OFDM-based Communication Systems Research Articles

On the Coexistence of OTFS Modulation With OFDM-Based Communication Systems

On the Coexistence of OTFS Modulation With OFDM-Based Communication Systems

Statistical analysis of the Middleton Class-A noise effects on multi-carrier OFDM-based communication system

Statistical analysis of the Middleton Class-A noise effects on multi-carrier OFDM-based communication system

Deep Learning for Channel Estimation and Signal Detection in OFDM-Based Communication Systems

The goal of 6G communication networks requires higher transmission speeds, tremendous data processing, and low-latency communication. Orthogonal frequency-division multiplexing (OFDM), which is widely utilized in 5G communication systems, may be a viable alternative for 6G. It significantly reduces inter symbol interference (ISI) in the frequency-selective fading environment. Channel estimation is critical in OFDM to optimize system performance. Deep learning has been employed as an appealing alternative for channel estimation and signal detection in OFDM-based communication systems due to its better potential for feature learning and representation. In this study, we examine the deep neural network (DNN) layers created from long-short term memory (LSTM) for detecting the signals by learning the received signal as well as channel information. We investigate the performance of the system under various conditions. The simulation results show that the signal bit error (SER) is equivalent to and better than that of the minimum mean squared error (MMSE) and least square (LS) methods.

Low-Complexity Sampling Frequency Offset Estimation and Compensation Scheme for OFDM-Based UWOC System

In this paper, a simple sampling frequency offset (SFO) estimation and compensation scheme based on two phase-conjugated pilots is proposed and experimentally demonstrated in an OFDM-based underwater wireless optical communication (UWOC) system. The phase shift is obtained by simple multiplication for phase-conjugated pilots, and the results are averaged to perform more accurate phase estimation. The experimental results show that the estimation offset is limited within ±3 ppm when the SFO ranges from −1000 ppm to +1000 ppm over a 1 m tap water channel. Moreover, with the help of the proposed scheme, up to ±300 ppm SFO can be well-compensated with error vector magnitude (EVM) penalties below 1 dB after 1 m underwater transmission. In addition, the results demonstrate that, compared with the ideal case without SFO, our proposed SFO compensation scheme can provide nearly negligible bit error rate (BER) penalties in saltwater with the highly scattering property.

Future OFDM-based Communication Systems Towards 6G and Beyond: Machine Learning Approaches

The vision towards 6G and beyond communication systems demands higher rate transmission, massive amount of data processing, and low latency communication. Orthogonal Frequency Division Modulation (OFDM) has been adopted in the current 5G networks and has become one of the potential candidates for the future communication systems. Although OFDM offers many benefits including high spectrum efficiency and high robustness against the multipath fading channels, it has major challenges such as frequency offset and high Peak to Power Ratio (PAPR). In 5G communication network, there is a significant increase in the number of sensors and other low-power devices where users or devices may create large amount of connection and dynamic data processing. In order to deal with the increasingly complex communication network, Machine Learning (ML) has been increasingly utilised to create intelligent and more efficient communication network. This paper discusses challenges and the impacts of embedding ML in OFDM-based communication systems.

On the simulation of the Middleton Class-A noise model for single- and multi-carrier modulation in power line communication

We propose a novel simulation approach of the Middleton Class-A model for impulsive noise generation considering symbol-wise transmission in a real Power Line Communication environment. Then, we validate the proposed approach for both single carrier binary FSK based—and multi-carrier OFDM-based communication systems. Established analytical formulations and obtained simulation results for the impulsive noise variance distribution and the communication system error probability show that in a binary FSK system, the second order of the noise variance per symbol, as well as the error floor, are closely related to the impulsive index A. The error floor decreases when A becomes large, and its asymptotic value is equal to the Bit Error Rate (BER) for an additive white Gaussian noise channel with noise variance equal to the average variance of the impulse noise. However, in an OFDM-based system, the noise variance per symbol at the output of the demodulator, as well as the error floor in the BER curves, are fixed and independent of the impulsive index A. The proposed analysis allows us to compare binary FSK and OFDM under the same theoretical noise conditions.

Two-Stage Method for Joint Estimation of Information Symbols and Channel Frequency Response in OFDM Communication Systems

The optimal and quasi-optimal algorithms of two-stage joint estimation of information symbols and frequency response (FR) of multibeam channels in OFDM-based communication systems have been synthesized. They involve the calculation of a posteriori probability density of estimated processes. At the first stage, the recurrent calculation of joint a posteriori distributions of information symbols and the frequency response is performed from two sides of the measurement vector. At the second stage, a posteriori distributions are combined on each of subcarriers that are obtained as a result of the first stage estimation. Based on the obtained a posteriori distributions, estimates of the information symbol and channel FR are determined by the criteria of a posteriori probability maximum and the average mean squared error minimum, respectively. The performance of synthesized algorithms similar to the well-known MMSE algorithm involves the need of knowledge of statistical properties of communication channel. The device implementing the optimal algorithm is multichannel, each channel of which is matched with the corresponding value of symbol from the modulation constellation. The quasi-optimal algorithm was obtained by using the Gaussian approximation of a posteriori probability density. It should be noted that this algorithm preserves its multichannel structure. The approbation of the presented algorithm was conducted using the computer-aided statistical simulation for different parameters of multibeam communication channels and the comparison of the obtained results with the results obtained by the MMSE and LS algorithms. The simulation results showed that the error probability decreases by about 2 times with a maximum signal propagation delay of 100 μs.

Delta-Sigma Modulation for Noise Cancellation in 5G-Compliant Network

The issue of accurate reception of signals in wireless communication systems is a constant concern due to the presence of noise/fading/interferences that may occur on the transmission path. Acknowledging that 5G requirements for these systems increase the standards related to high throughput and lowest bit error rate (BER), noise reduction must be performed to achieve reliable communication. Delta-sigma modulation (DSM) proved to be cost efficiency and reduced circuit complexity technique. Therefore, the performance of DSM is analyzed in a potential 5G-compliant system in Additive White Gaussian Noise, Nakagami-m and Weibull fading channels in the context of BER reduction. The main goal is to offer some landmarks related to expectations of DSM use in an OFDM-based communication system. The performance is evaluated for different sets of spreading sequences (Walsh-Hadamard and pseudo-noise) and based on the simulation results several conclusions are highlighted. Further improvement will be proposed for noise effects reduction and interference minimization in DSM-based 5G-compliant systems.

Palm Date Leaf Clipping: A New Method to Reduce PAPR in OFDM Systems

Orthogonal frequency division multiplexing (OFDM) is the key technology used in high-speed communication systems. One of the major drawbacks of OFDM systems is the high peak-to-average power ratio (PAPR) of the transmitted signal. The transmitted signal with a high PAPR requires a very large linear range of the Power Amplifier (PA) on the transmitter side. In this paper, we propose and study a new clipping method named Palm Clipping (Palm date leaf) based on hyperbolic cosine. To evaluate and analyze its performance in terms of the PAPR and Bit Error Rate (BER), we performed some computer simulations by varying the Clipping Ratio (CR) and modulation schemes. The obtained results show that it is possible to achieve a gain of between 7 and 9 dB in terms of PAPR reduction depending on the type of modulation. In addition, comparison with several techniques in terms of PAPR and BER shows that our method is a strong alternative that can be adopted as a PAPR reduction technique for OFDM-based communication systems.

An Underwater Acoustic OFDM System Based on NI CompactDAQ and LabVIEW

Recently the orthogonal frequency division multiplexing (OFDM) technique has attracted increasing interests in underwater acoustic (UA) communications. In this paper, we present an OFDM-based UA communication system, which is designed based on the National Instruments LabVIEW software and the CompactDAQ device. Details on both the transmitter and receiver system design are discussed. The performance of this UA OFDM system is verified through recent UA communication experiments performed in a tank, in the Canning River, and in the estuary of the Swan River, Western Australia. Experimental results show that the system achieves a reliable bit error rate performance even with high-order modulation schemes. Compared with conventional field-programmable gate array and digital signal processor based designs, the proposed implementation simplifies the prototype design process and reduces the software development time. The proposed system provides a flexible and reconfigurable prototype for researchers to test and validate the performance of UA communication algorithms in real UA channels.

Impact of phase noise on single-tap equalization for fast–OFDM signals under generic linear fading channels

In this correspondence, we present the performance evaluation of a low-complexity fast – orthogonal–frequency–division–multiplexing (F–OFDM) scheme, in the presence of phase-noise (PHN), working under the generic linear fading channels (like two-wave-with-diffuse-power (TWDP) multipath fading and modal dispersion in multi-mode-fiber optic channel). Here, a single-tap zero-forcing (ZF) equalizer is utilized to compensate the channel-impulse-response (CIR) without sacrificing data-rate, in which the discrete-cosine-transform (DCT) operation is replaced by the discrete-Fourier-transform (DFT) operation at the receiver. The phase noise variations are modelled by utilizing the random–walk paradigm, in which PHN is dependent on the model parameters/statistics. Therefore, main focus is on the impact of PHN on the performance of single-tap ZF equalization for F–OFDM signals. Simulation results are presented to illustrate efficiency and efficacy of underlying F–OFDM system, while working under TWDP, Rician and Rayleigh multipath fading linear channels. It can be inferred from results that the PHN severely affects/deteriorates the performance of F–OFDM based communication systems in terms of high bit-error-rate (BER), when the PHN variations are large. Moreover, the TWDP fading model is found to be quite appropriate for analyzing/investigating the BER performance of communication systems using the binary-shift-keying modulation technique.

Performance Enhancement for Unipolar OFDMbased Optical Wireless Communication Systems

Performance Enhancement for Unipolar OFDMbased Optical Wireless Communication Systems

A Wireless Covert Channel Based on Constellation Shaping Modulation

Wireless covert channel is an emerging covert communication technique which conceals the very existence of secret information in wireless signal including GSM, CDMA, and LTE. The secret message bits are always modulated into artificial noise superposed with cover signal, which is then demodulated with the shared codebook at the receiver. In this paper, we first extend the traditional KS test and regularity test in covert timing channel detection into wireless covert channel, which can be used to reveal the very existence of secret data in wireless covert channel from the aspect of multiorder statistics. In order to improve the undetectability, a wireless covert channel for OFDM-based communication system based on constellation shaping modulation is proposed, which generates additional constellation points around the standard points in normal constellations. The carrier signal is then modulated with the dirty constellation and the secret message bits are represented by the selection mode of the additional constellation points; shaping modulation is employed to keep the distribution of constellation errors unchanged. Experimental results show that the proposed wireless covert channel scheme can resist various statistical detections. The communication reliability under typical interference is also proved.

OFDM 기반 고속주행 철도통신 시스템의 ICI 소거 기법 연구

OFDM 기반 고속주행 철도통신 시스템의 ICI 소거 기법 연구

직교주파수분할다중화 통신 시스템을 위한 압축 센싱 기반 임펄스 잡음 및 클리핑 잡음 감쇄 기법

OFDM 기반 통신시스템에서 압축 센싱을 단계적으로 적용하여 임펄스 잡음과 클리핑 잡음을 제거하는 방법을 제안한다. 이 방법은 1단계로 적응적 임계값을 적용한 블랭킹 기법을, 2단계 및 3단계에서 압축 센싱 기법을 반복적으로 적용하며 판정 궤환을 통해 비트 오율을 점차 감소시킨다. 임펄스 잡음 채널에서 모의실험결과 비트 오율이 <TEX>$10^{-5}$</TEX>일 때 4.5dB의 SNR 이득을 얻을 수 있었다. A compressive sensing based iterative scheme for reducing both the impulsive noise as well as the clipping noise is proposed for OFDM-based communication systems. Nonlinear blanking using adaptive thresholds is used in the 1st stage followed by two consecutive compressive sensing based detection with the aid of decision feedback for reducing the BER gradually. Our simulation results revealed an SNR gain of 4.5dB at the BER of <TEX>$10^{-5}$</TEX>.

A Heterogeneous Multi-core DSP Architecture for OFDM-Based Communication Systems

A Heterogeneous Multi-core DSP Architecture for OFDM-Based Communication Systems

Evaluation of mixed permutation codes in PLC channels, using Hamming distance profile

We report a new concept involving an adaptive mixture of different sets of permutation codes (PC) in a single DPSK---OFDM modulation scheme. Since this scheme is robust and the algorithms involved are simple, it is a good candidate for implementation for OFDM-based power line communication (PLC) systems. By using a special and easy concept called Hamming distance profile, as a comparison tool, we are able to showcase the strength of the new PC scheme over other schemes reported in literature, in handling the incessant noise types associated with PLC channels. This prediction tool is also useful for selecting an efficient PC codebook out of a number of similar ones.

Cramér–Rao bounds for L‐band digital aeronautical communication system type 1 based passive multiple‐input multiple‐output radar

In this study, of concern is the achievable estimation accuracy for a non-coherent passive multiple-input multiple-output (MIMO) radar employing orthogonal frequency-division multiplexing (OFDM) based signals of opportunity. The motivation behind this investigation is the surveillance aspect of the air trac management modernisation process currently taking place in civil aviation. To this end, the surveillance capability of the OFDM-based L-band digital aeronautical communication system type 1 (LDACS1) is analysed. The extension of the LDACS1 communication system towards surveillance is of great importance since it would enable an alternative, non-cooperative surveillance application, and, together with the already validated navigation extension, establish a fully integrated LDACS1-based communication, navigation, and surveillance technology. The modied Cramer-Rao bound on the joint estimation of target location and velocity for a non-coherent passive MIMO radar, employing the OFDM-based LDACS1 signals as signals of opportunity, is investigated. The analysis is carried out assuming one target, multiple and widely separated transmit and receive antennas, orthogonal waveforms, independent reection coecients, and zero-mean white Gaussian noise. Closed-form expressions for the relevant elements of the modied Fisher information matrix are obtained. The results can be used to assess the estimation accuracy of a multiple antenna passive radar system employing any OFDM-based signals of opportunity.

Optimized threshold calculation for blanking nonlinearity at OFDM receivers based on impulsive noise estimation

AbstractImpulsive noise (IN) degrades the performance of OFDM-based communication systems. Performance degradation is usually measured in terms of signal-to-noise ratio (SNR) and symbol-error rate (SER). To improve the performance of the system of OFDM receivers, one of the effective methods is to use blanking nonlinearity. In this method, the samples whose magnitudes exceed a certain fixed threshold are considered to be IN-affected and are therefore blanked. A fixed threshold does not always determine the IN-affected samples truly for all probabilities of IN occurrence. This paper proposes an optimized threshold-calculation method for blanking nonlinearity which is based on distribution characteristics of the received signal, i.e., mean, median, and peak. The proposed method can calculate an optimized threshold for all probabilities of impulsive noise occurrence. Simulation results show over 2.2-dB gain in SNR and lower SER by using the proposed method as compared to fixed threshold.

DIT 기반 IFFT의 Bit-Reversal 메모리 감소 기법

OFDM 기반 통신시스템에서 IFFT는 중요한 핵심 컴포넌트 중의 하나이다. 본 논문에서는 OFDM 기반 통신시스템을 위한 메모리가 효율적인 새로운 IFFT 설계 방법을 제안한다. OFDM 기반 통신시스템에서 사용되는 IFFT의 입력신호는 데이터 변조신호, 파일럿과 널(null) 신호로 구성된다. 제안한 방법은 IFFT 입력신호의 매핑을 통해 IFFT에서 가장 큰 메모리를 차지하는 비트리버스의 메모리를 감소시키는 데 초점을 둔다. 비트리버스의 메모리 크기를 감소시키기 위해 DIT기반 구조에 적합한 선택 매핑기법을 제안한다. 시뮬레이션을 통해 제안한 방법이 기존 방법과 비교하여 약 50%의 메모리가 감소됨을 보인다.