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As single-carrier frequency division multiple access (SC-FDMA) is used in long-term evolution (LTE) uplink communications, high peak-to-average power ratio (PAPR) increases power consumption in mobile devices. It is severe when localized subcarrier mapping is used with higher-order modulations. Companding is an attractive technique that offers a tradeoff between PAPR and bit error rate (BER) performances. This paper proposes an exponential companding technique that uses two companding levels based on a threshold, to reduce PAPR in SC-FDMA systems. It does not increase the average power level of transmitted signal and maintains the BER level without significant degradation from the original system. The proposed scheme has three parameters that can be adjusted for a tradeoff between PAPR, BER, and power spectral density (PSD) performances. Hence it offers more flexibility than the conventional exponential companding scheme. We also present scatter plots to find the optimum threshold value and companding levels. Finally, we verify the proposed technique considering a real-time indoor channel by using a wireless open-access research platform (WARP).

In this paper, pilot-based time-domain channel estimation (CE) along with peak-to-average power ratio (PAPR) reduction is proposed for universal filtered multicarrier (UFMC) system. The pilots that are inserted in time domain not only estimate the channel behavior but also can be used in the reduction of PAPR. For PAPR reduction, a linear companding scheme, which can treat amplitudes of the UFMC signal separately with a different scale, is proposed. The proposed companding scheme offers more design flexibility and better performance gains by using two inflexion points. However, the proposed companding scheme requires side information (SI) to perform de-companding at the receiver. The transmission of SI decreases the data efficiency, so a pilot-assisted UFMC system that can perform both data recovery and PAPR reduction without the requirement of SI transmission is proposed. In pilot-assisted UFMC system, the inserted time-domain pilots can enable SI cancellation inherently. Furthermore, a hybrid transform, which improves PAPR performance by employing clipping scheme to the linear companded signal, is proposed. Simulation results confirm that the proposed joint CE with linear companding scheme achieves an improved net gain of 6.5dB. Additionally, the proposed hybrid scheme with clipping threshold of 1.4 provides an improved PAPR reduction of 8.8dB and enhanced net gain of 7.3dB. Moreover, the proposed joint time-domain CE with hybrid PAPR reduction scheme of UFMC system is validated over real time by employing wireless open-access research platform (WARP) board.

Nonorthogonal multiple access (NOMA) waveforms need to be tested for their performance and effectiveness using partial transmit sequence (PTS) techniques and peak-to-average power ratio (PAPR) analysis. This is an important part of the advanced radio framework. This paper examines the PAPR features of NOMA systems using PTS with different sub-carrier configurations (64, 256, and 512). We examine BER, PSD, and PAPR distributions by modeling NOMA waveforms with PTS to understand the impact of different sub-carrier counts on signal complexity and efficiency. The findings shed light on how sub-carrier quantity affects PAPR statistics and offer guidance on the best way to design NOMA waveforms for improved spectral efficiency and reduced signal distortion. The simulation results show that by lowering the PAPR while maintaining the BER performance, the suggested system performs better than the traditional PAPR algorithm.

Optical orthogonal time frequency space (OTFS) is better at handling Doppler shifts and multipath fading, making signals more reliable and valuable in places with much movement beyond the fifth generation (B5G). Using practical power amplifiers at the transmitter causes power inefficiency and signal distortion because of the OTFS system’s high peak-to-average power ratio (PAPR), severely reducing system efficiency. Combining partial transmit sequence (PTS) and selective mapping (SLM), a technique known as PTS+SLM, reduces peak power. While SLM generates numerous phase-modulated signal candidates and chooses the one with the lowest PAPR, PTS separates the signal into sub-blocks and optimizes their phases to decrease peak power. With few changes to the signal structure, this dual strategy effectively reduces PAPR while improving power spectral density (PSD) efficiency. As a result, we ensure the accuracy and dependability of the transferred data by maintaining the bit error rate (BER). Fractal optimization methods could be applied to these algorithms. For example, fractal-inspired optimization techniques might be used to explore the phase space more effectively or to discover new phase sequences that result in lower PAPR. According to the simulation findings, the suggested PTS+SLM method works better than the traditional PTS and SLM methods.

A new interspersed orthogonal frequency division multiplexing (OFDM) based on Hadamard coded Discrete Harmonic wavelet transform (DHWT), is proposed for complex modulation under exponential channel model. In this method, real part of complex signal is transformed by DCHWT and imaginary part by DSHWT and summed to form interspersed harmonic wavelet based OFDM (IHWT OFDM). DHWT exploits the useful properties of DCT and DST viz., energy compaction/low leakage, frequency resolution and its real nature, compared to DFT. This wavelet is simple as it has reduced processing due to its harmonic wavelet nature. The harmonic nature has built in decimation, easy interpolation by concatenation of different scales in frequency (DCT and DST) domain without associated anti-aliasing filters for analysis, image rejection filters and complicated delay compensation for synthesis. In this work, we have explored advantages of DHWT to implement IHWP-OFDM for QPSK modulated signals. Hadamard codes are employed in proposed method to further improve BER and PAPR performance. New OFDM provides PAPR reduction of 2.6, 3.8 and 1.4 dB as compared to Haar, Daubechies WT OFDM and DFT, respectively.