Maged Abdullah Esmail

Physical Layer Monitoring Techniques for TDM-Passive Optical Networks: A Survey

In order to enable new services that require high data rates over longer distances, the optical fiber substitutes the copper cable step by step in the access network area. Time division multiplexed - Passive optical network (TDM-PON) is a fast emerging architecture that uses only passive components between the customer and the central office. PON operators need a monitoring system for the physical layer to guarantee high service quality. This monitoring system is necessary during the fiber installation, final network installation testing, regular operation of the network, and for fault localization. First, in this paper, we present the motivations, requirements and challenges of TDM-PON monitoring. Second, we make an exhaustive review of the monitoring techniques and systems for TDM-PON, mostly proposed within the last five years. In our survey we include the approaches already available in the market even with limited performance and those still in research. Third, we make a detailed classification of all these approaches and qualitatively compare characteristics in a list of performance parameters and aspects. Finally, we outline open issues and future research perspectives in physical layer PON monitoring that may target higher performance, lower cost, or scalability to next generation PON architectures. This includes wavelength division multiplexing (WDM), TDM over WDM or long-reach PONs intended to extend the reach from 20 up to 100 km distances and beyond.

Novel Coding for PON Fault Identification

In this paper we propose a novel simple periodic optical encoder for centralized fault monitoring of fiber-to-the-X (FTTX) passive optical networks (PONs). This optical encoder exploits a fiber ring with a different length for each distribution/drop fiber to produce a different periodic code. This reduces the cost of monitoring system while maintains good performance and high capacity. We investigate the design issues of this coding based monitoring system and evaluate its performance in terms of signal to noise ratio (SNR), probability of false alarm (PFA) and probability of misdetection (PMD). We obtain an SNR of 12.5dB for a 32 customers network in one shot measurement. By repeating the measurement multiple times we achieve a capacity of 64 to 256 in expense of longer measurement time. Moreover, the system accomplishes a PMD ≈ 2 *10-9 for a PFA= 10-6 in a 64 customers network in 4ms.

Outdoor FSO Communications Under Fog: Attenuation Modeling and Performance Evaluation

Fog is considered to be a primary challenge for free space optics (FSO) systems. It may cause attenuation that is up to hundreds of decibels per kilometer. Hence, accurate modeling of fog attenuation will help telecommunication operators to engineer and appropriately manage their networks. In this paper, we examine fog measurement data coming from several locations in Europe and the United States and derive a unified channel attenuation model. Compared with existing attenuation models, our proposed model achieves a minimum of 9 dB, which is lower than the average root-mean-square error (RMSE). Moreover, we have investigated the statistical behavior of the channel and developed a probabilistic model under stochastic fog conditions. Furthermore, we studied the performance of the FSO system addressing various performance metrics, including signal-to-noise ratio (SNR), bit-error rate (BER), and channel capacity. Our results show that in communication environments with frequent fog, FSO is typically a short-range data transmission technology. Therefore, FSO will have its preferred market segment in future wireless fifth-generation/sixth-generation (5G/6G) networks having cell sizes that are lower than a 1-km diameter. Moreover, the results of our modeling and analysis can be applied in determining the switching/thresholding conditions in highly reliable hybrid FSO/radio-frequency (RF) networks.

Fiber Fault Management and Protection Solution for Ring-and-Spur WDM/TDM Long-Reach PON

In this paper, a network fault management and protection system for the ring-and-spur long-reach passive optical network (LR-PON) is proposed. We exploit an adapted, enhanced performance, and inexpensive passive optical components in the field and electronic switches in the central office (CO). Our system allows detecting and localizing not only faulty segments but also faulty nodes, hence alleviating the false alarm probability encountered in previous systems. We show that using ring duplication protection in LR-PON can save half the cost compared to full duplication protection with relatively high reliability performance (99.972%). We describe the implementation strategy of our system in several well known metro network topologies including: (1) single ring, (2) double ring and (3) double fiber pair based ring. The architecture of the remote nodes and the central office is described in addition to the appropriate placement of the passive monitoring devices. We derive an expression for the upper bound notification and recovery times. Moreover, we found that our system can recover from a fault in about 0.5ms as an upper bound.

Optical coding for next-generation survivable long-reach passive optical networks

Optical coding has been proposed and has been well investigated for the monitoring of standard time domain multiplexing passive optical networks (TDM-PONs). We propose a physical layer fault management and protection system for next-generation passive optical networks, so-called long-reach PON (LR-PON), based on passive optical coding. Our approach exploits adapted, performance enhanced, and inexpensive passive optical components in the field, and electronic switches in the central office (CO). This allows detection and localization of the faulty segments in addition to the faulty nodes, hence decreasing the false alarm probability encountered in previous proposed approaches. We show that ring duplication protection in LR-PON can save almost half the cost compared with full duplication protection, with relatively high availability (99.992%). We describe the implementation strategy of our system in various well-known metro network topologies, including (1) single-ring-, (2) double-ring-, and (3) double-fiber-pairs-based ring topologies; all are considered different varieties of ring-and-spur LR-PON. The internal architecture of the remote nodes and the CO are also described in addition to the appropriate placement of our passive monitors. We develop two novel symmetric coding settings. We call them symmetrical optical encoders, which are suitable for fault detection and localization in the ring. We also develop the algorithms required to be executed by the network management system in the CO for fault detection, localization, and protection. Expressions for the upper bound notification and recovery times are also derived. Finally, we estimate that our system can recover from a fault in less than 0.5 ms for a 100 km ring length.

Experimental demonstration of outdoor 2.2 Tbps super-channel FSO transmission system

Free space optic (FSO) is a wireless technology that promises high speed data rate with low deployment cost. Next generation wireless networks require more bandwidth which is not supported by todays wireless techniques. FSO can be a potential candidate for last mile bottle neck in wireless network and for many other applications. In this paper, we experimentally demonstrate a high speed FSO system using super-channel source and multi-format transmitter. The FSO system was installed outdoor on the building roof over 11.5 m distance and built using off-the-shelf components. We designed a comb source capable of generating multi-subcarriers with flexible spacing. Also we designed a multi-format transmitter capable of generating different complex modulation schemes. For single carrier transmission, we were able to transmit a 23 Gbaud 16-QAM signal over FSO link, achieving 320 Gbps with 6 b/s/Hz spectral efficiency. Then using our super-channel system, 12 equal gain subcarriers are generated and modulated by a DP-16QAM signal with different symbol rates. We achieved maximum symbol rate of 23 Gbaud (i.e. 2.2 Tbps) and spectral efficiency of 7.2 b/s/Hz.

An Experimental Study of FSO Link Performance in Desert Environment

Free space optical (FSO) communication systems are affected by dust particles suspended in the atmosphere in arid and semi-arid regions. The presence of these particles in the air severely affects the optical link, reduces its availability, and causes service outage. In the literature, the effect of dust on the microwave signals has been widely investigated. However, for FSO communication systems that exploit shorter wavelengths, information and research are still very limited, almost inexistent. Therefore, in this letter, we investigate the performance of FSO links under dust storms. We designed a chamber to emulate this specific environment and carry out measurements. From the experimental investigations, we derive and propose an empirical model for the signal attenuation as a function of the visibility range. The results show an acceptable performance for FSO links, under moderate and light dust, with potential reach distance of hundreds of meters to few kilometers. Furthermore, a comparison analysis shows that the dust induces seven times higher attenuation than fog.

Analysis of fog effects on terrestrial Free Space optical communication links

In this paper, we consider and examine fog measurement data, coming from several locations in Europe and USA, and attempt to derive a unified model for fog attenuation in free space optics (FSO) communication links. We evaluate and compare the performance of our proposed model to that of many well-known alternative models. We found that our proposed model, achieves an average RMSE that outperforms them by more than 9 dB. Furthermore, we have studied the performance of the FSO system using different performance metrics such as signal-to-noise (SNR) ratio, bit error rate (BER), and channel capacity. Our results show that FSO is a short range technology. Therefore, FSO is expected to find its place in future networks that will have small cell size, i.e., <;1 km diameter. Moreover, our investigation shows that under dense fog, it is difficult to maintain a communications link because of the high signal attenuation, which requires switching the communications to RF backup. Our results show that increasing the transmitted power will improve the system performance under light fog. However, under heavy fog, the effect is minor. To enhance the system performance under low visibility range, multi-hop link is used which can enhance the power budget by using short segments links. Using 22 dBm transmitted power, we obtained BER=10-3 over 1 km link length with 600 m visibility range which corresponds to light fog. However, under lower visibility range equals 40 m that corresponds to dense fog, we obtained the same BER but over 200 m link length.

Current and next-generation passive optical networks monitoring solution

In order to enable new services that require high data rates over longer distances, the optical fiber substitutes the copper cable step by step in the access network area. Time division multiplexed Passive optical network (TDM-PON) is a fast emerging architecture that uses passive components only between the customer and the central office. PON operators need a monitoring system for the physical layer to guarantee high service quality. This monitoring system is necessary during the fiber installation, final testing, regular operation of the network, and for fault localization. In this paper, we present our monitoring system based on optical coding for PON maintenance. This system has almost all the monitoring features required by a network operator. We explained the design and the principle operation of the technique. Moreover, we presents a management and protection solution for long-reach PON networks. Our system design achieves high reliability performance with almost half the cost if full network protection is used.

Outage Probability Analysis of FSO Links Over Foggy Channel

Outdoor free-space optic (FSO) communication systems are sensitive to atmospheric impairments, such as turbulence and fog, in addition to being subject to pointing errors. Fog is particularly severe because it induces an attenuation that may vary from few decibels up to few hundreds of decibels per kilometer. Pointing errors also distort the link alignment and cause signal fading. In this paper, we investigate and analyze the FSO systems performance under fog conditions and pointing errors in terms of outage probability. We then study the impact of several effective communication mitigation techniques that can improve the system performance including multi-hop, transmit laser selection, and hybrid radio-frequency (RF)/FSO transmission. Closed-form expressions for the outage probability are derived and practical and comprehensive numerical examples are suggested to assess the obtained results. We found that the FSO system has limited performance that prevents applying FSO in wireless microcells that have a 500-m minimum cell radius. The performance degrades more when pointing errors appear. Increasing the transmitted power can improve the performance under light to moderate fog. However, under thick and dense fog, the improvement is negligible. Using mitigation techniques can play a major role in improving the range and outage probability.