Wavelength Division Multiple Access Research Articles

Design and performance evaluation of a hybrid FSO-FTTx communication link utilizing UD-WDMA 1.28 Tbps data rates transmission under various weather conditions

Abstract The rapid growth of high-data-rate applications necessitates the development of new communication frameworks since bandwidth constraints for data-intensive applications hinder traditional networks and conventional microwave/radio frequency (RF) communications. This study explores a hybrid communication link that combines fiber-to-the-x (FTTx) and free-space optical (FSO) technologies, utilizing ultra-dense wavelength-division multiple access (UD-WDMA) with a channel spacing of 0.2 nm/25 GHz, under various weather conditions. Based on bit error rate (BER), optical signal-to-noise ratio (OSNR), and quality factor (QF), the performance of the suggested FSO-FTTx system was examined. The system performed well in diverse weather conditions, achieving a minimum BER of ≤10−5, QF values of 4 or higher, and OSNR levels between 10 and 20 dB. The proposed system successfully transmitted a data rate of 1.28 Tbps over 35 km in single-mode fiber (SMF), accommodating different FSO link ranges despite varying weather conditions. However, performance fluctuations were observed under adverse conditions, with attenuation ranging from 0.91 dB/km in extremely light mist to 273.39 dB/km in dense fog, impacting the FSO link range. The findings underscore the proposed hybrid system’s potential to enhance optical wireless communication for high data rates, making it promising for beyond 5G and early 6G applications.

Performance Enhancement of Indoor Cellular Visible Light Communication through Cell Size and Wavelength Reuse Pattern

The emerging technology of visible light communication (VLC) has become a promising solution for the requirements of wide-bandwidth, high-speed, and infinite-capacity wireless communication networks. A novel design of high-performance multi-user indoor visible light communication (VLC) based on hexagonal-cell arrangement is introduced in the present paper. The wavelength division multiple access (WDMA) is used to enable multiple users to communicate through the network of access point (APs) by assigning a unique wavelength division channel (WDC) to each user. A wavelength reuse scheme is utilized to increase the maximum number of users in the system and to enhance the VLC system capacity. The on–off keying (OOK) is used as the modulation technique for light signaling. The intercell interference (ICI) caused by the wavelength reuse is evaluated and its dependence on the cell radius and the wavelength reuse pattern size is numerically investigated. Both the received power density and the ICI at the location of the moving user are evaluated and the resulting signal-to-ICI ratio (SICIR) is calculated at every point over the indoor area. The VLC system capacity is evaluated and its dependence on the design parameters including the cell radius, the size of the wavelength reuse pattern, and the user data rate is numerically investigated. A design procedure is proposed to minimize the bit-error rate (BER) resulting from the ICI and to maximize the system capacity and the maximum allowable number of users in the system by selecting the optimal radius of the hexagonal cells and the most appropriate size of the frequency reuse pattern. The effect of the data rate per user on the system capacity is numerically investigated. It is shown that a SICR of greater than 21 dB and BER of less than 1 × 10−15 is achieved. Also, a system capacity of more than 4 bps/Hz is achieved by the application of the proposed VLC design optimization procedure.

Intelligent Encoding through OCDM for High Capacity and Connectivity in Wireless 5G and Beyond Networks

Multioperator multiservice support over mobile front haul networks would be an important requirement in the evolving 5G Wireless Communication architectures. This in turn dictates the need for high capacity and high connectivity front-haul options. Optical Code Division Multiplexing over Wavelength Division Multiple Access could be one of the most promising system architectures to support the last/first-mile bottleneck of the Mobile Networks. This paper reports a comparison impact of the energy efficiency and electromagnetic radiation effects for a multioperator multiservice OCDM-based Spectrally Amplitude Encoded Analog Radio over Fiber front-haul for a small cell configuration. The WDM multiplexed mm-wave signals at 60GHz and 28GHz and Prime code-based spectral amplitude patterns assigned for conventional services are analyzed and compared with theWavelength Division Multiple Access system of the same kind. The comparison results confirm that the proposed architecture will be a suitable candidate to meet the 5G challenges of Mobile fronthaul Networks.

Global P2P BitTorrent Real-Time Traffic Over SDN-Based Local-Aware NG-PON2

File sharing is one of the most common uses in Peer-to-peer (P2P) networks and structured P2P systems, such as BitTorrent (BT), which may overcome the limitations of features such as improved scalability, efficiency, and deterministic data location. Recent research has attempted to reduce inter-ISP P2P traffic by including locality awareness into neighbor-selection strategies of popular P2P apps, which prioritize adjacent peers over distant peers when transferring data, reducing server bandwidth burden, and inter-ISP traffic expense. However, the locality awareness P2P exchanged, handled and coordinated by the network infrastructure to turn around traffic as nearest as possible to the end users was proposed for the passive optical network (PON) because of the large amount of bandwidth in only one single fiber. The PON offers many system architectures; in particular, the NG-PON2 with colorless ONUs, adopting time and wavelength division multiple access technology is often recognized as the best access network solution for simplifying network operation, lowering installation costs, and maintenance costs under control. Software-defined networking (SDN) has sparked interest in various fields as a viable research topic, promising better agility, improved automation, security, and lower capital and operating costs. Taking advantage of the SDN’s OpenFlow protocol in NG-PON2, centralized control renders more flexible control over the BT traffic (P2P intra-traffic) file sharing application provided by different ISPs. Finally, we evaluated our proposed scheme in real-time traffic share collected by Sandvine’s report on 2020 despite the Covid-19 pandemic for different geographic regions, for example; Global, APAC, EMEA, and AMERICA.

Design of a Hybrid WDMA-Optical-CDMA over Multi-Mode Fiber Transmission System based on LG Modes for Short Haul-Local Area Network

Various optical communication technologies use Optical-Code Division Multiple Access (Optical-CDMA) as a channel access technique, which allows transmission of different users simultaneously over the optical communication channel. Therefore, Optical-CDMA permits free undue interference transmission of several users. Whereas Wavelength-division multiple access (WDMA) is a technique that can be implemented on how the optical channel can be divided into subchannels. This paper proposes a Hybrid WDMA-Optical-CDMA over multi-mode fiber (MMF) transmission system for short haul-local area network. The WDMA system is carried out by using four Laguerre-Gaussian (LG) modes that operate over four main wavelengths (1551 nm, 1550 nm, 1549 nm and 1548 nm). Additionally, the Optical-CDMA system is carried out by using one dimension Zero Cross-Correlation (ZCC) code to overcome multiple access interference (MAI) between the four ZCC codes. The performance of our system is evaluated based on eye diagrams, Q-Factor and bit-error rates (BER) measurements.

Random weather phenomena in free-space optical - FTTx communication system

In the last few decades, optical wireless communication became an essential technology in various applications. Researchers have paid more attention to achieving high bandwidth and low loss. However, the random weather phenomena cause attenuation of optical signals, thus will decrease the bandwidth in optical wireless communication. In this article, we investigate a hybrid free-space optical (FSO) and fiber-to-the-x (FTTx) communications link based on wavelength-division multiple access (WDMA) over different random weather phenomena that operate over different wavelengths. The performance of the hybrid FSO-FTTx system is evaluated under clear sky weather phenomena, heavy rain weather phenomena, and heavy haze weather phenomena based on BER and Q-Factor measurements. The results show that we can transmit 140 Gbit/s data over 9650 meters a hybrid link under the clear sky and heavy rain weather phenomena, 3950 meters over. Additionally, the transmission of 140 Gbit/s data can be achieved for 1450 meters under the heavy haze weather phenomenon.

Optimum resource allocation in optical wireless systems with energy-efficient fog and cloud architectures.

Optical wireless communication (OWC) is a promising technology that can provide high data rates while supporting multiple users. The optical wireless (OW) physical layer has been researched extensively, however, less work was devoted to multiple access and how the OW front end is connected to the network. In this paper, an OWC system which employs a wavelength division multiple access (WDMA) scheme is studied, for the purpose of supporting multiple users. In addition, a cloud/fog architecture is proposed for the first time for OWC to provide processing capabilities. The cloud/fog-integrated architecture uses visible indoor light to create high data rate connections with potential mobile nodes. These OW nodes are further clustered and used as fog mini servers to provide processing services through the OW channel for other users. Additional fog-processing units are located in the room, the building, the campus and at the metro level. Further processing capabilities are provided by remote cloud sites. Two mixed-integer linear programming (MILP) models were proposed to numerically study networking and processing in OW systems. The first MILP model was developed and used to optimize resource allocation in the indoor OWC systems, in particular, the allocation of access points (APs) and wavelengths to users, while the second MILP model was developed to optimize the placement of processing tasks in the different fog and cloud nodes available. The optimization of tasks placement in the cloud/fog-integrated architecture was analysed using the MILP models. Multiple scenarios were considered where the mobile node locations were varied in the room and the amount of processing and data rate requested by each OW node was varied. The results help to identify the optimum colour and AP to use for communication for a given mobile node location and OWC system configuration, the optimum location to place processing and the impact of the network architecture. This article is part of the theme issue 'Optical wireless communication'.

Performance Analysis of 2-D Prime Codes Encoded Optical CDMA System

Abstract Optical code division multiple access (OCDMA) system provides highly secured transmission in addition to its capabilities to support asynchronous transmission and soft blocking. Two-dimensional OCDMA codes are chosen in this paper due to their high cardinality, good spectral efficiency and flexibility in their construction methods against direct sequence codes. This paper focuses on study of impact of multiple access interference (MAI) at high data rates for 2-D prime codesbased OCDMA system. It is shown that how the change in number of simultaneous users affects the transmission quality. Further, performance of the system is analysed in terms of bit error rate, received electrical power and eye openings. In addition, this paper also shows a comparative analysis of 2-D codes-based OCDMA system and wavelength division multiple access (WDMA) system in order to justify the improved performance of the proposed system. It is observed that the performance of 2-D OCDMA system is much better than WDMA system in terms of quality as well as security.

Performance Evaluation of Bidirectional Wavelength Division Multiple Access Broadband Optical Passive Elastic Networks Operation Efficiency

Abstract The study has outlined the performance evaluation of bidirectional wavelength division multiple access broadband optical passive elastic networks operation efficiency. Signal power level, Q coefficient parameter, and minimum data error rates are measured numerically in both downstream and upstream directions based on broadband passive optical networks (BPONs). The transmission data rate available in the downstream direction is 10 Gb/s, while its value in the upstream direction is 2 Gb/s. The suitable operating wavelength is selected in the near-infrared region around 1550 nm for minimum losses. The bits sequence length of the optical transmitter is taken in to account for testing the optical network performance efficiency. The proposed model has presented better performance than the previous model by 25.76 % in downstream direction and by 12.28 % in upstream direction. As well as the bidirectional wavelength division multiple access broadband passive optical elastic networks performance efficiency is measured.

Wavelength assignment in quantum access networks with hybrid wireless-fiber links

We propose a low-complexity near-optimal wavelength allocation technique for quantum key distribution access networks that rely on wavelength division multiple access. Such networks would allow users to send quantum and classical signals simultaneously on the same optical fiber infrastructure. Users can be connected to the access network via optical wireless or wired links. We account for the background noise present in the environment, as well as the Raman noise generated by classical channels, and calculate the secret key generation rate for quantum channels in the finite-key setting. This allows us to examine the feasibility of such systems in realistic scenarios when the secret key exchange needs to be achieved in a limited time scale. Our numerical results show that, by proper choice of system parameters for this noisy system, it is possible to exchange a secret key in tens of seconds. Moreover, our proposed algorithm can enhance the key rate of quantum channels, especially in high noise and/or high loss regimes of operation.

Dynamic WDM-TDM access networks featuring wired-wireless convergence

Growth in the use of devices with Internet access and migration of telecommunications to IP technology have made the bandwidth demanded by users appear for the first time in a long time a limited resource. Optical fiber is demonstrating to be the solution to this issue based on the capability to provide enough bandwidth to manage large volumes of data at high speed featuring low loss transmission. Passive optical networks (PON) are presented as an alternative with respect to conventional copper-based access networks due to the use of distribution passive elements, which have a lower maintenance cost as compared to its active counterpart. In addition, the optical fiber capacity provides a future-proof platform to support the forthcoming bandwidth requested in the access segment. This paper presents and demonstrates through practical and simulation data analysis a proposal for next generation PON based on Time Division Multiple Access (TDMA) and Wavelength Division Multiple Access (WDM). Complying with a typical PON power budget, the architecture envisages dynamic wavelength allocation and converged transport of wired and wireless services on an unified optical platform architecture

A Novel Access and Control System in a WDM Passive Star-Coupled Network for Optical Backhaul

A passive star-coupled (PSC) optical wavelength division multiplexing (WDM) network is considered a promising candidate for optical backhaul particularly in densely populated urban areas. In this paper, we present the access and control system design for wireless backhaul transmission over a PSC wavelength division multiple access (WDMA) network. We employ an in-band control-signal technique, providing dedicated control slot access, and the length of the control slot is minimized and unconstrained by the length of a data slot, aiming at offering thorough control information and maximizing the system performance. A packet-by-packet, reservation-based, and frame-basis medium access control (MAC) scheme is presented. The MAC scheme ensures round-robin scheduling to flexibly transmit data packets within a data frame by simply adopting two initial variables. The simulation results show that the network achieves exceptionally high system performance when each node is equipped with only one tunable transmitter and one fixed-tuned receiver for uniform destination traffic scenarios. In a client/server traffic scenario, only the server node (which receives an additional proportion of the entire network traffic) is upgraded by replacing the fixed-tuned receiver with a fast tunable receiver; thus, exceptionally high delay-throughput performance is maintained, and the most cost-effective solutions are proposed.

Flexible TDMA/WDMA passive optical network: Energy efficient next-generation optical access solution

Access networks must further advance to address the intensification of the requirements of growing speeds and the usage of Internet applications, and time and wavelength division multiple access (TDMA/WDMA) based passive optical networks (TWDM-PONs) have been widely considered as one of the evolutionary steps of next-generation optical access (NGOA) networks. TWDM-PON combines the flexibility of TDMA with an increased capacity offered by the use of a WDM layer. Moreover, it offers interesting and challenging avenues to minimize energy consumption: especially, with current access networks consuming about 80% of the energy consumed in the Internet. Along with other efforts, reducing energy consumption of central offices is conspicuous as it directly minimizes the operational expenditures of network providers. In this paper, we explore the new paradigms to conserve energy at the central offices in TWDM-PONs. By extensive simulations, we evaluate the possible energy savings in the various flavors of TWDM-PON. Based on the findings, we propose a new architectural flavor of TWDM-PON and benchmark the architecture for cost, power consumption and reach. We also propose a novel energy saving scheme for the proposed architecture and evaluate the impact of the proposed algorithm on energy savings by extensive simulations.

Performance of indoor optical femtocell by visible light communication

Femotocell has been proposed and deployed to improve the indoor coverage and capacity of a cellular network. One big challenge in its deployment is the interference between the macrocell and femtocell cellular networks. In this paper we propose a new physical layer for the implementation of indoor femtocells – optical femtocells by LED-based visible light communication. A general system structure of the indoor optical femtocell network is first introduced. A combined wavelength division and code division multiple access scheme is proposed to differentiate cells and multiple users within a cell. This scheme coupled with directional beaming characteristics of the LEDs helps to mitigate intercell interference and intracell inference. The communication performance adopting the dimming compatible variable-PPM modulation suggested by the IEEE standard is analyzed. Monte-Carlo simulation is then carried out to reveal the system performance numerically under typical system settings and effects of various parameters.

Enhancing Performance of Optical Communication Systems with Advanced Optical Signal Processing

Growing needs to transport large amount of data, penetration of multimedia into our daily lives, and quickly expanding e-Commerce sector triggered an unparallel demand for the new generation of fast, secure, and energy savvy communication networks. Today we already benefit from many advances which revolutionized data and voice communication. Commercially deployed Dense Wavelength Division Multiple Access (DWDMA) networks today are capable of transporting tens of Gigabits of data per second over a single WDM channel thus offering tremendous aggregate data throughputs over a single optical fibre. As a consequence, new bottlenecks have emerged at the fibre endpoints where data detection, routing, and switching must take place. Today's routers use electronics to process all incoming optical traffic. However the available bandwidth offered by current electronics can no longer keep up with these rapidly growing demands. To address these challenges and with goal in mind to eliminate this bottleneck, the research community has been looking long and hard for appropriate alternative solutions. One of taken approaches can be described as optical signal processing. As we will demonstrate it can be very powerful tool to improve performance of advanced communication networks.

OpticalWireless Links for Intra-Satellite Communications: Reflection Models and Hardware Optimization

The present work is a study on the propagation channel (physical layer) for wireless infrared communications in intra-satellite environments. Substituting cables and connectors with optical links inside a spaceborn platform offers many advantages and represents some technical challenges. We show analytical calculations, simulations, and experimental results for reflection models for aerospace materials, as well as wavelength division multiple access techniques for channel multiplexing. Improvements in the selection and optimization of emitter‐detector pairs are also presented.

Hybrid WDMA/OCDM system with the capability of encoding multiple wavelength channels by employing one encoder and one corresponding optical code

A hybrid wavelength division multiple access (WDMA)/optical code division multiplexing (OCDM) system is proposed, where the optical code is not the same as the address of every optical network unit (ONU); rather, the code is a virtual fiber of hybrid passive optical network (PON). To our knowledge, this is the first report analyzing a single encoder/decoder with a single corresponding optical code being exploited to encode/decode multiple wavelength signals simultaneously. This system enables OCDM to become transparent to ONU so that the existing wavelength division multiplexing (WDM) PON can be upgraded. Thus, redesigning the optical line terminal and ONU can be easily accomplished, and greatly decreasing the number of encoder/decoder becomes possible. In experiment, we only employ two encoder/decoder pairs to combine two WDM-PONs in one fiber. Simulation results confirm the feasibility of the proposed system.

IP Routing and Transmission Analysis in Optical CDMA Networks: Coherent Modulation With Incoherent Demodulation

A novel Internet protocol (IP) transmission and routing is proposed over coherent multiple array (M-ary) frequency shift keying optical code-division multiple-access (FSK-OCDMA) network with incoherent demodulation. The architecture also benefits from the use of the co-channel interference canceller. In contrast to wavelength-division multiple-access (WDMA), a fewer set of wavelengths are needed as a result of M-ary source coding. As the spreading codes, double-padded modified prime codes (DPMPC) have been employed. The performance has been analyzed in terms of the users' channel utilization in the network and compared with common incoherent pulse-position modulation technique. The results indicate that this architecture is very power efficient and enhances the network capacity. With the advantage of shorter code length, DPMPC also improves the throughput. It is shown that for a maximum bit-rate, the network performance can be improved by reducing the channel utilization. Since each IP packet is buffered only at the edge of this network, the buffer delay is considerably reduced. The novel encoder adjusting time management reduces the switching time notably rather than traditional routing. Our analytical investigation clearly indicates that this OCDMA technique can be an excellent candidate for the future ultra-fast high bit-rate optical IP networks.

PONIARD: A Programmable Optical Networking Infrastructure for Advanced Research and Development of Future Internet

<para xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> Motivated by the design goals of Global Environment for Network Innovation (GENI), we consider how to support the slicing of link bandwidth resources as well as the virtualization of optical access networks and optical backbone mesh networks. Specifically, in this paper, we study a novel programmable mechanism called optical orthogonal frequency division multiplexing (OFDM)/orthogonal frequency division multiple access (OFDMA) for link virtualization. Unlike conventional time division multiplexing (TDM)/time division multiple access (TDMA) and wavelength division multiplexing (WDM)/wavelength division multiple access (WDMA) methods, optical OFDM/OFDMA utilizes advanced digital signal processing (DSP), parallel signal detection (PSD), and flexible resource management schemes for subwavelength level multiplexing and grooming. Simulations as well as experiments are conducted to demonstrate performance improvements and system benefits including cost-reduction and service transparency. </para>

Novel Channel Interference Reduction in Optical Synchronous FSK-CDMA Network Using a Data-Free Reference

In this paper, we propose a novel multiple-access interference (MAI) cancellation technique using a reference signal, which contains no data components (data-free) of the desired signal, and then simplifies the receiver configuration in synchronous M-ary frequency-shift keying optical code-division multiple-access (FSK-OCDMA) network. In doing so, we have taken advantage of a recently introduced energy-saving unipolar prime-code family, referred to as double-padded modified prime-code (DPMPC) as the spreading codes. In the theoretical analysis, the system upper bounded bit error rate (BER) is derived taking into account the Poisson effect on the I/O characteristics of the photodetectors. We have found that when the bit rate is constant, the capacity of this system increases by employing the proposed interference canceller and spreading code as compared with the synchronous M-ary pulse-position modulation OCDMA system with an existing interference canceller. In contrast to wavelength-division multiple access, a fewer set of wavelengths is needed as a result of only M-ary source coding.