On the Effective Capacity of Delay Constrained Cognitive Radio Networks with Relaying Capability Ahmed H. Anwar 1 ⋆ , Karim G. Seddik 2 , Tamer ElBatt 3,4 , and Ahmed H. Zahran 4 1 Electrical Engineering and Computer Science Dept., University of Central Florida, 32816, USA. a.h.anwar@knights.ucf.edu 2 Electronics Engineering Department, American University in Cairo, AUC Avenue, New Cairo 11835, Egypt. kseddik@aucegypt.edu 3 Wireless Intelligent Networks Center (WINC), Nile University, Smart Village, Egypt. 4 Dept. of EECE, Faculty of Engineering, Cairo University, Giza, Egypt. telbatt@ieee.org,ahzahran@ieee.org Abstract. In this paper we analyze the performance of a secondary link in a cognitive radio relaying system operating under a statistical quality of service (QoS) delay constraint. In particular, we quantify analytically the Effective Capacity improvement for the secondary user when it of- fers a packet relaying service to the primary user packets that are lost under the SINR interference model. Towards this objective, we utilize the concept of Effective Capacity introduced earlier in the literature as a metric to quantify the wireless link throughput under statistical QoS delay constraints, in an attempt to support real-time applications us- ing cognitive radios. We study a two-link network, a single secondary link and a primary network abstracted to a single primary link, with and without relaying capability. We analytically prove that exploiting the packet relaying capability at the secondary transmitter improves the Effective Capacity of the secondary user. Finally, we present numerical results that support our theoretical findings. 1 Introduction Over the past decade, there has been surge in demand for the wireless spectrum due to the bandwidth-hungry applications, e.g., multimedia communications. Moreover, there has been ample evidence that the wireless spectrum has been significantly underutilized. In [1], the cognitive radio (CR) concept has been first introduced as a promising technology due to its opportunistic, agile and efficient spectrum utilization merits. Cognitive radios enable secondary users (SUs) to co-exist with the primary (licensed) users (PUs) in the same frequency band ⋆ This work was made possible by grants number NPRP 4-1034-2-385 and NPRP 5- 782-2-322 from the Qatar National Research Fund (a member of Qatar Foundation). The statements made herein are solely the responsibility of the authors.