Habib Fathallah

Passive optical fast frequency-hop CDMA communications system

This paper proposes an all-fiber fast optical frequency-hop code division multiple access (FFH-CDMA) for high-bandwidth communications. The system does not require an optical frequency synthesizer allowing high communication bit rates. Encoding and decoding are passively achieved by Bragg gratings, Multiple Bragg gratings replace a frequency synthesizer, achieving a hopping rate in tens of GHz. A main lobe sine apodization can be used in writing the gratings to enhance the system capacity and the spectrum efficiency. All network users can use the same tunable encoder/decoder design. The simultaneous utilization of the time and frequency domains offers notable flexibility in code selection. Simulations show that the encoder efficiently performs the FFH spread spectrum signal generation and that the receiver easily extracts the desired signal from a received signal for several multiple access interference scenarios. We measure the system performance in terms of bit error rate, as well as auto-to cross-correlation contrast. A transmission rate of 500 Mb/s per user is supported in a system with up to 30 simultaneous users at 10/sup -9/ bit error rate. We compare FFH-CDMA to several direct sequence-CDMA systems in terms of bit error rate versus the number of simultaneous users. We show that an optical FFH-CDMA system requires new design criteria for code families, as optical device technology differs significantly from that of radio frequency communications.

Passive optical network monitoring: challenges and requirements

As PONs carry increasing amounts of data, issues relating to their protection and maintenance are becoming crucial. In-service monitoring of the PONs fiber infrastructure is a powerful enabling tool to those ends, and a number of techniques have been proposed, some of them based on optical time-domain reflectometry. In this work we address the required features of PON monitoring techniques and review the major candidate technologies. We highlight some of the limitations of standard and adapted OTDR techniques as well as non-OTDR schemes. Among the proposed optical-layer monitoring schemes, we describe our novel optical-coding-based reflection monitoring proposal and report on recent progress. We end with a discussion of promising solution paths.

Code-division multiplexing for in-service out-of-band monitoring of live FTTH-PONs

Feature Issue on Optical Code Division Multiple AccessWe propose, to the best of our knowledge, a novel in-service live fiber-to-the-home (FTTH) passive optical networks (PONs) management solution. Our solution uses a modified direct-sequence (DS) optical code-division multiplexing (OCDM) system and overcomes the optical time-domain reflectometry (OTDR) point-to-multipoint shortcomings. Our solution addresses various service provisioning and network maintenance challenges in PONs, alleviates their complexity, and reduces their operational cost. In addition, our system exploits passive devices (or encoders) to demark service provider ownership and responsibility from that of customers. Our OCDM-based management solution easily scales up from FTTH time-division multiplexing (TDM)-PON to WDM-PON and TDM/WDM-PON to support as many as a thousand customers, all using only one monitoring wavelength. We address the coding system and develop capacity curves for different PON scenarios.

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.

Robust optical FFH-CDMA communications: coding in place of frequency and temperature controls

In wavelength division multiplexing (WDM), transmitters require stringent and complex frequency control loops to avoid wavelength drifts due to temperature fluctuations. This makes the transmitters heavy, bulky, and inappropriate for local- and short-haul communications networks, as well as for manufacturing locales and other open areas where temperature control is not feasible. We propose and analyze a technique we call robust fast frequency hopping code division multiple access (FFH-CDMA), particularly suitable for severe, hostile, noncontrollable environments. This approach avoids all conditioning and frequency stabilization loops in the transmission end. We develop a modified version of extended hyperbolic congruence codes to achieve environment-resistant codes. We present expressions for the auto- and cross-correlation functions for optical implementation of the codes. We simulate the encoding/decoding operations with parameters from real Bragg gratings. We evaluate probability of error for a single user and as an average over all users versus capacity (the number of simultaneous users). Robust FFH-CDMA is an efficient access technique for hostile environments. It avoids the frequency and temperature control problems of WDM and nonrobust FFH-CDMA at the cost of lower overall capacity in terms of number of simultaneous users.

Fiber fault PON monitoring using optical coding: Effects of customer geographic distribution

We analyze the performance of fiber fault monitoring of a PON using a centralized, passive optical coding (OC) system. We develop an expression for the detected monitoring signal, study its statistics, and contrast our OC monitoring system with standard optical code division multiplexing (OCDM) data communication. We derive a new closed form lower bound expression for the interference probability, and use this to find the signal-to-interference ratio (SIR). A service provider cannot control the physical layout of homes in a coverage area; measuring performance for one network layout would be insufficient to test our proposed monitoring system. Client geographic distribution has a significant impact on the SIR. We consider five different PON geographical distributions and study their effect on OC monitoring performance. Our results show that SIR is sufficient to successfully monitor the network. In addition, we find that the uniform radial (UR) distribution, an analytically tractable distribution, gives good performance estimation and can therefore be a useful tool in characterizing performance in terms of both SIR and signal-to-noise ratio (SNR).

Interleaved polling versus multi-thread polling for bandwidth allocation in long-reach PONs

Long-reach passive optical networks (LR-PONs) suffer from extremely long propagation delays that degrade the performance of centralized algorithms proposed for upstream bandwidth allocation in traditional PONs. This is because these algorithms are based on bandwidth negotiation messages frequently exchanged between the optical line terminal in the central office and optical network units near the users, which become seriously delayed when the network is extended causing the performance to degrade. In this paper, we review and analyze two centralized dynamic bandwidth allocation algorithms, online interleaved polling and offline multi-thread polling that was recently proposed in the literature for LR-PONs. We investigate and compare their performances together in detail, by studying and observing their elemental delays. Unexpectedly, simulation results show that, although multi-thread polling succeeds in decreasing reporting and queueing delays, interleaved polling keeps a lower grant delay and therefore has better overall delay performance. The latter also achieves better throughput compared to multi-thread polling.

PON Monitoring: Periodic Encoders With Low Capital and Operational Cost

We propose a novel and simple coding device for centralized monitoring of passive optical networks. Encoders have dual Bragg gratings forming a cavity producing periodic codes. These encoders reduce the cost of manufacturing, installation, inventory, and operation, while maintaining good performance and high capacity. We evaluate monitoring efficiency in terms of signal-to-noise ratio.

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.

Dense SS-WDM Over Legacy PONs: Smooth Upgrade of Existing FTTH Networks

We propose a hybrid passive optical network (PON) architecture supporting time-division multiplexing (TDM) and dense spectrum-sliced wavelength-division multiplexing (SS-WDM) over the legacy PON infrastructure. We use a fiber Bragg grating (FBG)-based self-seeded reflective semiconductor optical amplifier (RSOA) transmitter in conjunction with a recently proposed balanced receiver (BR); identical transceiver pairs are placed at the central office and customer side. Self-seeded RSOAs obviate the need for centralized sources, providing a high power, directly modulated source. Intensity noise mitigation of this thermal source is investigated by operating the RSOA in saturation and employing the recently proposed BR. We study the optimal reflectivity for seeding that balances signal power and noise cleaning to achieve the best bit error rate (BER) possible; channel widths are comparable with dense WDM when using coherent sources.