On the Out of Band Emission Reduction for Orthogonal Frequency Division Multiplexing Based Systems
Due to its ability to transmit a high rate data stream with maintaining robustness against multipath fading, high spectrum efficiency and efficient implementation, OFDM has been widely used in various communications systems such as DVB, WIFI and WIMAX. It
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LTT Laboratory, Department of Telecommunications, Tlemcen University, Tlemcen, Algeria [email protected] Department of Informatics, Mascara University, Mascara, Algeria
Abstract. Due to its ability to transmit a high rate data stream with maintaining robustness against multipath fading, high spectrum efficiency and efficient implementation, OFDM has been widely used in various communications systems such as DVB, WIFI and WIMAX. It is also considered as a candidate for the air interface of the current and future high speed mobile communications standards such as LTE, LTE advanced. It is also very appropriate for multi-band cognitive radio systems. However, OFDM suffers from some drawbacks. One of them is the Out of Band (OOB) leakage due to high spectral sidelobe which produces interference in neighboring bands and then degrade the system performance. Several schemes have been proposed to reduce the OOB emission such as filtering, windowing and precoding etc. in this paper, a hybrid approach based on two different precoding techniques is proposed to optimize this reduction. Simulation results verified the advantages of this scheme as compared with other well known techniques. Keywords: OFDM
OOB emission SVD Orthogonal projection
1 Introduction OFDM has attracted significant attention and shows powerful characteristics that make it suitable for different wireless standards. Thanks for its favorable properties such as the easy and efficient implementation through FFT/IFFT, its high spectral efficiency and multipath delay spread tolerance [1]. On the other hand, it is widely recognized that one of the major problems of OFDM, that would limit its performance with nest generation systems, is the large side lobe of its subcarriers. As the subcarriers constituting OFDM symbols can be shown in the time domain as a set of sinusoids multiplied by a rectangular window. In the frequency domain, those windowed sinusoids are a set of orthogonal Sinc-functions shifted in frequency. Thus, a high OOB due to the slow decay of OFDM spectrum occurs. This can be interfering with other communications systems that operate on neighboring bands. Several schemes have been proposed to suppress or reduce this OOB emission of OFDM. Cancellation carriers (CC) [2], constellation extension [3] and pre-coding [4–7] that can be classified as a frequency domain treatment, where the OOB emission © Springer Nature Switzerland AG 2019 Y. Farhaoui and L. Moussaid (Eds.): ICBDSDE 2018, SBD 53, pp. 176–185, 2019. https://doi.org/10.1007/978-3-030-12048-1_19
On the Out of Band Emission Reduction
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reduction is performed before the Inverse Fast Fourier Transform (IFFT). The other treatment, where the OOB emission processes are carried out after the IFFT, is the time domain treatment. This treatment includes filtering [8] and windowing (also known as pulse shaping) etc. although any of those techniques can be efficient in OOB emission reduction, it suffers from some penalties. Such as cancellation carrier which requires an allocation of significa
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