Mohamed Elalem

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One of the challenging problems of cognitive radio networks is the interference which occurs when a cognitive radio accesses a licensed band but fails to notice the presence of the licensed user. To allow the cognitive radio to access the same spectrum band where the primary user is operating creates a problem, the cognitive radio may interfere with the(More)
WCDMA is becoming widely accepted as one of the most promising solutions to meet the increasing demand for high-capacity wireless networks of the future. The most important inherent characteristic of WCDMA systems is their interference-limited capacity. The user distribution is a very important issue. In most previous studies it is assumed that the spatial(More)
In this paper, the performance of multichannel transmission in cognitive radio is studied. Both constraints and interference limitations are considered. The activities of the primary users (PU)s are initially detected by cognitive users (CU)s who perform sensing process over multiple channels. They transmit in a single channel at variable power and rates(More)
As fundamental spectrum sensing and access techniques in cognitive radio networks (CRN) matured in last decade, the satisfaction of quality-of-service (QoS) demands for cognitive users (CU) has attracted lots of research attention. In this paper, we study how the delay QoS requirements affect the dynamic spectrum access (DSA) strategy on network(More)
Traditionally, the frequency spectrum is licensed to users in a rigid manner where the licensee has the exclusive right to access the allocated band. However, an unlicensed (cognitive) user may share a frequency band with a licensed (primary) owner as long as the interference is below a certain threshold. This makes power control a critical important issue(More)
Well-established fact shows that fixed spectrum allocation policy conveys to the low spectrum utilization. The cognitive radio technique promises to improve the low efficiency. This paper proposes an optimized access strategy combining overlay scheme and underlay scheme for the cognitive radio. We model the service state of the system as a continuous-time(More)
Traditionally, the frequency spectrum is licensed to users who have the exclusive right to access the allocated band. However, an unlicensed (cognitive) user may share a frequency band with a licensed (primary) owner as long as the interference is below a certain threshold. This makes capacity analysis a critical important issue in these networks. Lots of(More)
In order to utilize the spectrum efficiently, the FCC announced Cognitive Radio (CR) technology as a candidate to implement negotiated or opportunistic spectrum sharing. It has received a great attention due to the ability to improve the spectrum utilization. In such a CR network, power control can increase the efficiency by adjusting the transmission power(More)
In this paper, the performance of multichannel transmission in cognitive radio is studied. Both QoS constraints and interference limitations are considered. The activities of the primary user (PU) are initially detected by cognitive user (CU) who performs sensing process over multiple channels. The CU transmits over a single channel at variable power and(More)
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