Code Division Multiplexing Research Articles

Temperature measurement of overlapped fiber Bragg grating sensors in a series fiber sensor network

Fiber Bragg Gratings (FBGs) in a sensor network have been widely used for structural health and process monitoring. The number of FBGs with distinct wavelength that can be used in such a sensor network is limited by the bandwidth of the laser used. FBGs, with overlapping spectra cannot be interrogated in a series sensor network since they shadow each other. Methods like time division multiplexing (TDM), code division multiplexing (CDM) have been used to interrogate overlapped FBGs. TDM is limited by the power budget system and CDM is limited by the number of FBGs can be used. We propose a neural network based Spectral Division Multiplexing (SPDM) scheme, to monitor overlapped FBGs in a series fiber sensor network.

Interleaved Binary Demodulation Technique for Low-Cost and Fast-Response Visible Light Positioning Using Palindromic Sequences

Recent advancements in visible light positioning (VLP) systems have continuously improved positioning accuracy, extending the application fields in Internet-of-things and factory automation technologies. However, their multiplexing and modulation methods still limit the applicability of VLP systems. Multi-level driving and sensing techniques that use orthogonal frequencies increase the design complexity and are strictly constrained by the bandwidths of the illuminators and sensor devices. Existing binary modulations require additional amendments to the code synchronization. In addition, real-time VLP is fundamentally affected by the distorted signal after orthogonal demultiplexing. Herein, we present a low-cost expansion of VLP that employs binary demodulation in code-division multiplexing. The proposed method utilizes DC-biased binary sequences using the palindromic variant of the Hadamard matrix, which provides perfectly orthogonal sequences while maintaining robustness to signal changes. The proposed demodulation regroups the signal collections of orthogonal sequences in an interleaved manner and determines the source signals via re-modulation. Compared with existing methods, it does not require extra-synchronizing structures and naturally compensates for dynamic sensor signals solely via binary operations. Following its implementation in an FPGA using commercial LEDs and a PIN-PD, we validated that the method achieved 48 dB SNR at a source-to-sensor distance of 10 m. The experiments showed that the proposed method eliminates 45–66% of signal errors and 33–43% of positional displacement during the sensor movements at 800 mm/s. Combined with trilateration, the static positioning error is 0.0158 m on average in 1.31, 0.91, 2.36 m, whereas the standard deviation of the raw position is limited to 0.0016 m.

Demonstration of an 800G CDM-SDM coherent PON utilizing weakly coupled multicore fibers with CDM tributary manipulation

In this Letter, we present an experimental demonstration of downstream signaling in a 16 × 50 Gbit/s coherent passive optical network (CPON) using the code and space division multiplexing (CDM-SDM) approach. We realize optical SDM through the utilization of a 4-core weakly coupled multicore fiber (WC-MCF), enhancing the total available optical launch power at the optical line terminal (OLT). This enhancement significantly improves the power budget for CPONs that connect with a large number of optical network units (ONUs). At the second stage of the CPON, four CDM-assigned ONUs are connected to individual cores of the WC-MCF, thereby supporting the connectivity of up to 16 ONUs. Through experiments, we have noted substantial disparities in the downstream signaling performance among individual CDM-assigned ONUs, particularly as the capacity is increased to 800 Gbit/s. To address this issue, we have employed an innovative approach by leveraging space–time coding techniques to manipulate the CDM tributaries, to achieve a balanced reception performance for all ONUs within the CPON. We believe that the proposed CDM-SDM CPON scheme, complemented by the advanced DSP flow chart, holds significant promise for future PON systems characterized by substantial capacity and extensive connectivity.

Evaluation of Three-Level Code Division Multiplexing for High-Quality Radio over Fiber Communication

Radio over Fiber system (RoF) technology facilitates the transmission of wireless signals over optical fibers, which provides many benefits, including low signal loss, and immunity to electromagnetic interference. Despite these benefits, conventional RoF systems grapple with signal impairments and limited user capacity, as each user must be allocated a specific frequency. To address these limitations, this paper explores the implementation of the Three-Level Division Multiplexing (3LCDM) technique with RoF, a superior multiplexing strategy that allows two users to share a single channel, thereby doubling capacity. This innovative combination was evaluated for various cases using 2.4 GHz, 5 GHz, and the combination of 2.4 GHz and 5 GHz carrier frequencies, and its performance was compared with traditional RoF systems. Simulations were carried out using OptiSystem in cooperation with the MATLAB simulator. The findings of this study reveal that the 3LCDM-RoF system can accommodate twice the number of users as the conventional RoF system without the need for amplifiers. Furthermore, it supports higher bit rates and longer transmission distances. Specifically, the 3LCDM-RoF system achieved maximum data rates at maximum fiber length of 2 x 1.1 Gbps at 60 km, (2.4 GHz), 2 x 2 Gbps at 40 km (5 GHz), and 2 x 0.5 Gbps per channel at 43 km (combined 2.4 GHz and 5 GHz) respectively. Meanwhile, the conventional RoF with 2.4 GHz, 5GHz and the combination of 2.4 GHz and 5 GHz can only achieve maximum data rate at a maximum fiber length of 1.1 Gbps at 45 km, 1.6 Gbps at 35 km, and 0.4 Gbps at 35 km respectively

Integrated long reach and energy-efficient NGPON-VLC system with OCDM/WDM for smart green buildings

Smart green buildings (SGBs) are composed of numerous services and offer hopeful solutions to the world's continuous and rapid urbanization. Conventional data transmission systems are insufficient to deliver acceptable services because to the sudden surge in high-quality information transmission requirements over long distance for numerous linked residents in SGBs. Consequently, a hybrid next generation passive optical network (NGPON) along with visible light communication (VLC) indoor/outdoor broadcast network is presented in this work to increase the reliability with intelligence, exalted overall efficiency, cost efficiency, and security of SGBs. Bidirectional PON-VLC system incorporates the time and wavelength division multiplexing (TWDM), wavelength division multiplexing (WDM) and optical code division multiplexing (OCDM) techniques. In order to improve system performance, various OCDM codes are used in this work at 10/2.5 Gbps per channel throughput via fiber-VLC channels. According to the simulation results, the modified new zero cross-correlation (MNZCC) code performs better than previous codes and supports 200 active residents at reliable 100 km fiber along with 5 m VLC range. Furthermore, by expanding the received aperture diameter to 25 cm, VLC coverage may be increased till 10 m. Moreover, it provides adequate receiver sensitivities of − 13 to − 12 dB in uplink with − 9.8 to − 6 dBm in downlink for 200 to 600 fields of view angles compared to 00 view angle having sensitivity of − 15 dBm. Additionally, the numerical analysis and comparison performance show that PON-VLC outperforms fiber-VLC link-based scenarios when it comes to noise and channel impairments.

Simultaneous injection and measurement chirp division multiplexed Electrical Impedance Tomography and Spectroscopy

Electrical Impedance Tomography and Spectroscopy produce cross-sectional images of objects based on the objects’ internal impedance distribution. It commonly uses time division multiplexing, frequency division multiplexing, or code division multiplexing. These multiplexing methods have limitations of temporal data inconsistencies when applied to fast-changing objects; spectral inconsistencies due to the application of different excitation frequencies on different electrodes and inability to achieve frequency difference imaging; and capacitive spikes due to abrupt signal changes, respectively. This paper proposes the novel use of orthogonal chirp division multiplexing to overcome these challenges. Orthogonal chirps are simultaneously injected at all electrodes mounted on the object and potentials measured concurrently. Mathematical formulations and development of a 16-electrode FPGA-based prototype system are presented. It achieves an excitation bandwidth of 1 MHz and 870 frames/second measurements. The system has a position error of 7.74 % and a size error of 3.84 % comparable to other methods.

Operating Characteristic Curves of Optical Packet-Switching Using Optical Code-Division Multiplexing for Label Switching

In this paper, the operating characteristic curves (OCCs) of optical code-division multiplexing (OCDM) technology for label switching of an optical packet-switching (OPS) network was evaluated. A node structure for processing the packets, with spectral-amplitude-coding (SAC) labels, considering a balanced detector and an optical switch, was developed and modeled. The effects of decoding noises on the performance of both M-sequence and stuffed quadratic congruence (SQC) labeling systems were addressed. Hypothesis testing was applied to the decoder to investigate the results of label recognition. The null and alternative hypotheses were, respectively, defined as a decoder receiving the matching and mismatching labels. Due to the noise effects, the decoder output may not reflect the label status correctly. Type I error occurs when the null hypothesis is true while accepting the alternative one. Type II error occurs when the alternative hypothesis is true while accepting the null one. Analytic equations of both errors were given, considering a desired packet that was missed and an undesired packet shown in a switched path. The trade-off between these two errors, regarding the decoder threshold, was demonstrated in operating characteristic curves (OCCs). A better OCC could be found when a packet had more labeled payload bits, or when the utilized label code had a lower auto-to-cross-correlation ratio.

Reversible data hiding algorithm based on adaptive prediction and code division multiplexing

Reversible data hiding algorithm based on adaptive prediction and code division multiplexing

An Enhanced Probabilistic-Shaped SCMA NOMA for Wireless Networks

The future digital evolution poses challenges that need to be spectral and energy-efficient, as well as highly reliable and resilient. The non-orthogonal multiple access (NOMA) accomplishes massive connectivity, spectral efficiency, effective bandwidth utilization, and low latency. The proposed work involves the code domain NOMA scheme called Sparse Code Multiple Access (SCMA) which provides shaping gain through multi-dimensional constellation and the best performance in terms of bit error rate (BER). It achieves overloading of users through the non-orthogonal allocation of resources which enhances the spectral efficiency and serves more users. The shaping gain can be further improved by reducing the BER and enhancing the capacity of the channel through constellation shaping. This work employs a probabilistic-shaped (PS) constellation where each symbol is transmitted with different probabilities which achieves a reduction of average symbol power and forward error correction (FEC) through channel coding using polar codes which aid in energy efficiency. The output is two-dimensionally spread over Orthogonal Frequency Code Division Multiplexing (OFCDM) subcarriers to achieve a flexible transmission rate through a variable spreading factor. Computer simulations showed better BER performance under AWGN and Rayleigh channels with remarkable gain in SNR which paves the way for future applications in Fifth Generation (5G) beyond networks.

Underwater Acoustic Positioning for Close Sources Using Time Division and Code Division Multiplexing

Underwater acoustic positioning system (UAPS) is used to know the positions of underwater robots and underwater structures. In ultra-short baseline (USBL) acoustic positioning systems, the three-dimensional position is determined by measuring the time difference of arrival (TDOA). In this paper, we investigate the acoustic positioning system targeting multiple sound sources and propose a simultaneous multi-point measurement method using time division and code division multiplexing (TD-CDM). TD-CDM provides higher position accuracy than code division multiplexing (CDM) and has a much shorter positioning time than time division and multiplexing (TDM). The effectiveness of TD-CDM has been proven by the results of the water tank experiment and simulation.

High-Speed Spiral-Phase Donut-Modes-Based Hybrid FSO-MMF Communication System by Incorporating OCDMA Scheme

Hybrid free-space optics (FSO) and optical fiber have been viewed as vital transmission techniques to satisfy high bandwidth and extended transmission range requirements under adverse environment conditions in the future last-mile obstruction problem. In this investigation, 80 Gbps data is transmitted on a hybrid FSO and multimode fiber (MMF)-based network using mode division multiplexing of two donut modes, Donut mode 0 and 1, and optical code-division multiplexing (OCDMA) schemes. For the OCDMA schemes, modified new zero-cross-correlation (MNZCC) codes are used, whereas, to add the phases into donut modes, a spiral phase diffuser is used. The purpose of the investigation is to provide an economical, high-speed and advanced last-mile network with adequate resource utilization for hybrid wired/wireless-based systems. The results obtained show achievement of an acceptable BER up to a fixed 100 m FSO link, with the combination of a 385 m MMF link under clear weather conditions. In another case, when the MMF link was fixed at 100 m, an acceptable bit error rate (BER) is achieved at 2.07 km FSO link. Furthermore, the results were obtained in the presence of strong and weak turbulences. A comparison of log-normal and gamma-gamma modeling for scintillations is presented.

Time-sequential color code division multiplexing holographic display with metasurface

Color metasurface holograms are powerful and versatile platforms for modulating the amplitude, phase, polarization, and other properties of light at multiple operating wavelengths. However, the current color metasurface holography can only realize static manipulation. In this study, we propose and demonstrate a multiplexing metasurface technique combined with multiwavelength code-division multiplexing (CDM) to realize dynamic manipulation. Multicolor code references are utilized to record information within a single metasurface and increase the information capacity and security for anti-cracks. A total of 48 monochrome images consisting of pure color characters and multilevel color video frames were reconstructed in dual polarization channels of the birefringent metasurface to exhibit high information density, and a video was displayed via sequential illumination of the corresponding code patterns to verify the ability of dynamic manipulation. Our approach demonstrates significant application potential in optical data storage, optical encryption, multiwavelength-versatile diffractive optical elements, and stimulated emission depletion microscopy.

Analysis of the Performance of WDM-CDM Bragg Grating Interrogation System With High-Contrast Grating VCSEL

This article shows a novel approach for Bragg gratings interrogation, based on vertical-cavity surface-emitting laser with high-contrast grating cavity. It is shown that with such a light source, one may achieve simultaneous wavelength sweeping together with output light intensity modulation enabled by a single element. In turn, it allows for designing a two-dimensional (time and wavelength) Bragg grating interrogation scheme. The article consists of analytical deliberations that determine the limiting factors of such an interrogation unit, i.e. interrogation speed and size of the sensing network for given Bragg grating reflectivity, expressed in the form of signal-to-noise ratio. Moreover, an experimental and numerical proof of concept of the sensing unit consisting of fiber Bragg grating sensors with an interrogation speed of 1 kHz and the use of code division multiplexing is also presented.

A reach enhanced hybrid OCDMA-MDM multiplexing based IsOWC system incorporating EDFA, SOA, and RFA

Abstract Reach enhancement in inter-satellite optical wireless communication systems (IsOWC) is an utmost requirement due to ever-increasing internet usage all over the globe. Optical code division multiplexing is prominently incorporated for security enhancement in IsOWC systems, however, limited in terms of total reach. Therefore, in this work, a 120 Gbps capacity-based hybrid OCDMA and mode division multiplexed (MDM) IsOWC is presented using different optical amplifiers such as semiconductor optical amplifier (SOA), erbium-doped fiber amplifier (EDFA), and Raman fiber amplifier (RFA). Moreover, the combined effects of Laguerre–Gaussian (LG) with EDFA/SOA/RFA and Hermite–Gaussian (HG) modes with EDFA/SOA/RFA amplifiers are investigated. Results revealed that the proposed system can cover 5000 km IsOWC link within acceptable BER limits and EDFA with LG modes is found to be the best technique.

Capacity enhancement in fiber optic communication systems using space division multiplexing

Abstract Data rates in fiber optic communication (FOC) technology are highly increased and optical communication technology has been mostly advancing highly. There are different multiplexing techniques like frequency-division multiplexing (FDM), time-division multiplexing (TDM), wavelength division multiplexing (WDM), dense wavelength division multiplexing (DWDM), code division multiplexing (CDM), and digital coherent technology by using single mode fiber (SMF)/single core fiber (SCF), and using these multiplexing did not produce over 100 Tbps/fiber because of many factors like linearity and nonlinearities of fiber optic. To transmit a high capacity over 100 Tbps/fiber and long-haul transmission, the multiplexing techniques that are needed to break this bottleneck/capacity limit are termed space-division multiplexing, which uses single mode fiber (SMF) and multicore fiber (MCF). The target of this paper is to enhance the capacity of FOC systems using space-division multiplexing (SDM). The result produced during this paperwork is that the capacity enhanced is around 14.75 pb/s/fiber, after it is decreasing and thus the haul of transmission is 250 km with usable wavelength C + L band. The signal/noise ratio is 35 dB in FOC using single mode fiber (SMF) and multicore fiber (MCF). Finally, the SDM includes a great role in fiber optic just in case of effective information transmission by enhancing capacity, reduction of loss, distortion, cross talk, and power consumption reduction during information transmission; SDM in fiber optic is incredibly essential for effective communication systems with extremely high capacity and long haul transmission.

245Gb/s P2MP Mobile Fronthaul Downstream Transmission Using Code-Division Multiplexing and Self-Homodyne Coherent Technologies

We have proposed and experimentally demonstrated a high-speed and point-to-multipoint (P2MP) mobile fronthaul (MFH) downstream system based on the code-division multiplexing (CDM) and self-homodyne coherent (SHC) technologies. We find that compared with the traditional 16-ary quadrature amplitude modulation (16-QAM) signal transmission, the change of phase noise between two demultiplexed symbols is much larger in the CDM-16QAM signal transmission because it is the accumulation of phase noise change of n multiplexed symbols. Therefore, a low-complexity pilot sequence-assisted phase noise estimation algorithm is proposed and designed to compensate for the phase noise caused by fiber mismatch length, which makes it possible to use a low-cost distributed feedback (DFB) laser. Besides, the spread signal's distribution in the frequency domain of each code sequence is different, leading to different transmission performances between different remote radio units (RRUs). A power optimization scheme is proposed to balance the transmission performances of different RRUs by multiplying each channel's signal by a normalized weight factor at the transmitter. The experimental results show that the proposed system could successfully support the transmission of 245 Gb/s 16QAM signal from baseband unit (BBU) to 7 RRUs (each RRU could have 2 antennas to transmit signals at 2 polarizations) over 10 km standard single-mode fiber (SSMF). The measured worst bit error rate (BER) value of 14 channels is 1.77e-3 which is below the hard-decision forward error correction (HD-FEC) threshold (3.8e-3).

Performance analysis of code division multiplexing communication under evaporation duct environment

The evaporation duct is an effective means for realizing non-line-of-sight (NLOS) wireless transmission over the sea. However, the effects of marine weather conditions on electromagnetic propagation have rarely been studied. In this study, the influence of the marine atmospheric environment on electromagnetic propagation was analyzed through numerical simulation. Additionally, the impacts of antenna height, transmission distance, and electromagnetic wave frequency on path loss were studied. Finally, the link capacity of the code division multiplexing (CDM) communication system in the evaporation duct environment was studied via numerical analysis and simulations. Simulation results demonstrated that CDM communication technology can improve the link capacity under an evaporation duct compared with that of the spread-spectrum communication technology.

A multi-frame space-time coding method for the phase-coded signal in MIMO radars

Code-division multiplexing (CDM) has become the focus of designing orthogonal waveforms of multiple-input multiple-output (MIMO) radars as it occupies fewer resources than time-division multiplexing (TDM) and frequency-division multiplexing (FDM). As one of the standard CDM waveforms, conventional inter-pulse phase-coded waveform possesses non-ideal diversity performance. That is, the orthogonality of the signals will reach the threshold after the codes extend to a certain length. To circumvent the coding restrictions, space-time coding (STC) makes use of spatial resources. This paper proposes a multi-frame STC method to improve the orthogonality among waveforms. Specifically, we first design the orthogonal transmitted signals and corresponding matched filters for MIMO radars. Then the signal expressions and the radar ambiguity function (AF) are deduced to verify the proposed method theoretically. Compared with conventional STC, such a method can save half of the time domain resources and make the most of coding resources. Furthermore, the output signal-to-noise ratio (SNR) is well improved as the proposed method effectively suppresses the cross-correlation energy of the waveform. The proposed multi-frame STC waveform can be easily implemented in practical radar applications because of its constant waveform amplitude. The theoretical analysis and simulation results demonstrate the effectiveness of the method.

THE STUDY OF THE CROSS-CORRELATION PROPERTIES OF COMPLEX SIGNALS ENSEMBLES OBTAINED BY FILTERED FREQUENCY ELEMENTS PERMUTATIONS

Context. The relevance is to study the cross-correlation properties of the developed complex signals ensembles of large volume with a low level of multiple access interference, thereby increasing the efficiency of using a limited radio frequency range. The Object of Research is a method of bandpass filtering with permutations, which allows forming complex signals ensembles of large volume. Objective. The Objective is to determine the optimal cross-correlation properties for the formation of complex signals ensembles of large volume with a low level of multiple access interference. Method. The work has the study results of cross-correlation properties of complex signals ensembles obtained by applying the filtered elements permutation method. The formation of complex signals ensembles is based on pseudo-random sequences with improved cross-correlation properties in the time domain. Bandpass filtering is applied to such sequences, and the number of filter bands is determined based on the calculation of the frequency spectrum utilization coefficient. The filter band optimal width determination is based on a comparison of the maximum emissions of the side lobes values of the of cross-correlation function of signals from the elements number in the involved sequences. The signals obtained by frequency bands allocating are characterized by a difference in form in the minimal similarity condition. In order to reduce the multiple access interference impact, the frequency components transfer obtained by spectral filtering to the common frequency range is carried out. After that, the signals are transferred using the full search method. As a result, it was obtained all possible combinations of signal pairs permutations. The use of permutations in the complex signals ensemble formation can significantly increase the ensemble volume. The signals generated by frequency filtering, to which the transfer to the common frequency band and their subsequent permutation was applied, are subjected to correlation analysis based on the calculation of the maximum emissions values of the side lobes of the cross-correlation function. Comparative characteristic of cross-correlation properties of developed signals with known signals prove that signals generated based on pseudo-random sequences with improved cross-correlation properties have a much larger ensembles volume, are formed on the basis of simple algorithms that don’t require significant computing resources and have satisfactory cross-correlation characteristics. The use of bandpass filtering method with permutation allows the formation of large-volume ensembles whose signals differ inform, and the combination of different frequency bands reduces the vulnerability to multiple access interference. Results. Due to the software implementation of the bandpass filtering method with permutations, the comparison of crosscorrelation properties of nonlinear sequences, M-sequences, multiphase signals and developed signals based on sequences with improved cross-correlation properties was performed. In estimating the levels of maximum emissions of side lobes of the cross-correlation function, it was found that the generated signals obtained by bandpass filtering with permutations deteriorate cross-correlation characteristics by increasing the pulse duration proportional to the decrease in signal frequency band, but their value satisfies the minimal similarity condition, used in cognitive telecommunications systems. Conclusions. The study of the signals cross-correlation properties proves the effectiveness of the developed bandpass filtering with permutations method. The generated signals have cross-correlated characteristics no worse than ensembles based on known signals. At this level of maximum emissions of the side lobes of the cross-correlation function of the developed signals is 7–12% less than the known signals. Thus, the method of bandpass filtering with permutations can be used to increase the efficiency of radio frequency resource use of both existing and advanced cognitive telecommunication networks of wireless access based on systems with code division multiplexing.

A CDM-WDM Interrogation Scheme for Massive Serial FBG Sensor Networks

Structural health monitoring and other smart structures gain an increased attention which can be satisfied by the quasi-distributed optical sensing approach. Serial fiber optic sensors, such as fiber-Bragg gratings (FBGs) provide among others small size, immunity to electro-magnetic interference, an accurate sensing accuracy and a high multiplexing capability to increase the amount of sensing points in an optical sensor network. Different multiplexing approaches demonstrated a limited number of FBGs, such as time-division multiplex, optical frequency domain refractometry or frequency shifted interferometry. This work introduces a code-division multiplex (CDM) - wavelength-division multiplex (WDM) interrogator for massive serial FBG sensor networks. The interrogation of 4000 serial sensors in a network with a length of 113m, 200 identical WDM sections over a length of 200m and a network with 1000 sensors and a length of 1.6km show a massive multiplexing capability of up to 16000 sensors and possible network lengths of several kilometers. Strain measurements with FBGs in rear sections prove the sensing applicability of the CDM-WDM scheme.