Research Of Transport Control Protocol Using Cross-Layer For Cognitive Radio Networks

In Cognitive radio networks, it is one of the hot spots in current research that how to solve the performance degradation due to congestion loss and interruption loss caused by spectrum sensing in transport layer. The subject of this article comes from National Natural Science Foundation of China and has important theoretical significance and wide application prospects.Aim at the critical problems, this paper proposes an improvement of transport control protocol after an in-depth research on the principles and characteristics of cognitive radio networks as well as traditional transport control protocol. The improved protocol is based on cross-layer design and maintains its end-to-end characteristic at the same time. It can judge the node status and obtain the current channel information by interacting with lower layers, such as Mac layer, and modify the transmission rate and the timeout value of retransmission timer at source accordingly, that will avoid unnecessary retransmissions and decreases of congestion window as well as slow start threshold. Besides, this paper proposes the process of immediate retransmission based on priority queue that retransmits the interruption-loss packets as soon as the spectrum sensing ends; and differentiate the spectrum retransmission from quick retransmission so as not to diminish the congestion window and slow start threshold if the packet-loss is due to interruption in all probability; and improves the treatment to duplicate acks, which increases the efficiency of retransmission and the good throughput.This article uses NS2 to simulate the improved protocol after modifies the MAC layer to make it support the basic characteristics and function of cognitive radio network. Simulation results indicate that, compared to TCP-Reno and TCP-Vegas, the improved TCP increases the sending rate, reduces the retransmission ratio at the source, and improves the whole performance.