6377

5951

كارشناسي ارشد

مخابرات سيستم

اصفهان: دانشگاه صنعتي اصفهان، دانشكده برق و كامپيوتر

1390

نه،71ص.: مصور،نمودار

ص.ع.به فارسي و انگليسي

محمد جواد اميدي

6/9/90

محمود مدرس هاشمي، محمد دخيل عليان

مهندسي برق و كامپيوتر

ID5951

به فارسي و انگليسي: قابل رويت در نسخه ديجيتالي

Investigation and Compensation of Carrier Frequency Offset in OFDMA Systems Using Windowing method at Transmitter and Receiver Reza Khodabandeh Samani r khodabandehsamani@ec iut ac ir Date of submission Sep 14 2011 Department of Electrical and Computer Engineering Isfahan University of Technology Isfahan 84156 83111 Iran Degree M Sc Language Farsi Supervisor M J Omidi omidi@cc iut ac irAbstractRecently the demand for using multicarrier communication systems is growing fast and is predicted tocontinue in the future OFDM systems are the most useful type of multicarrier systems due to their ability tocombat frequency selective fading channels This system is used in IEEE802 11a g IEEE802 16a DVB andADSL OFDMA system as a combination of OFDM system with FDMA technique is considered in multiusercommunication In additional to attractive characteristics of OFDMA systems they have some challengessuch as frequency and time synchronization Carrier frequency offset is caused by Doppler effect and oroscillator frequency mismatch between transmitter and receiver Same as OFDM OFDMA systems havehigh sensitivity to carrier frequency offset Incorrect carrier frequency offset compensation will destroyorthogonality between subcarriers and result in inter carrier interference and multi access interference Thisstudy provides carrier frequency offset investigation and compensation in OFDMA systems Each user willreceive a signal with single carrier frequency offset in downlink mode where the received waveform is acombination of transmitted signals from different users with individual carrier frequency offsets in uplink Then the study and compensation of carrier frequency offset in downlink mode is similar to single userscenario However the carrier frequency offset compensation in uplink is a challenging task Carrierfrequency offset compensation can be performed before or after DFT block To improve the performance ofcarrier frequency offset compensation in OFDMA system some interference cancellation techniques havebeen proposed to reduce multiple access interference These result in some performance gain however at thecost of significant increase in complexity Reducing the level of sidelobes for each subcarrier decreasesmultiple access interference with less complexity than interference cancellation techniques Pulse shaping is acommon method to reduce the side lobe level in OFDM systems In this research we used raised cosinewindow in transmitter and receiver However this method improves the performance of direct compensationtechnique with block allocation scheme at the cost of less bandwidth efficiency KeyWords OFDMA systems Windowing Carrier frequency offset Carrier frequency offsetcompensation

محمد جواد اميدي

محمود مدرس هاشمي، محمد دخيل عليان