A Delay Sending Mechanism for a CR User's Handoff over CR Networks

It is well-known that the spurious fast retransmission and timeout widely exist in the course of vertical handover when a mobile node (MN) moves from a longer transmission delay network into a shorter one. Some solutions for the problems have been discussed in a lot of literatures for non-Cognitive Radio (non-CR) scenarios. One of them, bicasting is the main method to improve the transmission performance of the MN. However, in CR networks the mobile CR users (secondary users) only can use spectrum holes (that is, selective idle channel) to transmit their data packets. Once a licensed user (that is, primary user) selects the same channel, the CR user has to switch to another idle channel or other CR network. Unfortunately, the frequent spectrum switches and/or network handovers mean the longer handover delay and the more consumption of power energy. Hence, for a CR user it is more important to select a relative long term idle channel rather than to bicast in a hurry as soon as an idle channel is found. In this paper, a "delayed sending" mechanism is introduced for the CR uses to minimize the impacts mentioned above. Simulation results based on ns2 show that the "delayed sending" mechanism achieves the purpose of the design.