Approaches for Adaptive Resource Allocation inudCognitive Radio Networks.

摘要

Proposing efficient spectrum utilization techniques to alleviate spectrum congestion isudone of the most important challenges in wireless communication technologies operating atudspecific spectrum bands. In fact, the growth of wireless application demands has causedudthe frequency allocation table for wireless services to become over congested. On the otherudhand, recent measurement studies have shown that the radio frequency spectrum in its currentudshape is inefficiently utilized. Hence, for the purpose of alleviating the long-standingudproblem of spectrum congestion, the federal communication commission (FCC) is activelyudrevising the traditional spectrum allocation policies and moving towards the adoption ofudopportunistic spectrum-sharing techniques using cognitive radio. Cognitive radio (CR) isuda technology that has the ability of sensing the environment in which it operates and adaptingudto its changes. For instance, through sensing, CR detects the portions of the spectrumudthat are un-occupied (also referred to as spectrum holes) at a specific location or time.udOne of the most efficient ways to identify spectrum holes is to sense the activity of theudprimary users operating within the secondary users' (cognitive user) range of communication.udIn this dissertation, we study different approaches for adaptive resource allocation inudspectrum-sharing CR networks. In this context, we propose utilizing spectrum sensing informationudabout the primary users' activity and secondary channel knowledge to adaptivelyudadjust the secondary transmission parameters such as time, power and rate while adheringudto the generated interference at the primary receivers. In this case, a proper resource managementudis needed so as to maximize the throughput performance of the secondary usersudand avoid performance degradation for the primary users. The existence and specificationudof such resource allocation are necessary issues and will be investigated in this dissertationudfor different operating scenarios. We also propose adopting cooperative relayingudtechniques in spectrum-sharing CR systems to more effectively and efficiently utilize theudavailable transmission resources while adhering to the quality of service requirements ofudthe primary (licensed) users of the shared spectrum band. In particular, while the momentudgenerating function approach is commonly used to evaluate the performance analysis ofudcooperative relaying systems, we propose a unified framework which relies on the first-orderudstatistics and convolutional methods to investigate the end-to-end performance ofudcooperative relaying spectrum-sharing systems. Furthermore, we quantify the advantagesudof utilizing relaying transmissions in spectrum-sharing CR networks for different operatingudscenarios and conditions.