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In order to mitigate DFE error propagation to reduce bit error rate (BER), a 25Gb/s Non-Return-To-Zero (NRZ) transceiver including a five-tap decision feedback equalizer (DFE) combined with a dedicated feed forward equalizer (FFE) was first constructed and was found to be helpful in improving signal integrity and reduce errors in high-speed data transmission, which can lead to more reliable and efficient communication. In this transceiver, the effect of multi-tap FFE on error probability with different burst error run lengths was evaluated through a cumulative-probability distribution model. Then, forward error correction (FEC) with different correction capabilities can be also employed to correct burst errors for a better BER performance. Probability-based BER with single/double burst error correcting FEC was derived and a joint optimization of FFE and FEC can be further explored to achieve the target BER. Results show that compared with two-tap FFE, FFE with a post-cursor tap can obtain a BER improvement of 1.5dB at the BER of ${10}^{-7}$, and also enlarge the horizontal opening degree of DFE, which is 0.74 unit interval (UI). Double burst error correcting FEC obtaining 2.2dB coding gain at the BER of ${10}^{-7}$ outperforms single one. When the FEC error correcting capability is 16, the combination of double burst error correcting FEC and three-tap FFE can reduce BER from ${10}^{-9}$ to approximately ${10}^{-12}$. FEC with a larger error correction capability is more likely to achieve the target BER and reduce the complexity of the combination equalizer while ensuring a better equalization performance. The proposed NRZ transceiver, as a part of the physical interface, can be applied to high-speed interconnection scenarios, such as Ethernet, PCIe, and Chiplet.

A high data rate multi-carrier differential chaos shift keying system with hybrid index modulation, referred to as HDR-HIM-MC-DCSK, is proposed in this paper. In the proposed system, multiple data-bearing wavelets are parallelly transmitted with one reference signal. Different Walsh codes are utilized for separating these data-bearing wavelets. Some subcarriers are used for hybrid index modulation, in which the chaotic signal and its Hilbert transform are generated for representing the active and inactive subcarriers. In addition, the analytical Bit-Error-Rate (BER) expressions of the proposed HDR-HIM-MC-DCSK system are derived over the AWGN and the multipath Rayleigh fading channels. The hardware complexity, computational complexity, energy efficiency, spectral efficiency and data rate of the proposed system are analyzed. The analytical accuracy and the advantages of the proposed system are verified by relevant simulations.

In Radio over Fiber (RoF) technology, the optical network capacity is integrated with the wireless network. The main objective of this work is to enhance the performance behavior of optical fiber communication system in terms of BER, Received Power and Q-Factor. The proposed combined modulation technologies, such as Pulse Amplitude Frequency Modulation (PAFM), Differential Phase Shift Keying Amplitude Modulation (DPSKA), Offset Quadrature Phase Shift Keying Amplitude Modulation (OQPSKA), Quadrature Amplitude Frequency Modulation (QAFM), Frequency Phase Modulation (FPM) and Pulse Amplitude Phase Modulation (PAPM), are used to meet this objective. The input data are used for modulating the electrical carrier signal with a frequency of 250 and 255GHz. This hybrid modulation technique obtained the minimum BER of about ${10}^{-170}$ in FPM technique. The maximum Q-Factor of 33 is obtained in QAFM technique. The obtained maximum received power is 0.79mW in OQPSKA technique.

Binary differential phase-shift keying (2DPSK) signal is mainly used for high speed data transmission. However, the bit error rate of digital signal receiver is high in the case of wicked channel environment. In view of this situation, a novel method based on stochastic resonance (SR) is proposed, which is aimed to reduce the bit error rate of 2DPSK signal by coherent demodulation receiving. According to the theory of SR, a nonlinear receiver model is established, which is used to receive 2DPSK signal under small signal-to-noise ratio (SNR) circumstances (between −15 dB and 5 dB), and compared with the conventional demodulation method. The experimental results demonstrate that when the input SNR is in the range of −15 dB to 5 dB, the output bit error rate of nonlinear system model based on SR has a significant decline compared to the conventional model. It could reduce 86.15% when the input SNR equals −7 dB. Meanwhile, the peak value of the output signal spectrum is 4.25 times as that of the conventional model. Consequently, the output signal of the system is more likely to be detected and the accuracy can be greatly improved.

In this paper, a power saving optical receiver (Rx) module has been designed, fabricated using a 0.13-μm CMOS technology and demonstrated the performance with experimental results. In the Rx module, a power control block is designed to control the power of Rx according to the presence or absence of an incoming signal at the input of Rx. The Rx switches to a passive operation mode when there is no signal at Rx input. In the passive operation mode, the fabricated Rx shows a power saving efficiency of about 51%, where Rx is not receiving. When there is an input signal at Rx input, the Rx switches to an active operation mode with a system efficiency of about 97.5%. The experimental data shows that the Rx module consumes of about 67 mW at 1.3 V and power control block consumes of about 1.6 mW at 1.4 V. The measured 3-dB bandwidth of 2.56 GHz was recorded for optical Rx module. The bit error rate (BER) performance of 10−12 is achieved for the proposed optical Rx module up to 2.5 Gbps data rate with a clear eye-diagram by a very low optical input power of about −3 dBm.

In multi-carrier differential chaos shift keying (MC-DCSK) system, channel noises pollute both the reference and data signals, resulting in deteriorated performance. To reduce noises in received signals in MC-DCSK, a novel noise reduction MC-DCSK (NR-MC-DCSK) system is proposed in this paper. The proposed system utilizes duplicated chaotic samples, rather than different ones, as the reference. At the receiver side, identical samples can be averaged before correlation detection, which helps decrease the noise interferences and thus brings performance improvement. Theoretical bit error rate (BER) expressions are derived and verified by simulation results for additive white Gaussian noise and multipath Rayleigh fading channels. Finally, comparisons to MC-DCSK and other DCSK-based systems are given to confirm the superiority of the proposed system in BER performance.

Orthogonal frequency division multiplexing (OFDM) is a multicarrier transmission system that can achieve high data rate over wireless channels. At the same time, multiple input multiple output OFDM (MIMO-OFDM) in wireless communication systems has been exposed to offer significant improvement over wireless technology by providing transmit diversity. It has become a promising technique for high-performance 5G broadband wireless communications. However, the main problem associated with MIMO-OFDM is that its signal exhibits high peak-to-average power ratio (PAPR), which causes nonlinear distortion and consequently performance degradation. Besides, PAPR carries weaknesses such as an increase in power consumption of high power amplifier (HPA) and analog to digital converter (ADC). Thus, 5G base stations will push up power requirements because energy consumption grows with the number of transceiver elements. So, mobile operators must find the right compromise that, on the one hand, guarantees a certain level of performance to a data flow, and, on the other hand, the energy cost generated for the deployment of the network. For this, as part of the management of power consumption, we propose MIMO constant envelope OFDM (MIMO-CE-OFDM) technique. In this work, we used MIMO-CE-OFDM to mitigate the nonlinear effect of HPA and ADC. To perform practical simulations, we have used COST 2100 MIMO channel model. In this paper, a MIMO-CE-OFDM system has been presented and analyzed under COST 2100 channel model conditions. Simulation results are given to illustrate the performance of $2\times 2$ MIMO-CE-OFDM in the presence of both HPA and ADC nonlinearity. This work shows that the effect of nonlinearity is shown to be negligible on MIMO-CE-OFDM signal.

In this paper, a novel multi-user carrier index differential chaos shift keying (MU CI-DCSK) modulation scheme is proposed. For a better utilization of spectrum resources, each user is allocated a private subcarrier for reference signal transmission, while the remaining subcarriers are public and shared by all users to transmit their own data-bearing signals. To avoid user interferences in this design, users are distinguished in a code division multiple access (CDMA) way based on Walsh codes. By exploiting the redundancies in the transmitted signals, repeated segments of received signals are averaged, leading to greatly reduced noises and a noticeable improvement in bit error rate (BER) performance. BER expressions of this new system are derived over the additive white Gaussian noise (AWGN) and multi-path Rayleigh fading channels. Simulation results and comparisons are performed to verify the feasibility and advantages of this new scheme.

From the point of information theory, the baseband binary pulse amplitude modulated (PAM) signals transmission, via tuning the nonlinear receiver's parameters, is studied over an additive white Gaussian noise (AWGN) channel. It is demonstrated that the channel capacity of baseband binary communication systems, for a given signal added noise, can be maximized by optimal designed receivers. This new form of stochastic resonance (SR) is referred to as parameter-induced stochastic resonance (PSR) in a broad sense. PSR effect does not require that the input signals are subthreshold. The characteristic behavior of channel capacity versus transmission bit rate is also studied. For reproducing the original binary signals more correctly, time scale transformation method and the approach of ensemble average probability of error bits are introduced. We observe a marked enhancement of the channel capacity for binary PAM signals transmission by PSR in numerical simulations. With this theory and method, the practical applications are considered.

A new multiaddress Co-Chaos Shift keying communication scheme (MA-CoCSK) was proposed based on analyzing the permutation-based differential chaos-shift-keying (PMA-DCSK) scheme and the Antipodal Chaos-Shift-Keying (ACSK) scheme. We also analyzed the bit error rate of the new scheme in Gaussian white noise channel and compared its performance with that of the PMA-DCSK scheme. Theory analysis and simulation results both indicate that the scheme proposed in this paper can not only improve the transmission efficiency of a communication system, but also decrease the bit error rate significantly while increasing the speed compared to PMA-DCSK.

In this paper, a novel coupled code shifted M-ary differential chaos shift keying modulation scheme is proposed as a simple and low-cost solution to reference removal. In this scheme, only two information-bearing signals are transmitted. Both signals are modulated by selected Walsh code sequences with specific indices determined by the index bits, and one of them also carries an additional M-ary information symbol. Since these two information-bearing signals are coupled by the same chaotic message bearer, data bits can be easily recovered according to the correlation between these two signals so that the transmission of reference signals can be completely avoided. Theoretical Bit Error Rate (BER) expressions are derived over the additive white Gaussian noise and multipath Rayleigh fading channels. Furthermore, simulations and comparisons indicate that the proposed system can achieve better BER performance with lower complexity.

Peak-to-average power ratio (PAPR) in orthogonal time frequency space (OTFS) is vital for optimizing signal efficiency, minimizing distortion, and enhancing the performance of a beyond fifth-generation (B5G) system. The paper focuses on lowering the PAPR while retaining the bit error rate (BER) and power spectral density (PSD) for 64 and 256 sub-carriers. The PAPR is minimized by using a fractal optimization process known as selective mapping (SLM) and partial transmission sequence (PTS) at the transmitting block of the OTFS framework. The combination of SLM and PTS reduces peak power by selectively modifying the phase of transmitted symbols. SLM generates multiple versions of the signal, while PTS allocates power to these versions optimally, collectively mitigating amplitude peaks and minimizing PAPR. According to the simulation results, the suggested SLM+PTS works better than the traditional SLM and PTS, achieving low spectrum leakage and PAPR improvements of 5.5 dB and 4.9dB as well as SNR gains of 2.4dB and 2.1dB. In the future, SLM+PTS may work on lowering PAPR by making computers faster, researching adaptive algorithms, and combining machine learning methods for real-time optimization in various communication settings. Complex modeling, including fractal-based SLM and PTS approaches, provides a detailed understanding of waveform behavior and interference patterns, enabling more accurate and effective hybrid PAPR reduction techniques. This combination enhances the ability to manage to mitigate non-linear distortion across various sub-carriers, crucial for the performance and efficiency of 6G OTFS modulation.

Wavelength division multiplexing (WDM) has been emerging as an effective technique for making use of the full bandwidth offered by optical fiber. To achieve long-haul transmission, erbium-doped fiber amplifiers (EDFAs) are employed to compensate for signal attenuation without using optoelectronic/electro-optic conversions. Transmission in these systems is limited by fiber nonlinearities and amplified spontaneous emission noise from amplifiers. In this paper, the long-haul optical WDM system with EDFAs is investigated theoretically. The noise and bit error rate (BER) characteristics of the system with optical amplifiers are calculated and the dependence of the BER on interamplifier separation and input power is shown.

The amplifier separation and channel separation has conflicting effects on the noise generated due to the fiber non-linear effects (Stimulated Raman scattering SRS and Four wave mixing FWM) and the Amplified spontaneous emission (ASE) noise introduced by inline optical amplifications. While designing an efficient Dense Wavelength Division Multiplexing (DWDM) system, optimization of the channel separation and amplifier separation are required to minimize the non-linear effects (FWM and SRS) along with the ASE noise. In this paper, theoretical investigations of the optical DWDM systems have been presented to minimize the bit error rate (BER) by optimizing inter-channel separation and inter-amplifier separation at different data rates considering the combined effect of SRS, FWM, ASE, receiver and beat noises.

Multi-Input–Multi-Output (MIMO) technology has already become crucial in modern communication study, but the needs of anti-interference capability and spectral efficiency are always growing, which poses a significant challenge in future development. In the paper, by analyzing and summarizing the respective characteristics and problems of MIMO system and Orthogonal Frequency Division Multiplexing (OFDM), we investigate the knowledge of MIMO–OFDM system. The theoretical analysis proves that this system can effectively solve the shortcomings of MIMO system and improve the performance of communication system. In addition, in the experimental simulation part, we also evaluate the system performance mainly by analyzing the Bit Error Rate (BER) metrics, while other methods such as channel estimation algorithms and synchronization techniques are also considered.

The performance of an optical wavelength division multiplexed system is analyzed including the effect of four wave mixing (FWM) in presence of chromatic dispersion. FWM process in the single mode fiber as well as in the fiber amplifier is taken into account. It is observed that the efficiency of FWM generation can be greatly reduced by simultaneously making the spacing between channels unequal and by employing nonuniform chromatic dispersion along the fibers in the communication link. The power limitations are evaluated under various conditions of system parameters. The power depletion is compared under different channel spacing schemes.

An improved model is proposed to approximate the actual Raman gain profile of silica, which in turn is used to calculate the power depletion of the shortest-wavelength channel due to all other channels in the system. In this improved model, the stimulated Raman scattering (SRS) effects from channels at the tail of Raman gain profile are taken into account. A statistical analysis is done for the SRS crosstalk in a wavelength division multiplexed system including modulation statistics. The bit error rate and power penalty are estimated, where the improved model for the Raman gain spectrum is used.