Performance Of OFDM System Research Articles

Sparse channel estimation for underwater acoustic OFDM systems with super-nested pilot design

Underwater acoustic channels are usually sparse and have large delay spread. In this paper, super-nested array structure in the field of array signal processing is borrowed to be the pilot design of underwater acoustic OFDM systems, in order to better estimate large delay spread channels with limited number of pilots. Specifically, by constructing the pilot subcarriers’ covariance matrix and the pilot position difference, the virtual pilot on the differential co-array are employed for sparse channel estimation. In order to reduce the error between the estimated pilot subcarriers’ covariance matrix and the ideal covariance matrix, the cross-correlation matrix of pilot subcarriers is estimated in advance for interference cancellation. Then the sparse iterative covariance estimation algorithm (SPICE) is adopted to further refine the covariance matrix and improve the channel estimation performance. Simulation, pool and sea experimental results show that the proposed method can effectively estimate the large delay spread sparse channels and improve the performance of underwater acoustic OFDM systems.

Reliable Pilot Search Method for Enhancing BER Performance in Underwater Acoustic OFDM Systems with MMSE Estimator

Reliable Pilot Search Method for Enhancing BER Performance in Underwater Acoustic OFDM Systems with MMSE Estimator

Joint channel and impulse noise estimation based on compressed sensing and Kalman filter for OFDM system

Impulse noise (IN) widely exists in many communication systems, which seriously affects the performance of OFDM communication systems. A joint channel and IN estimation method based on all subcarriers is designed. This method uses a sparse Bayesian learning (SBL) algorithm incorporating forward–backward Kalman filter (FB-Kalman) to tackle the problem of joint channel and IN estimation and data detection for OFDM systems. Firstly, the channel impulse response and IN are regarded as unknown sparse vectors, and a SBL framework using all subcarriers is proposed to estimate the unknown vector. The SBL theory is used based on the prior distribution of variables, and then the forward–backward joint system is established, which applies the data detection simultaneously. We also propose the FB-Kalman implementation algorithm by using the expectation maximization updates. Explicit expressions of mean and covariance matrix of the posterior distribution are derived in the E-step. Simulation results show that the proposed algorithm improves the normalized mean square error and bit error rate performance of OFDM system in the presence of IN communication environment.

Increasing of bit error rate performance for OFDM systems over fading channels

A method for increasing performance of OFDM systems in multipath channels is proposed. The proposed method uses Kalman filter based channel estimator with block type pilot structure. Performance of the proposed method has been demonstrated for GSCM/EDGE channel models, typical for urban area and very small cells. The characteristics of the proposed algorithm are compared with other well-known methods. The impact of Doppler spread is considered. A computer simulation has been carried out to evaluate the required signal-to-noise ratio in case of fixed bit error probability. It is shown, that proposed method leads to lower bit error ratio for slow fading case, but its performance degrades with increasing Doppler frequency.

A Hybrid Optimization-Based Technique for Channel Estimation in OFDM System: A Parametric Approach

The performance of OFDM system depends on the how efficient channel estimation is, which directly impactsits bit error rate (BER). In this research work, the novel technique of pseudo-pilot aided OFDM system is usedits channel estimation with least square and Recursive Least Squares approach. In proposed technique, for channel estimation Pseudo-pilot technique is used in OFDM system over AWGN fading channels. A hybridization technique has been implemented to alleviate the error rate in the signals. The hybrid optimization approach is implemented on the estimated output for the optimum solution. The combination of the two optimization techniques is particle swarm optimization (PSO) and Moth Flame Optimization (MFO) method that is used for optimization of the performance rate. To get more optimum solutions (reducing BER) OFDM system is trained with neural network. The performance of the proposed techniques and the weighted scheme are compared and verified using computerized simulation carried out using Matrix Laboratory software. The hybrid approach is able to achieve low BER of the network. The BER of PSO is 1.004 × 10−7 whereas for hybrid optimization (PSO + MFO) BER is 6.275 × 10−8 at 18 dB SNR. After training of the whole system is done with BPNN which will further reduce the BER while increasing SNR. By using BPNN, BER will further reduce to 1.243 × 10−8 at 18 dB SNR. It means hybrid optimization is done to optimize the performance of the channel and reduce the BERs, which will help to increase the channel estimation process as well as channel capacity and further reduces the losses while transmission from one end to the other end.

Increasing the Performance of OFDM Systems by PAPR Reduction in PTS Technique using Election Optimization Algorithm

Increasing the Performance of OFDM Systems by PAPR Reduction in PTS Technique using Election Optimization Algorithm

Finite Radon Transform as Subcarriers Mapping Technique for OFDM System

Radon Transform (RT) becomes a mathematical basis for solving computerized tomography, and finds application in medical imaging and image processing. Finite groups represent digital images; the Finite Radon Transform (FRAT) is then applied. To overcome the periodization effect of a finite transform, Do and Vetterli [1] introduce a novel ordering of the FRAT coefficients. This paper introduced a detailed mathematical analysis of the optimal ordering of FRAT coefficients that introduces new normal vectors that are clearly identified with examples producing the FRAT transform. Lately FRAT is used with OFDM systems as an M-Ary mapping technique, thus, the signal constellation of some of the different orders of FRAT is presented as well as generating the OFDM symbols from the output of FRAT. This procedure leads to extra investigation on the performance of FRAT-based OFDM systems in comparison with the QAM mapping techniques.

Multi-User Interference Cancellation for Uplink FBMC-Based Multiple Access Channel

In the uplink of multi-user systems, signals from different users may arrive at the base station with different timing offsets (TO), which degrades the performance of conventional OFDM systems. In this letter, an FBMC-based multiple access channel with timing errors is considered under frequency selective channels. To eliminate the intrinsic interference (InI), TO-induced interference (TOI) and multi-user interference (MUI) terms, an iterative receiver is proposed. The proposed receiver combines bit-interleaved coded modulation with iterative decoding (BICM-ID) processing with parallel interference cancellation and iterative interference cancellation. The results show that FBMC is robust to timing errors and the proposed receiver can effectively eliminate the interference terms. This motivates the use of FBMC as an alternative to OFDM in applications that require asynchronous transmissions.

Simplified full precision offset estimation for timing and frequency synchronisation using factorised FFT processor

This paper presents a design methodology for highly reliable timing and frequency synchronisation through scaled floating point arithmetic-based factorised FFT processor. Radix factorisation is the main technique for achieving high energy efficiency, followed by errorless floating point arithmetic computation will increase the performance of the coarse timing and frequency synchronisation. Here representation of error propagation model for training sequence used for synchronisation process with fixed point arithmetic is derived to analyse the rounding effect. The effect of quantisation loss due to the fixed point arithmetic errors and in overall OFDM system performance with decimation-in-frequency (DIF) FFT configuration is analysed and compared with full precision floating arithmetic through simulation. Based on the results, a simple bit size optimisation is proposed to yield full precision accuracy with fewer bits. Finally radix-22 algorithm is proposed to compensate the area overhead due to inclusion of precision arithmetic in FFT computation.

CL-SA-OFDM: Cross-layer and smart antenna based ofdm system performance enhancement

The growing usage of wireless services is lacking in providing high-speed data communication in recent times. Hence, many of the modulation techniques are evolved to attain these communication needs. The recent researches have widely considered OFDM technology as the prominent modulation mechanism to fulfill the futuristic needs of wireless communication. The OFDM can bring effective usage of resources, bandwidth, and system performance enhancement in collaboration with the smart antenna and resource allocation mechanism (adaptive). However, the usage of adaptive beamforming with the OFDM leads to complication in the design of medium access layer and which causes a problem in adaptive resource allocation mechanism (ARAM). Hence, the proposed manuscript intends to design an OFDM system by considering different switched beam smart antenna (SBSA) along with the cross-layer adaptive resource allocation (CLARA) and hybrid adaptive array (HAA). In this, various smart antenna mechanism are considered to analyze the quality of service (QoS) and complexity reduction in the OFDM system. In this paper, various SA schemes are used as per the quality of service (QoS) requirement of the different users. The performance analysis is conducted by considering data traffic reduction, bit-rate reduction, and average delay.

Comparing the performance of OFDM and FBMC multicarrier systems in doubly-dispersive wireless channels

In mobile communications, the most widely used multicarrier technique, namely OFDM, is known to exhibit performance limitations in high speed scenarios. FBMC is an alternative approach and, among FBMC techniques, the recently introduced FBMC-PAM scheme has emerged as the most robust to CFO. Therefore, it is chosen here as the challenger of OFDM for performance comparison in doubly dispersive channels. After presentation of the system model, multicarrier scheme and wireless channel, an analytical evaluation of the BER in the particular case of single path time-varying channel is provided for FBMC-PAM and validated through simulations. Then, simulation results are reported for both OFDM and FBMC-PAM, using the 3GPP multipath channel models. It appears that FBMC-PAM can outperform OFDM in highly time-varying frequency-selective channels.

Efficient Transmission of an Encrypted Image Through a MIMO–OFDM System with Different Encryption Schemes

In today’s world, broadband multimedia services are growing at a rapid pace. It is very much essential to secure data in financial, defense, health care, government, and marketing services. To ensure the data from eavesdroppers, the physical layer security (channel coding, modulation schemes, and diversity techniques, etc.) is one of the best solutions. The security attributes at this level reduce maintenance, operational cost, and complexity without affecting the quality of service. Physical layer security with cryptographic techniques makes it well suited for transferring multimedia data through unsecure or potentially risky communication (wired and wireless) path. To provide security attributes to an image/data, one needs to protect the transmitted data from unauthorized access. Several encryption algorithms have been proposed to ensure confidentiality and security for multimedia data over an insecure wireless channel. Cryptography techniques do not involve any system complexity but add a little computation complexity. Use of advanced processors mitigates the computational burden. In this paper, efficient transmission of an encrypted image through a multiple-input multiple-output orthogonal frequency division multiplexing (MIMO–OFDM) system over an additive white Gaussian noise channel with different encryption schemes is presented. The advanced encryption standard (AES), data encryption standard (DES), and Rubik’s Cube encryption algorithms are incorporated to improve security aspects. The comparison aims to select the most appropriate wireless communication systems (2 × 2 MIMO–OFDM and 4 × 4 MIMO–OFDM), and the most suitable image encryption algorithm for efficient transmission of the encrypted image. The quality of the received image is evaluated using the peak signal-to-noise ratio between the original and decrypted image at different signal-to-noise (SNR) ratio. Performance estimates of the cryptosystems are also provided by computing the bit-error-rate at different SNR. The Performance estimates of encryption algorithms (irrespective of the MIMO–OFDM system) are also included, which consists of various performance metrics. The metrics are histogram, entropy, correlation coefficient, number of changing pixel rate, and unified averaged changed intensity. From the MATLAB simulation experiments, it is observed that the performance of 4 × 4 Crypto-MIMO–OFDM system configurations outperformed 2 × 2 Crypto-MIMO–OFDM system configurations. The performance of the Crypto-MIMO–OFDM system is compared with the original MIMO–OFDM system performance without encryption algorithm. For all variants of Crypto-MIMO–OFDM systems, the use of Rubik’s Cube encryption algorithm shows significant improvement over DES and AES.

FRFT-Based Interference Suppression for OFDM Systems in IoT Environment

The OFDM technology has been widely used in 4G, 5G, and other wireless communication systems for its anti-frequency selective fading and high spectral efficiency. However, OFDM systems are very sensitive to narrowband interference (NBI). There are many existing NBI suppression algorithms for OFDM systems. Unfortunately, in these existing algorithms, the NBI is typically modeled as a sinusoidal signal. With the widespread use of LoRa, which is one of the most imposing IoT technologies, the sinusoidal interference model is unreasonable since LoRa adopts non-stationary chirp signals. Toward this end, we study LoRa interference suppression for OFDM Systems (IEEE 802.11ah). First, we derive the analytical expression of LoRa signal in the fractional Fourier transform (FRFT) domain. Then, we present the principle and procedure of the proposed FRFT-domain interference suppression algorithm for OFDM systems interfered by LoRa. Simulation results show that the proposed FRFT-domain algorithm can significantly improve the BER performance of OFDM systems interfered by LoRa at different signal to interference ratios, compared with the frequency-domain algorithm.

Factors Influencing the PAPR Performance of OFDM and MIMO-OFDM Systems

Multiple-input multiple-output technology together with orthogonal frequency division multiplexing (MIMO-OFDM) is an effective technique to combat multi-channel fading and to improve bandwidth efficiency. Simultaneously, it also increases the system's ability to provide reliable transmission. However, the main disadvantage of OFDM is the high peak-to-average-power ratio (PAPR), which, if not mitigated, will negatively impact practical applications. The high PAPR increases complexity and Bit Error Rate. In this research, the authors investigate the factors influencing the PAPR performance of both OFDM and MIMO-OFDM systems. The objective of this research is to make researchers in this field become familiar with this problem as well as to impart an understanding of the factors that influence PAPR. In this study, the authors classify the factors that impact PAPR into modulation schemes and a number of sub-carriers. These parameters influence the PAPR performance have been analyzed and simulated by using MATLAB. It is observed that the numbers of sub-carriers have a great effect on the PAPR performance. However, modulation schemes can have a small effect on PAPR performance.

On the Effect of Relay Position in Carrier Interferometry OFDM for Cooperative Diversity by Wavelet Transform

In a wireless communication system, cooperative diversity can be used to combat fading effects. In cooperative diversity, the system uses idle antennas, which are located at different locations, as relays. Cooperative communication with OFDM is widely used in communication systems and it enhances communication performance of the system. There are different methods to enhance the performance of OFDM systems, carrier interferometry code is one of them. While, carrier interferometry code increase the performance of the system and also reduces PAPR level. Carrier interferometry codes can be implemented on an OFDM system by using FFT and wavelet. In this paper we investigate the effect of the relay position on the carrier interferometry cooperative OFDM system which uses wavelet transform. The effect of the relay position is investigated over different combiners and relaying strategies. The results show that, relay position effects the performance of the system and optimal location for the relay is right between source and destination.

Adaptation to the LEDs flicker requirement in visible light communication systems through CE-OFDM signals

Constant-envelope OFDM signals based on electrical phase modulation are proposed in visible light communication (VLC) systems to adapt to the LEDs flicker requirements. Experimental results demonstrate that this peak-to-average power ratio (PAPR) reduction technique thoroughly adapts to the flicker requirements in line-of-sight single-input single-output (SISO) VLC channels, at a cost of performance penalties, as indicated by the numerical evaluations provided in this paper. The performance of a 272.87 Mb/s CE-OFDM system, with 64-QAM subcarrier mapping in a bandwidth of 100 MHz, is compared with the performance of a conventional OFDM system, after propagation through SISO and multiple-input single-output (MISO) VLC channel models. Besides the strong dependence on the phase modulation index 2πh, the simulation results show that, in the SISO scenario, the CE-OFDM technique introduces performance penalties. However, with 2πh=1.3, the phase modulation based scheme outperforms traditional OFDM systems in the MISO architecture, due to the transmission of low PAPR signals.

Enhanced Performance of Amplify and Forward Cooperative OFDM System in a Hostile Environment

This paper introduces a cooperative orthogonal frequency division multiplexing (CO-OFDM) based on amplify and forward (AF) relay and utilizing a fast low complexity T-transform as a subcarriers modulation scheme. The proposed cooperative system is developed by changing the modulation/demodulation algorithms which significantly enhanced the immunity of the system to deep notches of the multipath channels. Thereafter, the paper presents a mathematical analytic model for the proposed amplify and forward CO-T-OFDM scheme. The use of T-transform in the transceiver of the proposed system enhances the signal diversity. Therefore, the presented AF cooperative system is efficient in enhancing the signal diversity, mitigating the effects of multipath fading channels and achieving more reliable bit-error-rate (BER) performance than the state-of-the-art cooperative system. It also moderates the peaks power of the signal. The BER of the developed AF cooperative system is evaluated by Monte Carlo simulation over frequency-selective multipath channels when AF relay is used, and compared with the BER performance of the standard AF cooperative system. The results show that the developed AF cooperative technology achieves better BER than the classic CO-OFDM under different transmission scenarios.

Analyzing the Impact of Diverse PAPR Reduction Techniques on BER Performance of OFDM System

Analyzing the Impact of Diverse PAPR Reduction Techniques on BER Performance of OFDM System

Effect of PAPR reduction techniques on BER Performance of OFDM System

Effect of PAPR reduction techniques on BER Performance of OFDM System

AI-enabled turbo-coded OFDM system for improved BER performance

The BER performance of any wireless communication system is the primary factor of consideration for the network under evaluation. Turbo-coded OFDM systems have always outperformed other communication standards in terms of delay of communication, overall system efficiency and flexibility. But the BER performance of turbo-coded OFDM systems has always been a challenge for network designers, due to the fact that turbo encoders vary largely in terms of their primary specifications like code length and code rate among other network parameters. In this paper, we propose an artificial intelligence (AI) layer for turbo-coded OFDM systems, which improves the BER performance of the system, and also reduces the delay of communication by intelligent selection of network specifications. Our AI is trained for minimizing the BER of the communication network, but it can be used to target one or many parameters as per the requirements of the network designer.