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ABSTRACT Nonorthogonal multiple access (NOMA) is a promising technique operating with limited resources. NOMA can be executed in both power and code domains. Cyclic interleaved NOMA strategies are debated in recent literature, combining power and code domains. Identical code cyclic shift (ICCS) transmission is viewed to be a bridge between code division access and NOMA. We propose identical code–data cyclic shift NOMA (ICDCS‐NOMA) in which the code and data are cyclically shifted in distinction to simple cyclic interleaved transmission introduced in our earlier work and the ICCS transmission. The cell‐edge user in a NOMA pair engages its signal transmission using ICDCS; in contrast, the cell‐center user prefers simple cyclic interleaved transmission. The spread data stream and its cyclic shifted version are blended in ICDCS, followed by cyclic interleaving. A distinct and extreme fading channel pair is assumed with the same number of paths for the edge and center users. Diversity combining multipath signals is embraced at the edge user terminal, and frequency domain equalization (FDE)/matched filter (MF) receiver is employed at the center user. The simulation indicates the dominance of the proposed ICDCS‐NOMA transmission in terms of the attained diversity gain over the conventional, ICCS, and simple cyclic interleaved transmissions. [ABSTRACT FROM AUTHOR]

In this paper, new schemes have been proposed for the estimation of the additive white Gaussian noise (AWGN) channel with intersymbol interference (ISI) in an iterative equalization and decoding system using low-density parity check (LDPC) codes. This article explores the use of the least squares algorithm in various scenarios. For example, the impulse response of the AWGN channel h was initially estimated using a training sequence. Subsequently, the impulse response was calculated based on the training sequence and then re-estimated once using the sequence estimated from the output of the LDPC decoder. Lastly, the impulse response was calculated based on the training sequence and re-estimated twice using the sequence estimated from the output of the LDPC decoder. Comparisons were made between the performances of the three mentioned situations, with the situation in which a perfect estimate of the impulse response of the channel is assumed. The performance analysis focused on how the bit error rate changes in relation to the signal-to-noise ratio. The BER performance comes close to the scenario of having a perfect estimate of the impulse response when the estimation is performed based on the training sequence and then re-estimated twice from the sequence obtained from the output of the LDPC decoder. [ABSTRACT FROM AUTHOR]

To solve this issue of phase estimation ambiguity induced by Gaussian-filtered minimum shift keying (GMSK) phase continuity, a GMSK coherent receiving algorithm based on optimal sampling point is proposed. For realizing the decoupling of symbols, a preceding method in constructed to encode original message to modulate and then the receiver samples at optimal time with minimal intersymbol interference to transform GMSK into offset quadrature phase shift keying (OQPSK), effectively avoiding this issue of Doppler frequency and phase inaccurate estimation induced by the introduction of initial phase ambiguity from previous unknown data. A coherent demodulator in built based on optimal sampling time to accomplish reliable receiving with low complexity. Simulation results indicate that the proposed method has a higher estimation range of Doppler frequency, while comparable estimation precision. Meanwhile, compared to optimal receiver, the proposed demodulation algorithm has very small complexity and comparable demodulation performance. [ABSTRACT FROM AUTHOR]

The paragraph introduces a proposed CP-free OFDM PDMA downlink transmission system. The main focus of the system is to address the capacity limitations caused by the overhead of cyclic prefix in traditional PDMA systems. The transmitter utilizes a pattern mapping unit before CP-free OFDM modulation to enhance system capacity and frequency efficiency. Decision feedback equalization (DFE) is employed in the receiver to eliminate intersymbol interference. The output signals from the DFE are then passed through a CP restoration unit to convert a linear-shifted signal into a cyclic-shifted signals. To assess the system's performance, simulations are conducted, investigating different key parameters such as overload rate, channel condition, and signal-to-noise ratio. The results indicate that, compared to CP OFDM PDMA systems, the proposed CP-free PDMA system significantly enhances system capacity under the same overload rate. Additionally, bit error rate is also evaluated during the simulations. Overall, the paragraph provides an overview of the proposed CP-free OFDM PDMA system, its components, and the simulation-based evaluation of its performance compared to traditional PDMA systems. [ABSTRACT FROM AUTHOR]

Underwater acoustic communication signals suffer from time dispersion due to time-varying multipath propagation in the ocean. This leads to intersymbol interference, which in turn degrades the performance of the communication system. Typically, the channel correlation functions are employed to describe these characteristics. In this paper, a metric called the channel average correlation coefficient (CACC) is proposed from the correlation function to quantify the time-varying characteristics. It has a theoretical negative relationship with communication performance. Comparative analysis involving simulations and experimental data processing highlights the superior effectiveness of CACC over the traditional metric, the channel coherence time. [ABSTRACT FROM AUTHOR]

This Letter proposes a low-complexity joint equalization and decoding reception scheme based on super-trellis per-survivor processing, making it possible to apply maximum likelihood sequence estimation in high-order underwater acoustic communications under fast time-varying channels. The technique combines trellis-coded modulation states and intersymbol interference states and uses per-survivor processing to track channel parameters. Furthermore, a general trellis configuration for arbitrary order quadrature amplitude modulation signal is provided when truncate the channel is used to describe the intersymbol interference state to 1. Sea trials results show that the performance of proposed method can be more than 1.4 dB superiority than conventional schemes. [ABSTRACT FROM AUTHOR]

This research conducted a comparative analysis of two communication systems. The first system utilizes a conventional series configuration consisting of a symbol-rate least mean square (LMS) equalizer followed by a timing recovery loop. The second system introduces an innovative approach that integrates a symbol-rate LMS equalizer and a timing recovery component within a single loop, allowing mutual feedback between the two blocks. In this integrated system, the equalizer also provides timing error information, thereby eliminating the requirement for a separate threshold error detector. This study examines the performance curves of both system configurations. The simulation results revealed that the integrated system may offer improved stability in terms of multiple transmission challenges, including phase and frequency offsets and intersymbol interference. Further analysis and discussion highlight the significant insights and implications of the proposed architecture. Overall, the present findings provide an alternative perspective on the joint implementation of equalization and timing recovery in communication systems. [ABSTRACT FROM AUTHOR]

Combined in-band full duplex-multiple input multiple output (IBFD–MIMO) technology can significantly improve spectrum efficiency and data throughput, and has broad application prospects in communications, radar, the Internet of Things (IoT), and other fields. Targeting the self-interference (SI) issue in microwave photonic-based IBFD–MIMO communication systems, a microwave photonic self-interference cancellation (SIC) method applied to the narrowband 2 × 2 IBFD–MIMO communication system was proposed, simulated, and analyzed. An interleaver was used to construct a polarization multiplexing dual optical frequency comb with a frequency shifting effect, generating a dual-channel reference interference signal. The programmable spectrum processor was employed for filtering, attenuation, and phase-shifting operations, ensuring amplitude and phase matching to eliminate the two self-interference (SI) signals. The simulation results show that the single-frequency SIC depth exceeds 45.8 dB, and the narrowband SIC depth under 30 MHz bandwidth exceeds 32.7 dB. After SIC, the desired signal, employing a 4QAM modulation format, can be demodulated with an error vector magnitude (EVM) as low as 4.7%. Additionally, further channel expansion and system performance optimization are prospected. [ABSTRACT FROM AUTHOR]

Abstract Wireless quantum optical communications over multipath channels with uncorrelated scattering still seem to be an open issue, although classical optical transmission was already considered, however, neglecting Bose–Einstein distributed thermal noise photons, leading to results that cannot be applied here. A viable way forward is proposed.

Wireless quantum optical communications over multipath channels with uncorrelated scattering still seem to be an open issue, although classical optical transmission was already considered, however, neglecting Bose–Einstein distributed thermal noise photons, leading to results that cannot be applied here. A viable way forward is proposed. [ABSTRACT FROM AUTHOR]

Objective In order to cope with the growing demand for ultra-gigabit, from gigabit to 10-gigabit, from The 5th Generation Fixed networks(F5G) to F5G-Advanced(F5. 5G), 50 Gbit/s Passive Optical Network (PON) is considered to be an important part of F5. 5G. Therefore, according to the current access network development situation, 50 Gbit/s PON technology is deeply studied in this paper. Methods This paper first introduces the difficulties in achieving high sensitivity of 50 Gbit/s PON, and proposes a solution. 50 Gbit/s Non-Return-Zero (NRZ) signals pass through Avalanche Photodiode (APD) detectors to form macroscopic currents that can be detected under the action of strong electric fields. The current is amplified by a Transresistance Amplifier (TIA) and converted into a voltage output. After balancing, the Feed Forward Equalizer (FFE) and Decision Feedback Equalizer (DFE) of optical Digital Signal Processing (oDSP) chip are used to compensate the trailing phenomenon of pulse signal, and then the influence of intersymbol interference is minimized by DFE. Then the paper analyses the key technologies such as APD, TIA and oDSP, and the receiving performance is compared with that of 25 Gbit/s APD. Results According to the experimental test results of the two groups, the received optical power of the 25 Gbit/s APD in the first group is -8.48 dBm when the receiving signal has no error code during the test time of 4 min, and the received optical power reaches -26.61 dBm when the Bit Error Rate(BER) is 2.78e-2. In the case of 50 Gbit/s APD, the received optical power is - 8.97 dBm when the received signal has no bit error in 4 min, and the received optical power reaches -27.05 dBm when the BER is 2.78e-2. The second set of 50 Gbit/s APD-2 data also achieves the same experimental results. Conclusion In conclusion, 50 Gbit/s APD has higher receiving sensitivity, better performance, and is more suitable for use in 50 Gbit/s PON optical modules to achieve high receiver sensitivity. Finally, a feasible scheme is proposed on the balance technology and APD for future cost reduction. [ABSTRACT FROM AUTHOR]

This paper outlines the development of an optical receiver capable of handling data at a rate of 4 Gb/s. The receiver makes use of a multi-dot PIN CMOS photodiode with a bandwidth of 930 MHz (capacitance of 48.8fF) and a responsivity of 0.294 A/W at a wavelength of 675 nm. It also features a single-to-differential (SDT) noise-suppressed transimpedance amplifier (TIA) equalizer. By implementing a low-frequency zero synthesis within the STD-TIA feedback path, the 3-dB frequency roll-off of the photodiode is extended by a factor of 2.63, resulting in an overall front-end bandwidth of 2.45 GHz with a transimpedance gain of 84 dB $\Omega $ . The SDT TIA eliminates the need for a dummy TIA, improving the noise performance of the receiver achieving the integrated input-referred current noise for the entire front-end to less than 717 nA rms. Additionally, a detailed theoretical analysis of equalization methods, as well as the impact of inter-symbol interference (ISI) and noise on bit error rate (BER) degradation is presented. The receiver has been successfully tested for data transmission at rates of 4 Gb/s, 3 Gb/s, and 2.5 Gb/s, achieving bit-error ratios of less than $10^{-9}$ at minimum average optical powers of -16.2 dBm, -17.2 dBm, and -18 dBm, respectively. Furthermore, the receiver consumes 28 mA from a 3.3V power supply and occupies a core area of 1.4 mm $\times 0.7$ mm.

This paper presents a transition-limited pulse-amplitude modulation (TLPAM) signaling method to enable a high data rate and robust wireline communications. TLPAM signaling addresses the impact of high intersymbol interference (ISI) ratios in conventional M-ary PAM signaling methods by limiting the maximum voltage transition level between adjacent symbols. The implementation of a TLPAM signaling encoder is realized by setting back the most significant bits (MSBs) in the queue. The correlation between TLPAM's maximum transition level, effective data rate, and eye width/height is analyzed with various channel loss parameters, followed by characterization and measurement results with a realistic channel setup. The analysis and experimental results reveal the effectiveness of the proposed TLPAM signaling scheme for achieving a high data rate with minimal interference.

In this paper, new schemes have been proposed for the estimation of the additive white Gaussian noise (AWGN) channel with intersymbol interference (ISI) in an iterative equalization and decoding system using low-density parity check (LDPC) codes. This article explores the use of the least squares algorithm in various scenarios. For example, the impulse response of the AWGN channel h was initially estimated using a training sequence. Subsequently, the impulse response was calculated based on the training sequence and then re-estimated once using the sequence estimated from the output of the LDPC decoder. Lastly, the impulse response was calculated based on the training sequence and re-estimated twice using the sequence estimated from the output of the LDPC decoder. Comparisons were made between the performances of the three mentioned situations, with the situation in which a perfect estimate of the impulse response of the channel is assumed. The performance analysis focused on how the bit error rate changes in relation to the signal-to-noise ratio. The BER performance comes close to the scenario of having a perfect estimate of the impulse response when the estimation is performed based on the training sequence and then re-estimated twice from the sequence obtained from the output of the LDPC decoder.

To address the problem of unreliable single-link underwater acoustic communication caused by large signal delays and strong multipath effects in shallow water environments, this paper proposes a distributed underwater acoustic diversity communication system (DUA-DCS). DUA-DCS employs a maneuverable distributed cross-medium buoy network to form multiple distributed, non-coherent, and parallel communication links. In the uplink, a receiving diversity processing mechanism of joint decision feedback equalizer embedded phase-locked loop and maximum signal-to-interference ratio combining (DFE-PLL-MSIRC) is proposed to achieve waveform-level diversity combining of underwater signals. A phase-locked loop module is embedded in each branch of the decision feedback equalizer to eliminate the residual frequency and phase errors after Doppler compensation. Meanwhile, the combining coefficients are determined based on the maximum signal-to-interference ratio criterion, taking into account the residual inter-symbol interference after equalization, resulting in efficient and accurate computation. Additionally, the combined decision values are fed back to the feedback filters in each branch to ensure more accurate feedback output. Simulation and lake experiment results demonstrate that, compared to the single-link communication system, DFE-PLL-MSIRC can achieve a diversity gain of more than 5.2 dB and obtain about 3 dB more diversity gain than the comparison algorithm. And the BER of DFE-PLL-MSIRC can be reduced by at least one order of magnitude, which is lower by at least 0.6 order of magnitude compared to the comparison algorithm. In the downlink, a transmitting diversity processing mechanism of complex orthogonal space-time block coding (COSTBC) is proposed. By utilizing a newly designed generalized complex orthogonal transmission matrix, complete transmission diversity can be achieved at the coding rate of 3/4. Compared to the single-link communication system, the system can achieve a diversity gain of more than 6 dB. [ABSTRACT FROM AUTHOR]

The Orthogonal Frequency Division Multiplexing (OFDM) method provides effective bandwidth utilization and straightforward Frequency Domain Equalization (FDE). The OFDM system can be applied without a group of modulators and demodulators by using the Inverse Fast Fourier Transform (IFFT) and Fast Fourier Transform (FFT). The Fast Walsh Hadamard Transform (FWHT) and Inverse Fast Walsh Hadamard Transform (IFWHT) can also be used to build the OFDM system. In this work, we employ the IFWHT and FWHT to build the OFDM. This is followed by a proposal for a Joint Low-Complexity Regularized Zero Forcing-Successive Interference Cancellation (JLCRZF-SIC) equalizer with respect to various linear and nonlinear equalizers at various antenna configurations. A closed form for arithmetic operation count for the proposed equalizer is proposed. The proposed equalizer executes the equalization process more accurately than other schemes with low-complexity deployments. The analysis results show that the proposed equalizer outperforms the conventional one. [ABSTRACT FROM AUTHOR]

In this work, subcarrier coordinate interleaving (CI) is implemented to orthogonal frequency division multiplexing (OFDM) systems with the aim of both enhancing the error performance and reducing the implementation complexity. To this end, the modulated symbols are independently chosen from a modified M-ary amplitude-shift keying signal constellation under a specific CI strategy. In addition to doubling the diversity level of the original OFDM scheme, the adopted CI approach also drastically reduces the inverse fast Fourier transform (IFFT) size at the transmit side by guaranteeing the first half of the input vector to be identical with the second half at the input to the IFFT block. It is further demonstrated that the proposed system has the ability to enhance the robustness against common practical impairments such as insufficient cyclic prefix and phase noise. The closed-form expression of symbol error probability of the system is derived and confirmed with the simulation results. [ABSTRACT FROM AUTHOR]

Hill pointed out in his landmark paper that “An interesting open problem is to determine which common distributions (or mixtures thereof) satisfy Benford’s law … ”. Ever-since, there has been many attempts in finding distributions that are precisely compliant with Benford’s law. Even though sufficient conditions were derived and some ad-hoc distributions were reported in the literature, the lack of a general framework for generating such distributions is sensed. Almost all of the reported Benford-compliant distributions are finite-length. This paper looks at the problem from an electrical engineer’s perspective; it harnesses the literature on Nyquist inter-symbol interference theorem and then proposes a framework for generating infinite-length or arbitrary long finite-length distributions satisfying Benford’s law. [ABSTRACT FROM AUTHOR]

This paper presents a transition‐limited pulse‐amplitude modulation (TLPAM) signaling method to enable a high data rate and robust wireline communications. TLPAM signaling addresses the impact of high intersymbol interference (ISI) ratios in conventional M‐ary PAM signaling methods by limiting the maximum voltage transition level between adjacent symbols. The implementation of a TLPAM signaling encoder is realized by setting back the most significant bits (MSBs) in the queue. The correlation between TLPAM's maximum transition level, effective data rate, and eye width/height is analyzed with various channel loss parameters, followed by characterization and measurement results with a realistic channel setup. The analysis and experimental results reveal the effectiveness of the proposed TLPAM signaling scheme for achieving a high data rate with minimal interference. [ABSTRACT FROM AUTHOR]

This paper presents an eye-opening monitor technique leveraging four-level pulse amplitude modulation (PAM-4) symbol transition characteristics. This approach facilitates the evaluation of data transmission quality concerning the adaptive coefficient settings of PAM-4 equalizers. The two-dimensional (2D) symbol transition mapping visually depicts the degree of intersymbol interference (ISI). This work expands upon the 2D mapping model introduced in [14], adding more theoretical analysis and new simulation results. Both simulation and empirical results indicate that 2D symbol mapping can assess the quality of PAM-4 data transmission impaired by ISI and can visually represent the equalization effect. [ABSTRACT FROM AUTHOR]

In this article we present an iterative system of equalization and decoding to manage the intersymbol interference over an additive white Gaussian noise (AWGN) channel. Following the classic turbo equalization scheme, the proposed system consists of low-density parity-check (LDPC) coding at the transmitter side; we applied a Log maximum a posteriori probability (Log-MAP) equalizer and min-sum LDPC decoding at the receiver side. The equalizer and decoder, linked through interleaving and deinterleaving, iteratively update each other's information. We performed the performance analysis of the proposed system, bit error rate (BER) vs. signal-to-noise ratio (SNR), considering three different impulse responses of the channel (h). Our experimental results indicated that increasing the number of iterations performed by the LDPC decoder from 10 to 20 during the iterative process of equalization and decoding leads to better outcomes. The proposed system was compared with turbo equalization and separate equalization, performed before the decoding process with minimum mean-square error (MMSE) and LDPC decoding, in terms of BER vs. SNR, considering the three different h. Based on the analyzed results, it can be concluded that the equalization performance depends on both the impulse responses of the channel and the chosen decoding and equalization method; therefore, the equalization method does not always offer good results for any h. [ABSTRACT FROM AUTHOR]

As a strategy to coordinate inter-cell interference in cellular networks, a fractional frequency reuse (FFR) system is proposed, in which the frequency bandwidth is split into two orthogonal bands; users staying near the center of a FFR cell use the band with a frequency reuse (FR) factor of one (i.e., full FR), and users located close to the cell edge utilize the band with a FR factor greater than one (i.e., partial FR). Full FR coverage, which identifies full FR and partial FR regions (that is, near-center and near-edge regions) within a FFR cell, has a crucial effect on system performance. Some of the authors of this paper recently investigated the optimization of full FR coverage to maximize system throughput. They analytically showed that under the constraint of satisfying a specified target outage probability, the optimal full FR coverage is a non-increasing function of base station power when all base station powers in the cellular network are scaled at an equal rate. Interestingly, in this paper, it is proven that as the power of a single base station is scaled, the optimal full FR coverage in that cell is a non-decreasing function of base station power. Our results provide useful insight into the design of full FR coverage in relation to the transmit power of a base station. It gives a deeper understanding of the intricate relationship between important FFR system parameters of base station power and full FR coverage. [ABSTRACT FROM AUTHOR]

Holographic data storage (HDS) utilizes the unique properties of light for writing and reading two-dimensional (2D) data from holographic media, providing significantly higher densities and faster data transfer rates than traditional storage media for short-term dependencies. With its ability to store terabytes of data in a single crystal, HDS has garnered attention as a promising candidate for next-generation storage technologies. However, the 2D interference caused by hologram dispersion during the reading process poses a significant obstacle to achieving reliable and efficient HDS systems. This study proposes a method for enhancing the accuracy of estimating the 2D intersymbol interference (ISI) using a recurrent neural network (RNN) equalizer for HDS systems. The proposed method leverages the ability of RNNs to model complex and temporal dependencies in data and more accurately estimate the interference caused by ISI and interchannel interference (ICI) in HDS systems. In addition, to recreate the relationship between the samples in the training process, RNN is applied to fields such as computer vision, natural language process, speech recognition, and so on. We evaluated the performance of our proposed method on a simulation model of HDS system and compared it with the previous studies. In the simulations, the proposed method outperformed the previous schemes in terms of bit error rate, indicating its potential for improving the reliability and efficiency of HDS systems. [ABSTRACT FROM AUTHOR]

This paper presents a real-time underwater wireless optical communication (UWOC) system. The transmitter of our UWOC system is equipped with four blue LEDs, and we have implemented pre-emphasis technology to extend the modulation bandwidth of these LEDs. At the receiver end, a 3 mm diameter APD is utilized. Both the transmitter and receiver are housed in watertight chassis and are submerged in a water pool to conduct real-time underwater experiments. Through these experiments, we have obtained impressive results. The data rate achieved by our system reaches up to 135 Mbps, with a BER of 5.9 × 10−3, at a distance of 10 m. Additionally, we have developed a convenient method for measuring the underwater attenuation coefficient, using which we have found the attenuation coefficient of the water in experiments to be 0.289 dB/m. Furthermore, we propose a technique to estimate the maximum communication distance of an on–off keying UWOC system with intersymbol interference, based on the Q factor. By applying this method, we conclude that under the same water quality conditions, our system can achieve a maximum communication distance of 25.4 m at 80 Mbps. Overall, our research showcases the successful implementation of a real-time UWOC system, along with novel methods for measuring the underwater attenuation coefficient and estimating the maximum communication distance. [ABSTRACT FROM AUTHOR]

Crosstalk is an undesirable factor that degrades the quality of data transmission in printed circuit boards (PCBs). The signal integrity (SI) in multiconductor transmission lines is controlled by using a large number of multiport tests and measurements, which require a lot of time and expensive laboratory equipment. Proposed signal processing methods based on blind identification allow a reduction in the measurement burden. Contrary to the traditional approach requiring knowledge of sampling time offset, input pseudorandom bit sequence (PRBS), and time delay between received data and transmitted PRBS, the proposed alternative method performs blind separation of measured data for the linear fit pulse response (LFPR) procedure. The waveform identification of the partial pulse responses is evaluated for additively mixed cyclostationary sources of the data, intersymbol interference, and crosstalk. A mixed matrix model of composed random vectors is considered. The proposed estimation procedure is based on preprocessing of measured data using principal component analysis (PCA) and following independent component analysis (ICA). It is shown that the proposed component analysis allows diagnostics of signal integrity using eye-diagram patterns and the channel operating margin (COM). [ABSTRACT FROM AUTHOR]

This paper proposes using direct adaptation (DA)-based turbo equalization in multiple-input-multiple-output (MIMO) filtered multitone (FMT) time reversal (TR) acoustic communications to jointly suppress noise, residual co-channel interference (CCI) and intersymbol interference (ISI) after the TR process. Soft information-based adaptive decision feedback equalization (ADFE) adjusted according to the recursive expected least squares (RELS) algorithm, including interference cancellation and decoding, is used to construct the DA-based turbo equalization. In the proposed method, soft information is exchanged between soft symbols with soft decisions of decoding iteratively, and interference suppression is proceeded successively and iteratively until the performance is stable. The principle of the proposed method is analyzed, and based on the acoustic channel responses measured in a real experiment, the performance is assessed in relation to that of anther two methods. Compared with the MIMO-FMT TR underwater acoustic communication using interference suppression without error control coding (ECC), the proposed method performs better, benefitting from the ECC included in turbo equalization. Additionally, compared with the MIMO-FMT TR underwater acoustic communication using interference suppression based on hard decision equalization and decoding, the proposed method exhibits superior performance by exploiting soft information. [ABSTRACT FROM AUTHOR]

To meet the needs of future wireless optical networks, this paper introduces a high-speed, hybrid multiplexed, coherent free-space optical (FSO) communication system that integrates an orbital angular momentum (OAM) multiplexed signal with an orthogonal frequency division multiplexing (OFDM) technique. Two independent QAM polarized beams, each carrying in-phase and quadrature (I/Q) phase 16-QAM-OFDM modulated data, are combined using mode division multiplexing (MDM) to increase the capacity of the proposed system. The reason of choosing OFDM is its capability to support higher data rate, and mitigating intersymbol interference (ISI). The signal is detected using a coherent detection-based digital signal processing (DSP) algorithm at the receiver end. The proposed hybrid FSO system is evaluated in low and heavy dust environments using bit error rate (BER), link distance, optical signal-to-noise ratio (OSNR), and received optical power performance matrices. The simulation results demonstrate the successful transmission of a 120 Gb/s single carrier over the longest link ranges of 1.5 and 0.40 km, respectively, under low and heavy dust weather environments below the signal degradation threshold value (forward error correction (FEC) limit) of BER 2.2 × 10-3 in strong turbulent conditions. [ABSTRACT FROM AUTHOR]

We describe challenges encountered in the design of continuoustime delta-sigma modulators that target high resolution (>16 bits) over wide bandwidths (several hundreds of kHz). The linearity of the feedback DAC and flicker noise introduced by the loop filter are primary problems that need to be addressed. We describe two techniques that are inherently more linear than prior-art DACs, namely the virtual-ground-switched resistor DAC and the zapped virtual-ground-switched dual return-to-open DAC. Flicker noise can be eliminated by chopping, but one needs to pay careful attention to minimize chopping artifacts. Example multi-bit and singlebit designs achieving in excess of 100 dB SNDR over a 250 kHz bandwidth, designed in a 180 nm CMOS technology, are used to illustrate the efficacy of the techniques described in this article. [ABSTRACT FROM AUTHOR]

In this study, an analysis of the performance of a digital communication system was conducted to improve the efficiency of the communication channel. The system was designed and evaluated in the MatLab/Simulink environment, specifically for the transmission of binary data in a multipath channel with static fading. One of the main advantages of this system is its ability to provide high noise immunity, even in the presence of noise, interference, and signal delays. The performance of the system was investigated in terms of bit error rate (BER) over both an additive white Gaussian noise (AWGN) channel and a multipath Rayleigh fading channel. The study also considered the impact of inter-symbol interference (131) and explored different parameters for a static channel, resembling a wireless LAN system based on IEEE 802.11 (as defined by Rec ITU-R M.1225). This study uses a solution to suppress inter-symbol interference using cascading coding (convolutional turbo codes with Reed Solomon code), Fast Fourier Transform (FFT) and Inverse Fast Fourier Transform (IFFT), amplifiers at the transmitter side and normalizer at the receiver side, by regulating the amplification ratios of transmitter and receiver sides. Modeling of a digital communication system for a wide-band fixed wireless LAN system (for Indoor office and Outdoor to indoor systems) has been performed. The modeling outcomes show that the applied method provides a good performance improvement in channels with ISI with static fading. The application of cascading coding (turbo code together with RS code), amplifiers, and FFT on the transmitter side, and IFFT on the receiver side will eliminate the effects of inter-symbol interference on digital signals in a multipath channel with static fading (as defined by Rec. ITU-R M.1225 for internal and external transmission systems) for wireless fixed systems. [ABSTRACT FROM AUTHOR]

In this paper, a new dual mode blind equalization method using neighborhood symbol‐based decision and decision‐directed (NSBD‐DD) algorithm is proposed to equalize the satellite communication signals. The proposed algorithm adopts the combined cost function to employ the advantages of symbol decision algorithm and the decision‐directed algorithm, which can further improve the universality of the proposed algorithm. Compared with the conventional blind equalization algorithm, the compensation ability of intersymbol interference and convergence speed of the proposed algorithm can be improved simultaneously. To verify the performance of the proposed algorithm, the computer simulation is performed, and the simulation results show that the residual intersymbol interference of the 64QAM signals can be decreased to −50 dB under the satellite channel, which has 30 dB lower than multi‐modulus algorithm (MMA), 26 dB lower than NSBD algorithm, and 10 dB lower than SBD algorithm. And compared with SBD algorithm, the number of iterations required for the NSBD‐DD algorithm can be decreased from 8000 iterations to 6000 iterations, which convergence speed is increased by 25%. © 2023 Institute of Electrical Engineers of Japan. Published by Wiley Periodicals LLC. [ABSTRACT FROM AUTHOR]

A hybrid electromagnetics and communications model is proposed to quantify the performance degradation of non-timed array antennas (e.g. phased arrays or reflectarray antennas) from time delay induced errors. Partial mitigation techniques are investigated. As a non-timed array increases in size, steering angle, frequency, or symbol rate the signal degradation due to lack of true time delay compensation increases from the combined effect of the various per-element fractional time delays. The authors propose that the signal degradation from intersymbol interference due to timing effects can be thought of as an efficiency term and be used to assign a relative energy per symbol to noise power spectral density (EsNo) degradation based on standard satellite communications protocols (specifically DVB-S2X) with an assumed acceptable link margin. From these results, design recommendations are proposed for maximum array size, steering angle, and symbol rate for assumed operating conditions in satellite communications. The work also explores how partial mitigation techniques (e.g. equalization-based, spatial-based or amplification-based approaches) might be applied to the problem as an alternative to true time delay.

To eliminate inter-symbol interferences (ISI) caused by nonlinear group delay effect in high-speed broadband satellite sensor networks, an efficient parallel adaptive blind equalization of improved block constant modulus algorithm (IBCMA) with decision-directed (DD) mode (IBCMA-DD) is proposed with block minimum mean square error (MMSE) criterion. First, nonlinear group delay models are introduced in satellite channels. Second, the criterion of the classical Godard’s constant modulus algorithm (CMA) is derived in the block vector form as the IBCMA for satellite signals with inter-symbol interference (ISI) caused by the above satellite channels. In the IBCMA, stochastic gradient descent and block minimum mean square error are adopted to reduce excess errors in equalization by adjusting block tap-weight vectors adaptively. Finally, the IBCMA is combined with the DD mode of equalization to both accelerate the parallel blind equalization with low complexity and improve the spectrum efficiency without any training data to occupy unnecessary bandwidth. Simulation results indicate that the proposed IBCMA-DD equalization possesses good performance in approaching ideal non-ISI transmissions. It achieves good bit error rate (BER) performance just within 0.3 dB of the theoretic performance under high signal-to-noise ratios (SNRs), even at satellite group delay channels by high-power nonlinear broadband filters. Therefore, it obtains excellent equalization under severely deteriorated group delay channels in broadband satellite sensor networks with high data rate.

This paper studies the application of neural networks to Viterbi detection of FTN signals in an intersymbol interference (ISI) channel. The main contribution of this paper is to propose a receiver structure for detecting FTN signals in unknown static ISI channel. In particular, we propose a novel low-complexity neural network structure for calculating the branch metrics, and we explore its suitability for FTN signalling with channel uncertainty. We compare the proposed network, which we call the Metric Net (MetNet), to a benchmark neural network-based technique for metric calculation, the ViterbiNet, which was originally designed for ISI channels. The simulation results confirm that the MetNet outperforms the ViterbiNet, with two orders of magnitude lower complexity, and is much more resilient to channel uncertainty than the traditional Viterbi detector, which uses Euclidean distance for metric calculations. We further show that the MetNet exhibits robustness to being trained at mismatched SNR values and FTN pulse acceleration factors, meaning that the number of trained models required can be significantly reduced. Additionally, the results show that the proposed MetNet remains a favorable alternative at much higher levels of channel uncertainties. The results also reflect that we can generalize the MetNet to work with different channel models defined by different decaying factors. Finally, we show that we succeed in achieving a bandwidth efficiency gain of 33% due to FTN by using the MetNet in the presence of channel uncertainty.

When using quadrature signals in radio channels, flat and selective fading, multipath radio reception, intersymbol interference, and jitter occur. In addition to the need to accurately estimate the value of the phase difference at the current and previous clock intervals, a critical factor in receiving and demodulating such signals is the accuracy of measuring the amplitude of their samples. When demodulating such signals, an approach is possible, the basis of which is to measure the values of individual signal samples at discrete time points with higher accuracy than in existing electronic devices. Such an approach can be implemented by an optoelectronic device in which a coherent luminous flux is formed, the parameters of which are modulated by a voltage proportional to the readings of the received radio signal. Using a modulated light flux, an interferogram is formed, the parameters of which are directly related to the parameters of this light flux and accordingly to the parameters of the received radio signal. This makes it possible, by increasing the accuracy of estimating radio signal samples, to increase the base of the alphabet used for code manipulation, the efficiency of using the allocated frequency band for transmitting information and reduce the probability of a bit error. The article presents a mathematical model for converting the parameters of the received radio signal into the parameters of the generated interferogram. By mathematical modeling the accuracy characteristics of an optoelectronic device for measuring radio signal samples were evaluated. The results of mathematical modeling illustrating the relationship of the parameters of the optical elements of the device with the accuracy of estimates of the radio signal counts are presented. The practical significance of the proposed optoelectronic device can be used as an independent device for analog-to-digital conversion of radio signals, as well as part of demodulators for QAM and OFDM signals in networks and communication systems of 5G and the next generations. [ABSTRACT FROM AUTHOR]

Tigris River is an environment of shallow waters because of its low depth and it has been identified as a multi-path channel. The underwater multi-path propagation leads to reverberation as well as fading, which causes large transmission loss. The present paper conducts 3 underwater acoustic simulation outcomes in the district of Abu Dali - Kazem Al Ali village - Tigris beaches - Baghdad - Iraq. The distance from the sender to the receiver are (100m, 1000 m, and 5000m). With the use Ray model, results have shown that the multi-path propagations dominate in a case where the distance from sender to receiver, has been increased, which resulted in decreasing the grazing angle, thereby, increasing the coefficient of reflection. The consecutive path amplitude values will not be decreased quickly. This is why differences in the time between different paths are minimal. This indicates that the consecutive path-ways will be converged with time, which will result in an intersymbol interference phenomenon, playing a role in an increase of the received data bit error rate. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Summary: A multi‐stream cyclic interleaving architecture for an interleaved frequency division multiple access (IFDMA) system is proposed. The proposed scheme exploits the full benefits of maximal length sequence (m‐sequence), in contrast to single data stream transmission scheme proposed in earlier works, thereby allowing simultaneous transmission of multiple data streams by each user. The cyclic spreading allows the separation of multiple data streams for each user in addition to intersymbol interference (ISI) minimization. The assignment of orthogonal subcarriers to each user compensates multiuser interference (MUI). The increase in the number of data stream transmission improves the data rate of the system. The proposed scheme employs maximal ratio combining (MRC) to maximize the instantaneous signal‐to‐noise ratio (SNR) of the multipath signal. The performances of the proposed interleaving scheme are compared with the minimum mean square error frequency domain equalization (MMSE‐FDE)‐based conventional interleaving scheme. Despite the simultaneous transmission of multiple data streams, the proposed scheme retains the performance of single data stream transmission. [ABSTRACT FROM AUTHOR]

Since the end of the 19th century, radioelectronic devices (REDs) have actively penetrated into all modern community spheres. Achievements in the fields of radio engineering and electronics, as well as computing, information, telecommunications, and other technologies, have greatly contributed to this. The main elements of REDs are antennas and microwave devices. For example, linear (wire) antennas are the basis of long-distance communication agency networks of various law enforcement agencies and departments. The manufacturing of REDs requires the regular and rapid appearance of more and more advanced types with minimal costs. At the same time, the design complexity of REDs and the tightening of EMC requirements caused by the growth of upper frequencies of useful and interfering signals, the mounting density, as well as the capabilities of generators of intentional electromagnetic impacts, together with the need to take into account inter-element, inter-unit, and inter-system interference, require more and more accurate designs of REDs. However, this becomes impossible without computer modeling, which saves the time and financial resources required for their development, as well as to evaluate the correctness of the proposed technical solutions. During the design process, as a rule, a multivariate analysis or optimization of the product is performed. In this case, methods of computational electrodynamics (one of which is the method of moments) are used. They are based on the replacement of continuous functions with their discrete analogues (construction of a grid), which reduces the problem to the solution of a system of linear algebraic equations (SLAE). The problem's complexity depends on the complexity of the SLAE solution, which is determined by its order (which in turn is determined by the complexity of the simulated object and its surrounding area) and by the number of the required SLAE solutions for each problem (determined by the upper frequency of the signal, the number, and range of the optimized parameters). This dramatically increases the computational cost, which becomes the main constraint for the optimal design. Therefore, reducing the computational cost for the analysis and optimization of RED elements (in particular, linear antennas) is an important scientific problem. Meanwhile, finding new antenna structures that meet all the desired features (low price, required characteristics, manufacturable design with small dimensions and windage, etc.) is no less important today. One of the promise solutions for these problems is using a wire grid and sparse antennas for modeling and constructing antennas. Since the last century, a lot of research has been performed on them. The aim of this paper is to review their history and the main related aspects such as computational, acceleration, and optimization used methods, the fields of their application, and their evolution to this moment. In addition, this paper provides a possible future implementation of wire-grid and sparse antennas from the authors' point of view by presenting a new method that is under research to obtain effective wire sparse antennas. [ABSTRACT FROM AUTHOR]

Underwater optical wireless communication (UOWC) has been a promising high data rate communication system. The performance of UOWC has numerous constraints in terms of maximum attainable distance, absorption, and scattering of the intensity, which vary depending on the quality of the water environment. This paper proposes a UOWC system based on filtered orthogonal frequency division multiplexing (F-OFDM). It has achieved large bandwidth while also addressing the issue of intersymbol interference (ISI). F-OFDM has attained lower out-of-band emission (OOB) while preserving bit error rate (BER) performance. Furthermore, to permit many users to share the entire UOWC system, non-orthogonal multiple access (NOMA) is adopted with F-OFDM, taking advantage of filtering subcarriers that reduce user interference. NOMA F-OFDM has been examined across harbor water channels under different power coefficients and modulation. Simulations have shown that F-OFDM is better than DC-biased optical OFDM (DCO-OFDM), with an OOB improvement of about 120 dB and a signal-to-noise ratio (SNR) gain of about 13 dB for BER = 10–3 using 4-QAM modulation. As well, NOMA F-OFDM has better BER performance than NOMA DCO-OFDM. [ABSTRACT FROM AUTHOR]

Chaotic baseband wireless communication system (CBWCS) suffers bit error rate (BER) degradation due to their intrinsic intersymbol interference (ISI). To this end, an ISI-free chaotic filter based on root-raised-cosine (RRC) division is constructed to generate a chaotic signal. A wireless communication system using this chaotic signal as a baseband waveform is proposed. The chaotic property is proved by the corresponding new hybrid dynamical system with topological conjugation to symbolic sequences and a positive Lyapunov exponent. Simulation results show that under a single-path channel and multi-path channel, the proposed method outperforms CBWCS in both BER performance and computational complexity. [ABSTRACT FROM AUTHOR]

In this study, an investigation into the small-scale and multipath fading of radio wave propagation in a complex building environment has been conducted by using Afe Babalola University Ado-Ekiti Nigeria, College of Engineering building as a case study. The study utilizes sliding correlator channel sounding measurement techniques, implemented on NI USRP 2920 modules by using GNU radio software. Moreover, single-input and single-output configurations have been employed by setting one module as a transmitter and the other one as a receiver, propagating at a carrier frequency of 1.2 GHz. Five scenarios within the first floor of the building have been considered and various cases in each one of the scenarios are either outdoor-to-indoor, indoor-to-outdoor, indoor or outdoor measurement. The analysis of the scatter plot of the maximum delay spread against the distance of experiments for the line-of-sight and non-line-ofsight cases show that analytical expression cannot be obtained due to the complexity of the building structure. The result obtained also shows that the maximum delay spread values are between 575 µs and 1023 µs, which points to the existence of a frequency selective fading condition that causes intersymbol interference and data rate reduction. [ABSTRACT FROM AUTHOR]

Molecular reuptake is a nature-inspired channel clearance strategy to mitigate intersymbol interference (ISI) in molecular communications. Reuptake is especially important if the communication medium is not cleared of the information-carrying molecules by other means, and if it is not done properly, it decreases the maximum signal rate. In a more practical sense, in nature, reuptake failure may be detrimental to the organisms. Many neurological disorders, including schizophrenia, are related to problems with the reuptake mechanisms in synaptic molecular communications (SMC). To understand the evolutionary solution to the ISI, we start with the glutamate reuptake process as part of SMC. We develop a stochastic approach to the reuptake problem and derive analytic expressions for the probability of absorption for rectangular volumes. To test the validity of perfectly absorbing boundary approximation for real systems, we derive the rate of first incidence and average glutamate transport time for EAAT2, the most prevalent transport molecule. When applied to SMC, our results indicate that perfectly absorbing boundaries assumption is not possible according to the available physiological data, due to the limited number of transporters and the finite amount of time a transporter requires to reuptake a glutamate molecule.

A joint channel estimation and equalization algorithm with noise-predictive minimum mean square error-residual intersymbol interference cancellation (MMSE-RISIC) is proposed for single carrier frequency domain equalization (SC-FDE) system with frame structure based on unique word (UW). The algorithm includes noise-predictive MMSE-RISIC equalization algorithm and UW based noise elimination time domain channel estimation algorithm, and combines frequency domain equalization algorithm with channel estimation algorithm. The parameters based on the 300 km troposcatter channel in north China are utilized to make a simulation, the results show that the performance of the noise elimination time-domain channel estimation algorithm based on UW is better than that of the UW based time-domain channel estimation algorithm, when the bit error rate (BER) is 10-2, the signal to noise ratio (SNR) has about 1.2 dB performance gain. The noise predictive MMSE-RISIC equalization algorithm has better performance than the improved MMSE-RISIC equalization algorithm and yield SNR gain of about 3.2 dB at BER = 10-2. [ABSTRACT FROM AUTHOR]