Study On Tcp Performance Improvement In Dynamic Spectrum Access Networks

Dynamic Spectrum Access(DSA) is supposed to be the key technology to improve wireless communication. However, Transport Control Protocol(TCP) may suffer significant decrease in end-to-end throughput performance caused by spectrum switches in typical DSA networks. Since then improving performance of TCP in DSA networks is significant.Traditional TCP may have a poor performance in DSA networks, cause it lacks the corresponding strategy to deal with the typical operations in DSA networks, such as spectrum sensing and spectrum switch, which would cause extra link delay and packet loss and significantly decrease TCP performance. In this dissertation, TCP DSA is proposed to mitigate this issue and to improve TCP performance in DSA networks which is achieved by monitoring the measured bandwidth periodically, and using them to indicate the spectrum switches.In this dissertation, we firstly analyzed the rationality of using measured bandwidth as the indicator of spectrum switches, and verified it through simulation experiments. Secondly we designed the algorithm to pinpoint the time when a spectrum switch occurs. And we also modified the congestion control algorithm of TCP. By combining these two algorithms, we can locate the spectrum switches as soon as it occurs, and adjust the congestion window to a proper value, thus to fully utilize the available spectrum resources. After all these, we provided the design details of TCP DSA, including collection and processing of measured bandwidth, modified congestion control flow, etc.In the end, for the purpose of verify the performance of TCP DSA, we implemented TCP DSA in NS2. Simulation results in several scenarios show that TCP can achieve a better end-to-end throughput with a comparable fairness.