scholarly journals Extreme Learning Machines to Combat Phase Noise in RoF-OFDM Schemes

Electronics ◽  
2019 ◽  
Vol 8 (9) ◽  
pp. 921 ◽  
Author(s):  
David Zabala-Blanco ◽  
Marco Mora ◽  
Cesar A. Azurdia-Meza ◽  
Ali Dehghan Firoozabadi
Keyword(s):  
Phase Noise ◽  
Orthogonal Frequency Division Multiplexing ◽  
Transmission Rate ◽  
Additive White Gaussian Noise ◽  
Laser Linewidth ◽  
Ofdm Systems ◽  
Classification Problems ◽  
Ofdm Symbol ◽  
Fiber Dispersion ◽  
The Real

Radio-over-fiber (RoF) orthogonal frequency division multiplexing (OFDM) systems have been revealed as the solution to support secure, cost-effective, and high-capacity wireless access for the future telecommunication systems. Unfortunately, the bandwidth-distance product in these schemes is mainly limited by phase noise that comes from the laser linewidth, as well as the chromatic fiber dispersion. On the other hand, the single-hidden layer feedforward neural network subject to the extreme learning machine (ELM) algorithm has been widely studied in regression and classification problems for different research fields, because of its good generalization performance and extremely fast learning speed. In this work, ELMs in the real and complex domains for direct-detection OFDM-based RoF schemes are proposed for the first time. These artificial neural networks are based on the use of pilot subcarriers as training samples and data subcarriers as testing samples, and consequently, their learning stages occur in real-time without decreasing the effective transmission rate. Regarding the feasible pilot-assisted equalization method, the effectiveness and simplicity of the ELM algorithm in the complex domain are highlighted by evaluation of a QPSK-OFDM signal over an additive white Gaussian noise channel at diverse laser linewidths and chromatic fiber dispersion effects and taking into account several OFDM symbol periods. Considering diverse relationships between the fiber transmission distance and the radio frequency (for practical design purposes) and the duration of a single OFDM symbol equal to 64 ns, the fully-complex ELM followed by the real ELM outperform the pilot-based correction channel in terms of the system performance tolerance against the signal-to-noise ratio and the laser linewidth.

scholarly journals Performance Enhancement of Coherent Optical OFDM System Using LMS Algorithm

2020 ◽  
Vol 1 ◽  
pp. 1-5
Author(s):  
Manisha Bharti
Keyword(s):  
Phase Noise ◽  
Bit Error Rate ◽  
Error Rate ◽  
Orthogonal Frequency Division Multiplexing ◽  
Performance Enhancement ◽  
Lms Algorithm ◽  
Frame Structure ◽  
Least Mean Square ◽  
Ofdm Systems ◽  
Ofdm System

Instability of the local oscillator causes phase noise – a phenomenon that is a disadvantage and is considered to be a major obstacle in the functioning of coherent optical orthogonal frequency division multiplexing (CO-OFDM) systems. An attempt has been made in this paper to reduce the effects of common phase errors generated by phase noise. In this paper, a least mean square (LMS) based algorithm is proposed for estimation of phase noise. Using this proposed algorithm, the major problem of phase ambiguity caused by cycle slip is avoided and the bit error rate is greatly improved. Further, there is no requirement for modifying the frame structure of OFDM using this algorithm. A CO-OFDM system with the 8-PSK technique is used to implement the algorithm concerned. Furthermore, the algorithm, using the 8-PSK modulation technique, is analyzed and compared with the existing QPSK technique and with other algorithms. The investigations reveal that 8-PSK outperforms existing LMS algorithms using other techniques and significantly reduces the bit error rate.

scholarly journals A Radon Slantlet Transforms Based OFDM System Design and Performance Simulation under Different Channel Conditions

2012 ◽  
Vol 2012 ◽  
pp. 1-8 ◽  
Author(s):  
Abbas Hasan Kattoush
Keyword(s):  
Radon Transform ◽  
Spectral Efficiency ◽  
Fading Channel ◽  
Orthogonal Frequency Division Multiplexing ◽  
Additive White Gaussian Noise ◽  
Mapping Technique ◽  
Intercarrier Interference ◽  
Ofdm Systems ◽  
Ofdm System ◽  
Channel Parameters

Due to its good orthogonality, slantlet transform (SLT) is used in orthogonal frequency division multiplexing (OFDM) systems to reduce intersymbol interference (ISI) and intercarrier interference (ICI). This eliminates the need for cyclic prefix (CP) and increases the spectral efficiency of the design. Finite Radon transform (FRAT) mapper has the ability to increase orthogonality of subcarriers, is nonsensitive to channel parameters variations, and has a small constellation energy compared with conventional fast-Fourier-transform- (FFT-) based OFDM. It is also able to work as a good interleaver, which significantly reduces the bit error rate (BER). In this paper both FRAT mapping technique and SLT modulator are implemented in a new design of an OFDM system. The new structure was tested and compared with conventional FFT-based OFDM, Radon transform-based OFDM, and SLT-based OFDM for additive white Gaussian noise (AWGN) channel, flat fading channel (FFC), and multipath selective fading channel (SFC). Simulation tests were generated for different channel parameters values. The obtained results showed that the proposed system has increased the spectral efficiency, reduced ISI and ICI, and improved BER performance compared with other systems.

A Modified DFT-Based Channel Estimator Using Dual-Tree Complex Wavelet Denoising for OFDM Systems with Null Carriers

2014 ◽  
Vol 668-669 ◽  
pp. 1215-1218
Author(s):  
Wei Cai Liu ◽  
Yuan An Liu ◽  
Kai Ming Liu ◽  
Yu Meng Guo
Keyword(s):  
Orthogonal Frequency Division Multiplexing ◽  
Additive White Gaussian Noise ◽  
Wavelet Denoising ◽  
Frequency Division ◽  
Ofdm Systems ◽  
Denoising Method ◽  
Performance Simulation ◽  
Channel Estimator ◽  
Suppression Method ◽  
Complex Wavelet

In this paper, we present a modified discrete Fourier transform (DFT)-based channel estimator for orthogonal frequency-division multiplexing (OFDM) systems with null carriers. Due to the channel leakage, the conventional DFT-based estimator has the problem of error floor. In order to suppress the leakage, we adopt the optimal leakage suppression method. Moreover, a novel denoising method based on dual-tree complex wavelet is proposed to further improve the performance. Simulation results show that the proposed channel estimator can effectively overcome the performance degradation caused by the leakage and additive-white gaussian noise (AWGN).

scholarly journals Performance evaluation of high mobility OFDM channel estimation techniques

2020 ◽  
Vol 10 (3) ◽  
pp. 2562
Author(s):  
Maryam K. Abboud ◽  
Bayan M. Sabbar
Keyword(s):  
Orthogonal Frequency Division Multiplexing ◽  
Performance Test ◽  
High Mobility ◽  
Doppler Frequency ◽  
Multipath Fading ◽  
Least Square ◽  
Mobile Systems ◽  
Estimation Methods ◽  
Ofdm Systems ◽  
Ofdm Symbol

In wireless communication, Orthogonal Frequency Division Multiplexing (OFDM) has been adopted due to its robustness to multipath fading and high data rate transmissions. At the other hand, the performance of OFDM systems severely degraded due to multi-path fading and Doppler frequency shifts in mobile systems, which causes inter-carrier-interference (ICI). Thus, Estimation of channel parameters is required at the receiver using a pre designed estimator where pilot tones are inserted in each OFDM symbol. In this paper, a random pilot data are generated and inserted in each OFDM symbol at equally spaced locations. The performance test of Least Square (LS) and Linear Minimum Mean Square (LMMSE) estimation methods are proposed with Discrete Fourier Transform (DFT) based on both LS and LMMSE, where different ITU channel models are considered in order to compare their performance for data transmission in high mobile systems with different Doppler frequencies exceeds 200 Hz and minimal number of pilots.

Compensation of Phase Noise Effects for IEEE 802.16e OFDMA Systems

2011 ◽  
Vol 204-210 ◽  
pp. 1330-1335
Author(s):  
Chien Sheng Chen ◽  
Yung Chuan Lin ◽  
He Nian Shou ◽  
Chi Tien Sun
Keyword(s):  
Phase Noise ◽  
Fading Channel ◽  
Orthogonal Frequency Division Multiplexing ◽  
Phase Error ◽  
Delay Spread ◽  
Ofdm Systems ◽  
Ofdm System ◽  
Ieee 802.16E ◽  
Noise Effects ◽  
Channel One

Orthogonal frequency division multiplexing (OFDM) system which provides high spectral efficiency has obvious advantages in robustness against the multipath delay spread and the fading channel. One of the major disadvantages of such a multi-carrier modulated system is the sensitivity of its performance to synchronization error, such as phase noise and frequency offset. Phase noise is caused by the mismatch between the transmitter and the receiver oscillators. Phase noise in an OFDM system can destroy the orthogonality of the subcarriers and cause inter-carrier interference (ICI). Phase noise resulting in common phase error (CPE) and Inter-Carrier Interference is a critical challenge to the implementation of OFDM systems. In this paper, the phase noise effects of the IEEE 802.16e OFDMA systems are compensated. The practical cluster-based method which is used to estimate either the CPE or the ICI coefficients in the fading channel and compensate the effects of phase error is also proposed. Numerical results demonstrate that the proposed algorithm can effectively improve the performance caused by phase noise.

scholarly journals Interference Analysis for OFDM Transmissions in the Presence of Time-Varying Channel Impairments

2013 ◽  
Vol 2 (3-4) ◽  
Author(s):  
Vien Nguyen-Duy-Nhat ◽  
Hung Nguyen-Le ◽  
Chien Tang-Tan
Keyword(s):  
Phase Noise ◽  
Orthogonal Frequency Division Multiplexing ◽  
Detrimental Effect ◽  
Approximate Expression ◽  
Frequency Division ◽  
Ofdm Systems ◽  
Channel Response ◽  
Selective Channel ◽  
Time Varying Channel

This paper is concerned with the detrimental effect of phase noise on the performance of orthogonal frequency division multiplexing (OFDM) transmissions over time-selective channels. In the literature, most of the existing papers analyze the performance of OFDM systems in the presence of either time-selective channels or phase noise. Unlike the existing studies, this paper formulates an approximate expression of signal-to-interference-plus-noise ratio (SINR) at an OFDM receiver in the presence of both phase noise and time-selective channel response. The formulated SINR expression can be used as a guideline in determining appropriate OFDM transmission settings under a given quality-of-service (QoS) requirement. To illustrate the tightness of the approximate SINR formulation, empirical and theoretical values of SINR under different OFDM system settings are presented in this paper.

scholarly journals A Novel LS/LMMSE Based PSO Approach for 3D-Channel Estimation in Rayleigh Fading

2018 ◽  
Vol 7 (4) ◽  
pp. 117-123
Author(s):  
D. N. Bhange ◽  
C. Dethe
Keyword(s):  
Channel Estimation ◽  
Bit Error Rate ◽  
Error Rate ◽  
Orthogonal Frequency Division Multiplexing ◽  
Transmission Rate ◽  
Least Square ◽  
High Signal ◽  
Mean Square ◽  
Ofdm Systems ◽  
Channel Parameters

A high transmission rate can be obtained using Multi Input Multi Output (MIMO) Orthogonal Frequency Division Multiplexing (OFDM) model. The most commonly used 3D-pilot aided channel estimation (PACE) techniques are Least Square (LS) and Least Minimum Mean Square (LMMSE) error. Both of the methods suffer from high mean square error and computational complexity. The LS is quite simple and LMMSE being superior in performance to LS providing low Bit Error Rate (BER) at high Signal to Noise ratio (SNR). Artificial Intelligence when combined with these two methods produces remarkable results by reducing the error between transmission and reception of data signal. The essence of LS and LMMSE is used priory to estimate the channel parameters. The bit error so obtained is compared and the least bit error value is fine-tuned using particle swarm optimization (PSO) to obtained better channel parameters and improved BER. The channel parameter corresponding to the low value of bit error rate obtained from LS/LMMSE is also used for particle initialization. Thus, the particles advance from the obtained channel parameters and are processed to find a better solution against the lowest bit error value obtained by LS/LMMSE. If the particles fail to do so, then the bit error value obtained by LS/LMMSE is finally considered. It has emerged from the simulated results that the performance of the proposed system is better than the LS/LMMSE estimations. The performance of OFDM systems using proposed technique can be observed from the imitation and relative results.

Analysis and mitigation of phase noise and sampling jitter in OFDM radio receivers

2010 ◽  
Vol 2 (2) ◽  
pp. 193-202 ◽  
Author(s):  
Ville Syrjälä ◽  
Mikko Valkama
Keyword(s):  
Signal Processing ◽  
Phase Noise ◽  
Orthogonal Frequency Division Multiplexing ◽  
Additive White Gaussian Noise ◽  
Digital Signal ◽  
Direct Conversion ◽  
Clock Jitter ◽  
Radio Receivers ◽  
Receiver Architecture ◽  
Mitigation Techniques

This article addresses the analysis and digital signal processing (DSP)-based mitigation of phase noise and sampling clock jitter in orthogonal frequency division multiplexing (OFDM) radios. In the phase noise studies, the basic direct-conversion receiver architecture case is assumed with noisy downconverting oscillator. In the sampling jitter case, on the other hand, the so-called direct-radio-frequency-sampling receiver architecture is deployed utilizing bandpass sub-sampling principle. The basis for the DSP-based impairment mitigation techniques is first formed using analytical receiver modeling with incoming OFDM waveform, where the effects of both oscillator phase noise and sampling clock jitter are mapped to certain type subcarrier cross-talk and distortion compared to ideal receiver case. Then iterative detection principles and interpolation techniques are developed to essentially estimate and cancel the subcarrier distortion. Also some related practical aspects, like channel estimation, are addressed. The performance of the proposed mitigation techniques is analyzed and verified with extensive computer simulations. In the simulations, realistic phase-locked-loop-based oscillator models are used for phase noise and sampling clock jitter. In addition, different received signal conditions like plain additive white Gaussian noise channel and extended ITU-R Vehicular A multipath channel are considered for practical purposes. Altogether the obtained results indicate that the effects of oscillator and sampling clock instabilities can be efficiently reduced using the developed signal processing techniques.

Sign in / Sign up

Export Citation Format

Share Document