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...will be reviewed in this article. To date, quite a few operation models have been proposed for CRs; however, there is no consensus yet on the terminology used for the associated definitions [1], [2], =-=[3]-=-. Generally speaking, there are two basic operation models for CRs: Opportunistic Spectrum Access (OSA) vs. Spectrum Sharing (SS). In the OSA model, the SUs are allowed to transmit over the band of in...

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...apore. (Email: ycliang@i2r.a-star.edu.sg)2 I. INTRODUCTION Cognitive radio (CR), since the name was coined by Mitola in his seminal work [1], has drawn intensive attentions from both academic (e.g., =-=[2]-=- and references therein) and industrial (e.g., [3] and references therein) communities; and to date, many interesting and important results have been obtained. In CR networks, a typical spectrum shari...

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...tifier 10.1109/JSAC.2011.110219. space dimensions. Therefore, opportunistic spectrum access together with a cognitive radio (CR) technology has become a promising solution to resolve this problem [3]–=-=[7]-=-. Opportunistic spectrum access creates the opening of underutilized portions of the licensed spectrum for reuse, provided that the transmissions of secondary radios do not cause harmful interference ...

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...entions from both academic and industrial communities. Generally speaking, there are three operational models for the CR known in the literature, namely, Interweave, Overlay, and Underlay (see, e.g., =-=[2]-=- and references therein). Interweave method is also known as opportunistic spectrum access (OSA), originally outlined in [1] and later introduced by DARPA, whereby the CR transmits over the spectrum a...

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...ference. For example, interference is a major source of performance impairment in the Code Division Multiple Access (CDMA) cellular network (see [1], [2]) and the cognitive wireless networks (see [3]–=-=[6]-=-). How to optimize performance in the presence of interference is thus an important issue. Power control is often used to improve the spectral utilization and the system performance, e.g., maximizing ...

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... or more of the figures in this paper are available online at http://ieeexplore.ieee.org. Digital Object Identifier 10.1109/TSP.2009.2032039 order to optimize the usage of the available resources [3]–=-=[5]-=-. The widely accepted debated position proposed for implementing the spectrum sharing idea of CR calls for a hierarchical access structure, distinguishing between primary users, or legacy spectrum hol...

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...t, we omit the data here. VI. RELATED WORK A plethora of works has been done on spectrum sharing based on cognitive radio. Generally, they fall into three paradigms, interweave, underlay, and overlay =-=[18]-=-. The interweave paradigm insists that SUs should only transmit when PUs are not, while the underlay paradigm allows them to transmit concurrently with PUs provided that their signals do not cause har...

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...6]. Many of the works in this area concentrate on the Gaussian channel and assume a genie-aided secondary that has non-causal access to the primary’s data. A recent survey of these efforts appears in =-=[7]-=-. Gastpar [8] formulated the problem of capacity under receive signal constraints in AWGN channels. The work in [9] investigates the limits of communication in ergodic fading channels subject to peak ...

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...primary and secondary users in a cognitive radio network. In particular, the idea of cooperation at the physical layer has been considered from an information-theoretic perspective in many works (see =-=[4]-=- and the references therein). These are motivated by the work on the classical interference and relay channels [5]–[8]. The main idea in these works is that the resources of the secondary user can be ...