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Abstract
Based on decode-and-forward (DF) protocol, this work focuses on the adaptive power allocation and outage performance of underlay cognitive radio and opportunistic relaying (UCR-OR) systems with direct path between cognitive source and destination. The UCR-OR systems suffer from the interference of multiple primary user (PU) pairs. Under the outage constraint of PUs and the cognitive peak transmit power limit, we first obtain the adaptive power allocation schemes for secondary transmitters. Secondly, we obtain the exact closed-form expression to the outage probability of UCR-OR systems by using appropriate mathematical proof. Finally, to obtain a clear insight and to highlight the effect of system parameters on the performance of UCR-OR systems, the asymptotic closed-form expression of outage probability is achieved with the assumption of high cognitive transmit power. The presented simulations show that, due to the adaptive power allocation employed, the outage probability of UCR-OR systems is decreasing with PUs' transmit power Pp when Pp is less than a specific value P � . Only when the value of Pp is
Highlights
Since the electromagnetic spectrum is becoming more and more scarce, improving spectrum efficiency is becoming extremely important for the sustainable development of wireless communication systems and service
Cognitive radio (CR) has been proposed as an effective solution to deal with these problems by allowing the access of unlicensed secondary users (SUs) to the frequency band that is allowed to licensed primary users (PUs), in a way that does not affect the quality of service (QoS) of the licensed primary systems [2,3]
Since we are assuming that all channels in each link experience i.i.d Rayleigh fading, the outage probability P2out does not depend on which relay nodes are in the decoding subset DS, but on how many relay nodes belong to the decnoding suobset
Summary
Since the electromagnetic spectrum is becoming more and more scarce, improving spectrum efficiency is becoming extremely important for the sustainable development of wireless communication systems and service. In [22], authors have considered a system where the primary system consists of multiple transceiver pairs This is a realistic consideration in large-scale cognitive systems where the SUs transmit over long distance and may suffer from the interference signals created by multiple primary users. As stated in previous, exploiting the direct path transmission can effectively compensate the performance loss of secondary systems caused by multiple primary users' interference, in [23], the direct link between cognitive source and destination was neglected. Combining the received SINRs via direct link and relay link, the total received SINR at destination is γTot 1⁄4 γSD þ γDRb ð7Þ In this phase, the received expectation signals by primary receivers PDm are corrupted by the interference from the selected best relay SRb. The corresponding SINR at PDm is given by γ PRbm. ð8Þ where b is defined by Equation 4
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