Print ISSN: 1681-6900

Online ISSN: 2412-0758

Keywords : OFDM


A Proposed Channel Estimation Based on Enhanced Sub-carrier Index Modulation and Packet-Discrete Wavelet Transform to Minimize Bit Error Rate

Ansam S. Jabbar

Engineering and Technology Journal, 2021, Volume 39, Issue 10, Pages 1506-1513
DOI: 10.30684/etj.v39i10.2206

For Orthogonal Frequency Division Multiplexing (OFDM) and other communication systems, many estimating approaches have been developed to estimate the channel state information and lower the Bit Error Rate (BER). These estimating methods, however, are still subject to the influence of large peak powers compared to average powers. Reduced computational complexity is one of the most significant factors to consider while developing a new estimate algorithm. This study aims to provide a novel design of the Packet-Discrete Wavelet Transform (P-DWT) algorithm for channel estimation in wireless OFDM instead of the fast Fourier transform (FFT). It is presented to retrieve the code of a spread spectrum signal and transmitted data bits, and it is compared to particle swarm optimization PSO and least mean square (LMS) optimization. The suggested approach reduces the computing cost of DWT by recognizing the Packet Wavelet Transform (PWT) coefficients and local points, findings utilizing P-DWT channels generated from both models and measurements show that the proposed technique outperforms pilot-based channel estimation in terms of bit error rate under sparseness conditions BER. Moreover, as compared to typical semi-blind approaches, the estimation accuracy is enhanced while computing cost is reduced.

Comparison of FFT-Based and DCT-Based Channel Estimation and ECC for OFDM System

Awatif Ali Jafaar

Engineering and Technology Journal, 2015, Volume 33, Issue 3, Pages 682-693

Orthogonal Frequency Division Multiplexing (OFDM) has become a popular modulation method for high data rate wireless communications. In this paper, two schemes are proposed. In the first scheme the Bit Error Rate (BER) and the Packet Error Rate(PER) performancesof Fast Fourier Transform-FFT based OFDM are compared with Discrete Cosine Transform DCT -based OFDM using (QPSK) and (16 QAM)as modulation techniques over Additive White Gaussian Noise environment (AWGN) and Multipath Rayleigh Fading environment.
To improve the performance of the uncoded OFDM schemes,the second coded scheme is investigated .Convolution coding is used to enhance the BER for the previous systems. The proposed systems have been tested and evaluated using MATLAB 7 package.

Low Complexity Spectrum Sensing System for GFDM Cognitive Radio Signals

Hussain K. Chaiel

Engineering and Technology Journal, 2014, Volume 32, Issue 6, Pages 1506-1518

Cognitive radio is a promising technology that aims to use the transmission spectrum efficiently. Each cognitive transmission process consists typically of two phases. During the first phase, which is called sensing phase, cognitive system attempts to detect an available spectrum hole. While in the second phase, data transmission phase, the secondary user data is transmitted to the destination via detected hole. The throughput of the cognitive radio system is mainly depending on the ratio of the transmission time to the sensing time. To reduce the sensing time, this paper suggests a design of simple spectrum sensing system capable for detecting Generalized Frequency Division Multiplexing (GFDM) signals. The reduction in sensing time is based on using XilinixVirtix-6 Field Programmable Gate Array (FPGA) as a target device for implementation the proposed design, which operates at 600 MHz clock frequency. This work includes a discussion of more than one approach to reduce the arithmetic operations needed to implement a sensing system with 250 subcarriers. The simulation results show that the power consumption represents the main challenge of such implementation.

OFDM Channel Estimation Based on Intelligent Systems

Ismail Mohammad Jaber; Hanan A. R. Akkar; Haraa Raheim Hatem

Engineering and Technology Journal, 2014, Volume 32, Issue 2, Pages 305-324

This work is dedicated to the study of reducing Bit Error Rate (BER) when transferring data in the system Orthogonal Frequency Division Multiplexing (OFDM) by estimating the carrier channel in different ways. The proposal design for Artificial Neural Network (ANN) is considered as a tool to improve performance BER and compared with the traditional method based on the use of the Least Square estimation algorithm (LS) to estimate the impulse response of frequency selective Rayleigh fading channel. A MATLAB 7.14 program is used in simulation.
The proposed method which integrates algorithm LS with ANN includes the following:
1. Training the neural network by Back-Propagation (BP) and using the trained neural network with algorithm (LS) to estimate the channel in different paths.
2. Using Resilient Back propagation algorithm (RProp)in the training of the neural network.
3. UsingLevenberg-Marquardt algorithm (LM) in the training of the neural network.
4.The comparison of results between the traditional method and the proposed method when taking BER = 0.001 at various tracks (one path, two path and three path) and showed that there profit of (1.5dB, 2dB, 2dB) between using the traditional method and the proposed method using RProp algorithm and a profit of (2dB,3dB, 2dB) using an algorithm LM. There is also comparison between the performance ofRProp algorithm and LMalgorithm and the results showed that the LM algorithm better thanRProp algorithm.

Design and Implementation of MC-CDMA Technique Using FPGA

il A. H. Hadi; Layla Hattim Abood

Engineering and Technology Journal, 2013, Volume 31, Issue 11, Pages 2085-2097

Multicarrier Code Division Multiple Access (MC-CDMA) is attractive technique for high speed wireless data transmission; it's a combination of Orthogonal Frequency Division Multiplexing (OFDM) and Code Division Multiple Access (CDMA). OFDM employs a number of orthogonal subcarriers, this increases the symbol duration while the CDMA technique provides high capacity over other conventional multiple access schemes. In this paper discusses implementation of base band MC-CDMA system using the FPGA technique, all modules are designed using VHDL programming language. The electronic functional performance of designed circuits is tested by simulations using VHDL programming language on XILINX ISE 9.2i. The proposed model is designed using (Fast Fourier Transform/ Inverse Fast Fourier Transform) and the spreading code used is the gold code, the implementation of the proposed model using Spartan-3A/3AN, XC3S700N-3FGG484 FPGA of Xilinx family.

Performance Evaluation of Dual Tree Complex Wavelet Packet Modulation (Dt-Cwpm) System Over Multipath Rayleigh Fading Channel

Hikmat N. Abdullah; Majid A. Alwan; Fadhil S. Hasan

Engineering and Technology Journal, 2013, Volume 31, Issue 5, Pages 992-1010

The effectiveness of Dual Tree Complex Wavelet Packet Modulation (DT-CWPM) with DQPSK modulation is investigated for communication over flat and frequency selective Rayleigh fading channel. The simulation results show that the performance of the proposed DT-CWPM system is better than that of Orthogonal Frequency Division Multiplexing (OFDM) and other types of Multicarrier Modulation (Slantlet based OFDM and FRAT-OFDM)for the same environment. The comparison of complementary cumulative distribution function (CCDF) of the peak to average power ratio ( PAPR) between different types of multicarrier modulation is also achieved.

Proposed Combined PTS with Clipping and Filtering Technique for PAPR Reduction in OFDM System

Ghanim Abd AL Kareem

Engineering and Technology Journal, 2012, Volume 30, Issue 12, Pages 2125-2137

One of the major drawbacks of OFDM is high Peak-to-Average Power Ratio
(PAPR) which can result in poor power efficiency and serious distortion in the transmitter amplifier. In this paper, the advantages of two different approaches to PAPR reduction are exploited in order to reduce the PAPR more significantly. The first approach is based on clipping and filtering which provides a high PAPR reduction at the cost of signal distortion. The second approach (Partial Transmit Sequence PTS or Selected Mapping SLM methods) results in no distortion. The
performance of the three proposed combined methods(Clipping And Filtering with PTS scheme, SLM with Clipping And Filtering scheme, and PTS with Clipping And Filtering scheme)are evaluated on the PAPR distribution function and on the Bit Error Rate as a function of Signal to Noise Ratio in Additive White Gaussian Noise Channel. The simulation results show that the proposed PTS with Clipping And Filtering scheme provides more PAPR reduction without degradation in the BER performance as compared to the other two proposed scheme (Clipping And Filtering
with PTS scheme and SLM with Clipping And Filtering scheme). The simulation results of PAPR reduction and BER performances are simulated using MATLAB R2009a computer simulation software.

Adaptive Modulation for Orthogonal Frequency Division Multiplexing

Maher K. Mahmood; Abbas Salman Hameed

Engineering and Technology Journal, 2012, Volume 30, Issue 9, Pages 1611-1624

Orthogonal frequency division multiplexing (OFDM) is one of the promising
technologies to improve the spectral efficiency, enhance system capacity and mitigate
inter-symbol interference in the wireless communication system. Adaptive
modulation (AM) with OFDM has been suggested as a bandwidth efficient
transmission technique in wireless fading environments. In this paper, adaptive
modulation techniques is used with OFDM system to improve the throughput
performance of the system using four modulation schemes BPSK, QPSK, 8QAM,
and 16QAM. Two algorithms to estimate SNR are suggested. The first algorithm is to
estimate the SNR for each OFDM symbol in the frame. The second algorithm is to
estimate the channel SNR for each subcarrier in the OFDM symbol. The comparison
between the results of the two algorithms on the performances of BER and
throughput for OFDM system is shown. Furthermore, the effect of various types of
channel equalization on performances of system will be determined. The obtained
results show that a significant improvements in terms of bit error rate (BER) and
throughput can be achieved demonstrating the superiority of the adaptive modulation
schemes compared to fixed transmission schemes.