Power Spectral Density Performance Research Articles

A BACTERIA FORAGING ALGORITHM-BASED HYBRID A-LAW AND PTS PAPR REDUCTION METHOD FOR BEYOND 5G WAVEFORM

One of the most advanced waveforms available in the beyond-fifth-generation radio (B5GR) framework is nonorthogonal multiple access (NOMA). The power amplifier (PA) of the NOMA structure performs less efficiently when the signal is strong and the peak-to-average power ratio (PAPR) is high. This study applies a hybrid algorithm to the NOMA structure, combining fractal partial transmit sequence (PTS), A-law companding, and the bacterial foraging algorithm (BFA). Fractals are known for their self-repeating structures at different scales, allowing for efficient coverage and exploration of space. Fractals enhance the bacteria foraging algorithm (BFA) by improving search efficiency, enabling better exploration of complex, multi-dimensional optimization landscapes. Similarly, BFA balances exploring the search in promising areas. We utilized BFA to achieve optimal phase factors for the PTS algorithm and applied A-Law companding to the NOMA symbols to further enhance the structure’s performance. The intermediate computational complexity in the Rician and Rayleigh channels improves PAPR, bit error rate (BER), and power spectral density performance. Simulation results reveal that the performance of the proposed hybrid method is superior to that of existing PAPR reduction algorithms and substantially enhances the efficiency of NOMA.

PAPR analysis in OTFS using the centre phase sequence matrix based PTS method

Orthogonal time–frequency space (OTFS) is a multicarrier modulation technique for high-speed data transfer in wireless communications. In an OTFS system, many subcarriers are used to send the modulated symbols. This makes OTFS signals have a high peak-to-average power ratio (PAPR). We suggest a partial transmit sequence (PTS) approach based on the Centre Phase Sequence Matrix (CPSM) to lower the high PAPR. Furthermore, the suggested method effectively searches for the best possible combination of phase rotation factors to reduce computing complexity. We examine the outcomes regarding bit error rate (BER), power spectral density (PSD), and PAPR to validate the competing transforms in the OTFS system. Along with non-orthogonal multiple access (NOMA), filter bank multi-carrier (FBMC), universal filter multi-carrier (UFMC), and orthogonal frequency division multiplexing (OFDM), the PAPR, BER, and PSD performance of OTFS were also compared. According to the data, the suggested PTS + CPSM reduces PAPR more effectively than the current PTS. It is also mentioned that by increasing the number of sub-blocks (s = 2 and 4), the suggested PTS + CPSM can achieve an even better PAPR rate. According to the experimental results, the suggested approach has dramatically decreased the PAPR while maintaining the BER and PSD performance with the least amount of computational complexity.

Curve Fitting Based Piecewise Nonlinear Companding Scheme for PAPR Reduction in OFDM Systems

Peak-to-average power ratio (PAPR) is an important issue for orthogonal frequency division multiplexing (OFDM) systems. In this letter, we derive a new piecewise nonlinear companding scheme for reducing PAPR in OFDM systems. Compared with current state-of-art companding scheme, the new companding scheme improves the power spectral density (PSD) performance. The companding function is derived according to the cumulative distribution function (CDF) of companded OFDM signals’ amplitudes, which is fitted by using several piecewise linear functions to approximate the original Rayleigh distribution CDF. The constraint optimization problem is formulated, and parameter selection method is provided. Simulation results verify that under precondition of similar PAPR reduction levels, the proposed companding scheme could achieve better bit error rate (BER) and PSD performance compared with other typical companding schemes.

Novel PAPR reduction scheme based on continuous nonlinear piecewise companding transform for OFDM systems

In this paper, a novel efficient continuous piecewise nonlinear companding scheme is proposed for reducing the peak-to-average power ratio (PAPR) of orthogonal frequency division multiplexing (OFDM) systems. In the proposed companding transform, signal samples with large amplitudes is clipped for peak power reduction, and the signal samples with medium amplitudes is nonlinear transformed with power compensation. While the signal samples with small amplitudes remain unchanged. The whole companding function is continuous and smooth in the range of positive numbers, which is beneficial for guaranteeing the bit error rate (BER) and power spectral density (PSD) performance. This scheme can achieve a significant reduction in PAPR. And at the same time, it cause little increment in BER and PSD performance. Simulation results indicate the superiority of the proposed scheme over existing companding schemes.

Early Alpha Reactivity is Associated with Long-Term Mental Fatigue Behavioral Impairments.

The quantitative analysis of electroencephalogram (qEEG) is a suitable tool for mental fatigue (MF) assessment. Here, we evaluated the effects of MF on behavioral performance and alpha power spectral density (PSD) and the association between early alpha PSD reactivity and long-term behavioral MF impairments. Nineteen right-handed adults (21.21 ± 1.77years old) had their EEG measured during five blocks of the visual oddball paradigm (~ 60min). A paired t-test was used to compare first and last block values of cognitive performance and alpha PSD. The sample was divided into high (HAG) and low alpha group (LAG) by early alpha PSD median values. The behavioral performance of the HAG and LAG was compared across the blocks by a two-way ANOVA with repeated measures (groups and blocks). MF impairs general behavioral performance and increases alpha PSD. The HAG presents more behavioral impairment when compared to LAG across the task. Simple linear regression between early alpha PSD and behavioral performance across the task can predict 19 to 39% of variation in general behavior impairment by MF. In conclusion, MF induction impairs general behavioral and increases alpha PSD. The other finding was that higher alpha PSD reactivity is associated to higher long-term behavioral impairments of MF. This work contributes to existing knowledge of MF by providing evidence that the possibility of investigating early electrophysiological biomarkers to predict long-term MF impairments.

Dual symbol optimization‐based partial transmit sequence technique for PAPR reduction in WOLA‐OFDM waveform

SummaryWeighted overlap and add‐orthogonal frequency division multiplexing (WOLA‐OFDM) is a new waveform proposed recently for meeting the requirements of fifth generation (5G) telecommunication standards. In spite of being a serious 5G waveform candidate, WOLA‐OFDM is exposed to the problem of high peak to average power ratio (PAPR) similar to the other waveforms in which multicarrier transmission strategy is employed. Due to the overlapping nature of WOLA‐OFDM waveform, where the extension of the current symbol is overlapped with the extension of the previous symbol, it will not be efficient to apply conventional PTS (C‐PTS) directly to the WOLA‐OFDM waveform. Therefore, in this paper, we propose dual symbol optimization‐based partial transmit sequence (DSO‐PTS) technique for PAPR reduction in WOLA‐OFDM waveform. In our proposed technique, two adjacent symbols are jointly considered when searching for the optimal data block with minimum PAPR unlike the C‐PTS where the adjacent symbols are optimized individually. In the simulations, our proposed DSO‐PTS technique, C‐PTS, and GreenOFDM that is developed recently by modifying the conventional selective mapping (SLM) method are compared with each other with regard to PAPR reduction performance for different search numbers (SNs). In addition, the effects of DSO‐PTS, C‐PTS, and GreenOFDM on the amount of out of band (OOB) radiation in the power spectral density (PSD) graph of WOLA‐OFDM employing solid state power amplifier (SSPA) is measured for different SNs and input back off (IBO) values. According to the simulation results, our proposed DSO‐PTS technique clearly demonstrates a superior PAPR reduction and PSD performance.

A Generalized Piecewise Linear Companding Transform for PAPR Reduction in OFDM Systems

Companding is a well-known technique for the peak-to-average-power ratio (PAPR) reduction of orthogonal frequency division multiplexing (OFDM) signals. Piecewise linear companding (PLC) scheme, compared with other companding schemes, can effectively reduce PAPR with much lower complexity, while achieving improved bit-error-rate (BER) performance. However, when the PAPR target value for companded signals is relatively small, such as 4 dB for 16-QAM or 5 dB for 64-QAM, there is a clear error floor of PLC in high SNR region for high-order QAM modulation. Focusing on this problem, we first analyze the reason for the error floor of PLC. Based on the analysis, we propose a generalized PLC scheme to reduce the distortion in decompanded signals with the relaxation of the constraint on the conservation of the average signal power. Finally, we formulate the optimization problems to obtain the parameters of the companding function in the pursuit of a preferable tradeoff between the BER and power spectral density performance under the constraint on PAPR. Simulation results verify that the proposed generalized PLC can significantly improve the BER performance while maintaining the same PAPR performance as PLC.

Modified Gamma Correction Companding for PAPR Reduction in OFDM Systems Considering Solid-State Power Amplifier and Wireless Channels

Orthogonal frequency division multiplexing is a special form of multicarrier modulation and suffers from a very high peak-to-average power ratio (PAPR) that degrades overall performance of the system. In this article, a modified gamma correction companding (MGCC) is proposed that provides a significant reduction in PAPR when compared with existing gamma correction companding and other nonlinear companding methods available in the literature for PAPR reduction. Additionally, with the introduction of $$\gamma $$ and A parameter, the proposed companding can provide more flexibility in PAPR reduction and therefore achieves better trade-offs among PAPR gain, bit error rate (BER) and power spectral density (PSD) levels. MGCC provides an additional immunity from noise by enlarging the small amplitudes of the signal selectively, while subcarriers with the large amplitudes are moderately amplified to reduce PAPR of the signal. Moreover, MGCC improves the BER and PSD performances by minimizing the nonlinear companding distortion. The proposed MGCC improves signal-to-noise ratio (SNR) degradation ( $$\Delta _\mathrm{SNR}$$ ) and total degradation performances by 2.0 and 2.3 dB, respectively, with an input back-off power of 2.5 dB when a practical solid-state power amplifier is considered. Computer simulations reveal that the MGCC can be applied to any modulation scheme and with arbitrary number of subcarriers (N) while it does not increase computational complexity when compared with existing schemes of companding.

A new modulation scheme in polymer optical fiber communications using Jacket matrix spreading

To mitigate the high peak-to-average power ratio (PAPR) of discrete multi-tone (DMT) modulation in polymer optical fibers (POF) communication systems, a novel DMT scheme based on Jacket matrix spreading (JS) is proposed. Approximations of PAPR distribution for DMT signals are accurately presented. Single band JS-DMT and multi-band (MB)-JS-DMT are introduced in POF transmission link for PAPR reduction. Offline processing and simulations are adopted to investigate the performance of these new schemes with regard to the PAPR reduction, power spectral density (PSD), data rate and bit error rate (BER). The results demonstrate that, applying the JS methodology, up to 4dB PAPR reduction is achieved. JS-DMT is sensitive to the bandwidth range whereas MB-JS-DMT owns the robustness ability against fiber nonlinearity. Compared with some well known PAPR reduction techniques, the proposed schemes can be easily applied to the DMT modem and achieve the PAPR reduction efficiently without degrading the BER, data rate and PSD performance, which demonstrate the feasibility and validity of these two methods in POF transmission.

A low complexity peak-to-average power ratio reduction scheme based on selected mapping and radix-II IFFT in OFDM systems

Because of its lack of feedback process and the simplicity of its searching algorithm, conventional selected mapping (CSLM) is an efficient peak-to-average power ratio (PAPR) reduction technique in orthogonal frequency division multiplexing systems compared to the present techniques such as partial transmit sequence and active constellation extension. The requirement for large numbers of inverse fast Fourier transform (IFFT) blocks to provide desired PAPR reduction performance is introduced as the most significant drawback of the CSLM. This paper uses the special structure of an N-point radix-II IFFT in the CSLM and proposes a low complexity method to reduce the redundant calculations with almost the same PAPR reduction, bit-error rate, and power spectral density performances as those of the CSLM. The simulation results show that the computational complexity is reduced by at least 46.8% compared to that of the CSLM with approximately the same PAPR performance.

Sparse frequency waveform analysis and design based on ambiguity function theory

This study presents new insights into sparse frequency waveform analysis and new waveform design methods. For a general radar waveform, the total ambiguity in its auto-correlation function (ACF) is equal to the total energy in its power spectral density (PSD) in the frequency domain. With this relationship, the total ambiguity in an ACF is found to be minimised when the corresponding PSD is uniformly distributed. This property is extended to the sparse frequency waveform by establishing the relationship between the optimal PSD and the minimum ambiguity in ACF. Based on this analysis, a new method of designing sparse frequency waveform with sidelobe constraint is proposed. The new method simultaneously optimises the sidelobe performance and the PSD performance through constrained non-linear optimisation. This is different from existing methods that compromise the performance of sidelobe to the performance of PSD in an ad-hoc manner by minimising the weighted sum of the total power in the stopbands and the total power in the sidelobe. The analysis and the design method have been extended to the case of multiple sparse frequency waveforms. Simulation studies are provided to demonstrate the effectiveness of the proposed new design methods.

IGCC for PAPR Reduction in OFDM Systems Over the Nonlinearity of SSPA and Wireless Fading Channels

High peak-to-average power ratio (PAPR) in orthogonal frequency division multiplexing (OFDM) systems seriously impacts power efficiency in radio frequency section due to the nonlinearity of high-power amplifiers. In this article, an improved gamma correction companding (IGCC) is proposed for PAPR reduction and investigated under multipath fading channels. It is shown that the proposed IGCC provides a significant PAPR reduction while improving power spectral levels and error performances when compared with the previous gamma correction companding. IGCC outperforms existing companding methods when a nonlinear solid-state power amplifier (SSPA) is considered. Additionally, with the introduction of $$\alpha , \beta , \gamma $$ź,β,ź, and $$\varDelta $$Δ parameters, the improved companding can offer more flexibility in the PAPR reduction and therefore achieves a better trade-off among the PAPR gain, bit error rate (BER), and power spectral density (PSD) performance. Moreover, IGCC improves the BER and PSD performances by minimizing the nonlinear companding distortion. Further, IGCC improves signal-to-noise ratio (SNR) degradation ($$\varDelta _{\mathrm{SNR}}$$ΔSNR) and total degradation performances by 12.2 and 12.8 dB, respectively, considering an SSPA with input power back-off of 3.0 dB. Computer simulation reveals that the performances of IGCC are independent of the modulation schemes and works with arbitrary number of subcarriers (N), while it does not increase computational complexity when compared with the existing companding schemes used for PAPR reduction in OFDM systems.

A Piecewise Linear Companding Transform for PAPR Reduction of OFDM Signals With Companding Distortion Mitigation

Companding is a well-known technique for the peak-to-average power ratio (PAPR) reduction of orthogonal frequency division multiplexing (OFDM) signals. However, as companding transform is an extra operation after the modulation of OFDM signals, companding schemes reduce PAPR at the expense of increasing the bit error rate (BER). In this paper, a new piecewise linear companding scheme is proposed aiming at mitigating companding distortion. In the design of the companding transform, we study the theoretical characterization of companding distortion. It demonstrates that companding larger signals with smaller amplitude increments are more favorable in reducing companding distortion. Based on the analysis results, a new piecewise linear companding transform is proposed by clipping the signals with amplitudes over a given companded peak amplitude for peak power reduction, and linearly transforming the signals with amplitudes close to the given companded peak amplitude for power compensation. With the careful design of the companded peak amplitude and the linear transform scale, the proposed transform can achieve enhanced BER and power spectral density performance, while reducing PAPR effectively.

Precoder designs for jointly suppressing out‐of‐band emission and peak‐to‐average power ratio in an orthogonal frequency division multiplexing system

High peak-to-average-ratio (PAPR) and large out-of-band emission (OOBE) are the two main shortcomings of orthogonal frequency division multiplexing (OFDM) signals for cognitive radios. Among all the existing techniques, it has been shown that precoding is an effective way for either reducing the PAPR or suppressing the OOBE. However, no work has focused on designing an effective precoding approach to reduce the PAPR and suppress the OOBE simultaneously. In this study, three new precoding approaches that can jointly suppress OOBE and reduce PAPR simultaneously are presented. The simulation results show that, firstly, all the three proposed precoding approaches can achieve the same power spectral density performance as the typical OOBE-suppression precoding approach with the same spectral efficiency. Secondly, their PAPR performances are only slightly worse than the typical PAPR-reduction precoding approach with a similar computational complexity. Finally, two of the three proposed precoding approaches do not cause any bit error rate (BER) performance degradation with respect to the conventional OFDM system. The abilities to suppress OOBE and PAPR jointly and to maintain the good BER performance make two of the three proposed approaches very favourable for practical applications.

Parameter‐adjustable piecewise exponential companding scheme for peak‐to‐average power ratio reduction in orthogonal frequency division multiplexing systems

High peak-to-average power ratio (PAPR) is a major drawback of orthogonal frequency division multiplexing (OFDM) systems. A new companding scheme is proposed to reduce PAPR by transforming the statistics of the companded signal into exponential distribution with adjustable parameters. The proposed scheme can enhance the bit error rate (BER) performance significantly by minimising the companding distortion in the reduction of PAPR. Moreover, with the introduction of an inflexion point and transform parameters, the proposed scheme can offer more flexibility in the PAPR reduction, and therefore achieves a better tradeoff among the PAPR reduction, BER and power spectral density (PSD) performance. With a theoretical analysis presented, the parameter selection criteria are derived. Simulation results verify that the proposed scheme can significantly improve the BER and PSD performance while reducing PAPR effectively.