In today’s society, the need for the right information at the right time and the right place as well asudincreased number of high bandwidth wireless multimedia services and the explosive proliferation of smartudphone and tablet devices has led to increase in demand for and use of radio spectrum, which is theudprimary enabler of wireless communications. With this increase, the principal engineering challenge inudwireless communications domain is now on how to effectively manage the radio spectrum to ensure itsudsustainability for future emerging wireless devices, since virtually all usable radio frequencies for wirelessudcommunications have been licensed to commercial users and government agencies.udTraditionally, the approach to radio spectrum management has been based on a fixed allocation policy,udwhereby licenses are issued to users or operators for the usage of frequency bands. With a license,udoperators have the exclusive right to use the allocated frequency bands for assigned services on a longtermudbasis. However, over the last ten years, this strict allocation policy has been subjected to a lot ofudcriticism because of its observed contribution to radio spectrum scarcity and underutilization.udIn mitigating these negative effects of the current radio spectrum management policy, one of theudsuggested measures is to open up the licensed frequency bands to unlicensed users on a non-interferenceudbasis to licensed users. In this new spectrum access system, an unlicensed or secondary user canudopportunistically operate in unused licensed spectrum bands without interfering with the licensed orudprimary user, thereby reducing radio spectrum scarcity and at the same time increasing the efficiency ofudthe radio spectrum utilization.udIn achieving this objective, there is a need to develop a radio engine that can sense its environment touddetermine the presence of primary users. Cognitive radio is seen as the enabling technology forudopportunistic spectrum sharing. It is a radio with the capability to sense and understand its environment,udand proactively alter its operational mode as needed to avoid interference with a primary user. To ensureudinterference-free use to the primary user, spectrum sensing and detection has been observed as a keyudfunctionality of cognitive radio.udHowever, there is currently no single sensing method that can reliably sense and detect all forms ofudprimary radios’ signals in a cognitive radio environment. Therefore, in order to achieve this goal, thisudthesis addresses the problem of accurate and reliable sensing and detecting of a primary radio signal in audcognitive radio environment. The principal research issue addressed is the possibility of sensing anduddetecting all forms of primary radio signals in a cognitive radio environment. This objective was achievedudby developing an adaptive cognitive radio engine that can automatically recognize different forms ofudmodulation schemes in a cognitive radio environment.udThe thesis pictures spectrum sensing as the combination of signal detection and modulation classification,udand uses the term Automatic Modulation Classification (AMC) to denote this combined process. Theudhypothesis behind this detection method is that, since all transmitters using the radio spectrum make useudof one modulation scheme or another, the ability to automatically recognize modulation schemes isudsufficient to confirm the presence of a primary user signal while the opposite confirms absence of audprimary user signal.udThe research work methodology was divided into two stages. The first stage involves the development ofudan automatic modulation recognition (AMR) or AMC using an Artificial Neural Network (ANN). Theudsecond stage involves the development of the Cognitive Radio Engine (CRE), which has the developedudAMR as its core component. The developed CRE was extensively evaluated to determine its performance.udThe overall numerical results obtained from the developed CRE’s evaluation shows that the developedudCRE can reliably and accurately detect all the modulation schemes considered without bias towards audparticular Signal-to-Noise Ratio (SNR) value, as well as any modulation scheme. The research work alsoudrevealed that single spectrum sensing and detection method can only be achieved when a general featureudcommon to all radio signals is employed in its development rather than using features that are limited toudcertain signal types.
展开▼
