Control Information Exchange In Cognitive Radio Networks Based On Hopping And Network Coding

In cognitive radio(CR) networks, the CR nodes need to exchange various kinds of control information such as clock synchronization, spectrum sensing results, network topology, and channel reservation, so as to negotiate appropriate communication channels available to both transmitter and receiver without interfering the communication between primary users(PUs). Therefore, the CR nodes can avoid the interference of authorized communication generated by a single fixed dedicated control channel through constantly switching the communication frequency bands. Making full use of the spectrum resources of multiple authorized channels to control the information exchange and it is better to avoid the problem of the interference of authorized users and the saturation of the channel flow. However, in the existing control information exchange mechanism based on frequency hopping, all of the intermediate nodes transmit control information by using the method of store and forward. Thus, it will lead to the increase of the number of switching times and energy consumption, which is not benefit to enhance the transmission performance of the whole cognitive radio network. For example, the intermediate nodes forward too much times will lead to excessive energy consumption. Data in the nodes which waiting too long will lead the network delay in the bad performance. Therefore, this paper innovatively apply network coding technology to the process of control information exchange which based on frequency hopping.Firstly, this paper presents a support network coding hopping sequence generation mechanism which based on m binary number. The mechanism design different channel hopping(CH) sequences for each encoding node and its neighbor in order to support network coding. To ensure that each encoding node can efficiently perform network coding reducing the times of forwarding and achieving frequency hopping rendezvous as far as possible with the upstream and downstream neighbor nodes in all access channels. In addition, it can also improve the interactive efficiency of the control information and avoid the mutual interference with the authorized communication. What’s more, this mechanism ensures that the average interval of rendezvous time between different CH sequences is sufficiently short, the performance of control information interaction is better than that of the traditional frequency hopping communication system.Secondly, in order to overcome the defects of higher channel load and lower utilization ratio of the above mechanism we also propose a scheme of frequency hopping sequences based on cyclic sequence generation for network coding. Although the set of frequency hopping sequences generated by the proposed scheme has a higher average rendezvous time, the lower average channel load and higher average channel utilization can make the whole network achieve stable in a shorter time and the less packet loss rate of the control information. Therefore, the mechanism is more suitable for the network which have certain requirements such as stability time and the network packet loss rate.Finally, we evaluate performance between the two kinds of control information interaction mechanism of frequency hopping based on network coding and the traditional frequency hopping in the opnet network simulation software, and then the superiority of the former in the control information interaction mechanism is verified. At the same time, the average throughput and packet loss rate of two kinds of frequency hopping control information exchange mechanism based on network coding which is proposed in this paper are simulated and compared. The simulation results show that in the aspect of throughput the performance of the former is better than that of the latter, but the latter is better than the former in terms of the packet loss rate,which the former based on the M system and the latter based on the rotation mode. In addition, the latter also make the network to achieve stability in a relatively short period of time. Therefore, both of them are suitable for different occasions.