scholarly journals OFDM impairment mitigation techniques

2021 ◽  
Author(s):  
Bharath Umasankar
Keyword(s):  
Iterative Decoding ◽  
Nonlinear Distortion ◽  
Adaptive Modulation ◽  
Average Power ◽  
Data Rate ◽  
Frequency Diversity ◽  
Ofdm Systems ◽  
Zero Forcing ◽  
Power Requirement ◽  
Ber Performance

In this thesis, we propose novel techniques to improve the performance of OFDM systems. We present a simple adaptive modulation technique to mitigate the nonlinear distortion effects of OFDM signals. Based on an estimation of the nonlinearity of the HPA/channel, for each OFDM symbol, a calculation is done at the transmitter side which identifies the subcarries with high distortion and correpsondingly reduces the modulation level on those subcarriers. This procedure is repeated until the nonlinear distortion is below a predetermined threshold. This technique is shown to improve the BER performance considerably while the reduction in data rate is small. The data rate is reduced by 4% for a system with 64 subcarriers and 16 QAM as primary and 4 QAM as secondary modulation levels. The tone reservation technique used in conventional PAPR reduction is suitably modified to provide a simple solution to reduce the average power requirement in intenstiy modulated optical OFDM systems. With two reserved subcarriers the reduction in power is approximately 2 dB for 16 QAM modulation with 64 subcarriers and 1dB for 256 subcarriers. We also describe techniques to improve the BER performance of grouped linear constellation precoding (GLCP) OFDM which is used to achieve frequency diversity. We present an Adaptive Weighting (AW) technique in which during MLSE, the distance of the possible constellation points from the received symbols are weighted according to the SNR of each subcarrier before the sequence with the minimum distance is chosen. We also analyze a sub optimum iterative decoding algorithm which improves the performance of an initial zero forcing detection iteratively on a symbol by symbol basis. Both techniques improve the performance of the GLCP-OFDM system considerably at the expense of increased complexity.

scholarly journals OFDM impairment mitigation techniques

2021 ◽  
Author(s):  
Bharath Umasankar
Keyword(s):  
Iterative Decoding ◽  
Nonlinear Distortion ◽  
Adaptive Modulation ◽  
Average Power ◽  
Data Rate ◽  
Frequency Diversity ◽  
Ofdm Systems ◽  
Zero Forcing ◽  
Power Requirement ◽  
Ber Performance

In this thesis, we propose novel techniques to improve the performance of OFDM systems. We present a simple adaptive modulation technique to mitigate the nonlinear distortion effects of OFDM signals. Based on an estimation of the nonlinearity of the HPA/channel, for each OFDM symbol, a calculation is done at the transmitter side which identifies the subcarries with high distortion and correpsondingly reduces the modulation level on those subcarriers. This procedure is repeated until the nonlinear distortion is below a predetermined threshold. This technique is shown to improve the BER performance considerably while the reduction in data rate is small. The data rate is reduced by 4% for a system with 64 subcarriers and 16 QAM as primary and 4 QAM as secondary modulation levels. The tone reservation technique used in conventional PAPR reduction is suitably modified to provide a simple solution to reduce the average power requirement in intenstiy modulated optical OFDM systems. With two reserved subcarriers the reduction in power is approximately 2 dB for 16 QAM modulation with 64 subcarriers and 1dB for 256 subcarriers. We also describe techniques to improve the BER performance of grouped linear constellation precoding (GLCP) OFDM which is used to achieve frequency diversity. We present an Adaptive Weighting (AW) technique in which during MLSE, the distance of the possible constellation points from the received symbols are weighted according to the SNR of each subcarrier before the sequence with the minimum distance is chosen. We also analyze a sub optimum iterative decoding algorithm which improves the performance of an initial zero forcing detection iteratively on a symbol by symbol basis. Both techniques improve the performance of the GLCP-OFDM system considerably at the expense of increased complexity.

Measured Data Rate from Adaptive Modulation in Wideband OFDM Systems

2006 ◽  
Author(s):  
Farinaz Edalat ◽  
Jit Ken Tan ◽  
Khoa M. Nguyen ◽  
Nir Matalon ◽  
Charles G. Sodini
Keyword(s):  
Adaptive Modulation ◽  
Data Rate ◽  
Measured Data ◽  
Ofdm Systems

scholarly journals Investigation on the PAPR performance of odd-bit QAM constellations for DFT spread OFDM systems

2021 ◽  
Vol 21 (2) ◽  
pp. 1005
Author(s):  
Ahmed M. Sana ◽  
Amer T. Saeed ◽  
Yaseen Kh. Yaseen
Keyword(s):  
Communication Systems ◽  
Adaptive Modulation ◽  
Average Power ◽  
Transmission Efficiency ◽  
Distribution Functions ◽  
Cumulative Distribution ◽  
Ofdm Systems ◽  
Single Carrier ◽  
Papr Performance

<p>Adaptive quadrature amplitude modulation (QAM) is a crucial scheme that enables the modern communication systems to overcome the adverse effects of channel fluctuations and maintain an acceptable spectral efficiency. In order to enhance adaptive modulation even further, adoption of odd-bit QAM constellations alongside even constellations had been suggested to improve the transmission efficiency of adaptive QAM modulation. Hence, odd-bit QAM had been extensively studied, analyzed, and tested by many researchers for various patterns, sizes, and communication systems in terms of bit error rate (BER) and peak to average power ratio (PAPR). However, the PAPR performance of odd-bit QAM constellation with single carrier transmission systems adopted in the uplink of the 4G long term evolution (LTE) standards caught almost no research interest. In this paper, the PAPR performance of both cross and rectangular odd-bit QAM constellations are investigated for DFT-S-OFDM systems. Complementary cumulative distribution functions (CCDFs) and probability density functions (PDFs) curves for PAPR are also obtained. Finally, an equation for PAPR PDF is empirically derived for odd-bit cross QAM based DFT-S-OFDM. The results show that cross odd-bit QAM outperforms the rectangular odd-bit QAM in terms of PAPR by 1.02 dB for 8-QAM and 1.3 dB for 32-QAM. This proves that cross odd-bit QAM is a better choice in terms of PAPR for DFT-S-OFDM systems. </p>

scholarly journals PAPR Reduction in MIMO-OFDM Systems Using Low- Complexity Additive Signal Mixing

2021 ◽  
pp. 468-478
Author(s):  
Stephen Kiambi ◽  
◽  
Elijah Mwangi ◽  
George Kamucha
Keyword(s):  
Communication Systems ◽  
Window Size ◽  
Low Complexity ◽  
Data Rate ◽  
Papr Reduction ◽  
Ofdm Systems ◽  
High Data ◽  
Communication Technique ◽  
Mimo Ofdm ◽  
Ber Performance

A MIMO-OFDM wireless communication technique possesses several advantages accrued from combining MIMO and OFDM techniques such as increased channel capacity and improved BER performance. This has made the technique very amiable to current and future generations of communication systems for high data-rate transmission. However, the technique also inherits the high PAPR problem associated with OFDM signals—a problem still requiring a practical solution. This work proposes a PAPR reduction algorithm for solving the problem of high PAPR in MIMO-OFDM systems. The proposed method uses a low-complexity signal mixing concept to combine the original transmit signal and a generated peak-cancelling signal. The computational complexity of the proposed method is O(M) , which is very much less than O(N log2 N) of the FFT algorithms. This is because M, which denotes the number of nonzero peakcancelling samples, is much less than N, the FFT window size. The proposed method was found to achieve high PAPR reductions while utilizing only a few nonzero peak-cancelling samples and it does not significantly change the power of the transmitted signal. For example, with M=5% of 256-point IFFT samples, corresponding to a data rate loss of 4.8%, a large PAPR reduction of 5.9 dB could be achieved at a small power loss of 0.09 dB. Compared with other methods proposed in literature, the proposed method was found to outperform them in terms of PAPR reductions and BER performance.

scholarly journals Performance Analysis of MIMO SFBC CI-COFDM System against the Nonlinear Distortion and Narrowband Interference

2012 ◽  
pp. 195-201
Author(s):  
Y.Suravardhana Reddy ◽  
K. Rama Naidu
Keyword(s):  
Orthogonal Frequency Division Multiplexing ◽  
Average Power ◽  
Frequency Diversity ◽  
Ofdm Systems ◽  
Mimo Antenna ◽  
Time Frequency ◽  
Carrier Interferometry ◽  
Mimo Ofdm ◽  
Space Frequency ◽  
Carrier Communication

Carrier Interferometry Coded Orthogonal Frequency Division Multiplexing (CI-COFDM) system has been widely studied in multi-carrier communication system. The CI-COFDM system spreads each coded information symbol across all N sub-carriers using orthogonal CI spreading codes. The CI-COFDM system shows the advantages of Peak to Average Power Ratio (PAPR) reduction, frequency diversity and coding gain without any loss of communication throughput. On the other side, a great attention has been devoted to Multi Input Multi Output (MIMO) antenna systems and space-time-frequency processing. In this paper, we focus on two Transmit (Tx)/one Receive (Rx) antennas configuration and evaluate the performance of MIMO OFDM, MIMO CIOFDM and MIMO CI-COFDM systems. Space Frequency Block Coding (SFBC) is applied to MIMO OFDM, MIMO CI-ODFM and MIMO CI-COFDM systems. For CI-COFDM realization, digital implemented CI-COFDM is used in which information conventional is encoded, CI code spreading operation and carrier allocation are processed by IFFT type operation. From simulation results, it is shown that MIMO SFBC CI-COFDM reduces PAPR significantly as compared with that of MIMO SFBC CI-OFDM and MIMO SFBC OFDM systems. In Narrow Band Interference (NBI) channel MIMO SFBC CI-COFDM systems achieve considerable Bit Error Rate (BER) improvement compared with MMO SFBC CI-OFDM and MIMO SFBC OFDM system.

scholarly journals Adaptive Modulation for SFBC-OFDM Systems with Zero-Forcing Equalization

2015 ◽  
Vol 3 (2) ◽  
pp. 6-11 ◽  
Author(s):  
P.N. Kota ◽  
A.N. Gaikwad ◽  
Pranav M.
Keyword(s):  
Adaptive Modulation ◽  
Ofdm Systems ◽  
Zero Forcing

BER Performance Improvement in Coded-OFDM Systems Using Equalization Algorithms

2011 ◽  
Vol 403-408 ◽  
pp. 1028-1034 ◽  
Author(s):  
Bhasker Gupta ◽  
Davinder S. Saini
Keyword(s):  
Performance Improvement ◽  
Ofdm Systems ◽  
Zero Forcing ◽  
High Data ◽  
Use Of Time ◽  
Rate Transmission ◽  
Coded Ofdm ◽  
Frequency Selective Channels ◽  
Data Rate Transmission ◽  
Ber Performance

Intersymbol interference is a major cause to limit high data rate transmission in wireless communication. To avoid ISI OFDM is the preferred modulation technique. For frequency selective channels pure OFDM may not be sufficient to eliminate ISI. The use of time coding (interleaver and convolution coder) improves the ISI affected reception but do not eliminate ISI completely. The paper investigates the presence of equalizers to improve BER performance in ISI affected reception. The performance improvement is observed for two novel equalizers namely zero forcing equalizers and MMSE equalizers. Simulation results are presented to demonstrate the superiority of the CODED OFDM method with equalizers

scholarly journals The Extended SLM Combined Autoencoder of the PAPR Reduction Scheme in DCO-OFDM Systems

2019 ◽  
Vol 9 (5) ◽  
pp. 852 ◽  
Author(s):  
Lili Hao ◽  
Dongyi Wang ◽  
Yang Tao ◽  
Wenyong Cheng ◽  
Jing Li ◽  
...  
Keyword(s):  
Loss Function ◽  
Communication Systems ◽  
Orthogonal Frequency Division Multiplexing ◽  
Average Power ◽  
Cumulative Distribution ◽  
Papr Reduction ◽  
Ofdm Systems ◽  
Communication Problems ◽  
Reduction Methods ◽  
Ber Performance

End-to-end learning in optical communication systems is a promising technique to solve difficult communication problems, especially for peak to average power ratio (PAPR) reduction in orthogonal frequency division multiplexing (OFDM) systems. The less complex, highly adaptive hardware and advantages in the analysis of unknown or complex channels make deep learning a valid tool to improve system performance. In this paper, we propose an autoencoder network combined with extended selected mapping methods (ESLM-AE) to reduce the PAPR for the DC-biased optical OFDM system and to minimize the bit error rate (BER). The constellation mapping/de-mapping of the transmitted symbols and the phase factor of each subcarrier are acquired and optimized adaptively by training the autoencoder with a combined loss function. In the loss function, both the PAPR and BER performance are taken into account. The simulation results show that a significant PAPR reduction of more than 10 dB has been achieved by using the ESLM-AE scheme in terms of the complementary cumulative distribution function. Furthermore, the proposed scheme exhibits better BER performance compared to the standard PAPR reduction methods.

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