Improved Bit Error Rate Research Articles

Analytical approach of an FSO Link with alamouti- type STBC considering weak atmospheric turbulence

An analytical approach is proposed to evaluate the bit error rate (BER) performance of a direct detection on-off keying (OOK) free space optical link over log-normal atmospheric turbulence-induced fading channels based on modified Alamouti code presented by Simon and Vilnrotter and maximal ratio combining (MRC) at the receiver. Simulations show that due to coding and diversity at the receiver, a significant improvement in the BER performance is obtained at a given BER. For diversity order of 2 in both transmitter and in receiver, the amount of BER improvement is 6.6dB at BER 10-5. Further increment of the receiver diversity from 2 to 4 gives additional 3dB improvement at the same BER. A drastic improvement of the BER performance is also possible for increasing number of receiver diversity which may increase hardware complexity. Simulation results are demonstrated to confirm the analytical results.Bangladesh J. Sci. Ind. Res.53(3), 205-210, 2018

Receiver Techniques for Diffusion-Based Molecular Nano Communications Using an Adaptive Neuro-Fuzzy-Based Multivariate Polynomial Approximation

Molecular communication (MC) nanonetworks, the interconnection of biological nanomachines (Bio-NMs), are envisaged to significantly expand the applications of nano-technology in the areas of the biomedical, material science, and electrical engineering. In this paper, we consider the scenario of a diffusion-based molecular communication (DMC) system that is a promising bio-inspired approach to implementing nanonetwork systems. Considering the limited computation capability, ultra-low energy assumption, and expensive information exchange cost among Bio-NMs, this paper proposes a pulse-based demodulation scheme in three biologically inspired techniques for the detection of the molecular pulses: 1) a multivariate polynomial approximation (MPA) scheme; 2) an adaptive fuzzy threshold-based detection (AFTD) scheme; and 3) an adaptive neuro-fuzzy-based MPA (ANF-MPA) scheme. These methods are suitable for binary ON- OFF keying (BOOK signaling), where the Rx Bio-NM adapts the 1/0-bit detection threshold based on the previously received bits that help to alleviate the inter-symbol interference (ISI) problem resulting from residual (tail) diffusion molecules arriving at the receiver due to past bit transmissions and reception noise. To evaluate the performance of DMC systems, the essential communication metrics in each detection scheme are identified, and the numerical results are obtained and validated by MATLAB simulation. Moreover, the complexity of the proposed schemes is calculated, and the performance evaluation in various noisy channel sources shows a promising improvement in the un-coded bit error rate (BER) performance compared with the threshold detection schemes in the literature. These results provide insights that may guide the implementation of future DMC nanonetworks.

Modal Diversity for Robust Free-Space Optical Communications

Modal diversity is an important advance in free-space optics, where propagation distances are limited by effects such as atmospheric turbulence. This experimental demonstration shows that orthogonal, coaxially propagating spatial modes of light from different bases are able to mitigate the effects of atmospheric turbulence. The different modes experience different perturbations, even when traveling along the same path, which removes the conventional need for physical separation of the transmitters, while also showing a significant improvement in bit-error rate. This approach could be applicable to a wide range of physical systems that are adversely affected by random aberrations.

Improvement of Bit Error Rate Using Novel Precoded Techniques

Improvement of Bit Error Rate Using Novel Precoded Techniques

Non‐linear companding based hybrid PAPR reduction approach for DCT‐SCFDMA system

This study presents a new hybrid scheme that effectively reduces the peak-to-average power ratio (PAPR) of discrete cosine transform based single-carrier frequency division multiple access (DCT-SCFDMA) signal as well as improves the bit error rate (BER) performance of system. The method is to consolidate pulse shaping process with a novel hyperbolic tangent companding technique so that the PAPR of the SCFDMA signals can be further reduced by enabling the transformation of the amplitude of modulated signals into uniform distribution. Through extensive computer simulations, it has been shown that proposed scheme achieves significant improvements in BER and PAPR reduction over the existing standard pulse shaping methods when used alone in DCT-SCFDMA system as far as the lowest PAPR is concerned without degrading the error performance of the system.

Semiconductor optical amplifier space switch BER improvement and guard-time reduction through feed-forward filtering

Analysis of the guard-time interval impact on bit error rate (BER) of a linear SOA-based space switch aiming the guard-time reduction is presented, including effects of fiber propagation. The characterization employed feed-forward filtering and optical switching techniques, through several types and lengths of fibers (with and without dispersion compensation). The Wiener filter (with 2 taps) consistently showed a switching performance improvement, with a guard-time (GT) reduction enough to achieve the BER pre-FEC limit. In most configurations the average GT was of 429ps (3 bits GT at 7Gbps). The overall best GT result achieved was using 100mA of SOA bias current and applying the Wiener Filter, resulting in a GT of 286ps (2 bits GT at 7Gbps). The space-switch operating parameters with focus on the bias current and switching technique configuration were also analyzed, aiming at reducing the SOA-based electro-optical space switch guard-time, allowing the achievement of high commutation rates.

A Hybrid Particle Swarm Optimization Technique for Adaptive Equalization

Adaptive equalization mitigates the distortions caused by radio channels. The least mean square (LMS) and the recursive least squares (RLS) algorithms are used for such purpose. Recently, particle swarm optimization (PSO) algorithms such as PSO using a linear time decreasing inertia weight (PSO-W) and the PSO using constant constriction factor (PSO-CCF) were shown to be very effective in handling systems having nonlinear behavior. However, these algorithms can be trapped in local minima. This paper presents a new PSO-based algorithm called the hybrid PSO (HPSO) that is capable to handle such problems. The HPSO includes the randomization of particles to improve the search capacity of the swarm, which in turn reduces the probability of being trapped in some local minima. It also adapts the inertia weight assignment to the particles. Extensive simulation results are conducted to confirm the consistency in the performance of the HPSO algorithm in different scenarios. The proposed HPSO secures the minimum steady-state error as compared to LMS and other PSO-based algorithms in both nonlinear and linear channels. Finally, the proposed HPSO algorithm shows a great improvements in Bit Error Rate and convergence rate.

A Unitary Precoder for Optimizing Spectrum and PAPR Characteristic of OFDMA Signal

In this paper, a unitary precoder is proposed to suppress the out-of-subband (OOSB) spectral leakage and reduce the peak-to-average-power-ratio (PAPR) for DFT-based orthogonal frequency division multiple access uplink signal. The optimum precoder is developed by solving a multi-objective optimization problem and a method which includes two steps is presented. First, employ eigenvalue decomposition to design the precoder with minimizing OOSB power radiation. Then search for the optimum permutation of columns to reduce the PAPR sufficiently. Besides, an iterative decoding algorithm for the proposed precoder is designed to improve the system performance on bit-error-rate (BER). Simulations show that the proposed precoding and decoding method offers significant performance advantages of spectral leakage suppression, PAPR reduction, and BER improvement at the same time.

Non-Data-Aided <italic>k</italic>-Nearest Neighbors Technique for Optical Fiber Nonlinearity Mitigation

We experimentally demonstrate a low-complexity and zero-redundancy fiber nonlinearity mitigation technique in the 16-QAM and 64-QAM coherent optical communication systems based on the non-data-aided (ND) k -nearest neighbors (KNN) algorithm. We measured the bit error rate (BER) performances of the 16-QAM and 64-QAM signals in the back-to-back case and in the single-mode-fiber transmission case and achieved notable BER improvement by the ND-KNN technique. The ND-KNN technique enables us to compensate any nondeterministic transmission impairments and does not require any extra training data, which is powerful to mitigate the fiber nonlinearity impairments in the 16-QAM and 64-QAM coherent optical communication systems. By utilizing the proposed ND-KNN method, we achieved 0.5-dB BER improvement in the 800-km single-mode fiber (SMF) 16-QAM transmission system and approximately 2-dB BER improvement in the 80-km SMF 64-QAM transmission system. The algorithm first utilizes the density parameter of the testing data to extract rapidly the center noiseless data and label them as the classification references and then applies the KNN method to classify the remaining testing data. Therefore, the algorithm is robust to the system noise and can achieve fast convergence. The proposed ND-KNN equalization technique can provide efficient compensation at a low computation cost and zero data redundancy and is promising for real-world application.

Design of Cyclic Prefix Characteristic-Based OFDM System for WiMAX Technology

Worldwide interoperability for microwave access (WiMAX) offers the wireless connectivity using orthogonal frequency division multiplexing (OFDM) modulation is a proficient wireless technology that capacities high-speed data transmission facilities. The existing WiMAX techniques have the problem of increase in inter-symbol interference (ISI) and bit error rate (BER) at reduced power spectrum that degrades the performance of WiMAX system due to high data rate transmission. The utilization of different adaptive modulation techniques seen as a potential solution to reduce the ISI and BER for high data rate transmission. In this paper, OFDM is adapted using advanced modulation technique for WiMAX system. The technique proposes the cyclic prefix (CP) is utilized that include supplementary bits at the stage of the transmitter. The proposed technique offers minimization of ISI and improvement in BER. It is defined that performance of the existing CP system is equated with the designed single cyclic prefix (SCP) and double cyclic prefix (DCP) and non-cyclic prefix (NCP). BER, probability of error, and power spectral density are utilized to analyse the performance of the designed system. The OFDM based SCP and DCP and NCP for WiMAX are demonstrated for modulation techniques such as; QPSK, BPSK, and QAM. It is determined that BPSK has the smallest BER when compared to QPSK, 16-QAM, and 64-QAM modulations. It is also demonstrated that QPSK is also very competent, however, it has a higher BER as compared to BPSK modulation. It is also observed that 16-QAM and 64-QAM are less efficient in terms of BER compared to QPSK and BPKS modulations. 64-QAM offers the high data rates, and due to high SNR ratio. The designed system is tested for under AWGN and Rayleigh fading channel, and effect power spectral density of signal to noise ratio on OFDM for rayleigh fading channel are demonstrated for SCP and DCP and NCP. It is determined that the OFDM transmitter with proposed DCP for random signals is efficiently reducing the BER and ISI for WiMAX system.

Analysis of Space Period Blocks Codes for Independent Channel Coefficient Using MIMI-CDMA Techniques

The future of communication system is changing towards high capacity and faster data transmission with error less environment. Wireless and effcient Communication Systems follows the Improvement in the Bit error rate (BER) over fading channel with decrease in the system level complexity. Multiple Input multiple output (MIMO) generally improves spectral effciency and link reliability. And CDMA is a simple technique that has many advantages, spread spectrum gives best results in CDMA technique, for the improvement in signal quality, the combination of both techniques rise to give a simple solution. For better Bit error rate (BER) there is permutation spreading technique runs on space time block code (STBC) matrices. Here the crucial part is spreading strategy that follows frequency of data bits and each transmit antenna uses different spreading sequences gives fewer errors in symbols. The assignment of spreading sequence allotment follows some permutation designs that should have required squared Euclidean distance from message to another message for better spatial diversity, orthogonality and code symmetry. Permutation spreading development can be achieved by changing the pattern of space time block code environment. The results indicate that, there is an improvement in Bit Error rate.

Nonlinear Distortion Mitigation by Machine Learning of SVM Classification for PAM-4 and PAM-8 Modulated Optical Interconnection

We demonstrated a support vector machine (SVM) based machine learning method to mitigate modulation nonlinearity distortion for PAM-4 and PAM-8 vertical cavity surface emitter laser multi-mode fiber (VCSEL-MMF) optical link. Simulations at 100 Gb/s data rate and experimental work at 60 Gb/s data rate were carried out. We achieved a significant improvement in bit error rate (BER) when complete binary tree SVMs (CBT-SVMs) are applied for both PAM-4 and PAM-8 signals. Quantitative analysis of the sensitivity gain versus modulation nonlinearity distortion is presented with experimentally verification. The results indicate that CBT-SVMs have better performance for PAM-8 compared to PAM-4. The sensitivity gain increases almost linearly with the increase of eye-linearity (increase of modulation nonlinearity distortion). Up to 2.5-dB sensitivity improvement is achieved by the proposed CBT-SVMs at eye-linearity of 1.72 for PAM-4.

Crosstalk mitigation using pilot assisted least square algorithm in OFDM-carrying orbital angular momentum multiplexed free-space-optical communication links.

In this paper, we experimentally investigate the performance of crosstalk mitigation for 16-ary quadrature amplitude modulation orthogonal frequency division multiplexing (16QAM-OFDM) signals carrying orbital angular momentum (OAM) multiplexed free-space-optical communication (FSO) links using the pilot assisted Least Square (LS) algorithm. At the demodulating spatial light modulators (SLMs), we launch the distorted phase holograms which have the information of atmospheric turbulence obeying the modified Hill spectrum. And crosstalk can be introduced by these holograms with the experimental verification. The pilot assisted LS algorithm can efficiently improve the quality of system performance, the points of constellations get closer to the reference points and around two orders of magnitude improvement of bit-error rate (BER) is obtained.

Critical side channel effects in random bit generation with multiple semiconductor lasers in a polarization-based quantum key distribution system.

Most polarization-based BB84 quantum key distribution (QKD) systems utilize multiple lasers to generate one of four polarization quantum states randomly. However, random bit generation with multiple lasers can potentially open critical side channels that significantly endangers the security of QKD systems. In this paper, we show unnoticed side channels of temporal disparity and intensity fluctuation, which possibly exist in the operation of multiple semiconductor laser diodes. Experimental results show that the side channels can enormously degrade security performance of QKD systems. An important system issue for the improvement of quantum bit error rate (QBER) related with laser driving condition is further addressed with experimental results.

Transmitter diversity scheme for OFCDMA systems based on space‐time spreading with iterative detection receiver

Orthogonal frequency code division multiple access (OFCDMA) system is one of the most promising multi-user wireless communications systems. It outperforms orthogonal frequency division multiplexing (OFDM) and multi-carrier CDMA (MC-CDMA) through utilisation of two-dimensional spreading. This study proposes a downlink air interface that targets data rate increase and bit error rate (BER) performance enhancement with low complexity receiver. The proposed system is an integration of space-time spreading (STS) and OFCDMA that exploits transmit diversity needed for BER enhancing and data rate boosting with low complexity advantage. Further BER improvement was achieved using an effective iterative interference cancellation (IIC) algorithm at the receiver. Analytical and complexity analyses for the proposed system performance are presented in addition to simulation results. The proposed system attains better performance with lower complexity compared to the STS-aided direct sequence MC-CDMA that uses beamforming as a closed-loop transmit diversity. Moreover, the effect of frequency domain spreading factor with different number of iteration loops is investigated. The achieved BER performance was very close to maximal ratio receive combining system with 1Tx and 4Rx. A considerable improvement was obtained by increasing the number of IIC iteration loops. The system performance was enhanced significantly with the frequency domain spreading factor increase.

Experimental research of adaptive OFDM and OCT precoding with a high SE for VLLC system

Abstract In this paper, an adaptive orthogonal frequency division multiplexing (OFDM) modulation scheme with 128/64/32/16-quadrature amplitude modulation (QAM) and orthogonal circulant matrix transform (OCT) precoding is proposed and experimentally demonstrated for a visible laser light communication (VLLC) system with a cost-effective 450-nm blue-light laser diode (LD). The performance of OCT precoding is compared with conventional the adaptive Discrete Fourier Transform-spread (DFT-spread) OFDM scheme, 32 QAM OCT precoding OFDM scheme, 64 QAM OCT precoding OFDM scheme and adaptive OCT precoding OFDM scheme. The experimental results show that OCT precoding can achieve a relatively flat signal-to-noise ratio (SNR) curve, and it can provide performance improvement in bit error rate (BER). Furthermore, the BER of the proposed OFDM signal with a raw bit rate 5.04 Gb/s after 5-m free space transmission is less than 20% of soft-decision forward error correlation (SD-FEC) threshold of 2.4 × 10 −2 , and the spectral efficiency (SE) of 4.2 bit/s/Hz can be successfully achieved.

Robust Secure Transmission of Using Main-Lobe-Integration-Based Leakage Beamforming in Directional Modulation MU-MIMO Systems

In the paper, we make an investigation of robust beamforming for secure directional modulation in the multi-user multiple-input and multiple output (MU-MIMO) systems in the presence of direction angle measurement errors. When statistical knowledge of direction angle measurement errors is unavailable, a novel robust beamforming scheme of combining main-lobe-integration (MLI) and leakage is proposed to simultaneously transmit multiple different independent parallel confidential message streams to the associated multiple distinct desired users. The proposed scheme includes two steps: designing the beamforming vectors of the useful confidential messages and constructing artificial noise (AN) projection matrix. Here, in its first step, the beamforming vectors for the useful confidential messages of desired user k are given by minimizing the useful signal power leakage from main-lobe of desired user k to the sum of main-lobes of the remaining desired directions plus main-lobes of all eavesdropper directions. In its second step, the AN projection matrix is constructed by simultaneously maximizing the AN power leakage to all eavesdropper directions such that all eavesdroppers are disrupted seriously, where AN is viewed by the transmitter as a useful signal for eavedroppers. Due to independent beamforming vectors for different desired users, a more secure transmission is achieved. Compared with conventional non-robust methods, the proposed method can provide a significant improvement in bit error rate along the desired directions and secrecy-sum-rate towards multiple desired users without needing statistical property or distribution of angle measurement errors.

BER Analysis of Coherent Free Space Optical Communication Systems with Holographic Modal Wavefront Sensor

Degradation of bit-error-rate (BER), caused by atmospheric turbulence, seriously hinders the performance of coherent Free Space Optical (FSO) communication systems. An adaptive optics system proves to be effective in suppressing the atmospheric turbulence. The holographic modal wavefront sensor (HMWFS) proposed in our previous work, noted for its fast detecting rates and insensitivity to beam scintillation, is applied to the coherent FSO communication systems. In this paper, based on our previous work, we first introduce the principle of the HMWFS in brief and give the BER of the coherent FSO with homodyne detection in theory, and then analyze the improvement of BER for a coherent FSO system based on our previous simulation works. The results show that the wavefront sensor we propose is better for weak atmospheric turbulence. The most obvious advantages of HMWFS are fast detecting rates and insensitivity to beam scintillation.

STT-RAM Energy Reduction Using Self-Referenced Differential Write Termination Technique

Spin-transfer torque random access memory (STT-RAM) has emerged as an attractive candidate for future nonvolatile memories. It advantages the benefits of current state-of-the-art memories including high-speed read operation (of static RAM), high density (of dynamic RAM), and nonvolatility (of flash memories). However, the write operation in the 1T-1MTJ STT-RAM bitcell is asymmetric and stochastic, which leads to high energy consumption and long latency. In this paper, a new write assist technique is proposed to terminate the write operation immediately after switching takes place in the magnetic tunneling junction (MTJ). As a result, both the write time and write energy consumption of 1T-1MTJ bitcells improves. Moreover, the proposed write assist technique leads to an error-free write operation. The simulation results using a 65-nm CMOS access transistor and a 40-nm MTJ technology confirm that the proposed write assist technique results in three orders of magnitude improvement in bit error rate compared with the best existing techniques. Moreover, the proposed write assist technique leads to 81% energy saving compared with a cell without write assist and adds only 9.6% area overhead to a 16-kbit STT-RAM array.

Design of linear precoder for correlated multiuser MIMO system with imperfect CSI

In this paper, we have designed a transceiver to minimize the mean square error (MSE) subject to total transmit power constraint for multi-user multiple input multiple output (MU-MIMO) system under imperfect channel state information (CSI). For the transmission, we presume spatially and temporarily correlated Rayleigh flat fading channel. Because of channel estimation error and feedback delay, the CSI existing at both transmit and receive side will be imperfect. In addition, mutual coupling significantly degrade the system performance. Thus, we also considered the mutual coupling of antenna at both sides of the downlink (DL) which was neglected in previous work. With the above scenario, the proposed precoder design shows significant improvement in bit error rate (BER) compared with the existing precoder model. The linear MMSE prediction algorithm for channel gain is proposed for further progression in performance. The simulation result shows the precoder with predicted CSI results in better BER performance than the existing method. The results are validated by comparing the simulation results with their analytical performance.