Study On Congestion Control Mechanism Based On Network State Measurement In Dynamic Spectrum Access Network

The radio spectrum resource is an important strategic resource of the country.As the need for radio spectrum resources increases,the spectrum resources that can be used by ordinary users are becoming increasingly scarce.As an important application of cognitive radio,dynamic spectrum access(DSA)can make use of the spectrum gap to communicate,which greatly alleviates the scarcity of radio spectrum resources and improves the spectrum utilization rate.However,the performance of the DSA network is greatly affected by the problem of the wireless network and the complex structure of the DSA network.Therefore,how to improve the performance of TCP of the DSA network TCP is the focus of this paper.In the communication process of DSA network,ordinary users will frequently perceive the spectrum,and access the new spectrum at the right time to switch spectrum.However,the switching of the spectrum will cause the rapid change of the network state,resulting in a series of problems such as increased link delay,packet loss and the decline of the network throughput.DSA technology is implemented in the MAC layer,the new TCP protocol must adapt to the change of the network state caused by the switching of the underlying spectrum.For the characteristic of DSA network,this paper improves the traditional congestion control based on the measurement of the network state,An improved protocol TCP Kda is proposed.The selection and accurate acquisition of the network state have a great influence on the implementation of effective congestion control.In this paper,the real-time throughput of ACK packet and round-trip delay RTT are selected as a tuple to represent the current network state,which provides an important basis for the improvement of DSA network congestion control mechanism.In the TCP Kda protocol,the congestion avoidance phase of the traditional congestion control mechanism is re-divided,adding the perceptual phase and putting the conventional Additive Increase(AI)into additive increase adjustment phase.For the packet loss,fast retransmission and fast recovery phase is added to the recovery phase to deal with both time-out packet loss and duplicate ACK acknowledgment packet loss.According to the measured network state,the protocol enters different phases and adjusts the window in different ways to adapt to the change of the DSA network state to improve the TCP protocol performance.Finally,through the performance evaluation of multiple simulation scenarios,TCP Kda is better adapted to the change of DSA network state and obtains better throughput.