Network State Conservation in Dynamic Spectrum Access: the IEEE 802.11 DCF Case

Abstract

The paper is on improving spectral efficiency in dynamic spectrum access (DSA). The proliferation of wireless devices has been straining the limited radio spectrum in recent years. The spectrum shortage problem will deteriorate as the ideas of Internet of things (IoT) and smart communities are gaining attention and acceptance. It is thus important to improve spectral efficiency in DSA, one of the most promising techniques addressing the spectrum shortage problem. One perspective to improving spectral efficiency in DSA is to study the impact of a cognitive-radio (CR) physical layer on the upper layers, such as the medium access control (MAC) sub-layer. A CR physical layer coupled with DSA may interrupt the activities at an upper layer at any given time, which can be costly in terms of spectral efficiency. For example, when a CR physical layer interrupts the ACK transmission in a RTS-CTS-DATA-ACK cycle of the IEEE 802.11 DCF, the spectrum used for accomplishing the RTS-CTS-DATA exchange are totally wasted, impairing spectral efficiency in the second user (SU) network. This type of spectrum waste caused by a CR physical layer in DSA can be reduced by the idea of network state conservation (NSC). Basically, second users with NSC conserve their protocol state information when the signal of primary user (PU) arrives in the channel. When the channel becomes available again for the SUs, they use their conserved network states to resume their protocol cycle from where it was interrupted by the PU’s signal, instead of starting the whole cycle over. We show that NSC can significantly improve the spectrum efficiency of an SU network of IEEE 802.11 DCF nodes, and the gain in spectrum efficiency increases with the intensity of the PU’s traffic.