Peak-to-average Power Ratio Of Signal Research Articles

PAPR Reduction in VLC-OFDM System Using a Combination of Shuffled Frog Leaping Algorithm and Hill-Climbing Algorithm

Orthogonal frequency division multiplexing (OFDM) technique has been widely used in visible light communications (VLC) system (VLC-OFDM). To minimize the performance degradation of VLC-OFDM system caused by high peak-to-average power ratio (PAPR), we propose a SFLAHC-PTS technique to reduce the PAPR of signal in this paper. The proposed SFLAHC-PTS is an improved PTS technique which takes advantages of shuffled frog leaping algorithm and hill-climbing algorithm to optimize conventional PTS technique, reducing the computational complexity of conventional PTS technique. We compare SFLAHC-PTS technique with other PTS techniques on the CCDF performance, as well as computational amount to analyze the superiority of SFLAHC-PTS technique. The results show that the proposed technique can greatly reduce the computational load of conventional PTS technique and has better performance in reducing PAPR than GA-PTS, SFLA-PTS technique.

Mitigating NLD for Wireless Networks: Effect of Nonlinear Power Amplifiers on Future Wireless Communication Networks

Efficient utilization of limited bandwidth with high-data-rate transmission while serving a large number of users is a prime requirement for present and future wireless communication systems. To meet this rising demand, orthogonal frequency-division multiplexing (OFDM) and cooperative communication have emerged as promising solutions due to their robustness in severely degraded channel conditions, link reliability, and spectral efficiency. Both OFDM and cooperative systems have challenged RF front-end specifications such as bandwidth and power-efficiency requirements for end users as well as for the base station due to the high peak-to-average power ratio (PAPR). In present and future communication systems, the power amplifier (PA) is a key component at the transmitter. To obtain maximum power efficiency, the PA is operated near its saturation point, which leads to nonlinear distortion (NLD), which is further exaggerated due to the high PAPR of the input signal. This NLD is expected to increase in future fifth-generation (5G) communication networks, due to the use of large bandwidth at millimeter-wave (mmW) frequencies.

A Low Complexity Modified SLM and Companding based PAPR Reduction in Localized OFDMA

In this paper, a low complexity modified selective mapping (SLM) and companding based PAPR reduction scheme has been proposed to reduce the peak-to-average power ratio (PAPR) as well as computational complexity in localized orthogonal frequency division multiple access (OFDMA) system. In long term evolution (LTE) downlink, OFDMA has been employed as a multiple access technique and uplink uses single carrier frequency division multiple access. OFDMA systems preserve all the advantages and disadvantages of OFDM. One of the major drawbacks in OFDMA is high PAPR. In practice, SLM algorithms are most widely used to reduce PAPR due to its simple structure. However, it suffers by more computational complexity. To reduce complexity, in this paper three low complexity SLM structures are considered. But, PAPR reduction is poorer than conventional SLM (C-SLM). Therefore, to further reduce PAPR, μ-law companding scheme is employed along with low complexity SLM in L-OFDMA. To generate v candidate signal, first scheme employs one IFFT, scheme II uses two IFFT blocks and third proposed method uses (v/2 + 1) IFFT blocks. In the first two proposed methods, the time domain sequences available at the output of IFFTs are convolved with perfect sequences. In the third method, input data sequence is partitioned into two subblocks, first half of the input sequence is convolved with perfect sequence and C-SLM is applied to second half of the input data sequence. μ-law companding is a non-linear companding transform which increases the average power of transmitting signals, thereby reducing PAPR of OFDM signal. The simulation results show that, the proposed methods are well reducing PAPR with less computational complexity, so it is suitable for LTE downlink.

DFT-spread combined with clipping method to reduce the PAPR in VLC-OFDM system

Orthogonal frequency division multiplexing (OFDM) is an attractive technique to realize high data rate in light emitting diodes (LEDs)-based visible light communication (VLC). However, high peak-to-average power ratio (PAPR) of OFDM makes VLC-OFDM very sensitive to the nonlinearity of LEDs. In this paper, the discrete Fourier transform-spread (DFT-spread) combined with clipping method is proposed to reduce the PAPR of OFDM signal in VLC system. Combining simulation with experiment, a performance comparison is made among conventional OFDM, DFT-spread-OFDM, and clipped DFT-spread-OFDM with different clipping ratios (CRs) in a single LED-based VLC system. The experimental results show that the proposed clipped DFT-spread-OFDM method can effectively improve the system performance compared with the other two methods. At the optimum signal peak-to-peak (PTP) value, by using the clipped DFT-spread-OFDM scheme with CR at 8 dB, the bit error rate (BER) of the system can be reduced from 0.003 7 to 0.000 287.1

Implement PAPR Reduction in OFDM System Using SAS DCT with Companding

OFDM has been adopted as a standard for various high data rate wireless communication systems due to several benefits. One of the major drawbacks in OFDM system is its high Peak-to-Average Power Ratio (PAPR) of its transmitted signals thereby making transmitter amplifier to operate beyond its linear range of operation resulting in signal distortion. In this research work a simple method for reducing Peak-to-Average Power Ratio in OFDM is presented. The method is based on Discrete Cosine Transform (DCT) aided successive addition and subtraction (SAS) of data symbols within a single OFDM frame. Performance of the proposed method is evaluated and compared with the existing techniques. Joint reduction in PAPR by combining SAS preprocessed DCT technique and companding is also presented where system utilizes companding technique to further reduce the PAPR of the OFDM signal. Keywords: OFDM; PAPR; DCT; SAS; CompandingOFDM has been adopted as a standard for various high data rate wireless communication systems due to several benefits. One of the major drawbacks in OFDM system is its high Peak-to-Average Power Ratio (PAPR) of its transmitted signals thereby making transmitter amplifier to operate beyond its linear range of operation resulting in signal distortion. In this research work a simple method for reducing Peak-to-Average Power Ratio in OFDM is presented. The method is based on Discrete Cosine Transform (DCT) aided successive addition and subtraction (SAS) of data symbols within a single OFDM frame. Performance of the proposed method is evaluated and compared with the existing techniques. Joint reduction in PAPR by combining SAS preprocessed DCT technique and companding is also presented where system utilizes companding technique to further reduce the PAPR of the OFDM signal. Keywords: OFDM; PAPR; DCT; SAS; Companding

Decision-directed iterative methods for PAPR reduction in optical wireless OFDM systems

Abstract In this paper, we propose two iterative decision-directed methods for peak-to-average power ratio (PAPR) reduction in optical-orthogonal frequency division multiplexing (O-OFDM) systems. The proposed methods are applicable to state-of-the-art intensity modulation-direct detection (IM-DD) O-OFDM techniques for optical wireless communication (OWC) systems, including both direct-current (DC) biased O-OFDM (DCO-OFDM), and asymmetrically clipped O-OFDM (ACO-OFDM). Conventional O-OFDM suffers from high power consumption due to high PAPR. The high PAPR of the O-OFDM signal can be counteracted by clipping the signal to a predefined threshold. However, because of clipping an inevitable distortion occurs due to the loss of useful information, thus, clipping mitigation methods are required. The proposed iterative decision-directed methods operate at the receiver, and recover the lost information by mitigating the clipping distortion. Simulation results acknowledge that the high PAPR of O-OFDM can be significantly reduced using clipping, and the proposed methods can successfully circumvent the clipping distortions. Furthermore, the proposed PAPR reduction methods exhibit a much lower computational complexity compared to standard PAPR reduction methods.

PAPR Reduction and Performance Improvement in OFDM Systems using WHT-based Schemes

Orthogonal frequency division multiplexing (OFDM) is a robust and reliable multicarrier modulation scheme that has proven to be adequate for broadband communications. It is widely used in broadcasting and broadband wireless and wireline systems. However, in scenarios where the communication devices are power-limited, such as mobile and satellite communications, OFDM has not been massively used or even not used at all. For instance, OFDM is used only in downlink of 4G networks, while the uplink uses single carrier frequency division multiplexing. One of the main culprits of this is the high peak to average power ratio (PAPR) of the OFDM signal. Reducing the PAPR of the OFDM signals is important for a large variety of application. Several PAPR reduction techniques for OFDM have been proposed recently.The aim of this paper is to present a tutorial about a set of algorithms based on Walsh-Hadamard transform (WHT) for reducing the PAPR of the OFDM symbols. We also propose a new technique, named selective mapping based on WHT without extended information (SLM-WHT-WEI), which does not convey the explicit information to the receiver. We will show that the approaches based on WHT can also improve the OFDM symbol error rate performance over frequency-selective channels. Different schemes based on the properties of the WHT are presented and compared, assuming linear and non-linear channels. The PAPR reduction performance analysis shows that the PAPR can be effectively reduced while good performance in terms of symbol error rate can be achieved even in severely constrained channel conditions.

PAPR analysis for OFDM visible light communication.

Orthogonal frequency-division multiplexing (OFDM) is a practical technology in visible light communication (VLC) for high-speed transmissions. However, one of its operational limitations is the peak-to-average power ratio (PAPR) of the transmitted signal. In this paper, we analyze the PAPR distributions of four VLC OFDM schemes, namely DC-biased optical OFDM (DCO-OFDM), asymmetrically clipped optical OFDM (ACO-OFDM), pulse amplitude modulated discrete multitone (PAM-DMT), and Flip-OFDM. Both lower and upper clippings are considered. We analytically derive the complementary cumulative distribution functions (CCDFs) of the PAPRs of the clipped VLC OFDM signals, and investigate the impact of lower and upper clippings on PAPR distributions. Our analytical results, as verified by numerical simulations, provide useful insights and guidelines for VLC OFDM system designs.

Dual-Stream Transceiver Structure With Single Antenna for Phase-Modulated OFDM

Constant envelope orthogonal frequency-division multiplexing (OFDM) can achieve 0-dB peak-to-average power ratio (PAPR) by transforming the OFDM signal to a constant envelope signal. However, its spectral efficiency is less than half of the OFDM. In this letter, a dual-stream transceiver structure with single antenna is proposed to increase the spectral efficiency. At the transmitter, the structure based on phase shifting is proposed to transmit two data streams simultaneously. At the receiver, the joint demodulation structure based on Taylor series expansion is proposed to separate the data streams and eliminate the need for a phase demodulator. The mathematical analysis reveals that the statistical PAPR of the baseband signal is 3 dB. The bit error rate performance is evaluated with additive white Gaussian noise channel and multipath fading channel under the condition of ideal power amplifier and solid-state power amplifier. Simulation results show that the proposed structure can improve the spectral efficiency and is robust against multipath fading.

Asymmetric peak to average power ratio impacts on direct‐detected optical OFDM transmission link

ABSTRACTIn this article, the impact of asymmetric peak to average power ratio (PAPR) of orthogonal frequency division multiplexing (OFDM) signal is investigated in direct detection OFDM transmission for the first time. The asymmetric PAPR is produced due to the positive definiteness of direct optical OFDM modulation. It gets bigger and bigger due to the generation of different time delay of each OFDM subcarrier, which is caused by chromatic dispersion. The performance of direct detection optical OFDM link in the presence of asymmetric PAPR is evaluated measuring error vector magnitude (EVM) of quadrature phase shift keying (QPSK) and 16‐qudrature amplitude modulation (QAM) symbols according to the optical transmission length and the transmission rate; 14% EVM (bit error rate of 10−3) of QPSK symbol is observed at the optical transmission length of 400 km despite the usage of channel equalization as well as the insertion of cyclic prefix when the asymmetric PAPR of input optical OFDM signal is above 25 dB. © 2016 Wiley Periodicals, Inc. Microwave Opt Technol Lett 58:2662–2665, 2016

Performance Improvement Techniques for OFDM system using Software Defined Radio

Improved spectral and energy efficiency are two key requirements for the next generation (5G) wireless communication systems. The inefficiency and non-linearity of traditional power amplifiers (PA) pose significant challenges to meet these requirements, especially for multicarrier modulation signals with high peak to average power ratio (PAPR). Orthogonal frequency division multiplexing (OFDM) is currently the most widely used multi carrier modulation technique; it has been adopted in many wireless communication standards including IEEE 802.11, 802.16, 3GPP Long Term Evolution and WiMAX. When a high PAPR signal process through a nonlinear power amplifier (PA), intermodulation distortion is generated, creating out-of-band emission that can interfere with other transmission in adjacent bands. In addition, in-band distortion, which degrades the bit error rate performance, occurs. Hence, I have addressed these problems by employing four different PAPR reduction techniques such as Phase modulation, Rail clipping, Sample and Hold approach and Threshold methods based on amplitude clipping. For practical proof of the proposed concepts, I have chosen software defined radio as an experimental setup that employs USRP N210 as hardware and GNU Radio as software.

An Efficient Bayesian PAPR Reduction Method for OFDM-Based Massive MIMO Systems

We consider the problem of peak-to-average power ratio (PAPR) reduction in orthogonal frequency-division multiplexing (OFDM) based massive multiple-input multiple-output (MIMO) downlink systems. Specifically, given a set of symbol vectors to be transmitted to $K$ users, the problem is to find an OFDM-modulated signal that has a low PAPR and meanwhile enables multiuser interference (MUI) cancelation. Unlike previous works that tackled the problem using convex optimization, we take a Bayesian approach and develop an efficient PAPR reduction method by exploiting the redundant degrees of freedom of the transmit array. The sought-after signal is treated as a random vector with a hierarchical truncated Gaussian mixture prior, which has the potential to encourage a low PAPR signal with most of its samples concentrated on the boundaries. A variational expectation-maximization (EM) strategy is developed to obtain estimates of the hyperparameters associated with the prior model, along with the signal. In addition, the generalized approximate message passing (GAMP) is embedded into the variational EM framework, which results in a significant reduction in computational complexity of the proposed algorithm. Simulation results show our proposed algorithm achieves a substantial performance improvement over existing methods in terms of both the PAPR reduction and computational complexity.

A linear receiver for visible light communication systems with phase modulated OFDM

In the orthogonal frequency-division multiplexing (OFDM) systems for visible light communication (VLC), the peak-to-average power ratio (PAPR) of OFDM signals is the primary concern of high-speed data transmission. In order to get low PAPR signals and reduce the influence of nonlinearity of the light-emitting diode (LED), a phase modulated OFDM (PM-OFDM) system is developed and a linear receiver is presented. Unlike the conventional angle detection receiver implemented by arctangent calculator, the linear receiver has lower computation complexity and is immune to the threshold effect. Simulation results indicate that the proposed PM-OFDM obtains significant performance gains over DC-biased optical OFDM (DCO-OFDM) and precoded OFDM.

A Simple OFDM Scheme for VLC Systems Based on u-Law Mapping

A simple orthogonal frequency division multiplexing (OFDM) scheme termed ${\mu }$ -OFDM is proposed for visible light communication (VLC). In this scheme, the peak-to-average power ratio (PAPR) reduction technique, ${\mu }$ -law companding, is first introduced in VLC systems to achieve the required signal format for VLC transmission. Due to the inherent characteristics of the companding operation, low PAPR signals are obtained in the scheme. Compared with most of the unipolar optical OFDM schemes, such as asymmetrically clipped optical OFDM scheme, ${\mu }$ -OFDM doubles the spectral efficiency. Furthermore, this scheme shows significant energy advantages over direct-current biased optical OFDM scheme and polar OFDM scheme. To the best of our knowledge, this is the first design of a unipolar optical OFDM scheme, which is able to achieve both high spectrum and energy efficiency under a constraint of the dynamic range of the light-emitting diodes.

Minimization of PAPR in OFDM Using SFBC and MIMO

Peak-to-Average Power Ratio (PAPR) reduction is one of the main key factors in orthogonal frequency division multiplexing (OFDM) systems. From the various existing PAPR reduction techniques, Neural Network (NN) has been one of the efficient and powerful techniques in reducing the PAPR due to its good generalization properties with flexible modeling and learning capabilities. In this paper, we propose a new method that uses NNs trained on the active constellation extension (ACE) signals to reduce the PAPR of OFDM signals. It employs a receiver NN unit, at the OFDM receiver side for achieving significant bit error rate (BER) improvement with low computational complexity. To reduce the time complexity SFBC (Space frequency block coding) block is used in NN and multiple input and multiple output (MIMO) technique is introduced.

PAPR and PICR Reduction of OFDM Signals with Clipping Noise-based Tone Injection Scheme

Orthogonal frequency-division multiplexing (OFDM) suffers from a high peak-to-average power ratio (PAPR). Tone injection (TI) extends the original constellation to several equivalent points so that these extra freedom degrees can be exploited for the PAPR reduction. However, optimal TI requires an exhaustive search over all possible constellations, which is a hard discrete optimization problem. To address this problem, a novel TI scheme that uses the clipping noise to find the optimal equivalent outer ring extended constellations (ECs) and hexagonal constellations (HCs) is proposed. By minimizing the mean rounding error of the clipping noise and possible equivalent constellations, the proposed scheme can easily determine the size and position of the optimal equivalent constellations. Second, a new TI scheme is also introduced to reduce the nonlinear distortion in the presence of a power amplifier (PA). This scheme takes the root-mean-square peak-interference-to-carrier-ratio (RMS-PICR) reduction as the target to obtain a better bit error rate (BER) performance. Simulation results show that, to achieve a considerable system performance, the proposed TI schemes only need 18 fast Fourier transforms (FFTs), whereas other TI and partial transmit sequence (PTS) schemes need hundreds of FFTs.

PAPR Influence Analysis in 8QAM-OFDM Optical Access Systems

In this article, the peak to average power ratio (PAPR) performance of 8 quadrature amplitude modulation-orthogonal frequency division multiplexing (8QAM-OFDM) optical signals has been researched in broadband optical access system. The complementary cumulative distribution functions (CCDFs) are analyzed of two different 8QAM-OFDMsignals with 16, 32, 64, 128, 256, 512 sub- carriers by simulation. The simulation results show that, with the increase of the number of subcarrier, the PAPR value becomes higher. When the numbers of subcarrier are16 and 512, the PAPR of 8QAM-OFDM optical signals are smaller than 5.2 dB and 5.3 dB respectively. Hence, the number of sub-carriers should be chosen according to practical application.

A PAPR-Aware Dual-Mode Subgigahertz CMOS Power Amplifier for Short-Range Wireless Communication

A peak-to-average power ratio (PAPR)-aware dual-mode power amplifier (PA) for short-range wireless communication in the subgigahertz band is proposed in this brief. By carefully choosing the bias, the dual-mode PA achieves the measured output P1 dB (OP1 dB) of 13.6 dBm with a PAE of 25.5%. Furthermore, a dynamic load modulation network is utilized to optimize the PA's efficiency at back-off power. A power-control loop is proposed to detect the input signal PAPR in real time and flexibly reconfigure the PA's operation modes. With these proposed techniques, the PAE has been improved by ×2.61 at 7-dB back-off power. The measurement shows that the subgigahertz-band PA archives an adjacent channel leakage ratio (ACLR1) of −37.3 dBc and an average/peak error vector magnitude of −30.4 dB/−20.5 dB at 8.9-dBm output power for ∼5-dB-PAPR 16-quadrature-magnitude-modulation LTE signals with 5-MHz bandwidth with the power control loop enabled. The PAPR-aware dual-mode PA, powered by a 2-V supply, occupies a 2.52-mm2 die area in a 180-nm CMOS.

60 GHz Millimeter-wave Bottom-Layer Solutions: Multiplexing Access, Energy Awareness, and Peak-to-Average-Power Ratio

A clear trend shows that cells are smaller, more homogeneously distributed, higher frequency oriented, and more energy conscious. This points toward wireless systems that implement millimeter-wave modulation; therefore, improving its usability is essential for the communication systems evolution. The proposed bottom-layer solutions are (1) a variable slot time multiplexing access technique with an energy-conservation feature that supports self-sustainability, and (2) SC-FDMA as the technology implemented at the physical layer to minimize the peak-to-average-power ratio (PAPR) of the system. It is shown that the multiplexing protocol has advantages over TDMA, self-sustainability is feasible, and SC-FDMA reduces the PAPR of the modulated signal.

Reducing PAPR of SC-FDMA Signals through Simple Amplitude Predistortion

A novel peak-to-average power ratio (PAPR) reduction method is proposed for single-carrier frequency-division multiple access (SC-FDMA) signals. The proposed method deliberately distorts the amplitude values of a few of the complex modulated symbols that cause peaks beyond a predetermined threshold in the samples of the output signal. The method then marks the location indices of the distorted symbols by using a pilot block at the transmitter without transmitting side information. At the receiver, the method is then able to recover the distorted amplitude values through the marked location indices. Computer simulation results show that when compared to conventional SC-FDMA signals, the proposed scheme can effectively reduce the PAPR of SC-FDMA signals with asymptotically consistent bit error rate (BER) performance.