OFDM Technology Research Articles

A Novel Machine Learning Approach for Blind Carrier Offset Estimation in OFDM Systems

As wireless networks continue to evolve with the emergence of sixth-generation networks and beyond, OFDM technology is expected to be an essential system component for providing reliable connectivity in an increasingly complex environment. Its high spectrum efficiency, efficiency against impulse noise, and resilience against frequency-selective multipath fading channels make it an invaluable component. Although OFDM technology has various capabilities and uses and is widely used, it has some issues and challenges, and one of these challenges is Carrier Frequency Offset (CFO). The CFO destroys orthogonality between subcarriers and causes subcarrier misalignment at the receiver, resulting in Inter- Carrier Interference (ICI) in OFDM systems. This interference impairs system performance by introducing errors and degrading signal-to-noise ratios (SNR). In this paper, a novel approach to estimate the CFO in OFDM systems via Feedforward Neural Network (FNN) has been proposed. The architecture is precisely designed for regression tasks, with a focus on accurately estimating the continuous parameter φ based on the input features. The multiple hidden layers facilitate the extraction of intricate patterns, while careful training options ensure efficient optimization and monitoring of the training process. The performance of the proposed FNN algorithm is assessed and compared with other subspace-based methods, ESPRIT, PM(MUSIC), and QR. Remarkably, the results demonstrate that the FNN algorithm consistently outperforms all subspace methods, especially in low SNR scenarios.

Efficient PAPR Reduction in Cyclic Prefix with Enhanced Selection Strategy

The OFDM system’s selective mapping (SLM) technique for reducing Peak to Average Power Ratio (PAPR) seems promising. The fundamental principle of SLM is to create unique send sequences from the same data source and choose the transmit signal with the lowest PAPR. This study presents an enhanced cyclic prefix selection system with a lower PAPR by using selective mapping approaches. With the use of a signal multiplexing technique called orthogonal frequency division multiplexing (OFDM), the available bandwidth is divided into a range of frequencies called sounds. OFDMA technology can be employed anywhere that radio waves are used for data transmission. Input data is moved to the transmitter side for channel encoding. Using in-channel encoding, the digital signal is digitized and superfluous binary digits are eliminated. The signal is then connected to add and remove prefixes in a cyclical manner. Faults between these processes are eliminated by the AWGN channel followed by Hilbert Transform to lower the complexity of the entire process. Finally, by combining the clipping and SLM methods, improved outcomes are attaining in terms of spectral efficiency and PAPR reduction value, while maintaining the performance of channel estimation. MATLAB simulation is employed to evaluate the recommended method.

Emergency communication service solution based on UAV swarm

It has a broad application prospect to provide communication services with UAVs. In this paper, the authors propose an emergency communication service scheme based on UAV swarm, which can provide users with stable network connection to communication services when they are far from the base station. In our design, multiple UAVs will be placed in the middle of the base station and the target area to form a multi-antenna array. Beamforming technology is applied to increase the signal strength through the UAV and transmit the signal from the base station to the target area. Above the target area, we will deploy multiple UAVs using OFDM technology to provide signal relay services for users below. Through simulation and calculation on MATLAB and python, we verify the feasibility and applicability of this scheme.

Method of adaptation of cascade codes to ensure reliability of information transmission of wireless data transmission systems

The article proposes a method of structural adaptation of cascade codes, designed to ensure the specified reliability of information transmission of wireless data transmission systems in the event of interference, due to the dynamic synthesis of combined structures of cascade codes under conditions of a priori uncertainty. The essence of the method is to identify the internal structure of the code, due to which the structure of the component codes of the turbo code is determined. It was developed using the gradient method due to the implementation of a multi-step iterative procedure for finding optimal system parameters. Implementation of the method allows to ensure the reliability of information transmission of wireless data transmission systems. To check the effectiveness of the method of structural adaptation of cascade codes, a simulation model was developed in the C++ programming language in the Visual Studio 2019 software environment, and wireless data transmission systems were simulated. The simulation results show that the combined structure of building cascade codes together with OFDM technology allows you to independently adapt the coding rate of each of the coding stages depending on the results of the analysis of the reliability of information in this cascade, which leads to the provision of the specified reliability of information transmission, while the BSPD bandwidth is reduced by 4–12% against 20–35% of known results. The use of Reed-Solomon codes in a sequential cascade scheme with turbo codes due to the adaptation of the coding rate of this cascade design allows obtaining an energy gain of 0.5–0.7 dB without increasing the bandwidth of the transmission system compared to systems that use only turbo codes. The obtained results are of significant relevance and can be implemented in the development of information transmission systems to ensure the reliability of data transmission, both in peacetime and in conditions of armed aggression of the Russian Federation against Ukraine.

Information Technology for Maximizing Energy Consumption for Useful Information Traffic in a Dense Wi-Fi 6/6E Ecosystem

In Wi-Fi standards, a relatively narrow range of frequency spectrums is declared as working, on the operation of which additional restrictions are imposed in different countries. When creating dense wireless network ecosystems focused on massive information traffic, this circumstance causes significant interference even in the case of using Wi-Fi 6/6E-compatible equipment. An effective solution to this problem is the implementation of a centralized management mechanism for the relevant parameters of the target network ecosystem. The growing attention to ecology and rational use of electricity makes the problem of maximizing energy consumption for useful information traffic in a dense Wi-Fi 6/6E ecosystem an urgent task. Only the addressed information traffic between the transmitter and the target subscriber, which are subjects of the OFDMA technology and the MU-MIMO multiple access system (with an emphasis on the latter), is considered useful. To solve the problem, the authors formalized the Wi-Fi 6/6E ecosystem’s energy consumption model, which takes into account the specifics of OFDMA and MU-MIMO, the influence of the communication channel characteristics on the speed of target information transfer, and detailed energy consumption for maintaining the network infrastructure in a functional state. Based on the created model, the research problem is represented by the difference between two monotonic functions, relative to which the problem of optimization with restrictions is set. The process of solving this problem is presented in the form of information technology with a branch-and-bound hierarchy and a nested unconditional optimization problem. The results of simulated modelling in the MATLAB-NS3 environment showed a significant advantage of the authors’ approach. The energy power consumption by the Wi-Fi 6/6E ecosystem, the parameters of which were adjusted with the help of the authors’ information technology, decreased by more than four times.

System optimization for index modulated OFDM

This paper introduces the system optimization scheme of OFDM-IM, an emerging modulation technology that combines OFDM technology and modulation index technology to improve spectral efficiency and system reliability while ensuring high-speed transmission. However, as a new technology, OFDM still has shortcomings. This paper investigates three system optimization schemes for OFDM-IM: he deep learning-based OFDM-IM optimization scheme, MIMO-OFDM-IM, and LDPC coding-assisted subcarrier index protection scheme. It is found that these three optimization schemes are indeed helpful for optimizing the performance of OFDM-IM through system simulation experiments. The IM-OFDM system optimization based on deep learning is very helpful for IM-OFDM in terms of channel estimation, signal detection, and modulation classification. MIMO-OFDM-IM can increase channel capacity and signal transmission reliability. By protecting the subcarrier index, LDPC codes can effectively reduce the subcarrier error rate and improve the reliability and performance of IM-OFDM systems. Due to their different technical characteristics, the three optimization schemes have different advantages. They also have their application scenarios in which they excel. However, considering these technologies are relatively new, there are still certain drawbacks to these three technologies. Researchers need to continue to study them in-depth and gradually overcome them.

Reducing the impact of interchannel interference on the efficiency of signal transmission in telecommunication systems of data transmission based on the ofdm signal

This paper considers the process that forms an interchannel transient interference in the structure of the signal created on the basis of the technology of parallel data transmission and frequency distribution with multiplexing of the phase-modulated signal – the OFDM signal. Based on the analysis of the OFDM signal structure, it was determined that changes in the position and parameters of the carrier symbol from the composition of this OFDM symbol create an interchannel transient interference. A list of OFDM signal parameters that can affect the appearance of interchannel interference and the value of its quantitative value was summarized and presented. A model for assessing the impact of interchannel interference on the efficiency of signal transmission in telecommunication data transmission systems based on the OFDM signal has been developed and proposed. Based on mathematical modeling using this model, the dependence of the quantitative assessment of the magnitude of the interchannel interference on the magnitude of the protective interval for different values of the interchannel value with a different number of signal pre-reception has been established. It is shown that an increase in the value of the interchannel value to 96 subchannels makes it possible to achieve an interchannel transient interference of less than 3 percent with a protective interval of more than 2 ms already with one pre-reception. This is explained by the fact that the increase in the interchannel value makes it possible to reduce the value of the protective interval and minimizes the effect of frequency distortions of the sub-channel of one channel. The data reported in this work and the recommendations substantiated on their basis confirm the possibility of the proposed model for assessing the value of the interchannel transient interference and justifying the recommendations for reducing its impact on the efficiency of signal transmission in telecommunication data transmission systems based on the OFDM signal. The proposed evaluation model can find practical application in improving existing and developing new telecommunication data transmission systems based on OFDM technology

PERFORMANCE OF MU-MC-DS-CDMA SYSTEM IN RAYLEIGH FADING CHANNEL

The Multi user Multi Carrier Direct sequencing Code Division Multiple Access (MU-MC-DS-CDMA) strategy was developed in response to rising demand for system capacity, higher data rates, and multimedia services. It's essentially a combination of CDMA and OFDM schemes. As a result, MC-CDMA takes the advantages of both CDMA and OFDM technologies. CDMA improves bandwidth consumption performance, whereas OFDM helps to minimize Inter Symbol Interference (ISI) and multipath fading. This dissertation suggests a method for evaluating the performance of multi user MC-DS-CDMA system. BER and PAPR are used to evaluate the results. The Bit Error Rate (BER) output of the proposed method is then examined using MATLAB for various modulation techniques. By using Walsh-Hadamard (W-H) code is used because it eliminates Multiple Access Interference (MAI). In terms of BER, it can be shown that BPSK performs better than QPSK. Key Words: AWGN, BER, ISI, MC-CDMA, Rayleigh Fading Channel, SNR, QPSK, MAI

The use of SDR as sensor nodes of the intelligent system of management of radio emission data collection

The article is devoted to the study of the use of software-controlled radio (SDR) in the context of the growing demand for wireless technologies and radio-electronic devices. It focuses on the problems of oversaturation of the radio spectrum, the need to automate the management of radio systems, security, the use of machine learning and AI, the integration of various systems, as well as economic benefits. The paper examines the SDR as a tool to address these challenges, particularly due to its ability to operate over a wide frequency range and the use of digital signal processing. The role of SDR in radio monitoring and its importance in identifying and eliminating sources of interference are also revealed. The main attention is paid to the development of the algorithm for performing OFDM-modulation operations in the SDR of intelligent control systems of the radio emission data collection network. The proposed algorithm aims to optimize data transmission, reducing the transmission of redundant bits of information and promoting efficient use of the radio spectrum. The article describes in detail the architecture and functionality of SDR, including an analysis of the impact of OFDM technologies on the efficiency of data transmission within software-controlled systems.

OFDM Spectrum Sensing Analysis and Implementation Method

OFDM is a carrier modulation technology, which realizes the parallel transmission of high-speed serial data through frequency division multiplexing. OFDM has an excellent ability to resist multipath fading and is commonly used in wireless communication transmission technology. Spectrum sensing technology is a technology that allows cognitive users to accurately obtain the authorized spectrum usage in wireless networks through signal detection and other processing methods. It is the basis for effectively using different idle channels in different time domains. This paper mainly discusses the OFDM technology, deduces the algorithm of the implementation principle and mathematical characteristics of OFDM, analyses its spectrum characteristics and performance advantages, focuses on the principle and method of OFDM spectrum sensing based on spectrum sensing technology, combs the characteristics of several existing commonly used OFDM spectrum sensing methods, and analyses the implementation cost, hardware requirements, transmission performance The performances of interference factors and other aspects are sorted out, the advantages and disadvantages of several existing OFDM spectrum sensing methods are compared, their respective applicable environments are compared, and their possible problems in the future development prospect of OFDM technology and the direction that needs further research and improvement are put forward.

Pricing‐based power allocation in cloud radio access network with multiple access technology selection

AbstractIn this article, we consider an uplink economy‐efficient resource allocation framework in a multicellular cloud radio access network (C‐RAN) architecture with network virtualization, where a mobile network operator (MNO) interacts with a number of mobile virtual network operators (MVNOs) with a predetermined business model. OFDMA and Massive MIMO multiple access technologies have been assumed to be available for each MVNO at two different prices. In this setup, we propose a multi‐access technology selection approach (MATSA) with the objective of maximizing delivered rate to end users, reducing operation costs and maximizing MVNOs' profit subject to a set of constraints, which leads to a nonconvex resource allocation problem with very high computational complexity. The utility function is defined as the difference between the total throughput and the utilization cost for each technology. To tackle this problem, we apply complementary geometric programming (CGP) and successive convex approximation (SCA), that results in a two‐step iterative solution. Simulation results demonstrate superiority of the proposed approach compared to a similar scenario with predetermined multi‐access technology, especially for large numbers of users.

Implementation of FBMCbased Massive MIMOusing Space Time Block Coding

In wireless communication multipath propagation of signal will cause major drawbacks like Intersymbol interference (ISI), Delay spread, Doppler Spread and Intercarrier interference. These drawbacks are efficiently handled by using OFDM technology with Cyclic Prefix, but at the cost of High PAPR increasing the non-linear behaviour of Power Amplifier thereby increases BER and inband distortion, high out of band emissions and loss of spectral efficiency.To reduce the PAPR several PAPR reduction techniques have been proposed over the last few decades but at high complexity. Due to above drawbacks, OFDM technology is not able to provide the requirements of next generation wireless communication and thereby making it un-favourable for 5G communications. To overcome above drawbacks of OFDM, I used a, Filter Bank multicarrier (FBMC), 5G candidate waveform and proposed a method for reducing PAPR, Out-of-band emissions and latency with improving spectral efficiency. I developed a novel precoding method based on a pruned Discrete Fourier Transform (pDFT) in combination with Poly Phase Network (PPN) architecture. The proposed technique has the same peak-to average power ratio as OFDM but does not require a cyclic-prefix and has much lower out-of-band emissions. Furthermore, my method restores complex orthogonality and the ramp-up and ramp-down period of FBMC is dramatically decreased, allowing low latency transmissions. PPN is processed after pDFT, which transforms the received data into ISI-free data.

Research on Mine OFDM Intelligent Receiver Based on Deep Learning

coal is an important energy. Coal mining needs a series of equipment, among which communication equipment can ensure the safety of underground workers in the mining process and improve production efficiency. Aiming at the problems of multipath fading and anti-interference of signal transmission in coal mine, researchers propose to optimize the quality of signal transmission in coal mine with OFDM technology. Compared with traditional OFDM technology, this paper proposes a method of mine OFDM intelligent receiver based on deep learning, which aims to use deep learning technology to replace the signal recovery process of the receiver of traditional OFDM technology. The simulation results show that in terms of bit error rate, the signal recovery of the receiver based on deep learning technology is obviously better than that of the traditional OFDM receiver. This will improve the economic benefits of coal mining in the future.

Аналитический обзор нововведений стандарта IEEE 802.11ax

Nowadays, due to the rapid development of small-scale wireless networks, the increase in the amount of the traffic consumption (due to the pandemic and the transfer of employees to remote work), the increase in the number of wireless devices and the requirements for the bandwidth of communication channels and different delays arising in them, characteristics of the 802.11ac standard the bandwidth described in this standard were no longer enough. To eliminate these shortcomings, the IEEE 802.11ax standard was introduced in 2019, and finally approved on February 1, 2021. This standard is commercially known as Wi-Fi 6. In the 802.11ax standard, developers focused on energy efficiency, capacity and bandwidth of the communication channel. Improving these parameters resulted in a quadruple increase in the average throughput per user and improved customer experience. These improvements are relevant for both external and internal subscribers. The article presented new technologies used in the IEEE 802.11ax (Wi-Fi 6) standard, such as MU-MIMO, OFDMA, Color Code BSS and Beamforming. MU-MIMO allows providers to simultaneously transmit different data to multiple subscriber stations. OFDMA technology allows providers to increase the bandwidth of the communication channel. The Color Code BSS technology allows us to identify the network as a “friend” or a “foe” when exchanging data between the router and other devices within the 802.11ax standard Wi-Fi network.

Design of Embedded Line Galloping Monitoring System Based on Wireless Communication Technology

In order to meet the requirements of multi-measurement nodes and high temperature resistance, this project draws extensive experience from relevant industries based on the relevant requirements. A bus temperature measurement system based on two-bus technology is developed. The system is based on two buses and combines OFDM technology to modulate signals on carriers with different frequencies. Through parallel transmission, the original signal is demodulated using differential coherent demodulation. The simulation results show that the system can effectively deal with channel signal interference.

A Systematic Perspective for 4Ghz Frequency Synthesizer Integration on to Single Systems

Abstract: In wireless medium, necessity of higher frequency is expanding day by day. For higher frequency deploy system data rates should be higher. In unguided medium, as signal passes a longer distance and due to intervention of noise, there is fallacy. In phases and frequencies and we get a drifted output. In view of this, we are prompted to make a low power frequency synthesizer which would provide a lower locking time, low settling time, average value of damping factor to give a regulated frequency response at the output. The suggested design aspect is for higher frequency which is executed in IEEE 802.11 WLAN standard and OFDM technology, Bluetooth technology, high frequency processor. We have used Microwind 3.1 55nm technology and ADS as outline tool to execute design. Keywords: Frequency synthesizer, phase frequency detector, voltage-controlled oscillators, Microwind 3.1, ADS, wireless communication

ЭФФЕКТИВНОСТЬ ВАРИАНТОВ МНОГОСТАНЦИОННОГО ДОСТУПА ДЛЯ СОТОВЫХ СЕТЕЙ 5G И 6G

Introduction: IMT2020 (5G) networks can significantly improve the performance of previous generation mobile communication systems in terms of improving broadband multiple access (eMBB – enhanced Mobile Broadband) and providing ultra-reliable low-latency communication (ULLRC – Ultra Low Latency Rellable Communication). The purpose of the work is to review and comparative analysis of multiple access technologies for promising mobile communication networks, which are based on OFDM. Result: The general principles of signal generation and processing when using variants of signals with OFDM using various methods of digital filtering of subcarrier frequencies are considered. For those OFDM options where a cyclic prefix may not be used (FBMC, UFMC), the possibility of increasing the information transfer rate is controversial, since the impulse responses of filters, for example, with FBMC, significantly exceed the duration of information signals, which increases intersymbol interference. Practical significance: The analysis of the general principles for constructing devices for generating and processing physical layer signals for OFDM variants with various methods of additional digital filtering of subcarrier frequencies shows that in all cases there is a significant complication of digital algorithms for generating and processing signals with a practical absence or in some cases a small gain (not more than (0.5&0.8) dB in relation to signal/noise) by the magnitude of the error per information bit. Based on the results of computer simulation, it is shown that OFDM technology and its variants do not allow obtaining breakthrough solutions in the field of physical layer signal characteristics for 5G and 6G networks, and alternative options for building group signal structures should be considered.

ОЦЕНКА СКРЫТНОСТИ OFDM!СИГНАЛОВ, ОСНОВАННЫХ НА BPSK МОДУЛЯЦИИ, С ПОМОЩЬЮ МЕТОДОВ НЕЛИНЕЙНОЙ ДИНАМИКИ

This article evaluates the stealth of signals based on the technology of orthogonal frequency discrete multiplexing (OFDM-signals) and BPSK modulation, using statistical methods for assessing stealth, represented by methods of nonlinear dynamics (Hurst exponent and BDS-statistics). As a result of the conducted studies, it was found that OFDM-signals based on BPSK modulation, in general, have insufficient stealth, since they can be detected using the Hurst exponent and BDS-statistics. The features of research using the Hurst exponent and BDS-statistics of OFDM-signals based on BPSK modulation are shown. Among such features, it should be noted that with an increase in the number of subcarriers, the values of the Hurst exponent and BDS-statistics also increase, in particular, the value of the Hurst exponent approaches values corresponding to the concept of white noise, and the value of BDS-statistics approaches values indicating that OFDM-signals with a large number of subcarriers can potentially be attributed to chaotic signals. From the above results, it can be seen that with an increase in the number of subcarriers OFDM-signals, some complication of the structure of the transmitted signals occurs, which, however, does not lead to an increase of stealth. The results obtained coincide with well-known studies from this field, which show that OFDM technology based on harmonic carrier modulation methods does not provide data transmission stealth. Further directions of research on the evaluation of the stealth of OFDM-signals using nonlinear dynamics methods are briefly described, in particular, the study of OFDM-signals with other types of modulation and a different number of subcarriers, as well as the study of OFDM-signals, which use additional methods to increase stealth.

Asymptotic characteristics of multichannel access systems with orthogonal filteration

The proposed article deals with digital modulation schemes that use a certain number of equidistant orthogonal subcarriers (the socalled OFDM technology). The theory of radio engineering chains and signals is used as the scientific and technical basis of the problem. The spectra of discrete signals were analysed, the influence of violations of the conditions of Kotelnikov's theorem and the asymptotics of the recovery errors of the original continuous signals were investigated. Methods of forming composite signals with arbitrary frequency difference of subcarriers have been developed. It is shown that when the amount of frequency shift of the basic series decomposition functions and the width of the spectrum of the main and side lobes in the spectrum of the output signal are matched, it is possible to count on the minimal influence of mutual interference and intersymbol interference of the composite signal. It was established that the method of orthogonal frequency multiplexing of channels (OFDM) allows to significantly increasing the bandwidth of the wireless communication system. In addition, with dynamic load changes in wireless networks, the impact of frequency collisions and an increase in the level of intra-system interference is minimized. Graphical analysis of the results of the series expansion on the quasiorthogonal system of basis functions shows that the errors of restoration of the original signals can reach unacceptable values. It was also established that when expanding into a non-orthogonal series with a larger number of members, the situation with the restoration of the original signals becomes a little more suitable, but no guarantees of monotonous improvement of the situation with restoration errors can be given in principle. This problem requires additional analytical research.

Errors of recovery of signals in multi-channel communication systems with orthogonal modulation

The errors of restoration of original continuous signals in digital communication systems with orthogonal modulation of equidistant subcarriers (the so-called OFDM technology) are considered. The theory of radio engineering circuits and signals is applied as a scientific and technical basis of the problem. The spectra of discrete signals were analyzed, the influence of violations of the conditions of Kotelnikov's theorem and the asymptotics of the recovery errors of the original continuous signals were investigated. Methods of analyzing composite signals with arbitrary selection of the sampling frequency of spaced subcarriers have been developed, and quantitative estimates of the quality of signal recovery on the receiving side using Euclidean distances have been obtained. . It is shown that when the amount of frequency shift of the basic series decomposition functions and the width of the spectrum of the main and side lobes in the spectrum of the output signal are matched, it is possible to count on the minimal influence of mutual interference and intersymbol interference of the composite signal. It was established that the correct selection of the sampling frequency of OFDM signals allows increasing the accuracy of signal recovery on the receiving side and the overall efficiency of the wireless communication system. In addition, with a dynamic change in the number of members of the decomposition series in wireless networks, the influence of frequency collisions, Gibbs ripples, and the level of intersystem interference is reduced. Graphical analysis of the results of the series expansion on the quasi-orthogonal system of basis functions shows that the errors of restoration of the original signals can reach unacceptable values. It was also established that when expanding into a non-orthogonal series with a larger number of members, the situation with the restoration of the original signals becomes a little more suitable, but guarantees of improving the situation with recovery errors can be given only when combining the correct selection of the sampling frequency with the number of members of the series expansion. This problem requires additional research of an analytical and computational nature.