Sharif Digital Repository

Rolling bearings are important parts in rotating machinery. Unsuitable practice of this bearing causes unsuitable output in this collection. In some machines like helicopters, sudden faults of this rolling bearing cause body dangers. According to this point, diagnose of bearing fault is an important case in condition monitoring domain. There are many ways for diagnose of fault in bearing which most of them are important subject in signal processing. In this project first of all, the most important and applicable signal processing methods, which are useful in diagnose of fault in bearings are introduced then three of these methods are chosen and applied on time signals of experimental... 

In recent years, the Cognitive Radio Network has received significant attentions due to its high potential for better employment of the spectrum. One of the most important parts of this technology is the spectrum sensing that requires being fast and accurate. The conventional algorithms proposed so far encounter some fundamental challenges at low SNR regimes and in wideband sensing. On the other hand, the compressed sensing algorithms, which take advantages of the sparsity of the signal of interest and utilize measurements instead of the samples, can reduce the sampling rate and thus decrease the complexity associated with the wideband sensing. In this thesis, by exploiting the... 

In this project, the effect of improper lubrication on vibrational behavior of rolling element bearings is investigated. Different lubrication conditions were deliberately produced using three oils with different viscosity grades on a bearing at different loads and speeds. The acceleration of bearing vibrations were measured, then analyzed by means of squared envelope analysis, a special case of cyclostationary analysis. The results and their comparison showed that decrease in lubricant’s viscosity grade can lead to an increase in magnitude of cyclic frequencies equal to cage frequency and its harmonics. This observation can be helpful in detection of lubricant degradation and in... 

Cognitive radio (CR) can successfully deal with the growing demand and scarcity of the wireless spectrum. To exploit limited spectrum efficiently, CR technology allows unlicensed users to access licensed spectrum bands. Since licensed users have priorities to use the bands, the unlicensed users need to continuously monitor the licensed users activities to avoid interference and collisions. How to obtain reliable results of the licensed users activities is the main task for spectrum sensing. Based on the sensing results, the unlicensed users should adapt their transmit powers and access strategies to protect the licensed communications. The requirement naturally presents challenges to the...