In underlay cognitive radio networks (CRNs), the connectivity of secondary users (SUs) is difficult to be guaranteed due to the existence of primary users. Most prior studies only consider cognitive radio networks equipped with omni-directional antennas causing high interference at SUs. We name such CRNs with omni-directional antennas as Omn-CRNs. Compared with an omni-directional antenna, a directional antenna can concentrate the transmitting/receiving capability at a certain direction, consequently resulting in the less interference. In this paper, we investigate the connectivity of SUs in CRNs with directional antennas (named as Dir-CRNs). In particular, we derive closed-form expressions of the connectivity of SUs of both Dir-CRNs and Omn-CRNs, thus enabling tractability. We show that the connectivity of SUs is mainly affected by two constraints: the spectrum availability of SUs and the topological connectivity of SUs. Extensive simulations validate the accuracy of our proposed models. Meanwhile, we also show that Dir-CRNs can have higher connectivity than Omn-CRNs mainly due to the lower interference, the higher spectrum availability, and the higher topological connectivity brought by directional antennas. Moreover, we also extend our analysis with considering transmission power efficiency. The simulation results show that Dir-CRNs require less transmission power to establish links than Omn-CRNs. We further investigate the throughput capacity of SUs, which is shown to heavily depend on the connectivity of SUs.
Bibliographical noteFunding Information:
Manuscript received July 16, 2017; revised December 23, 2017; accepted March 13, 2018. Date of publication April 10, 2018; date of current version August 13, 2018. This work was supported by the Macao Science and Technology Development Fund under Grant 0026/2018/A1. The review of this paper was coordinated by W. A. Hamouda. (Corresponding author: Hong-Ning Dai.) Q. Wang and H.-N. Dai are with the Faculty of Information Technology, Macau University of Science and Technology, Taipa, Macau (e-mail:,qiu_wang @foxmail.com; firstname.lastname@example.org).
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- Cognitive radio networks
- directional antennas
- spectrum availability
- stochastic geometry