Nonlinear noise mitigation by decision-aided reconstruction in OFDM system

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.

In response to the inefficiency of power amplifier in conventional Orthogonal Frequency Division Multiplexing (OFDM) system, a low Peak-to-Average Power Ratio (PAPR) scenario can be obtained by implementing several PAPR reduction techniques. Partial Transmit Sequence (PTS) is a well-known instance to provide zero distortion for the system, while clipping is one of the simplest methods but it is sacrificing the error rate performance. In this work, Authors focused on analyzing the implementation of PTS and Palm Date Leaf clipping technique on OFDM system with 16-, 64-, 256-, and 1024-QAM under various Nakagami channel. In addition, the High-Power Amplifier (HPA) was also considered by using Solid State Power Amplifier (SSPA) model. It was found that linear HPA serves as the lower boundary for non-linear HPA, and system under high saturation level performs similarly. In physical properties, high saturation level is equivalent to higher power consumption in amplifier. Thus, optimal level was obtained by considering taking the one with moderate BER performance. After the system’s PAPR was reduced, the optimum saturation level of HPA was found to be 5 dB, 8 dB, 9 dB, and 11 dB for each Quadrature Amplitude Modulation (QAM) under Nakagami channel with m value of 1.5. However, this value was found to be ample for lower m value such as 1 or 0.7. In this case, the system required lower saturation level on the HPA for Nakagami channel with lower m value.

Orthogonal frequency division multiplexing (OFDM) system has been widely used for the high speed digital communication area and it is very promising for the next generation communication standard because of high data rate capability. However, OFDM system has inherent serious problem of high peak-to-average power ratio (PAPR) that makes the OFDM signal be distorted in the nonlinear HPA (high power amplifier). In this paper, CI (carrier interferometry)-OFDM system is considered to overcome this problem and is newly analyzed in the selective fading and narrow-band interference channel. CI-OFDM system distributes each parallel data to all sub-carriers in differently phase-rotated form. So, PAPR becomes lowered and it shows the frequency diversity effects. BER (bit error rate) performance is analyzed in the selective fading and narrow-band interference environment. From the simulation results, it is confirmed that CI-OFDM system calms down the high PAPR problem and CI-OFDM system is more robust than the ordinary OFDM system in the selective fading and narrow-band interference channel.

Orthogonal frequency division multiplexing (OFDM) system suffers from a high peak-to-average (power) ratio (PAR) which leads to power inefficiency in radio frequency section and large performance degradation of system due to the nonlinearity of high power amplifiers (HPA). In this paper, a new downlink transmission scheme is designed based on orthogonal periodic function (OPF) precoding to achieve low PAR and investigated for single user and multi-user multiple-input multiple-output wireless systems. It is shown (through mathematical analysis and computer simulations) that the proposed transmission scheme can provide a significant PAR reduction using decorrelation, phase-rotation and orthogonality properties of OPF precoding, while it does not change power spectral levels or error performances due to the unitary property when compared with the normal OFDM systems with linear HPA. The OPF precoding outperforms existing precoding schemes when nonlinear solid state power amplifier (SSPA) is considered with several practical values of input back-off (IBO). Computer simulations show that the OPF precoding can achieve 3.1 and 4 dB PAR gain, while 2.2 and 1 dB SNR gain for IEEE 802.11a and DVB-T systems respectively. Moreover, OPF precoding leads to a total degradation improvement from 0.13 to 1.53 dB for 16 QAM, considering an SSPA with IBO = 8---4 dB respectively. OPF precoding does not increase computational complexity when compared with the existing precoding methods. It is shown that the performance of the proposed precoding is independent of modulation schemes and can work for any number of subcarriers.

In this paper, a novel scheme of the weighted distortion-to-signal ratio (WDSR) based partial transmit sequence (PTS) is proposed to enhance the bit error rate (BER) performance in nonlinear distorted orthogonal frequency-division multiplexing (OFDM) systems, and its key idea is to employ the WDSR metric to predict the nonlinear distortion caused by high power amplifier (HPA). Furthermore, several alternative signals can be generated by the PTS technique, and the signal with the minimum WDSR is selected as the transmitted OFDM signal. Since the WDSR metric predicts the nonlinear distortion of OFDM systems, the BER performance of nonlinear distorted OFDM systems can be significantly improved. Simulation results show that the proposed WDSR-PTS scheme offers better BER performance than the conventional peak-to-average power ratio (PAPR) based PTS scheme.

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.

A three-dimensional (3D) orthogonal frequency division multiplexing (OFDM) system with peak-to-average power ratio (PAPR) reduction method for the wireless sensor networks (WSNs) is presented. The transmit power of wireless nodes in an ad hoc network is strictly limited. Thus, high PAPR of the 3D OFDM system is a possible drawback when it is considered as a physical layer transmission scheme for the WSNs. Here, we propose an improved partial transmit sequence (PTS) technique to reduce PAPR of the OFDM system with 3D modulation formats. In the proposed algorithm, the components of 3D signals are assigned to different subblocks using a diagonal rule (DR), increasing randomness of the signals in the disjoint subblocks forcibly. As a result, the proposed method reduces PAPR of the 3D OFDM system significantly without increase in computational complexity. Hence, the proposed algorithm makes the 3D OFDM system be a possible candidate for a physical layer transmission scheme in future WSNs.

왈시-하다마다 변환(Walsh-Hadamard Transform, WHT)을 적용한 OFDM(Orthogonal Frequency Division Multiplexing) 변조방법은 시스템의 PAPR(Peak-to-Average Power Ratio)을 줄여주고, 시스템의 BER(Bit Error Rate) 성능을 향상시키는 장점이 있다. 그러나 기존의 이러한 왈시-하다마다 변환에 기반한 OFDM 시스템은 여전히 비교적으로 높은 PAPR문제가 있다. 그러므로 본 논문에서는 DGT(Data Grouping Technique)이라고 부르는 기술을 제안하고, 이 기술과 왈시-하다마다 변환 기술을 적용하여 PAPR을 더욱 줄여주는 OFDM 시스템을 설계한다. 제안한 DGT기술은 WHT-OFDM뿐만 아니라 일반 OFDM에서 PAPR을 줄여주는 방법들 중에서 큰 단점이 되는 부가정보(side information)가 성능에 대해 독립성을 가진다는 특징이 있다. 컴퓨터 시뮬레이션을 통해 제안한 시스템의 유용성을 검사하고 성능을 검증하였다. The conventional OFDM (Orthogonal Frequency Division Multiplexing) modulation can be combined with WHT (Walsh-Hadamard Transform) to reduce PAPR (Peak-to-Average Power Ratio) and improve BER (Bit Error Rate) performance. However, this WHT-based OFDM system still suffers a relatively high PAPR. Therefore, we suggest a new technique, called DGT (Data Grouping Technique) and design an OFDM system employing it and WHT to further decrease PAPR without the BER performance degradation. h salient property of DGT is the independence of the side information which is inherently a principal drawback of the well-known PAPR reduction techniques for OFDM system as well as WHT-based OFDM. The simulation programs have been also performed to verify the validity of the proposed system.

The impact of high power amplifier (HPA) on the performance of orthogonal frequency division multiplexing (OFDM) based wireless systems using link adaptation (LA) is analyzed in this work. LA maximizes throughput while maintaining a target bit error rate (BER) at the receiver. The non linear behaviour of the HPA introduces distortion in the OFDM signal which has high peak to average power ratio (PAPR). It is found in this work that this causes LA schemes to fail to meet the target BER. It is shown in this work that to make the LA system satisfy the BER constraint, the signal to noise ratio thresholds for changing the adaptive modulation needs to be updated.

One of the severe drawbacks of orthogonal fre-quency division multiplexing (OFDM) is high Peak-to-Average Power Ratio (PAPR) of transmitted OFDM signals. During modulation the sub-carriers are added together with same phase which increases the value of PAPR, leading to more interference and limits power efficiency of High Power Amplifier (HPA), it’s requires power amplifier’s (PAs) with large linear oper-ating ranges but such PAs are difficult to design and costly to manufacture. Therefore, to reduce PAPR various methods have been proposed. As a promising scheme, partial transmit sequences (PTS) provides an effective solution for PAPR reduction of OFDM signals. In this paper, we propose a PAPR reduction method for an OFDM system with variation of phases based on PTS schemes and Solid State Power Amplifiers (SSPA) of Saleh model in conjunction with digital predistortion (DPD), in order to improve the performance in terms of PAPR, the HPA linearity and for the sake of mitigating the in-band distortion and the spectrum regrowth. The simulation results show that the proposed algorithm can not only reduces the PAPR significantly, but also improves the out-of-band radiation and decreases the computational complexity.

We propose a CCP (companding combined with predistorter) scheme that maintains BER (bit error rate) performance, while effectively reducing PAPR (peak-to-average power ratio) of OFDM (orthogonal frequency division multiplexing) signals. The proposed CCP scheme combines the conventional companding scheme proposed by the authors with the predistorter, in order to prevent degradation of BER performance caused by signal distortion from nonlinear property of the HPA (high power amplifier) and the compression property of the companding scheme. Hence, the proposed scheme effectively reduces the PAPR and simultaneously maintains the BER performance independent of nonlinear property of the HPAs. Simulation results show that the proposed scheme provides the lower total degradation for all the modulations, when compared with the conventional companding scheme proposed by Wang and the clipping scheme.

SummaryIn wireless telecommunication, one of the modulation approaches used is the orthogonal frequency division multiplexing (OFDM). Moreover, the high peak‐to‐average power ratio (PAPR) is the one notorious demerit in OFDM systems. Hence, the high power amplifier (HPA) is used in its linear region. Otherwise, the bit error rate (BER) will be increased. Several approaches are proposed in the wireless communications for reducing the PAPR issue. In this paper, we propose a hybrid Discrete Hartley Matrix Transform (DHMT) precoding using both selected mapping (SLM) and partial transmit sequence (PTS) PAPR reduction strategies. For the multicarrier modulation process, instead of Inverse Fast Fourier transform (IFFT) operation, the DHMT operation is used because of its low computational complexity. Based on multi‐chaotic, the time‐frequency domain encryption (TFDE) approach is adopted for physical layer security to confirm the security in data transmission. For enhancing the physical layer security, the proposed encryption system generates chaotic sequences based on Logistic maps and Lozi in the frequency and time domains together. In this study, the implementation of the DHMT‐based OFDM system is processed to reduce the maximum PAPR. Implementation is performed on the MATLAB platform, and the performances are calculated using complementary cumulative distribution function (CCDF), BER regards to signal‐to‐noise ratio (SNR), and the outputs are compared based on the computation time. However, compared with the existing models, the proposed model produced better PAPR minimization regarding SNR.

Based on superposition of signals in the time domain, we propose a new low-complexity scheme for the reduction of the peak-to-average power ratio (PAPR) in orthogonal frequency division multiplexing (OFDM) systems. The proposed scheme first generates signal candidates by combining an OFDM signal and its cyclically delayed versions with different delays and phases, and then selects the candidate signal with minimum PAPR. It is shown that the complexity of the proposed scheme is significantly lower than that of the selective mapping (SLM) at the cost of some degradation in the bit error rate (BER) performance and, at similar PAPR and coded BER performance, is lower than that of the low-complexity SLM proposed recently.

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.

Tone Reservation (TR) is a method used to reduce the Peak to Average Power Ratio (PAPR) in Orthogonal Frequency Division Multiplexing (OFDM) systems. In this paper, we assess the importance of considering an improved model of the power amplifier (PA) to accurately evaluate the performance of TR method based on Conjugate-Gradient algorithm. Simulation results were carried out in the context of WLAN IEEE 802.11a standard in presence of two memoryless models and nonlinear polynomial model with memory. These models are obtained by an experimental based method, including measurements and parameters identification with a 2.4 GHz class AB PA from RF Micro Devices. The evaluation results as well as the experimental comparison show that TR method considerably improves the transmission quality, in terms of Bit Error Rate (BER) and Error Vector Magnitude (EVM). These results highlight the importance of considering memory effects in PA modelling.