Improved Clipping Technique for PAPR Reduction in OFDM

Orthogonal frequency division multiplexing (OFDM) signals have a generic problem of high peak to average power ratio (PAPR) which is defined as the ratio of the peak power to the average power of the OFDM signal. The drawback of the high PAPR is that the dynamic range of the power amplifiers (PA) & digital-to-analog (D/A) converters required during the transmission and reception of the signal is higher. As a result, the total cost of the transceiver increases, with reduced efficiency. This paper includes an idea of the PAPR constraint, along with the implementation and analysis of some specific algorithms for PAPR reduction of the OFDM signals. All the PAPR reduction algorithms are implemented and tested in the OFDM transceiver designed using Matlab. Analyzing some specific algorithms, we propose a novel algorithm by combining the subcarrier phase adjustment and linear combination of the time domain OFDM signals. Simulation results for a OFDM system employing Quadrature Amplitude Shift Keying (QASK) symbols and Quadrature Amplitude Modulation (QAM) can achieve a PAPR reduction of 5 dB.

Orthogonal Frequency Division Multiplexing (OFDM) is a multicarrier modulation technique that has been widely applied in wireless broadband communications such as the fourth-generation (4G) and supports the development of the fifth-generation (5G) technology because it is efficient and effective. However, OFDM has a high Peak to Average Power Ratio (PAPR) value where the system must use a Power Amplifier (PA) with a high linear range so that the signal can work on PA. Whereas, PA is a nonlinear component that has limited linear region according to the component specifications. If an OFDM signal with high PAPR passes through the nonlinear region of PA, the signal will be distorted nonlinearly and ultimately worsen the OFDM performance. Although many researchers are interested in studying this issue, several scenarios are still not explored. This work investigates a way to mitigate nonlinear distortion by a combination of PAPR reduction and PA linearization with predistortion. Memory-Hammerstein has been suggested as a model for predistorter and PA. The input of the predistorter is the PAPR reduced signal with companding technique, which is a simple and effective PAPR reduction technique for OFDM. The system performance will be evaluated using signal spectrum, PAPR, and Bit Error Rate (BER). The simulation results obtained are that the performance drops dramatically to more than 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">−1</sup> for the BER value when a nonlinear disturbance is given and the performance improves after a predistorter is applied. The combination of hybrid companding and predistorter offers better performance, it can reduce PAPR and compensating for nonlinear distortions caused by the PA. Hence, this combined scheme can be considered and adopted in future wireless communications systems including 5G.

One major Disadvantage of OFDM is the high peak-to average Power ratio (PAPR). One investigated technique Selected Mapping (SLM) is PAPR reduction techniques for Orthogonal Frequency Division Multiplexing (OFDM). In this paper we proposed a Modernize SLM (MSLM) scheme to reduce the PAPR by using the complex signal separate into real & imaginary parts and individually phase sequence multiple real as well as imaginary part of complex signal then select minimum PAPR signal of real & imaginary and these are combine. The simulation show achieves good PAPR., which is one of the strong candidate for Future wireless communication.

The most widely used technique for high-data-rate transmission is orthogonal frequency division multiplexing (OFDM). However, one disadvantage of OFDM systems is that the transmitted signals have a high peak-to-average power ratio (PAPR). High PAPR causes more interference and lower resolution in analogue to digital (A/D) and digital to analogue (D/A) converters. In this paper, Partial Transmit Sequence (PTS) technique using Improved Harmony Search (IHS) algorithm is proposed to solve the high PAPR problem. The PTS technique has a high search complexity because it involves an extensive random search over all possible phase vector combinations, which grows exponentially with the number of phase vectors. IHS improves the accuracy and convergence rate of conventional algorithms while requiring only a few parameters to be adjusted. The modulation method used is Quadrature Phase Shift Keying (QPSK). The performance of PTS and IHS-PTS are analyzed using CCDF graphs with different values of subcarriers and iterations. The PAPR reduction percentage increases more with using IHS-PTS compared to PTS only. To conclude, implementing IHS together with PTS can improve computational complexity in PTS and helps to reduce PAPR values even better in OFDM system.KeywordsImproved Harmony Search (IHS)Orthogonal frequency division multiplexing (OFDM)Peak average power ratio (PAPR)Partial Transmit Sequence (PTS)

Requirement of high data rate by the modern mobile communication system requires a linear power amplifier with extremely low power consumption and long battery life. Orthogonal frequency division multiplexing (OFDM) modulation technique promises to deliver high data rate with simple receiver structure. It is more spectral efficient and has been recommended to be used by many standards. But it has one major disadvantage of having high peak to average power ratio (PAPR). High PAPR drives the power amplifier in saturation region and causes it to operate in nonlinear region with reduced efficiency. There are several techniques to reduce PAPR of OFDM system. In this paper we have done FPGA implementation of selective mapping method (SLM) for PAPR reduction for 4 QAM baseband signal for 64, 128, 256, 512 and 1024 number of subcarriers. The result obtained have been compared with PAPR values obtained through mathematical analysis and Matlab simulations and also with original signal. For 1024 number of subcarriers at 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-3</sup> of CCDF value the PAPR value obtained with hardware implementation is 9.8 dB which is 2.8 dB less form the original OFDM signal obtained without applying SLM technique but 0.9 dB higher than the Matlab simulated value. This technique is simple in implementation, utilizes less resources and is effective in PAPR reduction.

Orthogonal Frequency Division Multiplexing (OFDM) has several desirable attributes, such as high immunity to inter-symbol interference, robustness with respect to multi-path fading, and ability for high data rates, all of which are making OFDM to be incorporated in wireless standards like IEEE 802.11a/g/n WLAN and ETSI terrestrial broadcasting. However one of the major problems posed by OFDM is its high Peak-to-Average-Power Ratio (PAPR), which seriously limits the power efficiency of the transmitter’s High Power Amplifier (HPA). This is because PAPR forces the HPA to operate beyond its linear range with a consequent nonlinear distortion in the transmitted signal. One of good solutions to mitigate this nonlinear distortion is put a Pre-Distorter before the High Power Amplifier and increase linear dynamic range up to a saturation region (1) (2) (3). However, the main disadvantage of Pre-Distorter technique is that these PD techniques only work in a limited range, that is, up to the saturation region of the amplifier. In this situation, Peak-to-Average Power Ratio (PAPR) reduction techniques which pull down high PAPR of OFDM signal to an acceptable range can be a good complementary solution. Due to practical importance of this, there are various PAPR reduction techniques for OFDM signals (4) (5) (6) (7) (8) (9). Among them, the PTS (Partial Transmit Sequence) technique is very promising because it does not give rise to any signal distortion (9). However, its high complexity makes it difficult to use in a practical system. To solve the complexity problem of the PTS technique, Cimini and Sollenberger proposed an iterative flipping algorithm (10). Even though the iterative flipping algorithm greatly reduces the complexity of the PTS technique, there is still some performance gap between the ordinary PTS and the iterative flipping algorithm. In this chapter, we propose an enhanced version of the iterative flipping algorithm to reduce the performance gap between the iterative flipping algorithm and the ordinary PTS technique. In the proposed algorithm, there is an adjustable parameter to allow a performance/complexity trade-off.

Orthogonal Frequency Division Multiplexing (OFDM) is an attractive technique for wireless communications applications. However, one of the main disadvantages of OFDM is its high Peak to Average Power Ratio (PAPR) that limits transmitter power efficiency. Without any measures, the OFDM signal is limited by the power amplifier (in the transmitter) what causes interference both on the signal itself and in adjacent frequency bands. In this paper we formulate the reduction of the PAPR problem as a Second Order Cone Programming problem (convex optimization). We extend two known methods by choosing unused carriers in standards to minimize PAPR. The results are presented for the 802.11a standard. The proposed method induces no in-band distortion and stay compatible towards the IEEE 802.11a spectrum masking. Moreover, they don't need any side information and can be applied for real or complex OFDM baseband.

SUMMARY The main disadvantage of orthogonal frequency divisionmultiplexing (OFDM) is the high time domain PAPR. The larger PAPRsignal would fatallydegrade BER performance in non-linear channels. Thispaper proposes an improved DSI method, which can achieve better PAPRand BER performances in the non-linear channel with less computationcomplexity than the conventional DSI method. The feature of proposedmethod is to employ the time-frequency domain swapping algorithm inthe determination of frequency data for dummy sub-carriers. This paperpresents various computer simulation results to verify the effectiveness ofproposed DSI method. key words: OFDM, PAPR, dummy sub-carriers, non-linear amplifier 1. Introduction The OFDM technique has been received a lot of attentionespecially in the field of wireless communications becauseof its efficient usage of frequency bandwidth and robustnessto multi-path fading. One of the limitations of using OFDMtechnique is the larger peak to averaged power ratio (PAPR)of its time domain signal [1]. The larger PAPR signal wouldcause the severe degradation of bit error rate (BER) perfor-mance due to the inter-modulation noise occurring in thenon-linear amplifier.To overcome the PAPR problem in OFDM systems,various PAPR reduction methods for OFDM signal havebeen proposed including the selected mapping method(SLM) [2], partial transmit sequence method (PTS) [3] anddummy sequence insertion method (DSI) [4]. All of thesemethods improve the PAPR performance by controlling thephase of data or dummy sub-carriers. The SLM and PTSmethods control the phase of data sub-carriers and the DSImethod controls the phase of dummy sub-carriers. First twomethods are required to inform the phase information con-trolled for the data sub-carriers to the receiver as the sideinformation. Since the side information is required to trans-mit separately from the data information through the data orcontrol channels with the higher signal quality for the cor-rect demodulation of data information at the receiver, the

In this paper, we propose a new peak-to-average power ratio (PAPR) reduction technique, which is referred to as trellis-assisted constellation subset selection ( TACSS , or TAX for short), for orthogonal frequency-division multiplexing (OFDM) signals. We control the signal transition by judiciously selecting the appropriate constellation subset for PAPR reduction with the controlling bits that are subject to the trellis-based constraint imposed by a bank of memories. A novel constellation design suitable for the proposed system is also introduced. A major property offered by the proposed approach is that the controlling bits and the information bits are perfectly separable at the receiver, which leads to a simple implementation of its soft-in–soft-out (SISO) decoder for coded OFDM systems. Through the performance analysis of PAPR reduction capability, power amplifier (PA) efficiency, average mutual information (AMI), and bit error rate (BER), the achievable tradeoff relationship between the transmitter and receiver performances of the proposed system is addressed. Furthermore, performance comparisons of the proposed scheme with other major PAPR reduction schemes such as trellis shaping, discrete Fourier transform (DFT) precoding, and clipping and filtering demonstrate its practical advantage in a high-spectral-efficiency regime.

Orthogonal frequency division multiplexing (OFDM) is an attractive and effective technique for wireless communications. However, an OFDM signal has a large peak-to-average power ratio (PAPR), which will cause serious nonlinear distortion especially when the signal passes through a nonlinear system. Adaptive symbol selection scheme (ASSS) is used to reduce the unwanted PAPR by selecting the adaptive OFDM signal with the smallest PAPR before transmitting. Because of the side information needed in ASSS, the effective data rate finally got in the receiver decreases. We develop a new modulation method using ASSS and channel estimation together, which can transmit the needed side information in the pilot tones made by channel estimation during the signal transmission. Our simulation results show that the method we proposed is a promising and valuable technique for reducing PAPR in OFDM signals.

In this paper, a linear moving average recursive filtering technique is proposed to reduce the peak-to-average power ratio (PAR) of orthogonal frequency division multiplexing (OFDM) signals. The proposed low complexity technique is analyzed in an oversampled OFDM system and a simple distribution approximation of the oversampled and linearly filtered OFDM signals is also proposed. Corresponding time domain linear equalizers are developed to recover originally transmitted data symbols. Through extensive computer simulations, effects of the new filtering technique on the oversampled OFDM peak-to-average power ratio (PAR), power spectral density (PSD) and corresponding linear equalizers on the frequency selective Rayleigh fading channel transmission symbol-error-rate (SER) performance are investigated. The newly proposed recursive filtering scheme results in attractive PAR reduction, requires no extra fast Fourier transform/inverse fast Fourier transform (FFT/IFFT) operations, refrains from transmitting any side information, and reduces out-of-band radiation. Also, corresponding linear receivers are shown to perform very close to their frequency domain counterparts.

We investigate a novel dispersion compensating technique in double sideband (DSB) modulated and directed-detected (DD) passive optical network (PON) systems using super-Nyquist image induced aliasing. We show that diversity is introduced to the higher frequency components by deliberate aliasing using the super-Nyquist images. We then propose to use fractional sampling and per-subcarrier maximum ratio combining (MRC) to harvest this diversity. We evaluate the performance of conventional orthogonal frequency division multiplexing (OFDM) signals along with discrete Fourier transform spread (DFT-S) OFDM and code-division multiplexing OFDM (CDM-OFDM) signals using the proposed scheme. The results show that the DFT-S OFDM signal has the best performance due to spectrum spreading and its superior peak-to-average power ratio (PAPR). By using the proposed scheme, the reach of a 10-GHz bandwidth QPSK modulated OFDM-PON can be extended to around 90 km. We also experimentally show that the achievable data rate of the OFDM signals can be effectively increased using the proposed scheme when adaptive bit loading is applied, depending on the transmission distance. A 10.5% and 5.2% increase in the achievable bit rate can be obtained for DSB modulated OFDM-PONs in 48.3-km and 83.2-km standard single mode fiber (SSMF) transmission cases, respectively, without any modification on the transmitter. A 40-Gb/s OFDM transmission over 83.2-km SSMF is successfully demonstrated.

Visible light communication (VLC) is a technology that is currently being employed to achieve high data rates. Orthogonal frequency division multiplexing (OFDM) is a powerful scheme for intensity modulation and direct detection (IM-DD) that is becoming increasingly important. OFDM systems based on VLC are accomplished through the implementation of IM-DD constraints, including direct current biased optical OFDM (DCO-OFDM), asymmetrically clipped optical OFDM (ACO-OFDM), and asymmetrically clipped DC-biased (ADO-OFDM), among others. The OFDM technique based on VLC is inefficient in terms of spectral efficiency and has a high peak to average power ratio (PAPR). In this article, the symbol time compression-image adjust (STC-IMADJS) technique will be proposed for throughput maximization and PAPR reduction in the DCO-OFDM, ACO-OFDM, and ADO-OFDM systems. Furthermore, the STC technique enables the simultaneous transmission of two sub-carriers through Walsh spreading codes without inference between them. As a result, the OFDM symbol has been reduced by 50%. The IMADJS strategy reduces the high PAPR of transmitted signals by compressing large signals and expanding small signals, as long as the average power level remains constant after compression. Therefore, the proposed STC-IMADJS technique doubles the throughput as well as significantly reduces the PAPR for OFDM systems based on VLC. The simulation results are performed using Matlab-2021a for 1024 sub-carriers. As a result, the simulation results show that the proposed technique reduces the PAPR by 3.7 dB (86%), 8.16 dB (93%), and 1.81 dB (20%) for DCO-OFDM, ACO-OFDM, and ADO-OFDM systems respectively. Furthermore, the technique has a significantly lower computational complexity than conventional OFDM systems based on VLC. Finally, the measures of performance through this article are bit error rate and complementary cumulative distribution function.

OFDM (orthogonal frequency division multiplexing) is usefully applied for DAB (digital audio broadcasting) and DVB (digital video broadcasting) systems due to its high spectral efficiency and robustness to ISI (intersymbol interference) and multipath fading. However, the OFDM signal has a large PAPR (peak-to-average power ratio), which results in significant nonlinear distortion when it passes through an HPA (high power amplifier) such as a TWTA (traveling wave tube amplifier) and a SSPA (solid state power amplifier). We propose a new PAPR reduction method using soft clipping and filtering. Unlike conventional hard clipping, soft clipping has non-zero slope in the clip region. Next, filtering, which uses additional FFT and IFFT processes, is applied in order to reject the out-of-band clip noise. Although the filtering removes the out-of-band noise, it oppositely increases PAPR by a small amount. Since an HPA increases the power consumption according to the linearity range, soft clipping for an SSPA lowers power consumption and is more efficient than the conventional hard clipping method. By the results of the proposed method, the wanted PAPR can be obtained and there is no out-of-band radiation caused by the clipping process.

Orthogonal frequency-division multiplexing (OFDM) waveform is known for its drawbacks that affect application in practice: high out-of-band (OOB) radiation and high peak-to-average power ratio (PAPR). In this paper, we propose a three-stage technique for the joint reduction of OOB radiation and PAPR, therefore minimizing the spectral regrowth after the power amplifier as well as signal distortion. In the first and the second stages, the OFDM data vector is partitioned into contiguous blocks that are naturally suited for PAPR reduction using partial transmit sequences (PTS). Since edge blocks/subcarriers have more impact on the OOB radiation, each edge block is further divided into smaller interleaved sub-blocks, and optimized phase rotations are applied to each sub-block to suppress the spectral sidelobes. Following the frequency domain techniques, optimum phase rotation for the time domain OFDM symbol is calculated to achieve smoother transition with the previous symbol, which further reduces the OOB spectrum. The proposed method improves the joint containment in frequency and power dimensions, along which the OFDM signal suffers from high spreading.