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Cognitive Radio is defined as a radio with the ability to change its transmitter parameters based on awareness in the environment in which it operates. It is classified as an intelligent tool with the capability for sensing, perceiving, orienting, planning, decision making, and autonomous learning of the surrounding communication environment. Cognitive radio is able to adapt to the current working environment based on the adjustments made on the parameters such as environment parameters and radio transmission parameters. Another important ability of the cognitive radio is to analyse and measure the state of the environment, and periodically check for spectral occupancy, better known as spectrum sensing. Figure 3.2 illustrates the basic building blocks of a cognitive radio communication system. As depicted in Figure 3.2, the radio reconfigurator collects information on previous cognitive systems from the radio component library and meanwhile the user's communication requirement will be inputted to the radio reconfigurator. The information from the radio reconfigurator will be passed on to the software defined radio unit to perform cognitive cycle of testing and generating results on the proper transmission parameters required to obtain the desired radio requirement.
In the presence of a dynamic wireless channel environment the cognitive radio will sensed the appropriate radio parameters and with integration of an adaption algorithm, the cognitive radio will be able to adapt and perform the necessary adjustment to maximize the efficiency of the wireless communication system. As for the adaption algorithm, genetics algorithm can function as an intelligent system in defining the process in achieving the goals of the cognitive radio. An engineer's role based on figure 3.2, by using genetic algorithm has to relate the transmission parameters from the sensory information to the cognitive radio's goals.
3.4.1 Functions of Cognitive Radio
Cognitive radio can be divided into 4 main functions. Spectrum sensing serves to be an important function to examine the spectral band and assign the vacant band to secondary users. Usually primary users are in a different pool from the secondary users. Hence the secondary users will not be able to instantly learn if the spectrum is available but depending on their scanning ability and the signal strength of primary user.
Another function of the cognitive radio is the spectrum decision making ability. Decision on allocating an available spectrum is an important step as it's has to be based on spectrum availability and also on the cognitive radio configured policies. Besides, this function is important as it is closely related to the wireless channel characteristics and operations of primary users. Another unique function of the cognitive radio is spectrum sharing ability which defines the sharing of the wireless channel. For example, if s single channel has 500 users trying to access it, cognitive radio will co-ordinate all the users in accessing the channel. Proper access coordination will be able to mitigate interference caused by user collision in the spectrum.
The fourth function of the cognitive radio is known as the spectrum mobility. This function defines the ability of the cognitive radio to transfer the system to another specific spectrum when the user has changed its frequency of operation or the current spectrum is being occupied. This process can also be defined as a spectrum handoff. The advantage of implementing spectrum mobility is, a smooth spectrum handoff is ensured free from any degradation of spectrum.
3.4.2 Cognitive Radio Architecture
Time Series Analysis
Toolbox and Libraries
Data Filtering & Sorting
CRM CoreThere are many different cognitive radio platforms being implemented around the world. Figure 3.3depicts conceptual architectural components of the cognitive resource manager . The CRM core illustrated in Figure 3.3 is responsible for coordinating the exchange of external information between the cognitive radio engine and the artificial intelligence language applied in the system.
Figure 3.3: Architectural components of the cognitive resource manager framework
The CRM core is like act like a computer motherboard, which enables the interoperability between the variety choices of artificial language toolbox and libraries tasked with modelling and optimization process and external information sensed periodically during the sensing period. The process of the cognitive radio system is illustrated in Figure 3.4. Any cognitive radio platform will be equipped with a small memory system to store the previously modelled system. Based on its recollection of previous models, the cognitive radio will analyze which knob to be adjusted, where the input to the system will be adjusted. Next the intelligent system toolbox as shown in Figure 3.3 will be performing simulations and trials to conduct a comparison between the predicted setting and the simulated settings. Based on this observation and modelling, the cognitive radio will be then making the necessary adjustment to the system through input knobs.
Figure 3.4: Loop cycle of a cognitive radio
Analyze Possible Knobs
Predict Optimum Settings
Compare to Predictions
Observe and Model