Browsing by Subject "Wireless Communications,"
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Item ANALYSIS OF SPECTRUM SENSING TECHNIQUES IN COGNITIVE RADIO FOR SPECTRUM S(Pulchowk Campus, 2012-11) ROY, SANJAY KUMARWith the advancement of wireless communications, recent researches by the FCC (Federal Communication Commission) shows that large portion of the available licensed spectrum band lies unused, that is only used by licensed users (primary users). The bandwidth becomes expensive due to a shortage of frequencies. Therefore for efficient utilization of the spectrum band, FCC allowed secondary (unlicensed) users to utilize the licensed band without interfering the primary (licensed) users when it is not in use by primary user named it as Cognitive Radio. Cognitive Radio (CR) defined as:”A radio system employing technology that allows the system: to obtain knowledge of its operational and geographical environment, established policies and its internal state; to dynamically and autonomously adjust its operational parameters and protocols according to its obtained knowledge in order to achieve predefined objectives; and to learn from the results obtained. This thesis work analyses the performance of the energy detector based on MAP for identifying the status of the primary user. Matlab simulation is used for received signal from Cognitive radio networks and energy detector to find whether the spectrum being used or not by the primary user and later thesis tries to establish relationship between signal to noise ratio and the detection of primary user signal by using maximum a posteriori energy detection method. This thesis work also analyzes the spectrum detection schemes based on dynamic threshold algorithm. Spectrum detection based on fixed threshold are sensitive to noise uncertainty, the energy detection and the matched filter detection are analyzed for the case of noise uncertainty and dynamic threshold algorithm and found that energy detection based on dynamic threshold can improve the antagonism of noise uncertainty; get good performance of detection without increasing the computer complexity and improves the detection performance for the schemes that are sensitive to noise uncertainty.Item Performance Evaluation of Space Diversity for Wireless Communication(Pulchowk Campus, 2010-02) Mahat, UpajIn wireless communications, diversity techniques are widely used to reduce the effects of multipath fading and improve the reliability of transmission without increasing the transmitted power or sacrificing the bandwidth. For spectral efficiency and improved Bit Error Rate, diversity provides an attractive option. Providing different replica of transmitted signal to the receiver is called diversity. There are many diversity techniques and among them space diversity technique is taken into main consideration in this thesis. During the detail study of Space Diversity one of the main reference paper was Sivash M. Alamouti ‘A Simple Transmit Diversity Technique For Wireless Communication’ 1998. This paper gives the possibility of transmit diversity with the use of BPSK as a modulation technique and Rayleigh as a fading model. Higher modulation technique such as QPSK is bandwidth efficient technique over BPSK and other fading model such as Ricean also exist in the environment. Rayleigh fading model is used when there are many objects in the environment where the signal is transmitted, resulting in the scatter of the signal before arriving at the receiver end. If the environment is such that, there is a presence of dominant path along with scattering between transmitter and receiver, then such situation is better modeled with Ricean fading model. Implementation of QPSK modulation technique and Ricean fading model along with the essential finding of this paper will be a additional benefit in space diversity technique. Simulated result shows that bandwidth efficient result with slightly higher BER in both receive diversity and transmit diversity is obtain from QPSK and very much low BER is obtain in Ricean fading model than that of the Rayleigh fading model which was proposed in the paper.