كاهش پيچيدگي محاسباتي جبران انحراف فركانس حامل در سيستم SC-FDMA

چكيده انگليسي :

111 Computational complexity reduction of CFO compensation in SC FDMA systems Javad Mohammadi Siahboomi j mohammadisiahboomi@ec iut ac ir Date of Submission 2013 04 27 Department of Electrical and Computer Engineering Isfahan University of Technology Isfahan 84156 83111 Iran Degree M Sc Language FarsiSupervisor s Name Dr M J Omidi omidi@cc iut ac irAdvisor s Name Dr H Saeedi Sourck hsaidi@gmail ir AbstractIn the recent decade the multi carrier modulation is considered by wireless systemdesigners due to its high data rate and resistance against multipath fading effects Orthogonal frequency division multiplexing OFDM is widely known and is the mostcommonly used multi carrier modulation scheme in many communication standards Also OFDM is generalized for use in multi user systems and is called orthogonalfrequency division multiple access OFDMA Two important applications of OFDMAare in WiMAX and LTE uplink Despite the advantages OFDMA systems have twomajor challenges First is high peek to average power ratio PAPR that results incoverage reduction and non linear signal amplification that decrease bandwidthefficiency High PAPR requires high power amplifier with very large dynamic range which results in increased system cost By adding a discrete Fourier transform DFT pre coder to OFDMA transmitter PAPR will be reduced significantly The amount of PAPRin this scheme which is called single carrier frequency division multiple access SC FDMA depends on subcarrier allocation scheme In the interleaved allocation scheme uniformly distributed subcarriers in the available bandwidth are assigned to each user and this results in the least amount of PAPR Therefore in the LTE uplink the SC FDMAis used to improve power characteristics The second challenge of OFDMA based systems is sensitivity to carrier frequency offsets CFO The CFO is caused by instability of local oscillators and Doppler effect Due tosynchronization errors in time varying channels it is not possible to remove CFOcompletely The effect of CFO on OFDM signal is the interference between subcarriers In uplink transmission the CFO causes interference between different user subcarrierscalled multiple access interference MAI which significantly reduces systemperformance There are several proposed techniques to compensate CFO effects inOFDMA and SC FDMA systems and their common challenge is high computationalcomplexity This thesis is focused on CFO problems in SC FDMA systems and comparison ofdifferent CFO compensation techniques An interleaved SC FDMA system that hashighest frequency diversity and lowest PAPR compared to other allocation schemes isconsidered and a new low complexity technique is proposed to compensate CFO Theproposed scheme compensates CFO by the goal of maximizing the average signal tointerference power ratio SIR It shows better performance compared to other techniqueswith comparable complexity To further improve performance a simple algorithm isproposed to remove MAI after CFO compensation The proposed technique provides asuitable performance with very low complexity Also despite other methods thistechnique shows good stability in systems with imperfect power control Keywords SC FDMA system carrier frequency offset CFO compensation inter carrierinterference multiple access interference interference cancellation algorithms

محمدي سياهبومي، جواد

كاهش پيچيدگي محاسباتي جبران انحراف فركانس حامل در سيستم SC-FDMA

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