestion control actions and keep onretransmitting the unacknowledged packets during the disconnection period of the linklayer. These blind actions will lead to series of serious consequences. For instance, thepackets will be accumulated in routers and TCP’s RTO (Retransmission Time-Out) willbecome too long to transmit any packets even after the link layer is resumed. Thosephenomena are called “flood restoration effect” and “sluggish effect” respectively.Secondly, high packet loss ratio will lead to a lot of unnecessary congestion controlactions which will waste lots of frequency resources.Consequently, we need to design a new TCP protocol for cognitive radio networks.Based on the comprehensive performance assessment of the traditional TCP protocol incognitive radio networks, a brand new TCP protocol is proposed, i.e. TCP_NSB.With cognitive ability of the network status, TCP_NSB can adjust its own internalstate continuously in order to adapt to the new network status. This ability can improvethe TCP_NSB’s performance greatly.TCP_NSB has three operating modes: normal mode, hang on mode, retransmissionmode. These three operating modes correspond to three typical network states incognitive radio networks: normal transmission state, link layer’s disconnection state andhigh packet loss ratio state. Simulation results show that TCP_NSB is better than otherversions of TCP protocol under the same conditions.We need to set up a simulation platform to compare the performances of traditionalTCP and TCP_NSB in cognitive radio networks. So NS2(Network Simulator Version2)is used to set up the corresponding TCP simulation platform in this thesis. According to the actual measurement, the platform can accurately simulate the scenario of cognitiveradio networks.