Orthogonal Frequency Division Multiplexing (OFDM) is a multicarrier modulation technique widely used in different wireless communication systems such as Digital Video Broadcasting (DVB), Digital Radio Mondiale (DRM), Wireless Local Area Network (WLAN), Long Term Evolution (LTE), etc.
But OFDM signals are prone to suffer from spectral spreading and in-band distortion due to the large envelope fluctuations.
As solutions to this problem, several methods have been presented. For reducing the signal envelope fluctuations without any in-band distortion, some methods such as Partial Transmit Sequence (PTS), Selected Mapping (SLM) and their hybrid techniques have been investigated, but they are in high computational complexity and need side information. Tone Reservation (TR) can reduce the signal envelope fluctuations significantly, but it does not use some subcarriers and depends on computationally intensive optimization. Systematic coding techniques are distortion-less methods, which can bound signal fluctuations but they require data rate compensation. As the simplest method, Amplitude Clipping could reduce the out-of-band radiation, but these non-linear techniques cause in-band distortion and the additional clipping noise compensation requires high computational complexity.
Among the presented methods, constellation extension based ACE would be one of the promising methods because ACE maintains the minimum Euclidean distance between symbols in a constellation and causes no reduction of BER performance and, especially, it does not require any side information. However, because the reduction performance of signal envelope fluctuations of ACE depends on the number of iterative computations, its computational complexity is usually very high. So, it is necessary to find an approach to maintain high reduction performance of signal envelope fluctuations and low computational complexity.
Jon Ji Hyon, a researcher at the Faculty of Communications, has proposed a novel ACE-DE approach to deal with this issue, where the anti-peak signal decomposition based double extension is applied to improving reduction performance of signal envelop fluctuations.
By using Fourier transform properties, an anti-peak signal is decomposed into 4 sub-signals in the time domain, and then recomposed via Second Order Cone Programming optimization. To realize the low computational complexity of ACE-DE, MPT algorithm is also proposed.
The simulation results show that ACE-DE with MPT outperforms other approaches in terms of CCDF, BER and OOB radiation.
For more information, please refer to his paper “Reduction of Signal Envelope Fluctuations in OFDM Systems Using ACE with Double Extension” in “Wireless Personal communications” (SCI).
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