Hmaied Shaiek

Theoretical analysis of BER performance of nonlinearly amplified FBMC/OQAM and OFDM signals

In this paper, we introduce an analytical study of the impact of high-power amplifier (HPA) nonlinear distortion (NLD) on the bit error rate (BER) of multicarrier techniques. Two schemes of multicarrier modulations are considered in this work: the classical orthogonal frequency division multiplexing (OFDM) and the filter bank-based multicarrier using offset quadrature amplitude modulation (FBMC/OQAM), including different HPA models. According to Bussgang’s theorem, the in-band NLD is modeled as a complex gain in addition to an independent noise term for a Gaussian input signal. The BER performance of OFDM and FBMC/OQAM modulations, transmitting over additive white Gaussian noise (AWGN) and Rayleigh fading channels, is theoretically investigated and compared to simulation results. For simple HPA models, such as the soft envelope limiter, it is easy to compute the BER theoretical expression. However, for other HPA models or for real measured HPA, BER derivation is generally intractable. In this paper, we propose a general method based on a polynomial fitting of the HPA characteristics and we give theoretical expressions for the BER for any HPA model.

Reduction of PAPR for FBMC-OQAM systems using dispersive SLM technique

The Filter Bank Multi-Carrier (FBMC) based systems are being seriously considered for 5G Radio Access Technology (RAT). As FBMC-OQAM is a multi-carrier technique, it suffers from the high Peak-to-Average Power Ratio (PAPR) and directly applying the PAPR reduction schemes proposed for OFDM to FBMC-OQAM turns out to be ineffective, due to its overlapping structure. In this paper, a scheme named as Dispersive Selective Mapping (DSLM) is proposed, which is an extended and generalized version of Overlapped Selective Mapping (OSLM). Simulation results show that performance of this method is very closely trailing to that of OFDM.

Closed-Form BER Expression for (QAM or OQAM)-Based OFDM System With HPA Nonlinearity Over Rayleigh Fading Channel

Nonlinear distortions caused by high-power amplifiers are considered the key impairment in multicarrier techniques-based communication systems. However, there are few past investigations addressing their effect on the performance of filter bank multicarrier-based systems. In this letter, we derive a closed-form expression for the BER of Gray-coded M-ary [quadrature amplitude modulation (QAM) or offset QAM]-based OFDM running under a frequency-flat-fading Rayleigh channel, which is valid for any memoryless nonlinearity model and can be evaluated without a numerical integration method.

WOLA-OFDM: A Potential Candidate for Asynchronous 5G

This paper investigates the performance, in relaxed synchronization scenario, of a new contender waveform making its appearance recently named Weighted Overlap and Add based OFDM (WOLA-OFDM). Indeed, its performance will be studied and compared to the classical CP-OFDM and the wellknown UFMC that offers particular benefits for 5G use cases. Results show that WOLA-OFDM could be a promising candidate waveform, outperforming both CP-OFDM and UFMC in any asynchronous scenario.

Adaptive Predistortion Techniques for Non-Linearly Amplified FBMC-OQAM Signals

The Filter Bank Multicarrier with Offset Quadrature Amplitude Modulation (FBMC-OQAM) is emerging as one of the alternatives to Orthogonal Frequency Division Multiplexing (OFDM) for next generation broadband wireless access systems. In this paper, we focus on the nonlinear distortion effects in a FBMC-OQAM system when the signal is passed through a nonlinear High Power Amplifier (HPA) which is modeled as Salehs one exhibiting amplitude and phase distortions. First, we develop an analysis showing that the FBMC-OQAM signals are more sensitive to the phase distortion than OFDM signals. Then, we address the problem of the compensation of these distortions in FBMC-OQAM systems using digital predistortion (DPD) at the transmitter. Therefore, two DPD schemes are considered in this investigation and their performance are compared in OFDM and FBMC-OQAM systems.

On the impact of the prototype filter on FBMC sensitivity to time asynchronism

This paper investigates the impact of the prototype filter on the sensitivity of the FBMC system to timing synchronization errors. A global evaluation of the average error rate has been made for OFDM and two FBMC systems using PHYDYAS and IOTA prototype filters. This evaluation has been performed taking into account different parameters: the timing error range, the guard band length and the load factor of the network. The validity of the simulation results will be verified by comparison with those obtained with the analytical expressions.

Potency of trellis-based SLM over symbol-by-symbol approach in reducing PAPR for FBMC-OQAM signals

The Filter bank multi-carrier (FBMC) with offset-quadrature amplitude modulation (OQAM) gained lot of attention recently. Both orthogonal frequency division multiplexing (OFDM) and FBMC-OQAM suffer from high peak-to-average power ratio (PAPR). The classical PAPR reduction schemes suggested for OFDM signals cannot be directly applied on the OFDM-OQM, due to the overlapping structure. In this paper we investigate the problem of PAPR reduction in FBMC-OQAM systems and a trellis-based selected mapping (TSLM) scheme with dynamic programming (DP) has been proposed, which probes for optimal phase rotation vectors. With selected mapping (SLM) scheme, multiple patterns of the modulated signal are generated. Theoretical and numerical analyses indicate that TSLM offer better PAPR reduction performance as compared to symbol-by-symbol approach. Simulation results show that performance of FBMC-OQAM system with this method is not only superior to any scheme based on symbol-by-symbol approach, but also outperforms that of the OFDM with classical SLM scheme. It has also been shown that this result holds for different prototype filter impulse responses that are more or less localized in time or frequency.

Prediction of spectral regrowth for FBMC-OQAM system using cumulants

Relevance of Filter Bank Multi-Carrier (FBMC) systems along with Offset Quadrature Amplitude Modulation (OQAM) for 5G Radio Access Technology (RAT) cannot be ruled out. FBMC-OQAM modulation technique has many attractive features over OFDM that make it more appealing to be the radio waveform in 5G. However, being a multi-carrier modulation technique, it has high PAPR and prone to spectral regrowth in the presence of a non-linear high power amplifier (HPA), which is a vital component in contemporary modern communication systems. This spectral regrowth indicate that the excellent frequency localization property of the FBMC-OQAM signals no longer holds in the presence of a non-linear HPA. So, there is a dire need to predict the extant of spectral regrowth induced by the HPA non-linearities. With cumulants, it is possible to predict the power spectral density (PSD) of the HPA output. Prediction of spectral regrowth in the case of OFDM systems was already done and in this paper it is extended to FBMC based systems. HPA of Salehs model is used for simulations but prediction can be done for any measured or modeled HPA after polynomial fitting of its AM/AM and AM/PM distortion characteristics.

Sensitivity analysis of FBMC signals to non linear phase distortion

In this paper, we present a theoretical analysis of the impact of High Power Amplifier (HPA) Non-Linear Distortion (NLD) on the Bit Error Rate (BER) of multicarrier techniques. For the aim of this study, the Salehs model was chosen for NL HPA. Two multicarrier schemes are considered: the classical Orthogonal Frequency Division Multiplexing (OFDM) and the Filter Bank based Multi-Carrier (FBMC). According to the Bussgang theorem, the in-band NLD is modeled as a complex gain and an independent additive noise term for both modulations. The BER performance of OFDM and FBMC modulations, transmitting over an Additive Withe Gaussian Noise (AWGN) and Rayleigh channels, is theoretically evaluated and compared to simulation results. We have established that OFDM and FBMC modulations show the same performances, in terms of BER, when just amplitude distortion is induced by the HPA. However, FBMC system is more sensitive to phase distortions when no correction is adopted at the receiver. This behavior has been explained by the difference between the probability distribution of the intrinsic interference present in both OFDM and FBMC modulations.

Reducing the PAPR in FBMC-OQAM systems with low-latency trellis-based SLM technique

Filter-bank multi-carrier (FBMC) modulations, and more specifically FBMC-offset quadrature amplitude modulation (OQAM), are seen as an interesting alternative to orthogonal frequency division multiplexing (OFDM) for the 5th generation radio access technology. In this paper, we investigate the problem of peak-to-average power ratio (PAPR) reduction for FBMC-OQAM signals. Recently, it has been shown that FBMC-OQAM with trellis-based selected mapping (TSLM) scheme not only is superior to any scheme based on symbol-by-symbol approach but also outperforms that of the OFDM with classical SLM scheme. This paper is an extension of that work, where we analyze the TSLM in terms of computational complexity, required hardware memory, and latency issues. We have proposed an improvement to the TSLM, which requires very less hardware memory, compared to the originally proposed TSLM, and also have low latency. Additionally, the impact of the time duration of partial PAPR on the performance of TSLM is studied, and its lower bound has been identified by proposing a suitable time duration. Also, a thorough and fair comparison of performance has been done with an existing trellis-based scheme proposed in literature. The simulation results show that the proposed low-latency TSLM yields better PAPR reduction performance with relatively less hardware memory requirements.