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URN etd-0708105-174833 Statistics This thesis had been viewed 2777 times. Download 1373 times. Author Hui-Wen Fan Author's Email Address No Public. Department Communication Engineering Year 2004 Semester 2 Degree Master Type of Document Master's Thesis Language English Page Count 71 Title Out-of-band power spectrum reduction with power limited-constraint for OFDM Keyword power mask out-of-band power OFDM 802.11a 802.11a OFDM out-of-band power power mask Abstract OFDM (Orthogonal Frequency Division Multiplexing) is a form of multi-carrier modulation technique. High spectral efficiency, robustness to channel fading, immunity to impulse interference, uniform average spectral density, capability of handling very strong echoes and less non linear distortion are among the favorite properties of OFDM. Even though there are many advantages of OFDM, it has a main drawback that the discontinuity at boundary between two different OFDM symbols will cause out-of-band emission. In other words, the emission becomes the interference to adjacent channels and will lower the quality of in band signal.
In order to reduce the out-of-band emission, we develop an approach to keep the boundary continuous. By using some null subcarriers to carry additional information, the goal is achieved absolutely. Besides, we don’t need to add extra subcarriers but just use original null subcarriers, so this approach will not change the original specification. Furthermore, in order to advance the compatibility of our approach, it is unnecessary to add the new hardware or to vary the hardware of existing systems, so this new approach can easily be applied.
From our simulated results, the out-of-band spectrum is decreased 2~3 dB at 10MHz perfectly and the result agrees with our original expectation. In addition, we also simulate a practical channel, which includes effects of channel interference, to see if our method could be successfully applied to the real wireless environment. In the end, we can see a good performance of reducing out-of-band spectrum even though the signals pass through a fading channel.
To sum up, the interference to adjacent channels can be decreased by our approach and the quality of service can be guaranteed. Besides, the PAPR values of signal are not increased, and there is no side effect. In addition, it will increase the spectral efficiency. Moreover, when our approach is applied, it is unnecessary to change the original specification and vary hardware of current systems. On a whole, our approach can be easily applied to existing systems and achieve high compatibility.
Advisor Committee Chau-Yun Hsu - advisor
Jie-Cherng Liu - co-chair
Ying Li - co-chair
Files Date of Defense 2005-06-10 Date of Submission 2005-07-08