AI SearchInvestigation of synchronization in OFDM system in mobile radio environment
Call Number: AIT Thesis no.TC-01-14 Material type:
SeriesSeries: Asian Institute of Technology. Thesis ; no. TC-01-14Publication details: Bangkok : Asian Institute of Technology, 2001Description: 39 pSubject(s): Online resources: Dissertation note: Thesis (M.Eng.) - Asian Institute of Technology, 2001 Summary: Orthogonal Frequency Division Multiplexing (OFDM) has recently become an attractive research area because of its desirable characteristics in mobile communications such as the robustness against multipath fading and impulse noise compared to single carrier systems. In OFDM, it is difficult to set up perfect synchronization between the transmitter and the receiver due to intercarrier interference (ICI) among the carriers that causes the frequencies to be shifted. This thesis investigates the synchronization techniques in OFDM system under this scenario. A new technique is proposed for carrier frequency offset (CFO) compensation as a combination of windowing and self ICI cancellation method. The transmitted data is mapped to two consecutive subcarriers with opposite signs according to self ICI coder. Then the whole signal is shaped by windowing functions to keep the orthogonality between subcarriers. To evaluate the performance of windowing method, self ICI method as well as the proposed scheme, simulations have been carried out for additive white gaussian noise (A WGN) and multipath fading channels. The results show that windowing scheme is better than normal system at low CFO. At high CFO, the performance of windowing became worse. Besides, the proposed scheme give better performance than self ICI cancellation scheme at offset up to 50 percent of subcarrier spacing. However, the combined scheme needs more bandwidth. A technique claimed for bandwidth efficiency by using symmetry property of Discrete Fourier Transform (DFT) is investigated. In this technique N/2 symbols are transmitted instead of N and the received signal will be constructed perfectly. The derivation shows that it is impossible to construct the transmitted OFDM signal from N/2 samples and the received signal has no symmetry when complex transmitted data and channel coefficient are taken into account. Consequently, the received signal cannot be completely reconstructed and bandwidth efficiency cannot be obtained.
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A thesis submitted in partial fulfillment of the requirements for the degree of Master of Engineering, School of Engineering and Technology
Thesis (M.Eng.) - Asian Institute of Technology, 2001
Orthogonal Frequency Division Multiplexing (OFDM) has recently become an attractive research area because of its desirable characteristics in mobile communications such as the robustness against multipath fading and impulse noise compared to single carrier systems. In OFDM, it is difficult to set up perfect synchronization between the transmitter and the receiver due to intercarrier interference (ICI) among the carriers that causes the frequencies to be shifted. This thesis investigates the synchronization techniques in OFDM system under this scenario. A new technique is proposed for carrier frequency offset (CFO) compensation as a combination of windowing and self ICI cancellation method. The transmitted data is mapped to two consecutive subcarriers with opposite signs according to self ICI coder. Then the whole signal is shaped by windowing functions to keep the orthogonality between subcarriers. To evaluate the performance of windowing method, self ICI method as well as the proposed scheme, simulations have been carried out for additive white gaussian noise (A WGN) and multipath fading channels. The results show that windowing scheme is better than normal system at low CFO. At high CFO, the performance of windowing became worse. Besides, the proposed scheme give better performance than self ICI cancellation scheme at offset up to 50 percent of subcarrier spacing. However, the combined scheme needs more bandwidth. A technique claimed for bandwidth efficiency by using symmetry property of Discrete Fourier Transform (DFT) is investigated. In this technique N/2 symbols are transmitted instead of N and the received signal will be constructed perfectly. The derivation shows that it is impossible to construct the transmitted OFDM signal from N/2 samples and the received signal has no symmetry when complex transmitted data and channel coefficient are taken into account. Consequently, the received signal cannot be completely reconstructed and bandwidth efficiency cannot be obtained.
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