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The authors focus on the waveform design for Code Division Multiple Access Multiple Input Multiple Output (CDMA‐MIMO) radar systems, with a specific emphasis on Compressed Sensing (CS) based target estimation. The selection of an appropriate waveform is a critical determinant in the effectiveness of estimation algorithms. Recent studies show the possibilities of optimising waveform parameters to improve the efficiency of CS based estimation. The authors introduce an optimisation framework designed to modify the phase components of code sequences used in CS‐CDMA MIMO radar systems. The objective of this optimisation is to minimise the l∞ norm of off‐diagonal elements within the Gramian matrix of the underlying sensing matrix, focusing on phase modulation of the waveform. Solving this optimisation problem requires dealing with a non‐convex, combinatorial and non‐linear scenario. Simulated Annealing is employed as the solution technique. To assess the effectiveness of the proposed optimisation approach, the resulting optimised sequence is rigorously compared against well‐established Hadamard and Gold sequences across various performance metrics. These metrics encompass correlation properties, ambiguity function behaviour, recovery percentage and recovery error. The study demonstrates that the generated poly‐phase sequences outperform existing sequences, leading to significantly improved target reconstruction results in the context of CDMA‐MIMO radar systems with CS‐based estimation. [ABSTRACT FROM AUTHOR]

Codebooks with small inner-product correlations are desirable in many fields, including compressed sensing, direct spread code division multiple access (CDMA) systems, and space-time codes. The objective of this paper is to present a class of codebooks and explore their applications in strongly regular Cayley graphs. The obtained codebooks are nearly optimal in the sense that their maximum cross-correlation amplitude nearly meets the Welch bound. As far as we know, this construction of codebooks provides new parameters. [ABSTRACT FROM AUTHOR]

Next to the legacy frequency division multiple access (FDMA) signals in the L1 and L2 band, modernized GLONASS satellites of the M+, K1, and K2 generation also transmit new code division multiple access (CDMA) signals on L3, and, in part, the L1 and L2 frequencies. Depending on the specific satellite platform, either a common antenna or two distinct antennas are used for the individual signals. As a novel feature, the new CDMA navigation messages provide information on the antenna phase center locations as well as the spacecraft orientation during rate-limited noon and midnight turns. We establish a comprehensive set of phase center positions for the individual GLONASS antennas from manufacturer data and information in the CDMA navigation messages, inferred from the comparison of FDMA and CDMA broadcast ephemerides, and obtained from antenna baseline estimates using a triple-frequency carrier phase combination. Based on these, reference values for the signal-specific PCOs of each block of modernized GLONASS spacecraft are derived that may be used to extend the current antenna model of the International GNSS Service (IGS) to all frequency bands. Complementary to the analysis of antenna phase center information, the new CDMA attitude model for GLONASS-K satellites is reviewed. Algorithms for computing relevant parameters of the rate-limited yaw slews including the ramp-up and -down phase based on the Sun/orbit geometry are derived that enable a concise attitude modeling in GLONASS orbit determination and precise point positioning. The model is validated through comparison with yaw angle estimates derived from triple-frequency observations showing consistency at the 1° level for the K2 satellite. On the other hand, unexpected accelerations during noon turns of GLONASS-M+ are identified, which may cause short-term yaw angle deviations of up to 20° relative to attitude models in common use within the IGS. [ABSTRACT FROM AUTHOR]

In this study, the hybrid unipolar-bipolar (U-B) optical code division multiple access (OCDMA) with mixed unipolar-bipolar scheme in free-space optical communication was proposed. Additionally, the codeword assigned introduced the quasi-polarized code, which could be used to transmit both the unipolar and bipolar section. Using OptiSystem simulations, the model was studied. According to the results from the simulation, the proposed hybrid U-B OCDMA can correctly decode the original optical signal from its matching encoder. Further testing of the hybrid U-B OCDMA system was conducted in turbulence conditions. According to the simulation results, walsh-zero cross correlation (ZCC) performs better than all other codes for the unipolar segment whereas walsh-hadamard (W-H) code performs best for the bipolar section. The simulations also showed that the performance deterioration of the walsh-ZCC algorithm was the greatest. [ABSTRACT FROM AUTHOR]

In this paper, a high-speed transmission system that combines a multimode fiber (MMF) with Free Space Optics (FSO) is proposed to accommodate the rapid growth of traffic. As Orbital Angular Beams Multiplexing (OAM) plays a crucial role in 6G networks by enhancing transmission capacity, four OAM beams ( LG 0 , 0 , LG 0 , 20 , LG 0 , 40 , and LG 0 , 40 ) are utilized in this study. Additionally, the Optical Code Division Multiple Access (OCDMA) technique is employed, known for its high level of confidentiality and the ability to allow multiple channels to transmit data simultaneously. To ensure ubiquitous data transmission, two channels: MMF and FSO are used. Accordingly, in our proposed MMF/FSO system, we employ four OAM beams, with each carrying four OCDMA channels assigned distinct Permutation Vector (PV) codes. With a data transmission rate of 10 Gbps on each OCDMA channel, the overall capacity of the system amounts to 160 Gbps (10 Gbps × 4 OCDMA channels × 4 OAM beams). Moreover, the performance is investigated and evaluated using two scenarios. The first assumes an FSO range of 5 km and Clear Air (CA) weather conditions, with a variable MMF length. In contrast, the second scenario maintains a fixed MMF length of 1 km while altering the FSO span. Weather conditions like CA and rain conditions; Light Rain (LR), Medium Rain (MR), and Heavy Rain (HR) are considered while evaluating the system performance in the second case. The bit error rate (BER), travelling distances in the channel either MMF or FSO, and eye diagrams are among the metrics used for evaluation. They all provide information about the received signal performance. Finally, the obtained results for the proposed MMF/FSO system, utilizing OAM beams and PV codes, indicate that in the first scenario, the system can support a total capacity of 160 Gbps across all channels. The performance is noteworthy, with a BER below 10 - 5 and a wide eye opening, enabling successful transmission over 6.2 km (1.2 km MMF length + fixed 5 km FSO span). For the second scenario, the achievable distance is decreased due to the attenuation caused by rain. It becomes 2.62 km (1 km MMF + 1.62 km FSO span), 5.2 km (1 km MMF + 1.2 km FSO span), and 1.77 km (1 km MMF + 0.77 km FSO span), under LR, MR, and HR, respectively. [ABSTRACT FROM AUTHOR]

Optimizing the correlation properties of spreading codes is critical for minimizing inter-channel interference in satellite navigation systems. By improving the codes' correlation sidelobes, we can enhance navigation performance while minimizing the required spreading code lengths. In the case of low-earth orbit (LEO) satellite navigation, shorter code lengths (on the order of a hundred) are preferred due to their ability to achieve fast signal acquisition. Additionally, the relatively high signal-to-noise ratio in LEO systems reduces the need for longer spreading codes to mitigate inter-channel interference. In this work, we propose a two-stage block coordinate descent (BCD) method which optimizes the codes' correlation properties while enforcing the autocorrelation sidelobe zero property. In each iteration of the BCD method, we solve a mixed-integer convex program over a block of 25 binary variables. Our method is applicable to spreading code families of arbitrary sizes and lengths, and we demonstrate its effectiveness for a problem with 66 length-127 codes and a problem with 130 length-257 codes. [ABSTRACT FROM AUTHOR]

This paper introduces a high transmission and secure Underwater Optical Wireless Communication (UOWC) system using Dual Polarization (DP) states, each of them carries three channels assigned with Optical Code Division Multiple Access (OCDMA) code; named, Fixed Right Shift (FRS). A comparison between different transmission powers is performed. The system performance is evaluated across five distinct water types; pure seawater (PS), clear ocean (CL), coastal ocean (CS), harbor I (HI), and harbor II (HII). Assessments encompass received power, Bit Error Rate (BER), eye diagrams, and Q-factor. Comparative analyses are conducted at data rates of 2.5, 5, and 10 Gbps across each water type. The results indicate that the Laser Diode (LD) sources with 15 dBm transmitted power yield higher received powers compared to that with 10 dBm. Additionally, the optimal system performance characterized by lower BER, higher Q-factor, and wider eye openings, is observed in water types with lower attenuation, such as PS and CL, and at lower data rates. Conversely, higher attenuation water types, like HI and HII, achieve lower performance metrics. Moreover, our model can successfully allow six channels, each delivering 10 Gbps data, propagate distances up to 35 m for PS, 22 m for CL, 13.6 m for CS, 7.1 m for HI, and 4.45 m for HII, demonstrating BER ∼ 10 - 4 and Q-factor of ∼ 4. [ABSTRACT FROM AUTHOR]

This paper investigates the performance of the Spectral Amplitude Coding (SAC) Optical Code Division Multiple-Access (OCDMA) system utilizing the Flexible Double Weight (FDW) code and a newly developed detection technique, the Direct AND (D-AND) detection technique. The newly proposed Direct AND (D-AND) technique comprises three decoder components: a primary decoder, a subtractive decoder (S-decoder), and an addition decoder (A-decoder). The numerous noises investigated in the theoretical research included phase-induced intensity noise, shot noise, thermal noise, and multiple-access interference effects. Bit Error Rate (BER) and signal-to-noise ratio (SNR) were used to gauge the system's performance. The Detection (DD) and Single-Photodiode Detection (SPD) results were compared to those of the study of the new detection technique. The newly developed detection technique, which was tested using the FDW code, can support more active users and improve system performance when compared to SPD and DD approaches. The simulation experiment demonstrates that the system's BER performance with the new detection technique is much better than with the earlier techniques. The new detection technique outperforms the previous technique, supporting 284 concurrent users compared to DD 172 concurrent users and SPD 116 concurrent users at a 10 Gbps bit rate. [ABSTRACT FROM AUTHOR]

Summary: This paper evaluates the performance of a spectral‐amplitude‐coding optical code division multiple access (SAC‐OCDMA) system over a free space optical (FSO) communication link under various weather conditions such as fog, snow, and rain. The system uses different code families, including modified quadrature congruence (MQC), random diagonal (RD), and diagonal eigenvalue unity (DEU), to address user codes and reduce the effects of multiple access interference (MAI). The system's bit error rate (BER) performance has been analyzed taking into account receiver noises and MAI, and calculates the required optical power for a BER value of 10−9 under different weather conditions. The results show that fog has the most significant impact on the system's performance, while rainy conditions require the lowest optical power. The performance of the system also declines with increasing transmission length and concurrent user count. Finally, the paper compares the performance of different code families under unfavorable weather conditions and concludes that DEU performs better than MQC and RD in bad weather. [ABSTRACT FROM AUTHOR]

Radiocommunications in the mmWave band present strong free-space attenuation, which requires power maximization at the receiver. A code division multiple access (CDMA) modulation system increases the receiver's ability to detect the transmitted signal by means of spectrum spreading. The main benefit of direct sequence spread spectrum for mmWaves is the increase in coverage due to the process gain. The main drawback of its use in high-speed communications is bandwidth reduction. Fortunately, this can be compensated for by the huge bandwidth available at mmWave frequencies. However, most of the codes available for CDMA have mutual interference. The zero correlation zone (ZCZ) codes are orthogonal to each other, but only under the condition that no multipath far echoes are received. This condition is fulfilled in mmWave radio communications, owing to strong propagation attenuation and also because of the beamforming that radio links usually do at this frequency. In this study, a field experiment is carried out consisting of data reception at 28 GHz from many different users who are simultaneously transmitting using CDMA on BPSK modulation and then comparing the performance of conventional maximal pseudorandom (PR) codes versus ZCZ codes. It is verified that the latter are received with the same process gain but no mutual interference, approximately resulting in a 12 dB improvement on the modulation error ratio (MER). [ABSTRACT FROM AUTHOR]

Water represents 71% of the globe, of which 95% reserved by oceans and the rest is made out of seas and other water bodies. Communication among entities floating and diving underwater is not typically available or meets the acceptable level in most areas of water bodies, even though many underwater communication systems exist nowadays. However, the main issue of underwater acoustic and radio frequency (RF) wireless communication systems is the short communication distance between the transmitter and receiver without repeater due to the frequency dependence. Where in the optical wireless communication (OWC) the distance depends on the operating wavelength of the used light source. Recently, many researches have appeared in the field of underwater communication using visible light communications (VLC) and invisible OWC. Underwater optical wireless communication (UOWC) at 450 nm wavelength has proven to be better than at 680 nm and 860 nm due to the attenuation and dispersion mechanisms. In this paper, we will present a new design for a passive optical wireless code division multiple access (OW-CDMA) network based on a M-arry differential pulse position modulation (M-DPPM) with a new spreading code called double length modified prime code (DL-MPC) with distinct correlation characteristics to enhance the transmission distance, minimize the system latency, security of data transmission through the network, enhance the data rate per user, network capacity, improve the system signal to noise ratio (SNR) and consequently enhance BER performance at long transmission distance. The simulation results proved that the proposed system can accommodate about 500 users at a BER equals 10–9 using the proposed DL-MPC sequence at a transmission distance of 880 m under pure water. [ABSTRACT FROM AUTHOR]

A novel 120 Gbps free space optics (FSO) is presented in this paper based on integrating three multiplexing techniques, namely, orthogonal frequency division multiplexing (OFDM), polarization division multiplexing (PDM), and optical code division multiple access (OCDMA). For PDM, two states are utilized, each of which carries three different OCDMA channels assigned with distinct Identity Column Shift Matrix (ISCM) code sequences. A 20 Gbps of information is modulated by OFDM and transmitted on each channel. The impact of inclement weather conditions on the FSO channel is investigated, focusing on hazy, rainy, and foggy weather. The performance evaluation includes analyzing parameters such as the bit error rate (BER), maximum FSO range, received optical power (ROP), and the constellation diagram. Furthermore, the applicability of this model in practical settings is discussed for two distinct cities: Alexandria, Egypt, and Hyderabad, India; each is characterized by unique geographical locations and correspondingly diverse weather conditions. The simulation results assure that the information signal can propagate over longer ranges of 5.8 and 5 km when applied in Alexandria and in the presence of light haze (LH), respectively, with BER below 10 - 3 and ROP ∼ −11.8 dBm. In contrast, the lower range of 0.91 km occurs in the presence of heavy fog (HF) due to the large attenuation caused by this weather condition. Accordingly, the proposed 120 Gbps (2 polarization states; each has 3 channels, and each channel carries 20 Gbps of information) FSO model is suggested to be used in high-speed transmission networks. [ABSTRACT FROM AUTHOR]

In the realm of future wireless networks, it is anticipated that high altitude platforms (HAP)-satellite links will serve as the primary facilitators. Optical wireless communication has become increasingly important due-to its exceptional features and ability to provide gigabit capacity communication. As such, this work explores an optical code division multiple access scheme centred on high-speed long-haul mode division multiplexing for HAP-to-satellite applications. The proposed design utilizes zero cross-correlation (ZCC) and multi-diagonal (MD) codes at donut modes 0 and 1. The main objective of this research is to create a cost-effective, secure, and cutting-edge last mile linkage that optimizes resource utilization for HAP systems. The results indicate that the system employing ZCC code outperforms the MD code. Moreover, the system accomplishes a minimum bit error rate limit of 10−3 at transmission distances of 5000 km and 4800 km at Donut mode 0 and 1, respectively, for the ZCC code. In addition, the system can tolerate maximum acceptable transmitter pointing errors of 3 µrad and receiver pointing errors of 4 µrad at minimum BER limit. Meanwhile the system using ZCC can offer better performance of maximum 28 dB optical signal to noise ratio till high split ratio of 1:4–1:64. It also indicates optimum performance over other existing ones. [ABSTRACT FROM AUTHOR]

In this paper, dual polarization (DP) states and optical code division multiple access (OCDMA) are utilized in an underwater optical wireless communication system (UOWCS). The diagonal permutation shift (DPS) code sequences are assigned to the six OCDMA channels that are utilized in the proposed model. These six channels are divided into two groups, each of which transmits its data on DP states. Attenuations of five water types are considered which have different inherent optical characteristics. Bit Error Rate (BER), Quality factor (Q-factor), data rate, underwater (UW) range, and eye patterns are metrics considered for evaluating the proposed UOWCS performance. The outcomes indicate that when the system is used in pure sea (PS) and clear ocean (CL), it shows longer UW ranges of 11 m and 9 m, respectively, with a BER less than 10–6, and a Q-factor ∼ 5. In contrast, this range is decreased to 2.75 m when harbor II (HA II) water is used. These ranges are obtained when each channel carries 10 Gbps and as six channels are used, accordingly, the overall achieved capacity is 6 × 10 Gbps = 60 Gbps. [ABSTRACT FROM AUTHOR]

The timely delivery of critical messages in real-time environments is an increasing requirement for industrial Internet of Things (IIoT) networks. Similar to wired time-sensitive networking (TSN) techniques, which bifurcate traffic flows based on priority, the proposed wireless method aims to ensure that critical traffic arrives rapidly across multiple hops to enable numerous IIoT use cases. IIoT architectures are migrating toward wirelessly connected edges, creating a desire to extend TSN-like functionality to a wireless format. Existing protocols possess inherent challenges to achieving this prioritized low-latency communication, ranging from rigidly scheduled time division transmissions, scalability/jitter of carrier-sense multiple access (CSMA) protocols, and encryption-induced latency. This paper presents a hardware-validated low-latency technique built upon receiver-assigned code division multiple access (RA-CDMA) techniques to implement a secure wireless TSN-like extension suitable for the IIoT. Results from our hardware prototype, constructed on the IntelFPGA Arria 10 platform, show that (sub-)millisecond single-hop latencies can be achieved for each of the available message types, ranging from 12 bits up to 224 bits of payload. By achieving one-way transmission of under 1 ms, a reliable wireless TSN extension with comparable timelines to 802.1Q and/or 5G is achievable and proven in concept through our hardware prototype. [ABSTRACT FROM AUTHOR]

Over the past decade, personal communications have witnessed exponential growth, fueled by the increasing number of connected users and the diversity of transmitted data types. This expansion necessitates a boost in the transmission systems’ capacity to accommodate higher user numbers and data rates, simultaneously striving to optimize cost and complexity. Consequently, future communication systems are pivoting towards multi-carrier spread spectrum techniques (MC-CDMA), capitalizing on the robustness of OFDM multi-carrier transmissions against multipath propagation and leveraging the flexibility of the code division multiple access (CDMA) technique. This study addresses data transmission quality-related concerns within an MC-CDMA system by implementing UTTCM error correction codes. These codes aim to enhance channel spectrum efficiency and mitigate error probability. Simulation results demonstrate that the proposed transmission scheme offers significant improvements in terms of bit error rate and signal-to-noise ratio, while maximizing the bandwidth shared among users. Additionally, the incorporation of such equalization techniques as zero forcing (ZF) and minimum mean square error (MMSE), ensures extensive compensation for the channel selectivity effect. [ABSTRACT FROM AUTHOR]

Codebooks with small cross-correlation amplitude have extensive applications in many fields including code division multiple access (CDMA) communications systems, space-time codes, and compressed sensing. In this paper, a class of asymptotically optimal codebooks was constructed, and the maximum inner-product of these presented codebooks was determined by using properties of character sums over finite fields. Furthermore, these codebooks provided new parameters. [ABSTRACT FROM AUTHOR]

The performance of a two-dimensional optical code division multiple access (2D-OCDMA) system using an underwater wireless optical (UWO) medium is assessed in this work. The optical source is an LED with a working wavelength of 532 nm, and the optical detector is a p-i-n photodiode. When calculating the bit error rate (BER), the phase-induced intensity noise (PIIN), thermal noises, and shot sounds are taken into account. The user code address is set using 2D perfect difference (2D-PD) codes. Link distance, inclination angle, beam divergence angle, transmitter power, and the number of concurrent users are all taken into account when determining the BER performance. For various water media, such as pure sea water (PSW), clear ocean water (CLOW), and coastal ocean water (CSOW), the performance of the suggested system is examined. [ABSTRACT FROM AUTHOR]

Small code sets are required for asynchronous code division multiple access (CDMA) communication in dispersive channels such as metamaterials, for applications including communications in conductive environments and wireless power transfer. Desirable properties of such codes include low autocorrelation sidelobes, low cross correlations, and low bandwidth. Pairs of polyphase codes in bases 2, 3, 4, 5 and 6 are investigated using a rapid numerical sieve with a spectral cost function. Optimum codes are selected from complex conjugate pairs with equal spectral costs, and codes with minimum bandwidth are identified for lengths up to 12 for all except base 2. Coded signaling and CDMA are investigated by simulation and experiment at high frequency (HF) in example metamaterial, a magneto-inductive waveguide.

In the past few decades, multi-linear algebra also known as tensor algebra has been adapted and employed as a tool for various engineering applications. Recent developments in tensor algebra have indicated that several well-known concepts from linear algebra can be extended to a multi-linear setting with the help of a special form of tensor contracted product, known as the Einstein product. Thus, the tensor contracted product and its properties can be harnessed to define the notions of multi-linear system theory where the input, output signals, and the system are inherently multi-domain or multi-modal. This study provides an overview of tensor algebra tools which can be seen as an extension of linear algebra, at the same time highlighting the differences and advantages that the multi-linear setting brings forth. In particular, the notions of tensor inversion, tensor singular value, and tensor eigenvalue decomposition using the Einstein product are explained. In addition, this study also introduces the notion of contracted convolution for both discrete and continuous multi-linear system tensors. Tensor network representation of various tensor operations is also presented. In addition, application of tensor tools in developing transceiver schemes for multi-domain communication systems, with an example of MIMO CDMA system, is presented. This study provides a foundation for professionals whose research involves multi-domain or multi-modal signals and systems. [ABSTRACT FROM AUTHOR]

A new underwater optical wireless communication (UOWC) system utilizing optical code division multiple access (OCDMA) is proposed based on diagonal permutation shift (DPS) code. Different data rates of 2.5 Gb/s, 5 Gb/s, and 10 Gb/s are transmitted simultaneously in this model, where three channels are utilized, each is assigned with a distinct DPS code-sequence. Additionally, laser diodes operating in the green spectrum range are modulated to carry the OCDMA optical signals of each channel. Moreover, attenuation caused by different types of waterbodies are considered. These waterbodies include those who are located near harbors like harbor I (HA I) and harbor II (HA II), near the coast that are known as coastal sea (CS), inside sea water 'pure sea (PS)', and in clear oceans (CL). The performance of the UOWC utilizing OCDMA/DPS code system is evaluated through bit error rate (BER), quality factor , and eye diagrams. The accomplished results assure a successful transmission of the three channels underwater for ranges of 13 m for PS, 10 m for CL, 7.2 m for CS, 4.3 m for HA I, and 3 m for HA II with BER below 10 - 5 at data rate 10 Gb/s. [ABSTRACT FROM AUTHOR]

This paper improves the bit error rate (BER) of the modern communication system by taking into account the effect of the wavelet shape and the number of carriers on the performance of the space time block code multi-carrier direct sequence code division multiple access (STBC-MC-DS-CDMA). Here the transmitter is moved with speeds 2 km/hr, 45 km/hr and 100 km/hr via Rayleigh flat fading channel. Here, 2 antennas are employed at the receiver to mitigate the multipath signal influence. The system's orthogonal frequencies are generated using Haar, Daubechies 4, Symlets 4, Cohen-Daubechies-Feauveau 1.1 with 9.7 and B-spline 3. The number of used carriers is 128, 512, and 1,024. Quadrature phase shift key (QPSK) is used with cyclic prefix 1/16 and a bandwidth of 20 MHz. traditional fast fourier transform (FFT) system is compared to the proposed discrete wavelet packet transform (DWPT) to show the BER enhancements. The space-time block coding (STBC) is used to enhance system cabability in error corection. The proposed system shows significant improvement in BER, so that, it reaches to the same BER when using FFT but with less signal to noise ratio (SNR), which interns reduce the power consumed within the system and the cost. [ABSTRACT FROM AUTHOR]

This study proposes a novel UWOC system that combines Orthogonal Frequency Division Multiplexing (OFDM) with Spectral Amplitude Coding-Optical Code Division Multiple Access (SAC-OCDMA). The integration of these technologies aims to enhance various quantitative parameters, including the number of simultaneous users, effective power, spectral occupancy, and quality of service. The system adopts m-Quadrature Amplitude Modulation (m-QAM) as the modulation scheme for OFDM, along with the utilization of the Latin Square Code (LSC) as the signature code for SAC-OCDMA. To prove the performance of the hybrid OFDM/SAC-OCDMA system, both analytical and numerical evaluations are investigated for different water types such as; pure seawater, clear ocean water, and coastal ocean water. The system's performance is assessed in terms of Bit Error Rate (BER) as a function of UWOC link range, transmitted power, number of simultaneous users, data rate, QAM constellations, inclination angle, and divergence angles of the optical beam. The results demonstrate that the implementation of the OFDM technique within the SAC-OCDMA system significantly enhances system performance by achieving impressive bit rates, reaching 860 Gbps in pure seawater, 736 Gbps in clear ocean water, and 7 Gbps in coastal water for 15 users, all while maintaining a BER of 10 - 9 . Additionally, the study identifies the minimal power levels at 15.27, 15.6 and 25.8 dBm for pure seawater, clear ocean water, and coastal ocean water, respectively. These findings highlight the superiority of the OFDM/SAC-OCDMA system over conventional SAC-OCDMA in terms of performance and capacity. [ABSTRACT FROM AUTHOR]

Free space optics (FSO) systems have gained considerable attention because of their numerous features and services. It has evolved into a promising technology for high data rate transmission in wireless communication systems. However, there are some atmospheric effects which inhibit its performance. In this paper, performance of code division multiple access–free space optics (CDMA–FSO) by combining multidiagonal (MD) codes and orthogonal frequency division multiplexing–free space optics (OFDM-FSO) systems over using advance line coding formats under the sway of turbulence conditions are investigated and compared. A comparative study has shown that CDMA–FSO offers better SNR with both CSRZ and AMI coding format under diverse conditions at data rate 15 and 20 Gbps. [ABSTRACT FROM AUTHOR]

A new architecture for increasing the number of simultaneous users in a hybrid system and providing a solution for the channel bottleneck problem has been designed and simulated. The 10G-TDM-OCDMA-PON system combines optical code division multiple access (OCDMA) and time-division multiplexed passive optical network (TDM-PON) techniques. The high bit rate TDM-PON system is based on a bit interleaving that uses noncontiguous order for data arranging manner, this system used to obtain ultra-high-speed data rate of 40 Gbps based on four TDM channels of 10 Gbps. The OCDMA system is based on two-dimensional single weight zero cross-correlation (2D-SWZCC) employing polarization and wavelength scheme with two orthogonal polarization angles (vertical and horizontal states). The proposed hybrid system increases the scalability by multiplexing M OCDMA codes in the same time slot of the TDM system that has N time slots. The results show that the proposed system with 2D-SWZCC has better performance with a high number of users and higher scalability than the system with 1D-SWZCC. [ABSTRACT FROM AUTHOR]

In order to improve the performance of the Spectral Amplitude Coding-Optical Code Division Multiple Access (SAC-OCDMA) system, a zero cross-correlation (ZCC) code named double weight multi-diagonal (DW-MD) is proposed with constant weight (CW) or variable weight (VW). Mathematical results illustrate that it is feasible to reduce the number of filters without sacrificing system performance by using the CW DW-MD code instead of the multi-diagonal (MD) code. And for the VW DW-MD code, the supportable number of users for lower code weight WL (3) at bit error rate (BER) of 10−3 (voice) is 43, medium code weight WM (4) at BER of 10−9 (data) is 29, and higher code weight WH (5) at BER of 10−12 (video) is 32. Finally, the analysis about the position of chips "1" is given, and the simulation setups show that the CW DW-MD code outperforms the MD code when Gaussian optical filter is used. [ABSTRACT FROM AUTHOR]

This paper presents for non-coherent Optical Code Division Multiple Access (OCDMA) systems a new optical code namely Two-Dimensional Half Spectral/Spatial Zero Cross Correlation (2D-HSSZCC) code based on a One-Dimensional Zero Cross Correlation (1D-ZCC) code already developed using block matrices characterized by a high capacity. The results of simulation show that the use of the new (2D-HSSZCC) code eliminates totally the Multiple Access Interferences (MAI) due to the zero cross correlation flexibility, and less complexity of the code construction which produces a very low bit error rate of closely (4×10−18) at 1 Gbps for four users with a low power source of −12.60 dBm to reach a high data rate and high number of simultaneous users upper to closely 149, save an effective power around −1.35 dBm, −3.3d Bm compared between those provides by (Two-Dimensional dynamic cyclic shift (2D-DCS) code and Two-Dimensional Dimensional Diluted Perfect Difference (2D-DPD) and (1D-ZCC) code, and increase the cardinality percentage upper to 1.58, 2.19, 2.33 and 3.9 times comparing to (2D-DCS) code, 2D-DPD code, 1D-ZCC code and Two-Dimensional Flexible Cross Corelation/Modified Double Weight (2D-FCC/MDW) code. On the other hand, 2D-HSSZCC code is comparied with other codes which has it same property namely Two-Dimensional zero cross correlation/multi diagonal (2D-ZCC/MD) and (2D-MD) codes where the increased percentage in system capacity was 1.38 and 1.05 times, respectively. Finally, the results obtained in part 1 (with Matlab software) were confirmed and validated with the Optisystem software, the proposed system gave a better BER minimum value around 10−21 and a maximum value of the Q factor of around 9.4 at 622 Mbps of data rate when the number of simultaneous users increases. [ABSTRACT FROM AUTHOR]

Due to atmospheric turbulence, the reliability and security of free space optical (FSO) communication will be affected seriously. In this paper, we propose a novel scheme of quasisynchronous spatial diversity free-space optical code division multiple access (FSO-CDMA) wiretap channel based on gamma-gamma distribution. Considering multiple access interference, shot noise, thermal noise and background noise, performances of bit error rate (BER) and physical-layer security are analyzed theoretically. The physical-layer security of quasisynchronous spatial diversity FSO-CDMA wiretap channel is evaluated by secrecy capacity and interception probability. Closed-form expression of interception probability is obtained. In order to compare the performances between conventional spatial diversity FSO-CDMA and the proposed scheme, Optisystem simulation is carried out. The results indicate that quasisynchronous spatial diversity FSO-CDMA scheme can improve the reliability and physical-layer security simultaneously. [ABSTRACT FROM AUTHOR]

Radio over free space optics (Ro-FSO) innovation saddles the vast limit of optical fiber and the portability from local to remote systems. To enhance the capacity of Ro-FSO systems without compromising the bandwidth, this work incorporates use of hybrid polarization division multiplexing (PDM) with optical code division multiplexing (OCDMA) schemes. Due to low deployment time and support cost, the vast majority of the current optical network application systems adopts free space optics (FSO) as the elective answer for suitably supplanting fiber optical cable. This study has incorporated PDM and OCDMA schemes to design a 50 Gbps Ro-FSO link. Ten channels, each with 5 Gbps of data, are transported via FSO link of 3500 m. In addition, the proposed PDM-OCDMA-Ro-FSO link is evaluated under various atmospheric commotions. [ABSTRACT FROM AUTHOR]

Spectral Amplitude Coding-Optical Codes Division Multiple Access (SAC-OCDMA) is a future multiplexing technique that witnessed a dramatic attraction for eliminating the problems of the internet in optical network field such as multiple-user access and speed's growth of the files or data traffic. In this research article, the performance of SAC-OCDMA system based on two encoding–decoding multidiagonal (MD) and Walsh Hadamard (WH) codes is enhanced utilizing three different schemes of dispersion compensating fiber (DCF): pre-, post- and symmetrical compensation. The system is simulated using Optisystem version 7.0 and Optigrating version 4.2. The performance of the proposed system is specified in terms of bit error rate (BER), Q-factor and eye diagram. It has been observed that the compensated system based on MD code is performs much better compared to the system based on WH code. On the other hand, the compensated SAC-OCDMA system with symmetrical DCF has the lowest values of BER and largest values of Q-factor, so it is considered the best simulated scheme contrasted with pre- and post-DCF. [ABSTRACT FROM AUTHOR]

One dimensional (1D) spectral amplitude coding-optical code division multiple access (SAC-OCDMA) systems are generally known by a strict limitation in the number of users that can simultaneously connect. A main solution to overcome this drawback consists of constructing a two-dimensional (2D) structure using a new hybrid spectral/spatial code through combining a one dimensional new zero cross correlation code (NZCC) to a one dimensional multi-diagonal code (1D MD) to easily provide null cross-correlation properties and totally remove the multiple access interferences. Accordingly, this research paper describes an easy and fast technique to construct a hybrid two-dimensional NZCC-MD code based on a non diagonal matrix for SAC-OCDMA systems with direct spectral/spatial dimension (SDD) detection technique and water-filling (WF) optimization. The novel code presents many advantages such as less complex structure, acceptable code length as well as the possibility to construct it for any weight value. The proposed code demonstrates a very good performance for systems with high debit and high simultaneous user number keeps a less complex structure. [ABSTRACT FROM AUTHOR]

Remote lab systems are one of the essential requirements for an increased academic productivity in the modern digital world. These systems support and facilitate effective migration from face-to-face classroom education to online education. Digital technology applications and processes are required to easily build a remote lab system. With the availability of multiple access techniques, users can comfortably share laboratory equipment among themselves. The sharing of resources using the remote lab system is highly required for a smooth deployment and implementation of online education. This paper therefore proposed and tested some techniques that combine Code Division Multiple Access (CDMA) and Orthogonal Frequency Division Multiplexing (OFDM) in remote lab systems. The tested techniques are Multi-Carrier Direct Sequence CDMA (MC-DS-CDMA), Multi-Tone CDMA (MT-CDMA), Multi-Carrier CDMA (MC-CDMA), and Spread Spectrum Multi-Carrier Multiple Access (SS-MC-MA). The first step proposed in this work had to do with the setting of the comparison criteria. At the second step, the solutions cited previously in the real equipment was tested and the best option that met the criteria was selected for the eLab system since the performance technique varies with the laboratory equipment characteristic. The four techniques that were tested demonstrated high performance in telecommunications and online laboratory systems. The implementation of these techniques will benefit universities in several ways, which include reduction of remote lab cost and optimization of sharing of online resources among users. This will further provide students with conducive learning environment by addressing the challenges of reservation and time slot limit. It is therefore recommended that MC-CDMA should be integrated into remote lab system. [ABSTRACT FROM AUTHOR]

With the increasing number of users in the Medium-Orbit (MEO) satellite communication system, multi-access interference (MAI) has become an important factor that restricts the reliability and capacity of the system. Additionally, the low carrier-power-to-noise-density ratio ( C / N 0 ) resulting from long-distance transmission poses a significant concern. The parallel interference cancellation (PIC) algorithm, utilized within the paradigm of multi-user detection (MUD), exhibits the capability to effectively mitigate the impact of MAI within the same system. Simultaneously, coherent accumulation serves as a means to substantially enhance the correct detection probability ( P c d ) at low C / N 0 . In this study, a signal acquisition method for multi-user spread spectrum satellite receivers is proposed, which employs interference cancellation and coherent accumulation as its core mechanisms. Furthermore, we introduce a power estimation method based on the outcomes of signal acquisition, which can be integrated into the signal reconstruction module of PIC. Finally, we implement the aforementioned algorithms in both simulation and hardware platforms. Remarkably, we observe that when the interference-to-signal ratio (ISR) caused by MAI equals 20 dB, the improved algorithm attains a maximum P c d of 0.95 within the high signal-to-noise ratio (SNR) region, closely approaching the theoretical limit for the bit error rate (BER). The experimental results prove the effectiveness and feasibility of the acquisition algorithm. In summary, the enhanced algorithm holds vast potential for widespread implementation in multi-user spread spectrum communication systems. [ABSTRACT FROM AUTHOR]

This paper presents a pioneering 2D spatial Optical Code-Division Multiple Access (OCDMA) encoding system that exploits Mode Division Multiplexing (MDM) and Multicore Fiber (MCF) technologies. This innovative approach utilizes two spatial dimensions to enhance the performance and security of OCDMA systems. In the first dimension, we employ Hermite-Gaussian modes (HG00, HG01, HG11) to modulate each user's signal individually. This unique approach offers a robust means of data transmission while ensuring minimal interference among users. The second-dimension leverages MCF encoding, introducing two incoherent OCDMA codes: the Zero Cross Correlation (ZCC) code (λc=0) and the ZFD code (λc=1). These codes are thoughtfully designed and simulated, taking into account their cross-correlation properties to guarantee minimal interference and heightened data security. To assess the efficiency of this novel OCDMA encoding system, we implemented simulations with three active users using the Opti system software. At the transmitter end, each user's signal is modulated individually by their designated HG mode (HG00, HG01, HG11), resulting in separate channels. Subsequently, at the multicore fiber, each user's data is encoded with a unique code-word, and they are directed through specific core groups, ensuring data isolation and integrity. In this paper, the BER and eye pattern are examined with respect to different parameters such as data rate and distance. At a distance of 5 km and data rate of 10 Gbit/s, a BER value around 10-70 is achieved. [ABSTRACT FROM AUTHOR]

Secrecy capacity is usually employed as the performance metric of the physical layer security in fiber-optic wiretap channels. However, secrecy capacity can only qualitatively evaluate the physical layer security, and it cannot quantitatively evaluate the physical layer security of an imperfect security system. Furthermore, secrecy capacity cannot quantitatively evaluate the amount of information leakage to the eavesdropper. Based on the channel model of an optical CDMA network using wiretap code, the information leakage rate is analyzed to evaluate the physical layer security. The numerical results show that the information leakage rate can quantitatively evaluate the physical layer security of an optical CDMA wiretap channel, and it is related to transmission distance, eavesdropping position, confidential information rate and optical code. [ABSTRACT FROM AUTHOR]

In this paper, new spectral optical codes based on the construction parity check matrix of LDPC codes were designed and implemented in an optical code-division multiple access communication system. Two types optical family codes can be obtained with respectively a cross correlation of λ c = 0 and λ c = 1. In each case, the codes can either be decoded using the direct detection or the balanced detection. Performance was evaluated by referring to the Q factor, the bit error rate and the eye pattern diagrams using Optisystem 9.0. [ABSTRACT FROM AUTHOR]

To overcome the multi-path effect in Visible Light Communication (VLC) Quasi-Synchronous (QS) Optical Code Division Multiple Access (OCDMA) system, Optical Zero Correlation Zone (OZCZ) code set pair have been proposed. In this article, new two methods for constructing OZCZ codes based on the Double Weight (DW) and the Zero Cross Correlation (ZCC) matrix are presented. The newly proposed methods are based on ZCC constructions that allow generating code sequences having all ZCC and OZCZ properties, ideal for use in VLC-QS-OCDMA transmission. The structure of the proposed ZCC-OZCZ code is simple, less complex, and their construction is more flexible than proposed DW-OZCZ and existing construction. In addition, the performance evaluation of the system adopting the proposed constructions, in terms of Bit Error Rate (BER), show that the proposed codes significantly reduce MAI compared to ZCC, and give the same performance as unipolar OZCZ codes with more simple and flexible construction. [ABSTRACT FROM AUTHOR]

Systems that employ multicarrier code division multiple access, commonly known as MC-CDMA, produce outstanding results in terms of both the performance of the system as a whole and the efficiency with which it uses the spectrum. However, multiple access strategies are susceptible to interference despite their high spectrum efficiency. This work aims to reduce multiple access interference (MAI) by developing an MC-CDMA receiver. When MC-CDMA deteriorates nonlinearly, standard receivers, namely, zero forcing (ZF), maximal ratio combining (MRC), minimum mean square error (MMSE), and equal gain combining (EGC), are unable to cancel MAI. Neural network (NN) receivers are a better option due to their nonlinear nature. Based on the simulation results, the suggested deep neural network- (DNN-)based schemes outperform the current baselines in terms of error handling and usability. This research explores the viability and effectiveness of a DNN-based receiver designed for MC-CDMA with nonlinearity degradations. The focus of this research is on MC-CDMA. [ABSTRACT FROM AUTHOR]

Free space optics (FSO) communication systems are preferred due to their high transmission capacity so it can support the ever-increasing volume of online traffic. Optical code division multiple access (OCDMA) is ideal for enhancing capacity by utilizing the same wavelengths for different information transmission. This paper presents a new FSO system based on the combination of orthogonal frequency division multiplexing (OFDM) and OCDMA systems. Three OCDMA channels, employing diagonal permutation shift (DPS) codes, carry 20 Gbps each, modulated by 4-level quadrature amplitude modulation (QAM) and OFDM. To assess performance, the proposed system considers severe climate conditions like rain, fog, and snow. The effectiveness is measured by bit error rate (BER) and received optical power (ROP). In addition, actual meteorological data for the cities of Alexandria, Egypt and Pune, India are evaluated to demonstrate the applicability of the proposed model in a real-world setting. The results reveal successful transmission with an overall capacity of 60 Gbps over a 3600 m FSO range in Alexandria, achieving a 0.27 dBm ROP. In Pune, with higher average rainfall, the maximum FSO link is 2750 m with a −0.06 ROP. Furthermore, the proposed model can propagate up to 850 m under weak turbulence (WT). [ABSTRACT FROM AUTHOR]

Free space optics (FSO)-based optical body area networks (OBANs) are receiving massive attention as an opportunity to address the limitations of their radio frequency (RF)-based counterparts. This boom in research interests is primarily due to multitude of benefits, including high capacity, immunity to electromagnetic interference (EMI), rapid installation, cost efficiency, and license-free use of spectrum. Securing the transmission of patient health data against interception in OBANs using insecure FSO channels is a challenging task. Therefore, we propose a low-cost, flexible, and secure OBAN based on FSO technology and a time-delayed two dimensional (2D) spectral/spatial optical code-division multiple access (OCDMA) system. The proposed architecture consists of eight sensors attached to the bodies of patients. The sensors operate at a rate of 50 kbps. Electrical data generated from each sensor are used to modulate an optical carrier and then encoded using 2D-spectral/spatial double weight–zero cross correlation (DW-ZCC) code. The 2D encoded optical signals are then time delayed to eliminate the multiple parallel FSO channels between the transmitter and medical center. The combined optical signal consists of eight 2D-encoded time-delayed optical signals transmitted towards a remote medical center over an FSO channel with a range of 1 km. The received signal is decoded and the data from each sensor are recovered after photodetection at the medical center for further analysis. The overall performance of the sensors is analyzed using bit-error rate (BER) and quality factor (Q-factor) plots for different weather conditions and lengths of the FSO channel, considering the log-normal channel model. The capital expenditure (CAPEX) of the proposed architecture is analyzed and compared with the conventional 2D-spectral/spatial FSO system to determine the overall impact of introducing time delay units on the cost of implementation. [ABSTRACT FROM AUTHOR]

This paper scrutinizes visible light communication (VLC) employing hybrid optical time division multiplexing (OTDM) wavelength division multiplexing (WDM). It also demonstrates the simulation of VLC using the direct sequence optical code division multiple access (DS-OCDMA) system developed by OptiSystem-Matlab Co-simulation. The profits of WDM and OTDM capacities have been combined using two levels of freedom to build up of the system. The performances are demonstrated in the simulated findings of the bit error rate (BER) in relationship with the data rate and the number of users. First, the simulated results display the usefulness of the system. Then, the number of users has been significantly enhanced. Besides, the OCDMA functions by appointing a specific code to each user and could provide asynchronous and simultaneous access to numerous users. One drawback is multiple access interference (MAI). The use of very long code sequences is crucial in order to lessen this effect. Hence, very large bandwidths are essential. This study aims at demonstrating, through system simulation, the practicability of an all-optical conventional correlation receiver dedicated to a DS-OCDMA access network link. Again, OptiSystem has been used to realize our blocks. [ABSTRACT FROM AUTHOR]

In this paper, the performance efficiency of the free‐space optical (FSO) communication link has been enhanced using a new hybrid prime code (NHPC) and M‐ary digital pulse position modulation (M‐ary DPPM) technique. The passive optical network (PON) optical code division multiple access (OCDMA) technique based on the FSO link is proposed. The analysis and optimization of the bit error rate (BER) performance of the Gaussian approximation techniques are investigated in the existence of both an atmospheric turbulence (AT) channels and multiple access interference (MAI). Additionally, 76 NHPC orthogonal sequences have been transmitted at a data rate of 10 Gbps over a turbulent FSO channel. In the proposed design, the NHPC M‐ary DPPM modulation is used to provide extra bits of information to enhance the system performance. Also, the adaptive optics technique to mitigate the AT effect and improve the modulation efficiency is offered in this design. Further, the impact of the turbulence effect on the proposed system performance based on NHPC-M ary-DPPM modulation as a function of M‐ary DPPM parameters and other atmospheric parameters is investigated. The NHPC M‐ary DPPM provides an optical signal‐to‐noise ratio (OSNR) of about 2–4 dB for the strong turbulence at a target BER of 10−9. Additionally, the proposed system performance is compared with another system that uses the on–off keying-DPPM (OOK-M ary- DPPM). The numerical results indicate that the proposed design can be enhanced with the NHPC M-ary DPPM for FSO-OCDMA systems and the OSNR can be increased 14–18 dB at a BER of 10−9 in comparison to other approaches. The simulation results show that the proposed modulation technique can be used in the FSO-OCDMA systems, having a significant increase in their efficiency. Finally, the use of the NHPC M‐ary DPPM modulation schemes is a new technique that is used to reduce the AT, interchannel crosstalk and the MAI noise for the FSO-OCDMA systems. [ABSTRACT FROM AUTHOR]

This study explores a composite space-time and frequency-domain spreading strategy, designed to augment the capacity of multicarrier 5G systems operating over frequencyselective Rayleigh fading channels. The focus is directed towards a comprehensive analysis of the Bit Error Rate (BER) performance of the proposed system, with adjustments made to various parametric values. In tandem, receiver optimization techniques are meticulously studied, and their outcomes are positioned against existing literature. Within this context, the Parallel Interference Canceller (PIC) emerges as a viable alternative to the De-correlating Detector (DD), a shift primarily driven by the latter's heightened complexity and noise amplification. Additionally, this study demonstrates the acquisition of a larger number of users exclusively employing transmission diversity, thereby eliminating the need for receiving diversity and additional code sets. This approach incrementally augments hardware complexity at both ends of the transmission link, a minor trade-off for the benefits garnered. The efficacy of this scheme is substantiated through MATLAB simulations, indicating a promising avenue for improving the capacity of multicarrier 5G systems. The findings pave the way for significant advancements in the development of efficient and robust communication systems for the 5G era and beyond. [ABSTRACT FROM AUTHOR]

Background: The mobile uses have been increased drastically, creating increased health concern about radiation effects emitted from mobile phone. Hence, this study aimed to evaluate the micronuclei (MN) frequency in exfoliated oral mucosal cells in high and low mobile users. Materials and Methods: The total of 50 subjects was divided into two major groups: low mobile phone users and high mobile phone users. Further, subjects who use mobile phone for more than 10 h a week were considered high talk time users and <4–5 h a week was low talk time users. The buccal mucosa cells are extracted by scraping the oral cavity with a wooden spatula. MN was evaluated in 1000 cells per individual at the microscope. Results: There was a significantly increase in MN count in high mobile users compared to low mobile users. There was a highly significant difference in the mean MN count of participants using code division multiple access than global system for mobiles mobile phones. The MN mean count was found to be significantly increased in nonheadphone users in comparison to headphone users. Furthermore, the MN count on the frequently used side of mobile phone was found to be statistically significantly elevated compared to the opposite side. Conclusions: Mobile phone radiation, even in the permissible range when used for a longer duration, can cause significant genotoxicity. The genotoxicity is noted when the mobile phone is used more frequently on the same side, which may be due to more amount of radiation and increase in the temperature. Headphone usage reduces the genotoxicity of mobile phone radiation to some extent. [ABSTRACT FROM AUTHOR]