ISSN (e): 2250 – 3005 || Volume, 08 || Issue, 11|| November – 2018 || International Journal of Computational Engineering Research (IJCER) www.ijceronline.com Open Access Journal Page 12 Optimal Power Allocation Strategy for Maximizing the Transmission Power of Cognitive Relay Nodes with S-AF Scheme M.Poonguzhali Professor, Department of ECE, Narasu’s Sarathy Institute of Technology, Salem –636305, Tamilnadu, India. Corresponding Author: M.Poonguzhali --------------------------------------------------------------------------------------------------------------------------------------- Date of Submission: 15-12-2018 Date of acceptance: 31-12-2018 --------------------------------------------------------------------------------------------------------------------------------------- I. INTRODUCTION The Cognitive Radio (CR), a key technology for future wireless communication is capable of sensing and adapting to environments. The CR is an intelligent radio that can be programmed and configured dynamically. The dramatic growth of wireless application and steadily increasing demands for higher quality of service have led to a perceived dearth of available radio bandwidth, which necessitates the search for more efficient utilization of spectrum resources. In this paradigm the wireless nodes can sense the spectrum adapt the transmission/reception to the available spectrum, and dynamically share the spectrum with other applications. Cognitive Radio Networks (CRN) is encouraged by the apparent lack of spectrum under the current spectrum management functionalities. In order to address the critical problem of a spectrum scarcity FCC (Federal Communications Commission) has recently approved the use of unlicensed devices in licensed bands (Akyildiz F etal, 2014). The emergence of cognitive and software defined radio concepts, multiple antenna and multi carrier techniques as well as Ultra Wide Band (UWB) technologies and mesh network topologies provide a technology panacea that proponents of this approach used to support their arguments. CR network however, impose unique challenges due to the high fluctuation in the available spectrum as well as diverse quality of service (QoS) requirement (S.Lee,R.Zhang (2016)). CR technology is entirely built using Multihop ad hoc architecture which is shown in Figure 1.1 ABSTRACT In this paper, the power allocation strategies of the wireless system is studied to minimize the outage probability subject to total and individual power constraints for cognitive relay nodes and subject to interference constraints for primary user nodes. The proposed system uses a two-step distributed relay-secondary user selection scheme. Specifically, a relay terminal R is first selected from a relay candidate set ℳ1 to assist the primary system in achieving a primary request target rate by serving as a DF relay. When the selection for R succeed, a secondary transmitter R which minimizes the secondary outage probability, is selected from a secondary transmitter candidate setℳ2 to access the spectrum band along with R, with a constraint that its transmission does not degrade the outage performance of the primary system. On the other hand, if the selection for R fails, a secondary transmitter R′ which minimizes the secondary outage probability is selected from ℳ2 to access the spectrum band while the primary system remains silent. The simulation results indicate that the AF with OPA and S-AF with OPA have significantly better outage behaviour and average throughput than AF and S-AF schemes respectively. The results shows that S-AF with OPA achieves a higher throughput, and hence lower outage probability than AF with OPA. KEYWORDS: Optimal power allocation(OPA),Amplify and forward(AF),Selection AF(S- AF),Cognitive relays, Outage probability