Performance Of OFDM System Research Articles

Analysis and iterative equalization of transient and adiabatic chirp effects in DML-based OFDM transmission systems

This work theoretically studies the transmission performance of a DML-based OFDM system by small-signal approximation, and the model considers both the transient and adiabatic chirps. The dispersion-induced distortion is modeled as subcarrier-to-subcarrier intermixing interference (SSII), and the theoretical SSII agrees with the distortion obtained from large-signal simulation statistically and deterministically. The analysis shows that the presence of the adiabatic chirp will ease power fading or even provide gain, but will increase the SSII to deteriorate OFDM signals after dispersive transmission. Furthermore, this work also proposes a novel iterative equalization to eliminate the SSII. From the simulation, the distortion could be effectively mitigated by the proposed equalization such that the maximum transmission distance of the DML-based OFDM signal is significantly improved. For instance, the transmission distance of a 30-Gbps DML-based OFDM signal can be extended from 10 km to more than 100 km. Besides, since the dispersion-induced distortion could be effectively mitigated by the equalization, negative power penalties are observed at some distances due to chirp-induced power gain.

Relay Selection Algorithms for Analog Network Coding OFDM Systems

We propose two relay selection schemes for analog network coding (ANC) OFDM systems. One uses OFDM Symbol-Based Max-Min-Min Selection Criterion (OSBM3SC) to select only one relay for signal transmission, and the other uses a Subcarrier-Based Max-Min Selection Criterion (SBM2SC) to select multiple relays for signal transmission. Assuming a frequency-domain fully-uncorrelated Rayleigh fading channel, we derive the asymptotic symbol error rate (SER) performance for both schemes, and show that they both can achieve full diversity. Using extensive simulations, we further show that the presented analytical results are useful to accurately predict the high SNR error performance of practical OFDM systems.

Low-Complexity Iterative Equalization for Symbol-Reconstruction-Based OFDM Receivers Over Doubly Selective Channels

Time selectivity of multipath channels introduces significant inter-carrier interference (ICI) in OFDM systems demanding high levels of mobility and capacity. In this paper, a piecewise channel approximation is presented for improving the structure of the frequency-domain channel gain matrix, leading to a low-complexity iterative equalization scheme for OFDM receivers. The equalization is a sequential data detection based on a parallel-filtering architecture, avoiding matrix inversion adopted by classical equalizers with ICI cancellation. Meanwhile, information redundancy in the traditional cyclically prefixed OFDM is investigated for time-invariant channels, then a method of symbol reconstruction (SR) is proposed to enhance OFDM system performance, including compensation for SNR loss and improvements on the accuracy of parameter estimation. On the basis of the appropriate channel modeling in this work, the SR processing is proved to be effective for OFDM receivers over doubly selective channels. The iterative equalization, combined with the SR processing, is applied to the DVB-H receiver design. Numerical simulation indicates that the proposed equalizer significantly improves the immunity of OFDM systems to time selectivity with very little complexity increased, in contrast to the conventional one-tap equalizer without ICI cancellation.

Analytical Expressions for Nonlinear Transmission Performance of Coherent Optical OFDM Systems With Frequency Guard Band

Closed-form expressions for nonlinear transmission performance of coherent optical OFDM systems (CO-OFDM) with frequency guard band are derived. The analytical expressions have been substantiated by numerical simulations using split-step method for various frequency spacings and fiber dispersion maps. The analytical solution shows good estimation accuracy, and the average absolute difference of Q factor between analytical results and numerical simulations are below 0.3 dB for the three typical systems simulated. Using this expression, the dependence of system performance for CO-OFDM on the frequency guard band spacing and fiber dispersion is also investigated analytically to provide insights for system design.

T-DMB 동일 채널 중계기의 주파수 영역에서 ICI를 고려한 적응형 채널 추정과 결정지향 잡음 제거

Recently, many papers have been proposed in order to improve the OFDM system performance in T-DMB DOCR (Digital On Channel Repeater), by using removing the feedback signal so that the transmitter power can be increased or by using the equalizer to remove ICI. Despite these efforts, however, signal quality at the receiving terminal has not been improved because of constellation smearing in T-DMB DOCR. In this paper, in order to suppress constellation smearing, we propose an effective equalizer algorithm that can improve system performance. We perform adaptive channel estimation and non-coherent decision directed noise cancellation method that can estimate the channel subsequently during data symbols period in the frequency domain. So we can obtain better quality of the signal at the receiving terminal. In order to secure QoS(Quality of Service) required in T-DMB handsets, we evaluate SNR and BER in T-DMB DOCR(Digital On Channel Repeater) and verified by simulation. In this simulation results, this system is satisfied the performance of BER

Bit Error Rate Evaluation of IEEE 802.16 (WiMAX) in OFDM System

This paper investigates several modulation techniques for IEEE 802.16 (WiMAX) based OFDM system including BPSK, QPSK, 8PSK and various levels of QAMs. The system performance is gained by dynamically choosing the modulation technique based on the channel conditions. The performance of OFDM system is accessed by using computer simulations performed using MATLAB 7.3. In this paper, transmitter and receiver models are simulated according to the parameters established by the standard, to evaluate the performance. Also, convolution coding is used to improve the system performance. Use of adaptive modulation can effectively control the BER of the transmission, as sub carriers that have a poor Eb/No (db) can be allocated a low modulation scheme such as BPSK. For good Eb/No (db), the high modulation scheme giving priority to spectral efficiency can be considered. Eb/No of the channel is estimated before the transmission. The modulation scheme is set based on the SNR of the channel. General Terms Coding data rate, Interleaving, additive white Gaussian Noise, Bit Error Rate, Adaptive Modulation, channel conditions etc.

채널정보를 이용한 STBC OFDM 시스템의 성능 분석

STBC 방식에서는 여러 개의 송신 안테나를 사용함으로서 우수한 성능의 전송이 가능하다. 본 논문에서는 파일럿 심볼을 이용하여 채널을 추정하는 OFDM 시스템에 STBC 안테나 다이버시티 기법을 적용할 때의 시스템 성능을 분석한다. OFDM 전송표준 IEEE 802.16e에서 전송채널의 정보를 송신 측에 다시 보내어 STBC 시스템 성능을 더욱 향상 시키는 방식이 제시되고 있다. 한편, 파일럿 심볼을 이용하여 전송채널을 추정하는 현 시스템에서는 전송채널 추정에러로 인하여 시스템 성능이 열화 된다. 그러므로 채널추정 에러의 영향을 고려하여, 송신 신호가 다중경로 페이딩 채널을 통하여 전송될 때, 채널정보를 이용하는 STBC OFDM 시스템의 데이터 비트 오류율 성능을 분석한다. STBC is a technique where a multiple antenna signals are transmitted. With this technique, antenna diversity can be achieved. The performance of STBC OFDM system using pilot symbol for the channel estimation is analyzed. IEEE 802.16e standards suggest that the BER performance of STBC system can be improved using channel state information. Pilot symbol is used for the channel estimation in OFDM systems. However, imperfect channel estimates in this systems degrade the performance. The performance of this STBC OFDM systems using channel state information, gauged by the average bit error rate, is analyzed considering the channel estimation error.

고속 처리와 성능 향상을 위한 LDPC 코드 기반 결정 궤환 등화기

본 논문에서는 OFDM 시스템에서 고속 처리와 성능 향상을 위한 LDPC 코드 기반 결정 궤환 등화기(Decision Feedback Equalizer: DFE)를 제안한다. LDPC 코드는 우수한 오류 정정 능력과 Shannon의 채널 용량에 근접하는 성능을 갖는다. 그러나, 많은 parity 검사 행렬과 반복 횟수를 가진다는 단점이 있다. 제안된 시스템에서는 판정된 신호와 복호기 사이의 신호의 MSE(Mean Square Error)를 등화기로 피드백한다. 이러한 방법을 사용하면 추정된 채널 응답을 보정해 주기 때문에 성능을 향상시킬 수 있다. 또한, 동일한 성능에서 피드백이 포함되지 않은 시스템보다 낮은 반복 횟수를 갖기 때문에 시스템의 복잡도를 줄일 수 있다. 시뮬레이션을 통해 다중 경로 채널에서 CFO(Carrier Frequency Offset)와 위상 잡음이 고려된 OFDM 시스템의 성능을 평가하여 제안 시스템의 우수성을 보인다. In this paper, we propose a decision feedback equalizer based on LDPC(Low Density Parity Check) code for the fast processing and performance improvement in OFDM system. LDPC code has good error correcting capability and its performance approaches the Shannon capacity limit. However, it has longer parity check matrix and needs more iteration numbers. In our proposed system, MSE(Mean Square Error) of signal between decision device and decoder is fed back to equalizer. This proposed system can improve BER performance because it corrects estimated channel response more accurately. In addition, the proposed system can reduce complexity because it has a lower number of iterations than system without feedback at the same performance. Simulation results evaluate and show the performance of OFDM system with the CFO and phase noise in multipath channel.

Non Linearity Analysis of High Power Amplifier in OFDM System

performance of OFDM system is highly affected by Amplifier nonlinearities. Nonlinearity in power amplifier response leads to nonlinear amplification of OFDM signal. In this paper, the effects of clipping and amplifier nonlinearities are studied for the OFDM system. It is shown that distortion due to these effects is highly related to the digital modulation techniques rather than the clipping level or the saturation level of the nonlinear amplifier. Simulations have been performed for the system with the help of programs in MATLAB 7. Computer simulations of the OFDM system also show the OFDM signal quality metrics such as time spectrum, BER, PAPR for the different type of modulations. Bit error rate and Peak to Average power Ratio have been calculated and then compared for the different modulation techniques.

PAPR Reduction Scheme for OFDM

This paper focused on peak to average power ratio (PAPR) reduction scheme for OFDM system. OFDM has several properties which make it an attractive modulation scheme for high speed transmission. the main draw back of OFDM is high PAPR. The high PAPR causes the interference and degraded the performance of the system while OFDM signal pass through the amplifier. Here a simple scheme clip and filter is used to reduce the PAPR of OFDM system. Simulation results are show that the improvement in performance of OFDM system by reducing the PAPR using clip and filter scheme.

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

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.

Performance Evaluation of MIMO-OFDM Modeling for UMTS-Long Term Evolution Downlink System

As the demand for the Mobile Communication Services increase, the research towards high data rate for meeting higher demands also increases. This made the path for the evolution towards the fourth generation Mobile Communication named as E-UTRA/UTRAN Long Term Evolution (LTE) given by 3GPP. In this paper LTE downlink performance is analyzed. Synchronization Error which degrades the OFDM System Performance is reduced by Synchronization Algorithm. This technique is implemented in Multiple Input Multiple Output (MIMO) to boost the capacity of the channel for to achieve higher data rate.

Channel Equalization with Single Interference Technique based on FFT for efficient OFDM System

In today’s scenario the over sampled OFDM system performance is significantly improved if the deep faded symbols on the sub carriers of each over sampled OFDM signal are discarded and then reconstructed from the remaining OFDM signal by a time domain iterative algorithm. Base on the results of FFT in OFDM demodulation, one new single frequency interference estimation scheme is proposed, which can estimate accurately the parameters of single frequency interference by analyzing and comparing two spectrum lines having higher energy and power consumption ratio than others. The complexity of the scheme is very low and its accuracy is much higher than that of the conventional scheme which using only single spectra line possessing maximum energy to estimate interference parameters.

Experimental demonstration of improved fiber nonlinearity tolerance for unique-word DFT-spread OFDM systems

In this paper we experimentally demonstrate transmission performance of optical DFT-spread OFDM systems in comparison with conventional OFDM systems. A 440.8-Gb/s superchannel consisting of 8 x 55.1-Gb/s densely-spaced DFT-S OFDM signal is successfully received after 1120-km transmission with a spectral efficiency of 3.5 b/s/Hz. It is shown that DFT-S OFDM can achieve an improvement of 1 dB in Q factor and 1 dB in launch power over conventional OFDM. Additionally, unique word aided phase estimation algorithm is proposed and demonstrated enabling extremely long OFDM symbol transmission.

A novel Haar wavelet‐based vector BPSK–OFDM robust to channel spectral nulls and with reduced cyclic prefix length and PAPR

SUMMARYThe performance of OFDM systems may be degraded when intersymbol interference (ISI) channels have spectral nulls. The communication overhead because of the insertion of the cyclic prefix is high when ISI channels have many taps. Recently, the precoded OFDM systems and vector OFDM (VOFDM) systems were proposed to combat these two problems, respectively. This paper proposes a novel vector binary phase‐shift keying (BPSK)–OFDM system based on Haar wavelet transformation. The Haar wavelet transformation performs decomposition over the vector information symbols produced by a BPSK modulator. It shows that half of the information symbols are zero and the rest are or . Then, the vector BPSK–OFDM becomes the precoded OFDM, which inserts one or more zeros between two sets of K consecutive information symbols. This precoding scheme is able to remove the spectral nulls of an ISI channel without knowing the ISI (like conventional precoded OFDM systems), and it has the same cyclic prefix length as VOFDM systems. The proposed OFDM systems show better robustness to the spectral nulls channel, compared with the conventional VOFDM systems. Because of the insertion of (M −K) zeros between two sets of K consecutive information symbols, the conventional precoded OFDM systems have the data rate expanded and signal‐to‐noise power ratio reduced by 10 log 10(M∕K) dB compared with the proposed OFDM systems. Moreover, because half of the information symbols are zeros after Haar wavelet transformation, the proposed OFDM system can further reduce the transmitting peak‐to‐average power ratio. Finally, we compare the proposed OFDM systems with the precoded OFDM and VOFDM systems. Copyright © 2011 John Wiley & Sons, Ltd.

Performance Analysis of OFDM Channel System

OFDM is a promising digital communications technique for high data rate transmissions. In this paper, we have analyzed the performance of mobile OFDM systems in the presence of channel estimation error. A new channel estimation error model is presented. Based on the estimation error model, new and simple expressions for the average bit error probability of M-QAM OFDM systems are derived for zero-forcing, minimum mean square error and maximum likelihood receivers. A complex correlation coefficient is used to quantify the quality of the channel estimation scheme. We have shown that if the complex correlation coefficient is a function of the signal to noise ratio, then the inter-carrier interference caused by channel variations is the dominant source of performance degradation. On the other hand, if the channel estimation scheme produces a constant value for the complex correlation coefficient (estimation quality is not a function of the signal to noise ratio), then the channel estimation error will cause an error floor that is larger than the one caused by the inter-carrier interference, and is considered as one of the dominant causes of degradation. And channel estimation using pilot symbols are discussed in terms of different pilot symbol placement schemes.

Effect of Coding Schemes with Clipping and Filtering Method to Reduce PAPR on the Performance of OFDM System over Noisy Channels

Effect of Coding Schemes with Clipping and Filtering Method to Reduce PAPR on the Performance of OFDM System over Noisy Channels

Joint channel estimation and ISI/ICI cancellation for MIMO OFDM systems

In MIMO OFDM systems, the multipath components whose delays exceed Cyclic Prefix cause Inter-Symbol Interference and Inter-Carrier Interference, which may degrade system performance severely. In this paper, we propose a joint channel estimation and ISI/ICI cancellation scheme in which a limited CP is used in a trade-off against high-rate performance in MIMO OFDM systems. A channel estimation scheme based on the criterion of Expectation-Maximisation (EM) algorithm can be proposed through the use of a training symbol. Simulation results show that the proposed method can significantly enhance the overall MIMO OFDM system performance after only a few iterations.

Low Complexity Discrete Bit-loading for OFDM Systems with Application in Power Line Communications

Adaptive bit-loading algorithms can improve the performance of OFDM systems significantly. The tradeoff between the performance of the algorithm and its computational complexity is essential for the implementation of loading algorithms. In this paper, we present a low complexity non-iterative discrete bit-loading algorithm to maximize the data rate subject to specified target BER and uniform power allocation. Simulation results show that the proposed algorithm outperforms the equal-BER loading and achieves similar rates to incremental allocation, yet with much lower complexity.

All-optical sampling OFDM system performance analysis

All-optical sampling OFDM system performance analysis