| Summary: | 碩士 === 大同大學 === 通訊工程研究所 === 95 === The broadcasting be digitized is an inevitable trend in the future, the DRM system was designed as an eventual replacement for current analogue AM broadcasting, but allow these new digital transmissions to co-exist with current analogue services from the outset. In order to make the best use in these limited and crowded bandwidth, the interference rejection between adjacent channels becomes an important issue.
The reduction of DRM out-of-band power is proposed in this thesis and it improved to reduce the adjacent interference indeed in order to gain high bandwidth efficiency. To eliminate this problem, we add the power of additional carriers with extra information, and solve it indeed for adjacent channel even better for co-channel with digital and current analogue AM service. Otherwise we did not impact the existing system, the object of gaining high bandwidth efficiency can achieve and more channels may be allowed in the specific frequency band.
As we knew a method called “Reduction of Out-of-Band Radiation in OFDM Systems by Insertion of Cancellation Carriers”. They use cancellation carriers at borders of the OFDM spectrum to reduce the out-of-band radiation of the OFDM signal. There is cost consumption for these results with a loss in BER performance and an increased computation complexity.
To compare with cancellation carriers method, our proposed methods has treated the boundary between current symbol and next symbol, but cancellation carriers method doesn’t. So out-of-band radiation of cancellation carriers method will still exist.
Based on our simulation, the advantages can be achieved below:
1. We only need to insert two or four auxiliary data into the original null subcarriers to reduce out-of-band power. It presents fully compatible to current existing system but don’t need to change any system’s set up.
2. The peak-power phenomenon can be controlled.
3. The simulated results indicates to improve the reduction out of band power with 2.68dB at 5.3kHz for co-exist channel using Zero Forcing Method with 1 of threshold value, and 13.05dB at 21.2kHz for adjacent channel.
4. To improve the reduction out of band power with 1.17dB at 5.3kHz for co-exist channel using Tail Tracking Method with 1 of threshold value, and 12.67dB at 21.2kHz for adjacent channel as well as can improve the peak power.
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