Better Bit Error Rate Research Articles

Performance evaluation of MIMO DFT-Spread WR-OFDM system for spectrum efficiency and power efficiency

ABSTRACT It is important to design a spectrum-efficient and power-efficient wireless communication system, which is the main design target in cellular and wireless communication engineering. Basically, to make it, the desired system must have a low peak-to-average power ratio (PAPR), low-level of out-of-band (OOB) power emission and can provide a high throughput. In this paper, we propose a high-throughput cellular communication system, namely Discrete Fourier Transform-Spread Windowing and Restructuring Orthogonal Frequency Division Multiplexing (DFT-Spread WR-OFDM), which has considerably low PAPR and low OOB power emission for upcoming next-generation beyond 5G (B5G) and 6G cellular communication systems. High PAPR is still one of the challenging issues for the MIMO-OFDM system. The proposed system is an effective arrangement of DFT-Spreading and windowing techniques to reduce PAPR and OOB power emission, respectively. Multiuser diversity is obtained using localized subcarrier mapping. We take advantages of spatial multiplexing to enhance the data throughput significantly. Additionally, frequency-domain equalization (FDE)-minimum mean squared error (MMSE) is used to combat the inter-symbol interference (ISI) effect. Simulation results verify that the suggested system considerably lowers PAPR and OOB power emission compared to the conventional systems. Furthermore, the proposed scheme shows better bit error rate (BER) performance over the MIMO Rayleigh fading channel environment. Simulation results also confirmed that the channel capacity of our suggested system is better than the conventional multi-carrier systems.

Phase‐index correlation delay shift keying modulation

High-data-rate phase-orthogonality correlation-delay-shift-keying (HPO-CDSK) transmits 2-bits orthogonal signal in parallel and achieve higher spectral efficiency in the category of non-coherent detection chaotic systems. However, the spectral efficiency gain mainly relies on the sacrifice of energy efficiency. The study of HPO-CDSK is extended and phase-index CDSK (PI-CDSK) is proposed. By virtue of index modulation (IM) technology in PI-CDSK, according to the index bit, the orthogonal phase is used to distinguish the active carrier which bears the information bit. Since two bits (including index bit and information bit) are borne in one carrier, compared with HPO-CDSK, PI-CDSK can achieve double energy efficiency gain. Moreover, PI-CDSK can decrease noise interference and eliminate the intra-signal interference (ISI) component in demodulation. Results show that, with the same energy efficiency, PI-CDSK has better bit-error rate (BER) performance than that of CDSK, DCSK and their improved schemes.

Improved Approximate Expectation Propagation Massive MIMO Detector with Second-Order Richardson Iteration

The expectation propagation (EP) detector achieves significantly better performance than the linear detectors (such as minimum mean squared error detector) in massive MIMO systems, which has drawn great attention recently. EP’s approximation (EPA) algorithm simplifies the update formula of the EP algorithm by reexpressing the moment matching condition so that the number of matrix inversions in the EP algorithm is reduced to one. However, the expense is that the EPA algorithm requires higher accuracy for this inversion; otherwise, the bit-error-rate (BER) performance will suffer serious losses. To tackle this issue, the SORI iterative algorithm is introduced to obtain the high-precision result of this inversion to ensure the good BER performance of the EPA algorithm. First, the new expression of the SORI iterative algorithm is derived under the equivalent real-valued system. Second, the improved EPA-SORI algorithm is then introduced by the SORI algorithm, which is used to approximate the initial value of the EPA algorithm under the real-valued system. Finally, by designing the initial solution and the relaxation factor of the EPA-SORI iterative algorithm, the convergence rate can be quickly increased without increasing the complexity. Simulation and complexity results exhibit that in various massive MIMO system configurations, the proposed EPA-SORI algorithm can achieve the same BER performance as the Exact EP algorithm with significantly lower complexity. At the same time, compared with MMSE and the existing EPA algorithms, the proposed EPA-SORI algorithm has a better performance-complexity trade-off advantage, which is more obvious in scenarios with high modulation order and a large number of users.

Free Space Optics Link Performance Estimation Under Diverse Conditions

Free Space Optics (FSO) uses air as a medium of transmission of signals and requires Line of Sight (LOS) for operation. Communication systems that employ FSO have gained prominence in recent times and have been used in mobile communications, broadcast, security, and other applications. They have proven a worthy substitute for fibre optics albeit with some notable disadvantages. FSO systems are usually installed above ground level and are therefore exposed to the prevailing atmospheric conditions which can negatively affect the optical signal. Tropical regions exhibit adverse weather conditions such as rain, fog, and haze that can affect FSO signals. There is a dearth of research on the use of FSO systems in tropical regions and on methods to mitigate the effect of FSO signal interference. In this research, we propose diversity techniques to improve the link performance of FSO systems in a tropical region. The simulation results indicate a better Bit Error Rate (BER) and Signal-to-Noise Ratio (SNR) compared to other techniques.

Sparsity Signal Detection for Indoor GSSK-VLC System

In this article, the signal detection problem in indoor visible light communication (VLC) system aided by generalized space shift keying (GSSK) is modeled as a sparse signal reconstruction problem, which has lower computational complexity by exploiting the sparse reconstruction algorithms in compressed sensing (CS). In order to satisfy the measurement matrix property to perform sparse signal reconstruction, a preprocessing approach of measurement matrix is proposed based on singular value decomposition (SVD), which theoretically guarantees the feasibility of utilizing CS based sparse signal detection method in indoor GSSK-VLC system. Then, by adopting classical orthogonal matching pursuit (OMP) algorithm and compressed sampling matching pursuit (CoSaMP) algorithm, the GSSK signals are efficiently detected in the considered indoor GSSK-VLC system. Furthermore, a more efficient detection algorithm combined with OMP and maximum likelihood (ML) is also presented especially for SSK scenario. Finally, the effectiveness of the proposed sparsity aided detection algorithms in indoor GSSK-VLC system are verified by computer simulations. The results show that the proposed algorithms can achieve better bit error rate (BER) and lower computation complexity than ML based detection method. Specifically, a signal-to-noise ratio (SNR) gain as high as 12 dB is observed in the SSK scenario and about 5 dB in case of a GSSK scenario upon employing our proposed detection methods.

Time-Gated Photon Counting Receivers for Optical Wireless Communication

Photon counting detectors such as single-photon avalanche diode (SPAD) arrays are commonly considered for reliable optical wireless communication at power limited regimes. However, SPAD-based receivers suffer from significant dead time induced intersymbol interference (ISI) especially when the incident photon rate is relatively high and the dead time is comparable or even larger than the symbol duration, i.e., sub-dead-time regime. In this work, we propose a novel time-gated SPAD receiver to mitigate such ISI effects and improve the communication performance. When operated in the gated mode, the SPAD can be activated and deactivated in well-defined time intervals. We investigate the statistics of the detected photon count for the proposed time-gated SPAD receiver. It is demonstrated that the gate-ON time interval can be optimized to achieve the best bit error rate (BER) performance. Our extensive performance analysis illustrates the superiority of the time-gated SPAD receiver over the traditional free-running receiver in terms of the BER performance and the tolerance to background light.

General Carrier Index Aided Dual-Mode Differential Chaos Shift Keying With Full Mapping: Design and Optimization

In this paper, we propose a general carrier index assisted dual-mode differential chaos shift keying with full mapping (GCI-DM-DCSK-FM) system, where a pair of distinguishable modem-mode signals is designed with the aid of general carrier index modulation. Specifically, the selected and unselected subcarriers are used to carry differential chaos shift keying (DCSK) and quadrature chaos shift keying (QCSK) signals, respectively, thereby obtaining higher data rate and spectral efficiency. To tackle the issue of discarding the subcarrier activation pattern (SAP), an effective full mapping method is proposed for the GCI-DM-DCSK-FM system to harvest better bit error rate (BER) performance and higher data rate. Moreover, a noise decontamination method is designed for the GCI-DM-DCSK-FM system to enhance the BER performance. To confirm the validness for our proposed systems, we derive the BER expressions of the GCI-DM-DCSK-FM system over additive white Gaussian noise (AWGN) and multipath Rayleigh fading channels. Finally, plenty of simulation results show the excellent BER performance of the GCI-DM-DCSK-FM system.

Spectral Analysis of (Multi-) Pulse-Position Modulation

Nowadays, laser communication has received great achievements owing to its advantages, e.g., large channel capacity, easy miniaturization of communication system and strong anti-interference ability in different conditions. Pulse position modulation (PPM), as an important modulation technology in laser communication system that transmit signal with lower power, is attracting much attention. However, the performance of the modulation scheme highly depends on the bandwidth of transmission. To remedy this defect of PPM, the multipulse position modulation (MPPM) scheme is proposed to increase the accuracy and bandwidth limit. This modulation scheme has stronger anti-interference ability than PPM. Therefore, there has been rising interest in studying the characteristics of the multi-PPM. In this article, we developed an appropriate mathematical model to represent a PPM transmission, analyzed the spectrum of the transmission and characterized the bandwidth of this transmission. Compared with benchmarks of MPPM scheme, its performance has been discussed. According to the analysis, MPPM strongly increases band-utilization efficiency, however PPM has a better bit error rate (BER) performance than MPPM.

Null Subcarrier Index Modulation in OFDM Systems for 6G and Beyond.

Computational complexity is one of the drawbacks of orthogonal frequency division multiplexing (OFDM)-index modulation (IM) systems. In this study, a novel IM technique is proposed for OFDM systems by considering the null subcarrier locations (NSC-OFDM-IM) within a predetermined group in the frequency domain. So far, a variety of index modulation techniques have been proposed for OFDM systems. However, they are almost always based on modulating the active subcarrier indices. We propose a novel index modulation technique by employing the part of the transmitted bit group into the null subcarrier location index within the predefined size of the subgroup. The novelty comes from modulating null subcarriers rather than actives and reducing the computational complexity of the index selection and index detection algorithms at the transmitter and receiver, respectively. The proposed method is physically straightforward and easy to implement owing to the size of the subgroups, which is defined as a power of two. Based on the results of our simulations, it appeared that the proposed NSC-OFDM-IM does not suffer from any performance degradation compared to the existing OFDM-IM, while achieving better bit error rate (BER) performance and improved spectral efficiency (SE) compared to conventional OFDM. Moreover, in terms of computational complexity, the proposed approach has a significantly reduced complexity over the traditional OFDM-IM scheme.

Performance enhancement of an FSO link using polarized quasi-diffuse transmitter

Free space optics (FSO) system has received much interest in recent years as a technology that exhibits cost-effective, better security, license-free, and comprehensive capacity access techniques for transmission of Giga data rate. However, despite all the many advantages demonstrated by its signal, alignment distortion from building sway, atmospheric disturbances from aerosol, scattering, turbulence, and scintillation have shackled the development of the high-speed FSO link and made it less attractive. These atmospheric disturbances have led to the cultivation of spatial diversity techniques for its performance improvement. This work proposes applying a polarized quasi-diffused system with a power divider/holographic beam splitter as a spatial diversity scheme instead of using multiple transmitters. The idea of both analytical and simulation design is considered. The proposed model with power divider/holographic beam splitter has shown a very high maximum quality factor, improved received power, better bit error rate (BER), and eye height depicting the link visibility as compared to the conventional point to point single input single output (SISO) 1TX/RX FSO system for the same transmitted power and link range. The results and data were collected through the help of optisystem software. The obtained results show better performance of an FSO link by using a single transmitter with multi-beam spots from a power divider/hologram instead of using multiple transmitters as a spatial diversity scheme.

A Simple and Robust Equalization Algorithm for Variable Modulation Systems

This paper proposes a simple and robust variable modulation-decision-directed least mean square (VM-DDLMS) algorithm for reducing the complexity of conventional equalization algorithms and improving the stability of variable modulation (VM) systems. Compared to conventional adaptive equalization algorithms, known information was used as training sequences to reduce the bandwidth consumption caused by inserting training sequences; compared with conventional blind equalization algorithms, the parameters and decisions of the equalizer were determinate, which was conducive to a stable equalization performance. The simulation and implementation results show that the proposed algorithm has a better bit error rate (BER) performance than that of the constant modulus algorithm (CMA) and modified constant modulus algorithm (MCMA) while maintaining the same level of consumption of hardware resources. Compared to the conventional decision-directed least mean square (DDLMS) algorithm, the proposed algorithm only needs to make quadrature phase shift keying (QPSK) symbol decisions, which reduces the computational complexity. In parallel 11th-order equalization algorithms, the operating frequency of VM-DDLMS can reach up to 333.33 MHz.

Coherent Detection-Based Optical OFDM, 60 GHz Radio-over-Fiber Link Using Frequency Quadrupling, and Channel and Carrier Phase Estimation

The optical orthogonal frequency division multiplexing (OFDM) is proven to be a most promising technology for the next-generation high-capacity and ultra-wide bandwidth 5G communication systems. 60 GHz millimeter-wave (mm-wave) frequency band is also becoming a most popular upcoming frequency spectrum due to today’s available dense frequency spectrum used for mobile, multimedia, and data communication, etc. We propose a system comprised of 60 GHz radio-over-fiber (RoF) model using optimized optical frequency quadrupling, coherent detection, channel estimation, and carrier phase correction techniques for ultra-wide bandwidth 16-quadrature amplitude modulation (QAM) OFDM baseband signal. The proposed RoF system’s outcomes have shown relatively better bit error rate (BER) of 3.1 × 10–3 to enable successful transmission of 110 Gbps data for more than 105 km optical link comprising of standard single-mode fiber (SSMF). System performance and obtained results show a potential to fulfill the requirements of 5G and cellular communication system.

Hollow-Core NANF for High-Speed Short-Reach Transmission in the S+C+L-Bands

Hollow-core fibers offer a range of beneficial properties for high-speed optical communication applications, including low latency, low chromatic dispersion and nonlinearity. Based on a system employing a ∼5-km span of hollow-core nested antiresonant nodeless fiber (NANF), we demonstrate in this paper, penalty-free Nyquist 4-ary pulse amplitude modulation transmission relative to the back-to-back at 80, 100 and 112 Gb/s over the S+C+L-bands. Furthermore, using multi-carrier direct-detection optical orthogonal frequency division multiplexing, we show that compared to a standard single-mode fiber of a similar length, the NANF exhibits a significantly better bit error rate (BER) performance at 1550 nm and offers more than 20% capacity enhancement. Consequently, up to 138.09-Gb/s capacity has been achieved at a BER threshold of 3.8 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">−3</sup> after ∼5-km transmission. We conclude that the use of NANF offers a promising solution for achieving simultaneously high capacity and low latency in future short-reach optical interconnects.

Robust interference cancellation for differential quadrature phase-shift keying modulation with band limiting and adaptive filter

Differential quadrature phase-shift keying (DQPSK) modulation techniques and their variants are widely applied in digital communication, such as for high-speed optical fiber, bluetooth, or satellite communication. In its implementation, DQPSK cannot be separated from the potential harmful interference. In this research, a system model has been made for observation and analysis of the interference cancellation process. Discrete finite-duration impulse response (FIR) filters for band limiting and adaptive filter are the key components of the supporting block for this system model. Robust Simulink results have shown a significant increase in system performance in the existence of these key components. The indication has been shown by the best bit error rate (BER) of 3.3e-05. Constellation and eye pattern diagrams have supported the BER.

Visible light communication using new Flip-FBMC modulation system technique

Filter bank multi-carrier (FBMC) modulation in the visible light communication (VLC) system is one of the most promising modulation systems in optical wireless communications (OWC), especially in 5G and 6G future applications. FBMC has a wide bandwidth compared to other modulation systems. One of the highest degree essential conditions for utilising the signal in VLC is that the signal is real positive, the signal is agreeable with intensity modulation/direct detection (IM/DD), where Hermitian symmetry (H.S) is utilised to get a real signal (RE) and to be unipolar direct current (DC)-bias is used. Here the challenge arises as this method increases complicating, due to the modulation of the N number of frequency symbols, these symbols need 2N inverse fast fourier transform (IFFT) and fast fourier transform (FFT), in addition to energy consumption. This research focused on the time domain and not the frequency domain by using the traditional complex FBMC generation signal, and to obtain the RE signal by placing the RE signal side by side with the imaginary signal (IMs) in a row, and then using new Flip-FBMC technology, which saves more energy. The proposed technologies provide approximately 57% of the number of IFFT/FFT. The use of Flip-FBMC technology consumes less energy than traditional technologies with better bit error rate (BER) performance.

DSP-enabled 50G OOK-PON with beyond 29 dB power budget using O-band 10G DML and 10G APD

In this paper, we experimentally demonstrate a digital signal processing (DSP)-enabled 50G on–off keying passive optical network (PON) using cost-effective O-band 10G directly modulated laser and 10G avalanche photodiode. The bandwidth-limited devices induce serious spectral distortions, leading to an unacceptable performance. Digital pre-distortion at the transmitter and post-detection at the receiver are proposed to jointly compensate the serious spectral distortions. The digital pre-distortion at the transmitter can compensate for a part of spectral distortions, but cannot deal with the fast power fading within the high-frequency range. At the receiver, the digital post-detection is proposed to compensate the high-frequency distortions, which mainly includes the polynomial nonlinear equalizer, two-tap post filter, and maximum likelihood sequence estimation (MLSE) with channel estimator. Different from the conventional digital post-detection, the channel estimator can estimate more accurate channel information for MLSE, leading to a better bit error rate (BER) performance. By using the proposed digital signal processing, power budget beyond 29 dB is achieved at BER of 2×10−2 after 20 km standard single-mode fiber transmission. In conclusion, the proposed DSP-enabled 50G-PON shows great application potentials for the next-generation PON.

Double Spatial Modulation with Transmit Antenna Group for Communication Signal Transmission

In this paper, to make use of the idle transmit antennas for the improvement of multiplexing gain and the spectral efficiency, a new design of double spatial modulation (DSM) with transmit antenna group (DSM-TG) is proposed. More specifically, all of transmit antennas are grouped into G groups, each group implements a DSM system independently. Then, by using the vector combiner, G groups of DSM symbol vectors are constructed into a transmitted spatial vector. Furthermore, the average bit error ratio is analyzed. Finally, to make a fair comparison, simulation results are presented for the transmission of same data rate, and show the proposed DSM-TG achieves the better bit error rate (BER) performance gain as compared with other spatial modulation schemes.

An End-to-End Demodulation System Based on Convolutional Neural Networks

The demodulation of digital signal plays a key role in the communication system. The traditional demodulator is usually realized by special hardware platform, which has the disadvantages of high cost and long development cycle. In this paper, we propose an end-to-end digital signal demodulator based on convolutional neural network (CNN). It consists of an encoder and a decoder, in which the encoder encodes the input symbol sequence and maps the signal features to the hidden layer space. Then, the decoder decodes the features of the hidden layer space to obtain the demodulation result of the input sequence. The proposed algorithm can automatically learn how to demodulate the received signal without manually extracting the features. Compared with the traditional demodulator, the proposed CNN demodulator has better bit error rate (BER) performance.

Iterative Threshold Channel Estimation in ORGV Convolutional Code MISO-OFDM System

ABSTRACT In the orthogonal frequency division multiplexing (OFDM) transmission system, when the digital symbols are transmitted in the wireless channel, it would be affected by a lot of noise interference due to the unsatisfactory condition characteristics of the wireless channel itself, therefore, the symbol error and bit error would be generated. To achieve a certain bit error rate (BER) under the condition of known signal-to-noise ratio (SNR), convolutional channel coding and block interleaver should be utilized to further reduce the BER. Moreover, convolutional code is almost utilized in all wireless communication systems. This paper proposes a convolutional code channel estimation method in multiple-input single-output (MISO)-based OFDM (MISO-OFDM) system with frequency-shift m-sequence (FSMS) as guard interval (GI) for avoiding inter-symbol interference (ISI). The proposed space-frequency block code (SFBC) MISO-OFDM system achieves higher transmit diversity gains and better BER performance. Simulation results verify that the proposed iterative threshold channel estimation (ITCE) method in octal representation generation vector (ORGV) convolutional code 4 × 1 MISO-OFDM system provides good BER and normalized mean squared error (NMSE) performance with significant coding gains in both static and dynamic multipath channels.

Interleaved superposed-64QAM-constellation design for spatial multiplexing visible light communication systems

Superposed constellation combined with spatial multiplexing multiple-input multiple-output (MIMO) techniques have been increasingly utilized in visible light communication (VLC) systems, as multiplexing gains can be achieved regardless of the correlation extent of the VLC channel. Herein, we propose a novel superposed 64-quadrature amplitude modulation (QAM) constellation scheme for 2 × 2 MIMO VLC systems. Considering the nonlinearity of light-emitting diodes (LEDs), two geometrically shaped 8QAM constellations are introduced to reduce the peak-to-average power ratio at the transmitter. Because the two 8QAM constellations are superposed in an interleaved manner, the required power ratio between two transmitted signals is 1, which further reduces the risk of nonlinear distortion and avoids signal-to-noise ratio deterioration induced by power competition. The proposed superposed 64QAM constellation scheme is experimentally investigated comprehensively, where the system performance is evaluated under different transmitted powers, direct current bias currents, and driving peak-to-peak voltages (Vpps). The experimental results show that the proposed scheme achieves better bit error rate (BER) performance than the traditional superposed 64QAM constellation schemes. Below the 7% pre-forward error correction BER threshold of 3.8 × 10-3, the dynamic range of the driving Vpps of the two LEDs improves from 0.06 to 0.4 V and 0.23 to 0.4 V when the optimal power ratio is achieved.