Marwa Chafii

A Necessary Condition for Waveforms With Better PAPR Than OFDM

This paper establishes a necessary condition that must be satisfied by the modulation waveforms of any generalized waveforms for multicarrier (GWMC) system with better peak-to-average power ratio (PAPR) than conventional orthogonal frequency division multiplexing (OFDM). GWMC systems include in particular all classical multicarrier modulation systems. As a consequence, we show that OFDM has the best PAPR performance over all GWMC systems that do not satisfy this necessary condition. We also identify an infinite family of GWMC systems with the same PAPR performance as OFDM. To illustrate our results, we present the simulations of the PAPR behavior for different GWMC systems, including some with better PAPR performance than OFDM.

DCT-OFDM With Index Modulation

In this letter, index modulation (IM) is proposed for OFDM systems based on a discrete cosine transform (DCT) implementation. The new DCT-OFDM-IM scheme is shown to yield spectral efficiency improvements of up to 38% relative to OFDM-IM and up to 55% relative to OFDM while occupying the same bandwidth and maintaining similar robustness against the frequency selective fading channels for low modulation orders.

Wavelet-OFDM vs. OFDM: Performance comparison

Wavelet-OFDM based on the discrete wavelet transform, has received a considerable attention in the scientific community, because of certain promising characteristics. In this paper, we compare the performance of Wavelet-OFDM based on Meyer wavelet, and OFDM in terms of peak-to-average power ratio (PAPR), bit error rate (BER) for different channels and different equalizers, complexity of implementation, and power spectral density. The simulation results show that, without decreasing the bandwidth efficiency, the proposed scheme based on Meyer Wavelet-OFDM, outperforms OFDM in terms of PAPR by up to 4.5 dB, and in terms of BER by up to 6.5 dB of signal to noise ratio when using the minimum mean-square error equalizer without channel coding, at the cost of a computational complexity increase.

Power spectral density limitations of the wavelet-OFDM system

Wavelet-OFDM based on the discrete wavelet transform is a multicarrier modulation technique of considerable interest, due to its good performance in several respects such as the peak-to-average power ratio and the interference cancellation, as investigated in the literature. More specifically, the Haar wavelet has been proposed by various researchers as the most attractive wavelet for data transmission. In this paper, we address the power spectral density limitations of Wavelet-OFDM, and we show analytically and experimentally that the bandwidth efficiency of Haar Wavelet-OFDM is significantly poorer than OFDM, having larger main lobe and side lobes compared with OFDM, which reduces the attractiveness of the scheme.

Modified tone reservation for PAPR reduction in OFDM systems

One of the main drawbacks of orthogonal frequency division multiplex modulation is its high peak-to-average power ratio (PAPR) which can induce poor power efficiency at high power amplifier. Tone reservation (TR) is the most popular PAPR mitigation technique that uses a set of reserved tones to design peak cancelling signal for PAPR reduction. Finding an effective peak cancelling for PAPR reduction in the time domain by using only a small number of reserved tones, is not straightforward. Therefore, we are led to a trade-off between computational complexity and PAPR reduction. The TR method based on the gradient projection algorithm gives the best compromise. In this paper, we propose to modify the classical TR structure. The new proposed method achieves an improvement up to 1.2 dB in terms of PAPR performance without increasing the complexity. The effectiveness of this solution is confirmed through theoretical analysis and simulation results.

Low-PAPR condition for 5G-candidate waveforms

To meet 5G networks challenges in terms of high data rates and spectral efficiency, one solution might be using multicarrier modulations (MCM)s. However, using MCMs is synonymous with low energy efficiency due to their high peak-to-average power ratio (PAPR). Indeed, high PAPR signals drive power amplifiers to operate most of the time in the linear zone. This latter corresponds to low power efficiency. This leads to a trade-off between spectral and energy efficiency. For this reason, PAPR reduction techniques have been highly addressed in literature. In this work, this trade-off is addressed differently: a necessary condition to achieve better PAPR performance than orthogonal frequency division multiplexing (OFDM) is established. This theoretical condition is verified by simulation results carried on Fourier-based and wavelet-based MCMs. The established condition classifies the MCMs into three categories regarding the PAPR: same as, higher than and lower than the OFDM PAPR level.

Adaptive Tone Reservation for Better BER Performance in a Frequency Selective Fading Channel

Multicarrier modulation systems suffer from large peak-to-average power ratio (PAPR). Tone reservation is a popular technique for PAPR reduction. It consists in reserving a number of carriers to produce a redundant additive signal which reduces the peak power. There are several schemes to select the reserved carriers. In this paper, we propose a new selection method for adaptive tone reservation. It is showed through simulations that this new proposed selection technique allows 5 dB gain in terms of signal-to- noise ratio for a bit error rate of 10-3, for different constellations, in frequency-selective Rayleigh fading channel.