scholarly journals A comparative simulation study of different decoding schemes in LDPC coded OFDM systems for NB-PLC channel

2019 ◽  
Vol 15 (1) ◽  
pp. 306
Author(s):  
Nejwa El maammar ◽  
Seddik Bri ◽  
Jaouad Foshi
Keyword(s):  
Orthogonal Frequency Division Multiplexing ◽  
Belief Propagation ◽  
Channel Model ◽  
Impulsive Noise ◽  
Multipath Propagation ◽  
Ofdm Systems ◽  
Ldpc Decoder ◽  
Power Line Communications ◽  
Decoding Algorithms ◽  
Coded Ofdm

In this paper, we study the performance of Low density Parity Check (LDPC) coded orthogonal frequency-division multiplexing (COFDM) systems  when they are applied on the short data block of a narrowband (NB) power line communications (PLC) channel. In the modelled system simulations have been performed using different code lengths. It is assumed that the channel has a multipath propagation with two different noise scenarios: AWGN background noise with and without the presence of impulsive noise. Performances of Various soft and hard decision LDPC decoder schemes such as belief propagation (BP), weighted bit flipping (WBF), improved weighted bit flipping (IWBF) and implementation-efficient reliability ratio based weighted bit flipping (IRRWBF) decoders were investigated. It has been shown for all simulations performed in PLC channel model showed that remarkable performance improvement can be achieved by using short-length LDPC codes. Especially, the improvements are striking when the BP decoding algorithms are employed on the receiver side.

scholarly journals Adaptive Prediction of Channels with Sparse Features in OFDM Systems

2013 ◽  
Vol 2013 ◽  
pp. 1-5 ◽  
Author(s):  
Changwei Lv ◽  
Shujuan Hou ◽  
Wenbo Mei
Keyword(s):  
Time Domain ◽  
Orthogonal Frequency Division Multiplexing ◽  
Channel Model ◽  
Prediction Method ◽  
Frequency Domain Method ◽  
Ofdm Systems ◽  
Physical Channel ◽  
The Time Domain ◽  
Sparse Features ◽  
Sparse Channel

A time domain channel prediction method exploiting features of sparse channel is proposed for orthogonal frequency division multiplexing (OFDM) systems. The proposed predictor operates in the time domain on each channel tap and separates the negligible taps from significant channel taps before performing prediction. We also compare the proposed prediction method with the classical frequency domain method realized at each OFDM subcarrier and demonstrate that our method increases the prediction accuracy and reduces the computational complexity. Simulations on the physical channel model verify the performance of the proposed method.

scholarly journals Desarrollo Y Simulación De Un Modelo De Transceptor Basado En Prime Para Simulación Sobre Canal PLC

2018 ◽  
Vol 14 (27) ◽  
pp. 229
Author(s):  
Jorge E. Veglia ◽  
David L. La Red Martinez ◽  
Reinaldo J.R. Scappini
Keyword(s):  
Fourier Transform ◽  
Error Correction ◽  
Orthogonal Frequency Division Multiplexing ◽  
Channel Model ◽  
Point Of View ◽  
Power Line Communications ◽  
Inverse Discrete Fourier Transform ◽  
Correction Technique ◽  
Implementation Costs ◽  
Communications System

The choice of modification technique for a communications system depends to a large extent on the nature and characteristics of the medium in which it must operate (Hrasnica et al., 2005). In a PLC (Power Line Communications) system, the first applications in the LDR band (oriented to the control of devices) operated with monocarrier modulations, such as ASK, BPSK, and FSK. This allows for low implementation costs, provided that it operates at low data rates and with an error correction system. It is clear that applications require a higher data rate. The modulation technique must overcome challenges such as the necessary equalization for the cause of the non-linearity of the channel, or avoid the propagation delays and the multipath caused by the impedance differences in the branches. Likewise, it must offer flexibility and avoid the use of certain frequencies if they are altered or assigned to another service and, therefore, cannot be used in PLC. In this scenario, one of the techniques that have been imposed in the most used developments in NB-PLC as in BB-PLC has been Orthogonal Frequency Division Multiplexing (OFDM). One of its most attractive aspects from the point of view of its complexity is the possibility of implementing the structure of its multifrequency modulation and demodulation scheme through a simple Inverse Discrete Fourier Transform (IDFT) and its corresponding direct transform, Fast Fourier Transform (FFT). Based on this technique, an appropriate transceiver scheme for operating on a PLC channel model was presented. This development implements the error correction technique proposed for NB-PLC.

scholarly journals Impact of Inter-Channel Interference on Shallow Underwater Acoustic OFDM Systems

2020 ◽  
Vol 2020 (1) ◽  
pp. 42-49
Author(s):  
Tiến Hoa Nguyễn ◽  
Việt Hà Đỗ ◽  
Văn Đức Nguyễn
Keyword(s):  
Simulation Model ◽  
Channel Capacity ◽  
Orthogonal Frequency Division Multiplexing ◽  
Channel Model ◽  
Wide Band ◽  
Frequency Division ◽  
Ofdm Systems ◽  
Underwater Acoustic ◽  
Channel Interference ◽  
Wide Band Transmission

This paper investigates the impacts of Inter-Channel Interference (ICI) effects on a shallow underwater acoustic (UWA) orthogonal frequency-division multiplexing (OFDM) communication system. Considering both the turbulence of the water surface and the roughness of the bottom, a stochastic geometry-based channel model utilized for a wide-band transmission scenario has been exploited to derive a simulation model. Since the system bandwidth and the sub-carrier spacing is very limited in the range of a few kHz, the channel capacity of a UWA system is severely suffered by the ICI and Doppler effects. For further investigation, we construct the signal-to-noise-plus-interference ratio (SINR) based on the simulation model, then evaluate the channel capacity. Numerical results show that the various factors of a UWA-OFDM system as subcarriers, bandwidth, and OFDM symbols affects the channel capacity under the different Doppler frequencies. Those observations give hints to select the good parameters for UWA-OFDM systems.

scholarly journals Downlink Linear Precoders Based on Statistical CSI for Multicell MIMO-OFDM

2017 ◽  
Vol 2017 ◽  
pp. 1-18
Author(s):  
Ebrahim Baktash ◽  
Chi-Heng Lin ◽  
Xiaodong Wang ◽  
Mahmood Karimi
Keyword(s):  
Communication Systems ◽  
Orthogonal Frequency Division Multiplexing ◽  
Channel Model ◽  
Matrix Theory ◽  
Covariance Structure ◽  
Optimal Solution ◽  
Closed Form Expression ◽  
Ofdm Systems ◽  
Precoder Design ◽  
Mimo Ofdm

With 5G communication systems on the horizon, efficient interference management in heterogeneous multicell networks is more vital than ever. This paper investigates the linear precoder design for downlink multicell multiple-input multiple-output orthogonal frequency-division multiplexing (MIMO-OFDM) systems, where base stations (BSs) coordinate to reduce the interference across space and frequency. In order to minimize the overall feedback overhead in next-generation systems, we consider precoding schemes that require statistical channel state information (CSI) only. We apply the random matrix theory to approximate the ergodic weighted sum rate of the system with a closed form expression. After formulating the approximation for general channels, we reduce the results to a more compact form using the Kronecker channel model for which several multicarrier concepts such as frequency selectivity, channel tap correlations, and intercarrier interference (ICI) are rigorously represented. We find the local optimal solution for the maximization of the approximate rate using a gradient method that requires only the covariance structure of the MIMO-OFDM channels. Within this covariance structure are the channel tap correlations and ICI information, both of which are taken into consideration in the precoder design. Simulation results show that the rate approximation is very accurate even for very small MIMO-OFDM systems and the proposed method converges rapidly to a near-optimal solution that competes with networked MIMO and precoders based on instantaneous full CSI.

A MMSE Channel Estimation Method in QC-LDPC Coded OFDM Systems

2014 ◽  
Vol 989-994 ◽  
pp. 3759-3762 ◽  
Author(s):  
Gulomjon Sangirov ◽  
Yong Qing Fu ◽  
Ye Fang
Keyword(s):  
Channel Estimation ◽  
Orthogonal Frequency Division Multiplexing ◽  
Wireless Channels ◽  
Minimum Mean Square Error ◽  
Estimation Method ◽  
Coherent Detection ◽  
Estimation Methods ◽  
Ofdm Systems ◽  
Computationally Efficient ◽  
Coded Ofdm

An orthogonal frequency division multiplexing (OFDM) is one of the effective techniques used in wireless communications. In OFDM systems, channel impairments due to multipath dispersive wireless channels can cause deep fades in wireless channels. The OFDM receiver also requires an accurate and computationally efficient channel state information when coherent detection is involved. Therefore, it needs a good robust estimation method of the channel in wireless communication for OFDM systems. And one of these channel estimation methods is minimum mean square error (MMSE) channel estimation. MMSE channel estimation one most used method in OFDM systems. In this work we enhanced robustness of MMSE channel estimation by using it in base of quasi-cyclic low density parity check (QC-LDPC) coded OFDM system.

scholarly journals Sparse DFT Based Channel Estimation In OFDM Systems

2020 ◽  
Vol 3 (2) ◽  
pp. 1-10
Author(s):  
Maryam K. Abboud ◽  
Bayan M. Sabbar
Keyword(s):  
Channel Estimation ◽  
Communication Systems ◽  
Orthogonal Frequency Division Multiplexing ◽  
Channel Model ◽  
Doppler Frequency ◽  
Mobile Systems ◽  
Vehicle Speed ◽  
Ofdm Systems ◽  
Estimation Algorithms ◽  
Doppler Frequency Shifts

Channel estimation is an essential part of Orthogonal Frequency Division Multiplexing (OFDM) communication systems. In this paper, two Discrete Fourier Transform (DFT) improvement algorithms are proposed and compared where the 1st one exploits channel sparsity concept while the other considers significant channel coefficients only. In the proposed algorithms; Enhanced and Sparse DFT (E-DFT and S-DFT), different number of significant channel components is selected either by a threshold determining procedure such as in    E-DFT, or through determining channel sparsity level such as in S-DFT. In the presence of Doppler frequency shifts, the Inter Symbol Interference (ISI) effect on channel coefficients is successfully reduced using the proposed estimation algorithms. Vehicular A-ITU channel model is considered with a relatively high vehicle speed up to 68 Km/h in order to test the suitability of the proposed algorithms for mobile systems. E-DFT and S-DFT improves conventional as well as previous DFT improvement methods (I-DFT) suggested by [7], [8], [9], [15]. For 64 subcarriers, S-DFT outperforms E-DFT and I-DFT by about 3dB at a BER of 0.01 with a mobility reaches 45 Km/h, and by about 0.4dB and 2.5dB at a BER of 0.02 with a mobility reaches 68Km/h.

scholarly journals Physical layer simulation results for IEEE 802.15.3c with different channel models

2011 ◽  
Vol 9 ◽  
pp. 173-177 ◽  
Author(s):  
M. Liso Nicolás ◽  
M. Jacob ◽  
T. Kürner
Keyword(s):  
Orthogonal Frequency Division Multiplexing ◽  
High Speed ◽  
Channel Model ◽  
Multipath Propagation ◽  
Signal To Noise Ratio ◽  
Physical Layer ◽  
Link Quality ◽  
60 Ghz ◽  
Single Carrier ◽  
Ieee 802.15.3C

Abstract. This paper investigates the performance of the 60 GHz IEEE 802.15.3c physical layer (PHY) specification in terms of bit error rate (BER) against signal to noise ratio. Two PHY modes of the standard have been implemented and simulated, i.e., Single Carrier and High Speed Interface. The first mode uses single carrier (SC) block transmission and the second mode uses orthogonal frequency division multiplexing (OFDM). One of the main issues in the new 60 GHz standards is multipath propagation, which plays an important role in the link quality. Thus, we have tested the PHY with the IEEE standard channel model, ray tracing simulations and real 60 GHz measurements.

scholarly journals Sparse Channel Estimation for DCO-OFDM VLC Systems in the Presence of Clipping Noise

2021 ◽  
Author(s):  
Ekin Basak Bektas ◽  
Erdal Panayirci
Keyword(s):  
Channel Estimation ◽  
Time Domain ◽  
Orthogonal Frequency Division Multiplexing ◽  
Channel Model ◽  
Estimation Algorithm ◽  
Visible Light Communications ◽  
Ofdm Systems ◽  
Noise Mitigation ◽  
The Time Domain ◽  
Sparse Channel

Abstract In this paper, a new iterative channel estimation algorithm is proposed that exploits channel sparsity in the time domain for DC-biased optical orthogonal frequency division multiplexing OFDM (DCO-OFDM) systems in indoor visible light communications (VLC) in the presence of a clipping noise. A path-based channel model is used, in which the channel is described by a limited number of paths, each characterized by a delay and channel gain. Making use of the pilot symbols, overall sparse channel tap delays and path gains were initially estimated by the compressed sensing approach, in the form of the Orthogonal Matching Pursuit (OMP) and the least-squares (LS) algorithms, respectively. Then a computationally efficient and novel iterative channel estimation algorithm is developed that estimates the clipping noise in the time-domain and compensated for its effect in the frequency-domain. Computer simulation results show that the algorithm converges in maximum two iterations and that yields excellent mean square error (MSE) and bit error rate (BER) performance, outperforming those channel estimation algorithms, which do not have the clipping noise mitigation capability.

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