Statistical Peak to Average Power Ratio Bound

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.

Threshold-based piecewise companding transform for PAPR reduction in OFDM systems

OFDM (orthogonal frequency division multiplexing) systems are very sensitive to carrier frequency offset. Although frequency offset is generally compensated for by an automatic frequency control (AFC), residual frequency offset remains after the AFC. Moreover, OFDM signals are also affected by phase noise. Thus, a kind of phase tracking is needed to compensate for these effects. In an OFDM system such as IEEE 802.11a, a phase tracking scheme that uses pilot subcarriers to detect the phase rotation caused by residual frequency offset and phase noise is employed. However, the spectrum of the AFC output signal is shifted by residual frequency offset. That is, the detected phase is the composite phase of the pilot subcarrier and the adjacent subcarrier because of inter-carrier interference (ICI). The compensation based on the composite phase sometimes overcorrects or undercorrects the phase rotation. In this paper, we propose a phase tracking scheme using iterative estimation of residual frequency offset in OFDM systems. The proposed phase tracking scheme estimates residual frequency offset in the frequency domain, and compensates for it in the time domain. The compensation in the time domain mitigates the spectrum shift of the AFC output. Therefore, the proposed scheme can reduce ICI, and track phases more accurately than the conventional phase tracking scheme.

Low cost video sensors used for streaming video signals to help firefighters, require high bit rate due to uncompressed images. To increase spectral efficiency given a limited bandwidth, very high order constellations in high signal to noise ratio regimes can be used. However, noise is not the only factor effecting the high order constellations. These constellations are also sensitive to hardware impairments and system non‐linearities. Therefore, in this paper, the effect of carrier frequency offset (CFO) on the performance of an orthogonal frequency division multiplexing (OFDM) system with high order quadrature amplitude modulation (QAM) is studied. A closed form expression is derived for the maximum normalized residual CFO that an OFDM system with M ‐QAM constellation can resist to have an error free symbol detection. Finally, the suitability of common previous CFO estimation techniques such as the cyclic prefix based technique and the Moose technique in these systems are investigate. The results show that the maximum residual CFO that an OFDM system with M ‐QAM constellation can resist is proportional to the inverse of . The results also show that very large order QAM constellations such as 4096‐QAM are very sensitive to even small residual CFO values and their performance degrades, significantly. However, the bit error rate analysis indicate that the Moose CFO estimation technique can be used in these systems to compensate the CFO effect, accurately.

This paper presents an analysis of amplitude distortions happening in an orthogonal frequency division multiplexing (OFDM) signal at communication receivers. It is shown in this paper that the amplitude distortion causes inter-carrier interference (ICI) in an OFDM system. Simple but efficient solutions are proposed for combating different amplitude distortions and subsequent ICI cancellation. Simulation results in typical urban channel and Gaussian channel show that extra gains are obtained by introducing these techniques into an existing OFDM receiver system.

Signa1 modulation recognition (SMR) is an essential and challenging topic in orthogonal frequency-division multiplexing (OFDM) systems, and also it is the fundamental technique for signal detection and recovery. However, traditional feature extraction based SMR methods cannot effectively acquire the characteristics of the OFDM signals. Hence, the modulated OFD-M signal cannot be reliably identified. In this paper, we propose a deep learning (DL) based SMR method for recognizing OFDM signals, which is combined with a convolutional neural network (CNN) trained on in-phase and quadrature (IQ) samples. In the network model, the batch normalization (BN) layer and dropout layer are used to speed up model training and prevent overfitting, respectively. Three convolution layers with different convolution kernels perform well than traditional feature extraction methods in obtaining intrinsic properties of OFDM signals. The same number of multiple modulated signals are mixed and sent to the trained model for identification. Experiments are conducted to show that the method we proposed performs better than the traditional methods, mainly reflected in a higher probability of correct classification (PCC) and better consistency.

Peak-to-average power ratio (PAPR) one of the most important issues in orthogonal frequency division multiplexing (OFDM). Iterative clipping and filtering (CF) is a high efficiency technique to reduce PAPR in OFDM systems, but it needs numerous iterations to minimize the peak regrowth problem. This paper presents a new CF method which requires one iteration. The previous method needs 2K+1 IFFT/FFT blocks where K is iterations number. By using this algorithm, the number of FFT and IFFT operations have been decreased to three. The simulated results show that the QPSK modulated OFDM signal with 528 sub-carriers achieves a P APR reduction of 6.1 dB by passing the OFDM signal from white Gaussian noise channel with a good bit error rate performance at the receiver.

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.

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.

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.

ABSTRACTIn this paper, we study the impact of nonlinear distortion effects on adaptive orthogonal frequency division multiplexing systems. An analytical statistical characterisation of the transmitted signals, which is obtained by taking advantage of the Gaussian‐like nature of the orthogonal frequency division multiplexing signals when the number of subcarriers is high, is included. This statistical characterisation is used to evaluate loading algorithms in the presence of strong nonlinear distortion effects and to redefine loading algorithms taking into account nonlinear distortion issues. Copyright © 2011 John Wiley & Sons, Ltd.

In this study, the authors present a novel method to improve the performance of automatic repeat request (ARQ) protocol for multiple-input–multiple-output systems that use orthogonal frequency division multiplexing signalling by incorporating partial ARQ (PARQ) mechanism. As a typical ARQ frame has few number of errors, it is useful to retransmit partial sequence of symbols and recover from errors by consuming relatively low bandwidth. The observations from the first transmission and subsequent retransmission are used for joint detection. As a direct consequence of partial retransmission, the bandwidth and power efficiency of the overall system is improved considerably without substantial decrease in the performance. They achieve further bandwidth saving by omitting pilot sequence from the partial retransmission and acquire channel estimate in semi-blind fashion. Partial retransmission of the original information symbol sequence allows the authors to formulate second-order statistics based joint blind channel estimation problem by combining observations from two transmissions. Channel estimation ambiguity inherent to blind methods is resolved by combining cost functions of blind detection and least-square estimator. To evaluate efficacy of the proposed PARQ method, they compare throughput of chase-type hybrid-ARQ and the proposed PARQ methods.

Orthogonal Frequency Division Multiplexing (OFDM) technology has high spectrum efficiency and good anti-multipath interference capacity, but it has an inherent shortcoming that high peak-average power ratio (PAPR). Select Mapping (SLM) method is an effective algorithm to reduce Peak to Average Power Ratio (PAPR) of OFDM (Orthogonal Frequency Division Multiplexing) signal, and does not bring about any distortion of the signal. However, the biggest disadvantage of SLM method is that computational complexity is very large. In this paper, we propose a kind of improved SLM scheme which combines superimposed training sequence method, which using the a pre-set threshold method to select sub-optimization phase sequence as the phase factor in the procession of SLM method on signals. The simulation results show that the proposed scheme can not only effectively reduce the PAPR of system, not only reduce the computational complexity of the system, at the same time, there is no significant effect on system performance.

A definition of least cyclostationary order (LCO) is proposed based on the inner cyclic period of single carrier and orthogonal frequency division multiplexing (OFDM) signals. The LCOs of single carrier and OFDM signals are derived. Since the LCO has a relationship with the carrier frequency offset (CFO), a blind CFO estimation scheme for single carrier and OFDM signals can be proposed. The novel scheme is entirely blind without any priori information and is proved to be the same as cumulants estimation when the LCO is known. However, the new scheme is superior to the estimation based on cumulant when the LCO is unknown. The mean-square error of M-phase shift keying signals approaches the Cramer–Rao bound in additive white Gaussian noise (AWGN) channel. Simulation results are given to verify the effectiveness of the proposed blind estimation scheme in Rician fading channel and in AWGN channel.

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.