Peak-to-average Power Ratio Of OFDM Signal Research Articles

Low complexity partition-recombined SLM scheme for reducing PAPR in coherent optical OFDM systems

High peak-to-average power ratio (PAPR) remains the main challenge of coherent optical orthogonal frequency division multiplexing (CO-OFDM) systems. Selective mapping (SLM) is a well-known effective PAPR reduction technique, but it suffers from high computational complexity. To reduce the PAPR of OFDM signals, a low-complexity, partition-recombined SLM (PRSLM) scheme is proposed. The PRSLM scheme can generate more candidate signals than that of the conventional-original SLM (COSLM) scheme. The real and imaginary components of time-domain symbols are first partitioned, and then recombined to generate new candidate signals, which reduces computational complexity significantly. A 40-GBaud single-polarization CO-OFDM transmission system is set up to evaluate the performance of the PRSLM scheme. Simulation results show that the proposed scheme achieves 61.9% reduction in complex multiplication complexity, and 60.3% reduction in addition complexity compared with the COSLM scheme when the FFT size is 128. Furthermore, the proposed scheme achieves a similar PAPR reduction performance to the COSLM scheme without bit error rate degradation. In a nutshell, the PRSLM scheme improves noise tolerance and implementation efficiency of high-speed optical communication as well as alleviates nonlinear impairments.

PAPR Reduction in OFDM Signals by Self-Adjustment Gain Method

OFDM in 5G wireless communication networks has the advantages of a high transmission volume and data rate. However, the problem of a high peak-to-average power ratio (PAPR) of OFDM signals may lead to serious performance degradation and distortion in the high-power amplifier at the transmitter. In this paper, with the clipping process, the self-adjustment gain (SAG) method is proposed, to tune up the positions of the clipped signals, for reducing the PAPR of OFDM signals without increasing the error probability. The distance between the estimated and clipped signal points in the signal space is measured. An updated process is developed to produce the new signal points based on the measured distance and the self-adjustment gain that is obtained from the clipping noise power and measurement power. The simulation results show that for QPSK/OFDM, SAG reduces up to 2 dB and 0.7 dB more PAPR than ACE with one and three iterations, respectively. For 16QAM/OFDM, SAG reduces up to 1.3 dB and 0.5 dB more PAPR than ACE with one and three iterations, respectively. SAG also outperforms the active constellation extension, with the projection onto convex sets (ACE-POCS) and gradient project (SGP) methods in first two iterations. Hence, the proposed method really reduces the PAPR value more effectively, within an acceptable error probability, and its computational complexity is also much lower in comparison with those methods based on the active constellation extension (ACE) with iterations.

On Optimizing the PAPR of OFDM Signals With Coding, Companding, and MIMO

One main disadvantage of the multiple-input-multiple-output orthogonal frequency-division multiplexing (MIMO-OFDM) system is that the signals transmitted on each antenna may experience high peak-to-average-power ratio (PAPR). We will present a new hybrid PAPR reduction technique that combines and optimizes three methods, namely convolutional code, successive suboptimal cross-antenna rotation and inversion (SS-CARI), and iterative modified companding and filtering. The results for the hybrid PAPR reduction technique show that this scheme significantly reduces the PAPR compared with SS-CARI alone; it can improve the bit error rate to levels better than what obtains with the space–time block coding MIMO-OFDM system, and the spectral splatter due to companding is also controlled by the use of frequency-domain filtering. In addition, it is a flexible technique in which the net gain can be optimized based on the requirements of scheme parameters, such as the code rate, the constraint length of the convolutional code, the number of subblocks for SS-CARI, and the companding parameters.

Interleaving Technique Implementation to Reduce PAPR of OFDM Signal in Presence of Nonlinear Amplification with Memory Effects

In OFDM systems, peak-to-average power ratio (PAPR) reduction of the signal is one of the main challenges that need to be overcome in order to use the transmitter in an efficient manner. As one of attractive techniques, interleaving can be used in PAPR reduction for multicarrier signals without spectrum distortion. In this paper, the authors propose to extend the possibilities of interleaving to improve PAPR reduction, to use a new coding of interleaver keys at the transmitter and a robust decoding procedure at the receiver. In order not to degrade the data rate, the use of null subcarriers to transmit side information to the receiver is proposed and evaluated. Simulation results in the context of the WLAN 802.11a standard in the presence of a nonlinear power amplifier model with memory, show a reduction of PAPR of approximately 5.2 dB, and an improvement of bit error rate and error vector magnitude of about 2 decades and 4% respectively, while respecting the spectral mask specification.

Reduction of Peak-to-Average Power Ratio of OFDM System Using Triangular Distribution Based Modified Companding Scheme

ABSTRACTOrthogonal frequency division multiplexing (OFDM) is an attractive multicarrier modulation technique, which is widely introduced in the present as well as future broadband wireless communication systems due to high data rate, high spectral efficiency, and robustness to the multipath fading channel. Despite its popularity, OFDM system suffers from the critical drawback of large peak-to-average power ratio (PAPR) of the transmitted signal, which may lead to undesired spectral re-growth, poor power efficiency, and overall performance degradation. In this paper, we propose an efficient non-linear companding transform (NCT) technique for reducing the PAPR of OFDM signals. Our proposed scheme coined as triangular distribution (TR) based companding offers an improved bit error rate (BER), better design flexibility, and more degrees of freedom while reducing PAPR effectively compared to the other existing companding schemes. The PAPR reduction performance of our proposed scheme for the different modulation approaches like QPSK, 4QAM, 16QAM, 32QAM, and 64QAM is also presented here. The theoretical analysis of the proposed scheme and comparative study with the existing algorithms are presented. Simulation results demonstrate that our proposed companding scheme can substantially outperform the existing NCT techniques in terms of PAPR reduction, BER performance, and bandwidth efficiency for each of the modulation approaches under different noisy channel conditions.

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.

Performance Comparison of DFT-Spread and Pre-Equalization for 8 × 244.2-Gb/s PDM-16QAM-OFDM

In this paper, we experimentally compared the performance of discrete-Fourier-transform spread (DFT-spread) and pre-equalization in a 244.2-Gb/s polarization-division-multiplexed 16-ary quadrature amplitude-modulation orthogonal frequency-division multiplexing (PDM-16QAM-OFDM) transmission system. The pre-equalization is effective to overcome the high-frequency power attenuation in the channel. However, the acquisition of static channel response for pre-equalization is really complicated and the peak-to-average power ratio (PAPR) of the signal after pre-equalization even becomes a little higher. The DFT-spread can be applied to simultaneously resist high-frequency power attenuation and reduce the PAPR of OFDM signal. The experimental results also show that one band DFT-spread demonstrates the best narrow optical filtering tolerance. The transmission distance for 8 × 244.2-Gb/s wavelength-division-multiplexing (WDM) PDM-16QAM-OFDM at the soft-decision forward-error correction threshold of 2.4×10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-2</sup> is 2× 420 km based on pre-equalization, while extended to over 3×420 km based on one band DFT-spread, which well illustrates one band DFT-spread is more efficient for high-bandwidth coherent WDM-OFDM system.

Reduction PAPR of OFDM Signals by Combining Grouped DCT Precoding with PTS

The high peak-to-average power ratio (PAPR) is one of the serious problems in the application of OFDM technology. In this paper, an improved partial transmit sequence (PTS) scheme based on combining the grouped discrete cosine transform (DCT) with PTS technique is proposed. In the proposed scheme, the adjacent partitioned data are firstly transformed by a DCT into new modified data. After that the proposed scheme utilizes the conventional PTS technique to further reduce the PAPR of the OFDM signal. The performance of the PAPR is evaluated using a computer simulation. The simulation results indicate that the proposed scheme may improve the PAPR performance compared with the conventional PTS scheme, the grouped DCT scheme, and original OFDM respectively.

PAPR Reduction in OFDM using Active and Non-Active Channels

According to the request of advance communication field there should be high data rate in addition to both power efficiency and lower bit error rate. This request of high data rate can be achieved by the multi carrier modulation scheme using the OFDM technique. But the great drawback of the OFDM technique is its high peak to average power ratio (PAPR). High PAPR reduces OFDM signals by driving the analog amplifier to work in the nonlinear region, changing this way the signal and making the amplifier to consume more power. To reduce the PAPR methods exist which adjust or present new signals to battle large signal peaks. The methods which use data carrying channels are called active channel methods and which use redundant channel are called non active channel methods. This work deals with reduction of the PAPR of OFDM signal using both Active and Non Active Channels. Clipping technique has been applied to active channels and Tone reservation has been applied to Non Active Channels. By using both channels we can get considerable reduction in PAPR.

Reducing the PAPR of OFDM Signals Based on SCHT Precoding

The precoding scheme based on real Hadamard transform is an effective and flexible way for reducing the peak-to-average power ratio (PAPR) of OFDM signals. However, the reduction capacity of PAPR is limited for real Hadamard transform method. In this paper, the new scheme based on complex Hadamard transform is proposed. The simulation results indicate that the proposed scheme may obtain a 1.2 dB PAPR reduction of OFDM signal with only moderate complexity compared with the real Hadamard transform.

Companding transform based SPM compensation in coherent optical OFDM transmission

We demonstrate a mitigation of fiber nonlinearity based on μ-law companding transform in coherent optical OFDM transmissions. High peak-to-average power ratio (PAPR) increases fiber nonlinear impairments caused by the Kerr effect in optical fiber. The μ-law companding modifies amplitude profile of OFDM signal with time domain signal processing, which reduces high PAPR of OFDM signal. The effects of companding parameter on noise enhancement and PAPR variation are presented. The impacts of companding transform on system performances are evaluated in a single polarization system as well as polarization multiplexed system. The resolution of analog-to-digital converter (ADC), dispersion map of transmission link, and launch power tolerance are also considered. The results of bit-error-rate (BER) measurements show that the μ-law companding improves OSNR margin over 5.5 dB after transmission of 1,040 km over SMF.

REDUCING PAPR OF OFDM BASED WIRELESS SYSTEMS USING COMPANDING WITH CONVOLUTIONAL CODES

OFDM is a promising broadband technique. However, the implementation disadvantage of OFDM is Peak-to-Average Power Ratio (PAPR) which outweighs all the potential benefits of OFDM. In this paper, a new scheme will be introduced, that combines selective mapping and companding technique to reduce PAPR. However, companding technique is a distortion technique but by using convolutional codes with companding also improves BER performance of the OFDM system. It also removes the disadvantage of SLM technique of extra side information i.e. this technique does not require any side information unlike in conventional SLM. By considering the example of OFDM with BPSK modulation, it is shown in simulation results that the proposed scheme performs well in both reducing PAPR and improving BER performance without the need of any side information. It has been calculated that PAPR of OFDM signal can be reduced by 5dB over the original system with the proposed scheme.

Reduction PAPR of OFDM Signals by Combining SLM with DCT Transform

One of main disadvantage of OFDM is high peak-to-average power ratio (PAPR). In this paper, two effective PAPR reduction schemes are proposed. These techniques combine DCT and SLM techniques. The scheme 1 is composed of the DCT followed by SLM technique, and the DCT is used followed by conventional SLM in proposed scheme 2. Simulation results show that the proposed schemes can obtain significant PAPR reduction performance with that of ordinary SLM techniques.

A novel PAPR reduction with trellis shaping for NC-OFDM in cognitive radio

In this paper, trellis shaping is applied to reducing the Peak-to-Average Power Ratio (PAPR) of NC-OFDM signals due to the fact that the total number of active subcarriers and their locations might change continuously in a dynamic spectrum access network. A new branch metric of trellis shaping is proposed which reduces the PAPR of OFDM signals through minimizing the variance of the power by VA decoder. The overall performance considerably depends on the type of signal mapping, and therefore a new type of 64QAM mapping method is designed. Simulation results show that this scheme significantly reduces the PAPR. Finally, a significant phenomenon is demonstrated that the PAPR of NC-OFDM signals in which the deactivated carriers is distributed in the Bernoulli distribution has better performance than that of OFDM signals.

The continuous-time peak-to-average power ratio of OFDM signals using complex modulation schemes

Computing the continuous-time peak-to-average- power ratio (PAPR) of OFDM signals is computationally challenging. The pioneering work by Tellambura applies only to OFDM signals using real-valued modulation schemes. In this paper, a practical technique for evaluating the continuous-time PAPR of OFDM signals using complex modulation is presented. Using the proposed scheme, it is confirmed that the four-time oversampled discrete-time PAPR is a good approximation of the continuous-time PAPR even for complex OFDM signals. Furthermore, the proposed scheme is employed to verify some existing analytical bounds on continuous PAPR in the literature.