Code Division Multiple Access Technique Research Articles

Improving Performance of MC-CDMA Systems Using UTTCM Channel Coding

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.

160 Gbps MMF/FSO system based on OAM beams and PV code under rainy weather

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 (LG0,0\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${LG}_{\\mathrm{0,0}}$$\\end{document}, LG0,20\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${LG}_{\\mathrm{0,20}}$$\\end{document}, LG0,40\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${LG}_{\\mathrm{0,40}}$$\\end{document}, and LG0,40\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${LG}_{\\mathrm{0,40}}$$\\end{document}) 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\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${10}^{-5}$$\\end{document} 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.

Low-Latency Wireless Network Extension for Industrial Internet of Things.

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.

Performance evaluation of a UOWC system based on the FRS/OCDMA code for different types of Jerlov waters.

In this work, the fixed right shift (FRS) code is utilized for the optical code division multiple access (OCDMA) technique in an underwater optical wireless communication (UOWC) system. Additionally, in this system, a 532nm laser diode (LD) source is employed to generate optical signals. The investigation encompasses an analysis of five distinct Jerlov water types, each exhibiting diverse chlorophyll concentrations. The performance of the proposed system is evaluated when each channel that is assigned a unique FRS code sequence carries different data rates (2.5, 5, and 10Gbps). Underwater (UW) ranges, bit error rate (BER), eye diagrams, and quality factor (Q-factor) are the performance metrics used to evaluate the system performance. The proposed UOWC-FRS/OCDMA system is simulated, and the obtained results show that the eye diagram openings close, the BER increases, and the Q-factor decreases as the data rate per each channel increases from 2.5 to 10Gbps, and the attenuation of water becomes higher. Moreover, the lower attenuation values caused by the Jerlov type I (JI) waterbody allow each channel to carry 10Gbps of data to propagate longer UW for a range of 35m with a log(BER) ≤-6.33 and Q-factor greater than 4.9. On the other hand, at the same values of BER and Q-factor, the shortest ranges of 12 and 5.15m are obtained for JII and JIII waters, respectively, where their attenuation coefficient values are 0.5297 (JII) and 1.8998 m -1 (JIII). Furthermore, as our model uses three channels, the overall achieved capacity is 3×10G b p s=30G b p s.

Satellite continuous-variable quantum key distribution systems using code-division multiple access

In this paper, we propose a novel architecture of the satellite continuous-variable quantum key distribution (CV-QKD) system that can not only support multiple users but also enhance the security. The satellite CV-QKD system is based on a code-division multiple access (CDMA) technique to simultaneously transmit multiple key streams from a trusted satellite to a ground station, which passively forwards these key streams to multiple users nearby via optical fibers. Our proposed architecture avoids using multiple ground stations that result in high costs. We analyze the performance of the proposed system under the negative impacts of atmospheric attenuation and atmospheric turbulence, as well as beam spreading and pointing error loss. Especially, the impact of multiple user interference is also considered in our analysis. The numerical results show that the proposed QKD system using CDMA can support multiple users, whose performance metrics such as quantum bit-error rate (QBER), sifted probability, and secret key rate meet the designed targets. The eavesdroppers suffer high QBER and low sifted probability, thus the security is guaranteed.

Acquisition Time and Probabilities of Detection and False Alarm in Direct Sequence Code Division Multiple Access Systems

Multiple access interference (MAI) is one of the most important issues to consider in the design, implementation and operation of 5G systems using code division multiple access (CDMA) technique based on spread spectrum that offers a more flexible solution, compared to other techniques. Especially, it permits a much higher user bit rate, due to the bandwidth allocated to the emitted signal; thus, allowing very attractive multimedia services. In this paper, we develop the expressions of the detection probability, false alarm probability and the average acquisition time - in a direct sequence CDMA (DS-CDMA) transmission system - using a serial search and taking into consideration MAI. The evolution of these parameters according to the signal- to-noise ratio (SNR) and the decision threshold leads to study performances of the system in terms of detection and average acquisition time. The obtained results reveal that the acquisition time decreases when the SNR increases. Additionally, it is found that the probability of detection increases when the threshold decreases, and increasing SNR it reaches a constant value for an SNR/chip around 0 dB for all thresholds.

Deployment of multiservice code in FSO-based hybrid subcarrier system

Abstract This research aims to investigate and improve multi-user free space optic systems (FSO) based on a hybrid subcarrier multiplexing spectral amplitude coding-optical code division multiple access (SCM-SAC-OCDMA) technique using MS code with a direct decoding technique. The performance is observed under different weather conditions including clear, rain, and haze conditions. The investigation includes analyzing the proposed system mathematically using MATLAB and OptiSystem software. The simulation is carried out using a laser diode. Furthermore, the performances of the MS code in terms of angles of bit rate, beam divergence and noise are evaluated based on bit error rate (BER), received power, and transmission distance. The performance of the MS code-based system was subsequently compared with Khazani Syed code (KS), multi-diagonal (MD), and modified quadratic congruence code (MQC) codes under different weather conditions at a bit rate of 1 Gb/s and BER threshold of 10−9. Heavy rain indicates the worst performance in terms of transmission distance of 0.9 km. Nevertheless, the system designed using the MS code outperformed the KS, MD and MQC systems as it is capable of supporting up to 6.3, 0.8, 0.9, and 1.5 km, respectively, under clear weather. In conclusion, this study provides a means of improving FSO communications that suits tropical and Malaysia weather conditions.

An expert algorithm for spectrum sensing and signal detection in NOMA-enabled 5G networks

The Spectrum sensing is an essential function in the various types of fifth-generation (5G) networks and beyond, which can address some of the fundamental challenges for 5G, including spectral efficiency and the reliable connectivity of internet of things (IoT) devices. In this article, we aim to present a real-time and expert spectrum sensing algorithm for 5G cellular networks. The novel method exploits the cyclostationary nature of the spread spectrum signal without any prior knowledge of its structure. In the proposed algorithm, the multi-carrier code division multiple access (MC-CDMA) technique will be utilized by the users. The multidimensional spectrum sensing method introduces a novel correlation measurement based on the algebraic characteristics of pseudo-noise (PN) sequences. The existence of periodic peaks in the new correlation function presents new modelling of the emergence of the spread-spectrum signal. Our basis for this is to use the cyclostatic property of the pseudo-noise code and obtain the distance between the two main peaks in the received signal correlation. According to the simulation results, the proposed algorithm exhibits excellent performance in signal detection and exact estimation of PN code length in low SNRs and multipath fading environments.

6G Network Architecture Using FSO-PDM/PV-OCDMA System with Weather Performance Analysis

This paper presents a novel 160 Gbps free space optics (FSO) communication system for 6G applications. Polarization division multiplexing (PDM) is integrated with an optical code division multiple access (OCDMA) technique to form a PDM-OCDMA hybrid. There are two polarization states: one is X-polarization generated from adjusting the azimuthal angle of a light source at 0° while the other is Y-polarization which is generated by adjusting the azimuthal angle of a light source at 90°. Each polarization state is used for the transmission of four independent users. Each channel is assigned by permutation vector (PV) codes and carries 20 Gbps data. Four different weather conditions are considered for evaluating the performance of our proposed model. These weather conditions are clear air (CA), foggy conditions (low fog (LF), medium fog (MF), and heavy fog (HF)), dust storms (low dust storm (LD), moderate dust storm (MD), heavy dust storm (HD)), and snowfall (wet snow (WS) and dry snow (DS)). Bit error rate (BER), Q-factors, maximum propagation range, channel capacity, and eye diagrams are used for evaluating the performance of the proposed model. Simulation results assure successful transmission of 160 Gbps overall capacity for eight channels. The longest FSO range is 7 km which occurred under CA while the minimum is achieved under HD, which is 0.112 km due to large attenuation caused by HD. Within fog conditions, the maximum propagation distances are 1.525 km in LF, 1.05 km in MF, and 0.85 km in HF. Likewise, under WS and DS, the proposed system can support transmission distances of 1.15 km and 0.28 km, respectively. All these transmission distances are achieved at BER less than 10−5.

Capacity Enhancement for Free Space Optics Transmission System Using Orbital Angular Momentum Optical Code Division Multiple Access in 5G and beyond Networks

This paper introduces a novel free space optics (FSO) communication system for future-generation high-speed networks. The proposed system integrates orbital angular momentum (OAM) modes with an optical code division multiple access (OCDMA) technique. Two OAM beams are used (LG0,0 and LG0,10), each of which is used for transmitting three independent channels. Each channel is assigned by fixed right shift (FRS) codes and carries 10 Gbps of information data. The performance of the proposed model is evaluated under different foggy and dust storm conditions. Furthermore, the performance of two cities with different geographical locations, Alexandria city in Egypt and Srinagar city in India, is investigated to demonstrate its ability to be implemented in future generations. Bit error rate (BER), eye diagrams, received optical power (ROP), and channel capacity are used for studying the performance of the proposed system. The observed simulation results show successful transmission of 60 Gbps overall capacity with the longest propagation FSO range for Alexandria city, which is 1400 m. Because dust storms have a large attenuation when compared to different foggy conditions, the proposed model had the shortest propagation range of 315 m under low dust (LD), 105 m under moderate dust (MD), and 40 m under heavy dust (HD). Furthermore, the cloudy weather conditions that affect Srinagar city, which is considered a hilly area, make our suggested model achieve 1000 m.

Robust or nonrobust: On MC-DS-CDMA acquisition in LEO satellite communications

Low Earth Orbit (LEO) satellite communications can provide global coverage in the sixth generation communication (6G) networks. To combat the strong Partial Band Interferences (PBIs) and multipath fading in LEO satellite communication systems, the Multicarrier Direct Sequence Code Division Multiple Access (MC-DS-CDMA) technique is a promising alternative to the traditional Single-carrier Direct Sequence Code Division Multiple Access (SC-DS-CDMA) system for its advantages of high bandwidth efficiency, superior interference rejection capability, and low complexity of parallel signal processing. However, limited studies have been conducted on the performance analysis of MC-DS-CDMA acquisition systems in the presence of a large Doppler shift, a unique characteristic of LEO satellite communications. To bridge this gap, we investigate the performance of MC-DS-CDMA systems with two-dimensional acquisition and noncoherent equal gain combining over Rician fading channel in the presence of the Doppler shift and PBIs. The performance metrics are detection probability and Mean Square Error (MSE) of the Doppler factor and delay. Specifically, we derive the closed-form expressions for the MSE and the Probability Density Function (PDF) of the acquisition decision variable and obtain the detection probability. We conduct extensive numerical experiments to verify the theoretical analysis and performance gain of MC-DS-CDMA over the SC-DS-CDMA. The results show that MC-DS-CDMA with two-dimensional acquisition is more robust to multipath Rician fading than SC-DS-CDMA. Moreover, MC-DS-CDMA outperforms SC-DS-CDMA regarding the detection probability and MSE when combating the strong PBIs.

Quantum CDMA Communication Systems

Barcoding photons can provide a host of functionalities that could benefit future quantum communication systems and networks beyond today's imagination. As a significant application of barcoding photons, we introduce code division multiple-access (CDMA) communication systems for various applications. In this context, we introduce and discuss the fundamental principles of a novel quantum CDMA (QCDMA) technique based on spectrally encoding and decoding of continuous-mode quantum light pulses. In particular, we present the mathematical models of various QCDMA modules that are fundamental in describing an ideal and typical QCDMA system, such as quantum signal sources, quantum spectral encoding phase operators, M$\times$M quantum broadcasting star-coupler, quantum spectral phase decoding operators, and the quantum receivers. In describing a QCDMA system, this paper considers a unified approach where the input continuous-mode quantum light pulses can take on any form of pure states such as Glauber states and quantum number states. For input number states, one can observe features like entanglement and quantum interference. More interestingly, due to Heisenberg's uncertainty principle, the quantum signals sent by photon number states obtain complete phase uncertainty at the time of measurement. Therefore, at the receiver output, the multiaccess inter-signal interference vanishes. Due to Heisenberg's uncertainty principle, the received signal intensity at the photodetector's output changes from a coherent detection scheme for input Glauber states to an incoherent detection scheme for input number states. Our mathematical model is valuable in the signal design and data modulations of point-to-point quantum communications, quantum pulse shaping, and quantum radar signals and systems where the inputs are continuous mode quantum signals.

CE-OFDM-CDMA Phase Modulation for 5G System

In the present work, we propose a novel modulation scheme for 5G wireless communication system. Our contribution is to combine PM-OFDM (Phase Modulation Orthogonal Frequency Division Multiplexing) and CDMA (Code Division Multiple Access) to exploit their distinctive advantages. On the one hand, PM-OFDM is an effective technique to combat multipath fading effects. On the other hand, CDMA can serve multiple users who are using the same resources of time/frequency. The aim is to make a combination of PM-OFDM and CDMA techniques. In this paper, the OFDM-CDMA scheme and its PAPR (Peak-to-Average Power Ratio) statistics are reviewed. In this paper, the proposed scheme PM-OFDM-CDMA is described and its performances in terms of PAPR, power spectral density, and BER (Bit Error Rate) are analyzed. Moreover, MMSE (Minimum Mean Square Error) equalizer is used to avoid multipath and noise effects simultaneously. The simulation through AWGN (Additive white Gaussian noise) and Rayleigh channels is performed using MATLAB. From the simulation results, we observed that PM-OFDM-CDMA is an efficient technique in terms of energy consumption (PAPR = 0dB). Besides, CE-OFDM-CDMA offers high spectral efficiency with low BER due to its low PAPR. In CE-OFDM-CDMA method, the shape of the spectrum varies according to the value of the modulation index h. The band occupied by the spectrum increases with the value of h. Therefore, CE-OFDM-CDMA could be considered as a suitable technique for 5G applications.

Implementation of Underground Water for Wireless Optical Communication System using CDMA

Optical wireless communications is a powerful and cost-effective approach for high-speed wireless links that have been tightly guarded For underwater optical wireless communication, the following three optical code division multiple access (CDMA) techniques have been used. systems are associated, investigated, and presented in this paper, such as AC-biased optical CDMA (ACO-CDMA), symmetrically-SCO-OFDM (clipped optical OFDM), and unipolar CDMA (U-CDMA). Peak power constraints, light source bandwidth tag, there are so many factors to recognize, such turbulence, fading underwater signals, and channel estimation error. Advocate for a bit loading algorithm and a simplified modulation index that determines signal magnitude is being used to minimize the achievable data propagation distance. In this optimization procedure, the signal-to-noise ratio and the clipping distortion triggered by the peak power limitation are balanced (SNR). The SNR and clipping effects of the three compared CDMA techniques are represented in this paper. When the transmitted bit index is greater than the channel bandwidth, ACO-OFDM outperforms SCO- and UCDMA, according to the determined model. U-CDMA, on the other end, has a longer propagation distance but needs less transmitted power.

Design of Bipolar Optical Code-Division Multiple-Access Techniques Using Phase Modulator for Polarization Coding in Wireless Optical Communication

In this study, a bipolar optical code-division multiple-access (Bi-OCDMA) technique based on spectral amplitude coding (SAC) was proposed by using a phase modulator to realize polarization coding through a free-space optical (FSO) channel. Various types of noise, such as amplified spontaneous emission (ASE) noise, thermal noise, and shot noise, were included in the simulation to approach the real application. The first simulation, utilizing a modified M-sequence as signature code, demonstrated that the proposed Bi-OCDMA system could be implemented in FSO communication. The proposed Bi-OCDMA scheme improves the transmission rate and power efficiency compared with the previous scheme. The structure of the proposed system alleviates multiple-access interference (MAI) with a simple and cost-effective design. The second simulation observed the performance of the proposed Bi-OCDMA for two users with several well-known SAC codes, i.e., multi-diagonal (MD) code, modified quadratic congruence (MQC) code, modified maximum length sequence (M-sequence) code, and Walsh–Hadamard code, in extreme weather conditions, both for additive white Gaussian noise (AWGN) and turbulence-induced fading channel. The simulation results indicated that the Walsh–Hadamard code has superior performance compared to other codes. The results show the MD code can be implemented in the proposed Bi-OCDMA scheme for a medium-distance FSO.

Multi-carrier Visible Light Communication System Using Enhanced Sub-carrier Index Modulation and Discrete Wavelet Transform

This work is aimed at providing a novel design of the Visible Light Communication (VLC) system that uses the Multi-Carrier Code-Division Multiple Access (MC-CDMA) technique to send and receive data through intensity-modulated/direct detected (IM/DD) VLC channel. The state-of-the-art framework of Enhanced Sub-Carrier Index Modulation (ESIM) is utilized to reduce the inherent peak-to-average power ratio (PAPR) in Orthogonal Frequency Division Multiplexing. Additionally, the use of cyclic prefix is omitted through the Discrete Wavelet Transform in the current system. Hence, the performance of the system is optimized in terms of PAPR, Bit Error Rate (BER), and data rate. The work presents the closed-form BER expressions for both conventional and proposed techniques in line-of-sight VLC channel. Correspondingly, the simulation programs are also executed to compared the proposed ESIM based WT-MC-CDMA system with both existing systems followed by an analysis of the results. Simulation results show the superior performance of the proposed system compared to existing systems.

Design of high scalability multi-subcarrier rof hybrid system based on optical CDMA/TDM

<span>The technology of radio over fiber (RoF) regard a crucial point to solve problems in wireless communication system. As well as, the growth of internet applications also reveals a tremendous increase in bandwidth for different applications. Therefore, the development of optical networks is very important that have maximum bandwidth by using different multiple access techniques. Optical code division multiple access (OCDMA) technique has considered as a good solution for high bandwidth network. Hybrid optical systems of OCDMA and time division multiplexing (OTDM) has been proposed in this paper to increase the number of simultaneous users. The results of hybrid OCDMA and OTDM system demonstrate that this system can make a considerable increase in the network scalability while ensuring sufficient data rate and an acceptable bit error rate. Where M-user OCDMA signals can be transmitted in different channels of an OTDM system. Due to its wide band facility compared with other access techniques, OCDMA used here. In addition to its high scalability for our radio network, the OTDM and SCM utilized. The combination of these efficient access technique and powerful time-sharing media are lead to increase the framework system scalability.</span>

Detecting Relative Amplitude of IR Signals with Active Sensors and Its Application to a Positioning System

Nowadays, there is an increasing interest in smart systems, e.g., smart metering or smart spaces, for which active sensing plays an important role. In such systems, the sample or environment to be measured is irradiated with a signal (acoustic, infrared, radio-frequency…) and some of their features are determined from the transmitted or reflected part of the original signal. In this work, infrared (IR) signals are emitted from different sources (four in this case) and received by a unique quadrature angular diversity aperture (QADA) sensor. A code division multiple access (CDMA) technique is used to deal with the simultaneous transmission of all the signals and their separation (depending on the source) at the receiver’s processing stage. Furthermore, the use of correlation techniques allows the receiver to determine the amount of energy received from each transmitter, by quantifying the main correlation peaks. This technique can be used in any system requiring active sensing; in the particular case of the IR positioning system presented here, the relative amplitudes of those peaks are used to determine the central incidence point of the light from each emitter on the QADA. The proposal tackles the typical phenomena, such as distortions caused by the transducer impulse response, the near-far effect in CDMA-based systems, multipath transmissions, the correlation degradation from non-coherent demodulations, etc. Finally, for each emitter, the angle of incidence on the QADA receiver is estimated, assuming that it is on a horizontal plane, although with any rotation on the vertical axis Z. With the estimated angles and the known positions of the LED emitters, the position (x, y, z) of the receiver is determined. The system is validated at different positions in a volume of 3 × 3 × 3.4 m3 obtaining average errors of 7.1, 5.4, and 47.3 cm in the X, Y and Z axes, respectively.

Performance analysis of hybrid SAC-OCDMA-OFDM model over free space optical communication

Recently, free space optical (FSO) communication network has gained popularity because of its unlicensed spectrum, high data rate, low power consumption and ease of installation. Spectral amplitude coded optical code division multiple access (SAC-OCDMA) technique has become significant because of enhanced network capacity, privacy, and simultaneous use of multiple asynchronous users. However, the climatic turbulence causes signal fluctuations and degrades the quality of the received signal. Therefore, to improve the quality of the received signal in this work, SAC-OCDMA technique is integrated with orthogonal frequency division multiplexing (OFDM) technique and performance of such hybrid model is investigated. Two SAC-OCDMA codes are proposed in this work referred as triangular matrix-zero cross correlation (TM-ZCC) and pulse shifting substitution-zero cross correlation (PSS-ZCC) codes. The hybrid model uses the novel one dimensional (1D) SAC-OCDMA codes with two different types of receivers such as modified AND (M-AND), and single photodiode detection (SPD) receivers over Gamma-Gamma fading channel to evaluate the bit error rate (BER) performance of the proposed hybrid model. It is observed from the simulation results that the hybrid SAC-OCDMA-OFDM model with SPD detection receiver performs better in terms of bit error rate (BER) than that of M-AND detection receiver. Furthermore, it is also observed from the simulation results that the hybrid model based on the proposed TM-ZCC code performs better than the proposed PSS-ZCC code in terms of BER and higher FSO distance coverage. The performance of the proposed model is estimated for 20 and 30 active users simultaneously at various data rates. The TM-ZCC and PSS-ZCC codes are generated using MATLAB platform and the proposed hybrid SAC-OCDMA-OFDM model is validated using optisystem version 15 over the Gamma-Gamma fading channel.

Bipolar Optical Code Division Multiple Access Techniques Using a Dual Electro-Optical Modulator Implemented in Free-Space Optics Communications.

This study developed a bipolar optical code division multiple access (Bi-OCDMA) technique based on spectral amplitude coding for the formation and transmission of optical-polarized and coded signals over wireless optical channels. Compared with conventional Bi-OCDMA schemes, the proposed free-space optics communication system that uses a dual electro-optical modulator design improves the transmission rate. In theory, multiple access interference can be removed by using correlation subtraction schemes. The experiment results revealed that the proposed system can be employed to accurately extract codewords from an M-sequence and subsequently reconstruct the desired original data. Moreover, the proposed architecture can be implemented easily in simple and cost-effective designs and may be beneficial for broadening the use of Bi-OCDMA schemes in wireless optical communications.