| Cognitive Radio (CR) can improve the spectrum utilization efficiency through theway of dynamic spectrum share, which addresses the spectrum scarcity problem that isencountered in many countries. CR is widely regarded as one of the most promisingtechnologies for future wireless communications.However, the ability of wireless scenario acquisition is limited in traditionalcognitive radio. The cognitive radio “monitoring” technique is based on spectrumsensing, which is always sensing the spectrum usage by monitoring the radioelectromagnetic environment passively. It is lack of the panoramic andmultidimensional radio environment. The parameters cognized by “monitoring” arelimited on the signal characters. The buildings around the users, the intensity of theusers, and the mobile trend of the users are not available. In order to obtain moreenvironment information for improving the environmental adaptability of the wirelesscommunication system, visual cognitive radio is proposed.Visual cognitive radio studies the cognitive theory and key technologies of themobile wireless cognitive radio network based on the visual image meaning.“Visualimage meaning” cognition captures the image of the wireless channel environment,cognizes the image by wireless scenario analysis and resource decision, recognizes thecommunication resource information about the wireless scenario, namely the meaningof the image--“image meaning”, optimzes the configuration of the wireless networksystem, and so as to improve the network performance.Location is one of the most important components in visual cognitive radio. In thispaper, two key technologies around the location are studied, which are locationoptimization and location appilication.Firstly, the optimal location of the sensing antenna for the sencondary user (SU) incognitive radio is studied.(1) A closed-form expression of the spectrum sensing performance is derived in the composite Rayleigh and shadowed fading environment for the SU with onesensing antenna. The effects on the performance from the pathloss and thedistribution of primary users (PUs) are further analyzed. The optimal locationsof the sensing antennas are derived so as to minimize the spectrum sensingerror probability.(2) Following the similar procedures, the locations optimization is studied for twoantennas.(3) The theory analysis shows that, the optimal loation is the cell center for oneantenna. As for two antennas, they should be placed symmetrically. Thedistance between the two antennas depends on the channel condition and thecell range, which can be determined by the application of the convexoptimization theory. Both theory analysis and simulation results show that, theoptimal distance between two antennas is33.6m if the energy detectorthreshold, the interval of the energy detector, the cell radius, the noise variance,the pathloss exponent, the standard deviation of shadow, and the shadowcoefficience are26,10,100m,－100dBm,4,6dB, respectively.Secondly, the optimal location of the secondary base station (SBS) is studied forbroadcasting cognitive radio networks with spectrum underlay.(1) Considering the interference constraints for the PU and the quality of service(QoS) constaints for the SU, the coverage area of the SU network is calculated.The optimal SBS location is derived so as to maximize the coverage area ofthe SU network.(2) The analysis is extended to the scenario with an obstacle located between thePU and SBS, the optimal SBS location is discussed in this scene.(3) The theory analysis shows that, the optimal location of the SBS will be largerand will converge to a fixed point with the increase of the distance between thePU and the obstacle. This fixed point is the optimal location of the SBSwithout the obstacle. Both theory analysis and simulation results show that, theoptimal location of the SBS is8,200m without obstacle, under the conditionthat the antenna heights of the PU and SBS are20m, and the cell radius of the PU network is10,000m, the maximum of the PU transmit power is30dBm,the maximum of the SBS transmit power is10dBm, the interference thresholdof the PU is40dBm, and the receive SIR threshold of the SU is10dB. Theoptimal SBS location is600m if the distance between the PU and the obstacleis300m. The optimal SBS location will converge to8200m if the distancebetween the PU and the obstacle is larger than800m.At last, location usage is studied, since the location optimization in most cases isdifficulty for analysis or can not be solved out.(1) A location-based cooperation spectrum sensing scheme is proposed. Energydetection is performed to obtain a local hard decision, which is thentransmitted to the data fusion center. Combining the weighted local decisionswith location information, a global decision is obtained at the data fusioncenter.(2) The performance on the proposed scheme is analyzed. The global performance,namely the global detection probability and the global false alarm probability,are derived based on the local sensing reliability and the transmissionreliability; The Gaussian approximation method is introduced to calculate theglobal performance, since the exact calculation is too complicated. When theaverage local SNRs are12dB,8dB, and4dB, the global error probability inthe location-based cooperation spectrum sensing scheme proposed is0.103,while it is0.447in the conventional scheme.(3) The location estimation error is inevitable, therefore, the error analysis of theproposed scheme is given and the error measurement rule is described.The work in this paper provides the theory and method for the deep study in visualcognitive radio. It is full of theory and practical value. The location optimization can beused for the plan of wireless communication system. The location application can beintroduced to improve the performance of wireless communication system. |
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