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Study and SDR implementation of OFDM modulation

Zekai Oresti

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Summary

Digital bandpass modulation techniques can be broadly classified into two categories. The first is single-carrier modulation, where data is transmitted by using a single radio frequency (RF) carrier. The other is multicarrier modulation, where data is transmitted by simultaneously modulating multiple RF carriers. This thesis is concerned with a particular type of multi-carrier modulation known as orthogonal frequency division multiplexing (OFDM). OFDM has gained popularity in a number of applications including digital subscriber loops, wireless local area networks,etc. It is also the chosen technique for fourth generation (4G) cellular land mobile radio systems.OFDM transmits data in parallel by modulating a set of orthogonal subcarriers. It is attractive because it admits relatively easy solutions to some difficult challenges that are encountered when using single-carrier modulation schemes on wireless channels. The greatest benefit of using OFDM is that the modulation of closely-spaced orthogonal sub-carriers partitions the available bandwidth into a collection of narrow sub-bands. On the other hand, although OFDM waveforms are resilient to timing errors, they are highly sensitive to frequency offsets and phase noise at the transmitter and receiver RF and sampling clock oscillators.In this thesis, we will deal with synchronization issues in OFDM systems. Also,we will study frequency offset estimation and cancellation and channel estimation.Finally, we will implement an OFDM system using USRP N200 kits.

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