Channel Idle Time Statistics Based Spectrum Accessing Strategies With CSMA Based Primary Networks

Channel statistics based secondary transmission strategy design has been studied intensively in the past. In this work, we consider the same problem but with a carrier sensing multiple access based primary networks, i.e., the primary users that would react to interference. In such primary networks, users always need to perform carrier sensing before accessing the channel. Such networks include 802.11 WLAN and 802.15 WPAN. The secondary transmission strategy design when the primary network uses carrier sensing based network access differs a lot from what has been considered in the literature. Here, we show through experiments with 802.11 networks that under secondary interference, the primary users can experience not only packet collisions but also transmission delay. Under long-term secondary interference, the primary users might even choose to transmit in another channel. This phenomenon is known as the channel capture effect. Next, with this in mind, we formulate a novel transmission strategy design problem that aims to maximize secondary transmission time with design constraints on the probability of packet collision or delay, as well as the probability that the primary user switches channel. Finally, we describe a software-defined radio device that we built to execute the designed transmission strategies on the 2.4 GHz band. The performance of both the primary and secondary users are studied. Results show that our consideration for the primary user reactions is necessary. In particular, the designed transmission strategy better protects the primary user transmission while maintaining secondary user performance.