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Study and implementation of widely linear (WL) receiver for filter bank based multicarrier (FBMC-OQAM) modulations over frequency selective channels

Abstract : The increasing demand of user’s requirements is one of the main reasons in technical progress and development of modern wireless communication systems. Thus, since 2G and beyond, there have been many changes, especially, the switch from the mono carrier to the multi-carrier (MC), introduced for the Down-Link (DL) 4G transmission. Indeed, the predo- minant idea behind introducing MC waveforms (WF) is to get rid of the propagation channel effects, by relaxing the equalization process through the transmission of the data symbols over flat fading sub-channels or sub-carriers. Furthermore, the widely adopted MC WF is the ortho- gonal frequency division multiplexing (OFDM), which became very popular and widely used in many wireless standards like long term evolution (LTE)- Advanced (LTE-A) andWi-Fi. The standardization of OFDM, for these applications and also for some others, is related to the ad- vantages shown by this MC WF. One of these advantages is its simple implementation through the use of the inverse fast Fourier transform (IFFT) at the transmitter side, and a FFT at the receiver side. Also, OFDM introduces a cyclic prefix (CP), making the transmission free from inter-symbol-interference (ISI).Despite the large success of the OFDM WF, this technique suffers from the loss of spec- tral efficiency due to the use of the CP. Besides, it suffers from bad frequency localization due the use of a rectangular prototype filter. These OFDM drawbacks, have motivated researchers to design new MC WF, with better frequency domain localization, better robustness to user’s synchronism, while keeping moderate implementation complexity. In this context, high num- ber of post-OFDM MC WF have been proposed and implemented to meet 5G scenarios and requirements in a flexible manner.Therefore, the offset-quadratureamplitudemodulation-based filter-bankmulti-carrier(FBMC- OQAM) has been proposed as an alternative to overcome some drawbacks of the OFDM WF. Indeed, FBMC-OQAM is characterized by owning one of the best frequency localiza- tion among all the post-OFDM WFs, thanks to its prototype filter (Phydyas), providing then the best performance in supporting asynchronous and mixed numerologies transmissions. Be- sides, it offers high spectrum efficiency since it avoids the use of CP and large guard bands. Furthermore, the orthogonality in real domain is guaranteed thanks to the use of the OQAM modulation. However, this orthogonality is lost under frequency selective channels which re- quires advanced equalization techniques.In this context, the main objective of this thesis is to study different types of equalization applied on FBMC-OQAM system. Since the modulation used in the FBMC-OQAM system can be seen as the transmission of two M−PAM modulations over one single carrier and since the widely linear processing outperforms the classical one for M−PAM modulation, we will focus on the advantages of using the widely linear processing over FBMC-OQAM system. Ad- ditionally, and based on the cyclo-stationarity of the FBMC-OQAM signal, we have proposed an advanced equalization structure based on FRESH processing that have been applied in to a FBMC-OQAM system using different numerologies.
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Hayfa Fhima. Study and implementation of widely linear (WL) receiver for filter bank based multicarrier (FBMC-OQAM) modulations over frequency selective channels. Signal and Image processing. Conservatoire national des arts et metiers - CNAM; École supérieure des communications de Tunis (Tunisie), 2019. English. ⟨NNT : 2019CNAM1266⟩. ⟨tel-02496085⟩

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