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In this paper, we have studied a Spectral Amplitude Coding Optical Code Division Multiple Access (SAC-OCDMA) system performance using fiber Bragg gratings equivalent to very narrow filters used in the system as encoders and decoders in both the transmitter and the receiver block. The system performance depends on several variables such as: the optical power; the fiber length; the data rate and the bandwidth. Different simulations have been realized in terms of the bit error rate (BER) and the quality factor (Q) to evaluate the effect of each parameter on the system performance and also to examine the impact of number of users. The obtained results using Optisystem network show clearly that the studied SAC-OCDMA system of three users remains efficient for fiber lengths up to 25 km at a data rate of 200 Mbits/s and a FBGs bandwidth of 0.6 nm. These results are realized with an acceptable bit error rate B E R < 10 - 9 . In addition, a SAC-OCDMA system of 9 users was also simulated to assess the effect of the number of users. The results obtained show that for a fiber length L = 5 Km, the system remains efficient for a number of users set at 8 users, then the longer the fiber length increases the more the number of possible users decreases. For L = 35 Km, the number of users for whom all users obtain a good BER value is 6 users.

The growing need for high-speed services, coupled with data-intensive technologies like the Internet of Things (IoT), is expected to exacerbate congestion within existing Radio Frequency (RF) communication systems. As a result, Free Space Optics (FSO) has emerged as a promising alternative to RF, offering superior data transmission capabilities. Additionally, ensuring security has become a crucial concern to safeguard sensitive information. Accordingly, in this paper, an FSO system is proposed that uses an Identity Column Shift Matrix (ICSM) code for higher and confidential data transformation. The ICSM code is one of the Spectral-Amplitude-Optical-Code-Division-Multiple Access (SAC-OCDMA) codes which is characterized by easy construction due to zero cross-correlation property. Moreover, the effectiveness of clear, haze, fog and rain conditions are considered while examining the proposed model performance in addition to real meteorological data for two cities (Alexandria, Egypt, and Pune, India). Eye diagrams, received power, and Bit Error Rate (BER) are the evaluation parameters used for the proposed model performance. The simulation results reveal that as weather becomes severe, the FSO span decreases, and the performance becomes worst. As for clear weather, an FSO link of 26 km is obtained which is decreased to 1.1 km under the dense level of fog. Regarding the two cities, the distance covered by the information signal during rainy weather in Pune is 6.7 km, which is smaller than that in Alexandria due to Pune's higher attenuation value. These transmission ranges are obtained with an overall capacity of 3 × 10 Gbps, received power < − 22.8 dBm, and BER below 10 –5.6 .

High-capacity communication networks are built to provide high throughput and low latency to accommodate the growing demand for bandwidth. However, the provision of these features is subject to a robust underlying network, which can provide high capacity with maximum reliability in terms of the system’s connection availability. This work optimizes an existing 2D spectral–spatial optical code division multiple access (OCDMA) passive optical network (PON) to maximize connection availability while maintaining desirable communication capacity and capital expenditure. Optimization is performed by employing ring topology at the feeder level, which is used to provide a redundant path in case of connection failures. Furthermore, high transmission capacity is ensured by utilizing a pseudo-3D double-weight zero cross-correlation (DW-ZCC) code. The analysis is performed with Optisystem simulations to observe the performance of the system in terms of bit error rate (BER), received power, and eye openings. It is observed that the introduction of ring topology at the feeder level of the PON does not impact the overall transmission capacity of the system. The system can still support maximum transmission capacity at receiver sensitivities of up to −19 dB. Reliability analysis also shows that the optimized ring-based architecture can provide desirable connection availability compared to the existing system.

This paper introduces a novel underwater (UW) optical communication system that utilizes optical code division multiple access transmission technique using the permutation vector code. Three scenarios of water are considered, pure sea (PS), clear ocean (CL), and coastal ocean (CO). The performance is evaluated analytically in terms of bit error rate (BER), received power, signal to noise ratio for different UW links and data rates. The results show that the shortest UW range is achieved in the case of CO, achieving the highest extinction ratio compared to CL and PS. Considering a BER below the forward error correction (FEC) limit of 3 ×  10 - 3 , the maximum UW ranges reached are 21 m for PS, 12 m for CL, and 8 m for CO at 3 Gbps with 20 dBm transmitted power. The propagation range could be increased when the transmitted power is increased to 25 dBm, achieving the ranges of 31 m, 18 m, and 9 m, for PS, CL, and CO, respectively.

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.

Oceans and deep seas have always been a root of great paradox to mankind. The oceans, covering greater than 75% of the Earth surface, are unexplored and implausible to investigate because of diverse phenomena practices in the underwater medium. Under water communication plays a significant role in observation of water pollution, natural disaster surveillance, coastal securities naval tactical activities, marine life and to investigate the variations in the underwater environment. However, under water channel is ambiguous in nature and causes low bandwidth, security issue, low transmission range and cost limitations because of interaction with the water channel. In this regards, a high speed hybrid passive optical network (PON) and visible light communication (VLC) using red-green-blue light emitting diodes system for land-to-underwater applications has been proposed and investigated for the data transmission over a hybrid fiber-wireless link under different water types. Time and wavelength division multiplexing wavelength division multiplexing PON employing different optical code division multiple access codes offering data security to different under ocean connected devices with minimum energy consumption, is analysed. The results shows that shift zero cross-correlation code offers a faithful 100 km fiber length and 5 m VLC range at high data rate of 10 Gbps having 76 dB optical signal to noise ratio for 200 undersea devices in both downstream and upstream transmission. Moreover, undersea VLC range can be improved up to 10 m with blue LED. The mathematical analysis and comparative performance reveal the superiority of proposed system than existing literature.

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.

The demand for fault protection transmission link with high-speed, high security and long-reach in an optical access network is growing at an exponential rate. It is quite difficult to accommodate huge number of users with several connected devices in different geographical locations without deteriorating the quality of service at low cost. So, strong communication technique is needed that can offers high-speed, long-reach transmission and high data security along with multiple connected users or devices. In this paper, a ring-topology based hybrid passive optical network free space optics system using optical add/drop multiplexer with fault protection optical access network has been proposed. It is a promising network with fault-protection link for enhanced survivability and reliability of the network especially for the remote areas when the primary fiber link is broken or cut in the network. The results show that generated signal can propagate through a hybrid 10 km fiber along with FSO link of 35 km in downstream and 40 km in upstream transmission at symmetric 1 Tbps data rate considering turbulence effects and atmospheric conditions. Also, using single weight zero-cross correlation code in the proposed system offers the received optical power from − 5 to – 25 dBm under different atmospheric conditions. For hybrid fiber-FSO link, the maximum power penalties of 3 and 5 dB among 50 users can be achieved with respect to back-to-back and fiber links respectively, under 10 –9 BER. The comparison of the obtained results with literature, show that the hybrid fiber-FSO link offers cost-effective long-reach, high transmission rate and security.

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.

The growing demand for extensive and reliable structural health monitoring resulted in the development of advanced optical sensing systems (OSS) that in conjunction with wireless optical networks (WON) are capable of extending the reach of optical sensing to places where fibre provision is not feasible. To support this effort, the paper proposes a new type of a variable weight code called multiweight zero cross-correlation (MW-ZCC) code for its application in wireless optical networks based optical code division multiple access (WON-OCDMA). The code provides improved quality of service (QoS) and better support for simultaneous transmission of video surveillance, comms and sensor data by reducing the impact of multiple access interference (MAI). The MW-ZCC code’s power of two code-weight properties provide enhanced support for the needed service differentiation provisioning. The performance of this novel code has been studied by simulations. This investigation revealed that for a minimum allowable bit error rate of 10−3, 10−9 and 10−12 when supporting triple-play services (sensing, datacomms and video surveillance, respectively), the proposed WON-OCDMA using MW-ZCC codes could support up to 32 simultaneous services over transmission distances up to 32 km in the presence of moderate atmospheric turbulence.