Generation Optical Access Networks Research Articles

What is beyond 50G: future standards of optical access networks [Invited

In the past two decades, optical access networks have been widely deployed by operators around the world. The global optical access network market reaches about 1 billion users with a revenue of over 10 billion US dollars. As strategic tools to facilitate mass production, the optical access network standards play a crucial role in driving the product deployment and market growth. This paper overviews the latest effort in international standards bodies on the next generation optical access networks. It discusses projects in this area within the International Telecommunication Union’s Telecommunication Standardization Section (ITU-T), the IEEE, and the European Telecommunications Standards Institute (ETSI). Promising technologies are investigated with the goal of providing rates beyond 50 Gbps. Challenges are highlighted to satisfy the requirements on balancing access rates, loss budgets, and cost. Candidate systems are analyzed in three categories: point-to-multipoint (PtMP), point-to-point (PtP), and new applications. These standardization endeavors will jointly guarantee optical access networks as the premiere solution of wireline broadband access.

Flexible and adaptive coherent PON for next-generation optical access network [Invited

With the official adoption of the single-wavelength 50G PON standard at the International Telecommunication Union Study Group 15 (ITU-T SG15) meeting, both industry and academia have started extensive research on the next-generation optical access network beyond 50G. It is envisioned that 100G and 200G per wavelength and even beyond will be required in the next-generation optical access network to support the continuously growing bandwidth demands. Coherent passive optical network (C-PON), which is based on multi-access coherent optics and digital signal processing (DSP), appears to be a promising candidate for future 100/200G and even beyond single-wavelength PON, thanks to its superior sensitivity compared with current direct-detection based PONs. Actually, multi-access coherent optics brings many benefits to the optical access network beyond the improvement of sensitivity. In this invited paper, we review recent studies and progress on the flexible C-PON for optical access network in terms of access speed, multiple-access architecture, and deployment scenarios. Rate-adaptive coherent access is first introduced in this paper as a promising solution to achieve flexible C-PON. Adaptive modulation formats based on constellation shaping is highlighted to realize fine granularity of information rate and wide flexibility. We have also discussed the flexible multiplexing schemes beyond TDM, to take the full advantages of coherent access. Finally, we analyze the flexible deployment scenarios under the large power budgets thanks to coherent detection. All these flexibilities provided by coherent access would be interesting and beneficial in the next generation optical access network.

A DYNAMIC BANDWIDTH ALLOCATION SYSTEM IN XG-PONS BASED ON STATISTICAL ESTIMATION OF BUFFER INPUTS AND OUTPUTS

The exchanges in the New Generation Optical Access Network (NG-PON), are mainly based on the bandwidth request by the Optical Network Units (ONU) and its granting by the Optical Line Termination (OLT). This process (request-grant) not being synchronized, will create in the ONU buffer a long delay and the loss of sensitive packets. Many authors, from signaling to prediction, have proposed models to control these parameters, however only those based on prediction reduce the delay in the queues but also waste bandwidth by over- or under-allocating. Our goal is to propose a model that accurately allocates bandwidth to ONU while minimizing their queue delay. As such, we propose a Statistical Queue Estimation model based on ONU Buffer Inputs and Outputs (ESTEST). In its execution ESTEST memorizes the ONU bandwidth requirements and the bandwidth used to transmit their data in the ith upstream frames. With these two parameters (requirements and bandwidth used), our algorithm computes the traffic intensity (𝜌) and predicts the queue size of the ONU. On 100 observations we compute the mean and standard deviation of the 𝜌th values and with the reduced centered normal distribution, find the confidence interval of size estimation.

SSB Single Carrier and Multicarrier in C-Band FSO Transmission With KK Receiver

With the increasing demand of bandwidth, a higher capacity communication system is required for optical short link and access network. Intensity modulation/direct detection (IM-DD) is considered as a reasonable method in access network, due to its low cost and power consumption. However, it reduces the spectral efficiency compared with IQ modulation. In addition, single-sideband (SSB) signal occupies less bandwidth than double-sideband signal (DSB). However, SSB systems suffer from signal-signal beat interference (SSBI) from photodiodes (PDs). Recently, Kramers–Kronig (KK) receiver is proposed to mitigate SSBI. Meanwhile, single-sideband (SSB) signal is the prerequisite for KK scheme, and this kind of signal is also tolerant to fiber chromatic dispersion and multipath-fading. On the other hand, free-space optical (FSO) communication is becoming a promising candidate for next generation optical access network. Thus we experimentally demonstrate the KK scheme in 20 km SSMF and 20 m FSO links with both single carrier signal and multicarrier signal. We compare the performance between them with and without pre-equalization (pre-EQ). With the help of probabilistically shaped (PS) mapping to gives an increase in the sensitivity over an additive white Gaussian noise (AWGN). We reach a 117bit/s transmission with a spectral efficiency of 5.85 bit/s/Hz of 20 Ghz bandwidth with single modulator and single photodiode (PD) in fiber-FSO system.

Editorial: JLT Special Issue on DSP in Next Generation Optical Access Networks

Editorial: JLT Special Issue on DSP in Next Generation Optical Access Networks

Performance of 1550 nm VCSEL at 10 Gb/s in G.655 and G.652 SSMF

Vertical cavity surface emitting lasers (VCSELs) are now major optical sources in optical communication and technology. The VCSEL-based transmission systems satisfy the next generation optical fibre access networks requirements such as low output power, low threshold currents, no optical amplification and use of single fibre for signal transmission. High speed and long wavelength 1550 nm VCSEL are attractive candidates for use in short distance transmission system due to its cost effectiveness and low drive currents. The performance of VCSEL, especially with respect to the low output power characteristics, has made significant progress. However, dispersion and attenuation is a major hurdle to VCSELs transmission at bit rate of 10 Gb/s and above. In this study, we experimentally and theoretically evaluate the capability of 1550 nm VCSEL to operate upto 10 Gb/s on G.655 and G.652 fibres. We present VCSEL characterization and BER performance as a function of received power. A 1550 nm VCSEL was directly modulated with 10 Gb/s NRZ PRBS 2⁷-1 and transmitted over 25 km ITU. T G.652 and ITU. T G.655 fibres. Error free transmission (with bit error rate, BER, of 10^-9) over 25 km G.655 single mode fibre (SMF) has been demonstrated. The Q factor was used theoretically to quantify the performance of the VCSEL. The Q factor increased with the increase in the output power at the receiver. High Q factor values of 6 and above were achieved when 1550 nm VCSEL was transmitted over G.655 fibre. These results show the feasibility of long-wavelength VCSELs in the deployment of enhanced optical access networks.

Considerations on the Use of Digital Signal Processing in Future Optical Access Networks

In this invited article, we address the impacts of the rise of signal processing for increased capacity per wavelength and better receiver sensitivities in next generation optical access networks. We start by recalling the main channel limitations of currently deployed intensity modulated, directly detected, passive optical networks. Then, with the intention of providing a benchmarking of signal processing approaches used in communication systems other than optical access, we provide a historic perspective on how digital signal processing emerged in copper access systems, and we evaluate powerful techniques envisaged for future mobile generation in both air interface and radio access networks. We also assess signal processing in light of multi-vendor interoperability by providing insights on burst mode operation and the needed protocol and monitoring procedures. Interoperability with regard to optical transceivers is also considered. Last but not least, we evaluate power consumption of digital signal processing and forward error correction solutions used in disruptive, coherent transmission approaches.

A Heavy Load Optimized Dynamic Bandwidth Allocation Algorithm for Hybrid WDM/TDM VPONs

Abstract Hybrid wavelength division multiplexed (WDM)/Time division multiplexed (TDM) virtual passive optical networks (VPONs) are considered to provide cost efficient solutions for ever increasing bandwidth requirements of next generation optical access networks. With the development in technology effective bandwidth assignment has emerged as a major concern area. In this paper a novel heavy load optimized dynamic bandwidth allocation algorithm (HLO-DBA) is proposed for the hybrid WDM/TDM VPONs. Multi point control protocol of Ethernet passive optical network (EPON) is implemented for WDM/TDM VPONs subscribers. The excess bandwidth of lightly loaded subscribers is distributed among heavily loaded users through an efficient mechanism. The proposed technique effectively utilize the idle period between the last transmitted REPORT messages from previous transmission cycle (t-1) to the first GRANT message in the current cycle (t). Optical network units (ONUs) connecting the subscribers are scheduled in such a way so as to reduce the wastage of bandwidth. Performance evaluation of HLO-DBA in terms of quality of service (QOS) metrics like throughput and average delay is done to validate the optimization of the proposed mechanism.

Exact Mean Packet Delay for Delayed Report Messages Multipoint Control Protocol in EPON

The infrastructure to develop the next generation optical access network is the Ethernet passive optical network (EPON). Interleaved polling with adaptive cycle time (IPACT) is a common polling method of an EPON. However, the mean waiting time of packets (= the mean packet delay) with IPACT is large depending on the arriving time of the packets. In this paper, a novel media access method for IPACT is proposed in order to minimize the mean packet delay. The mean packet delay with the proposed method is also derived as the exact solution. This solution is based on the non-trivial simplification of the previous work on the analytical solution for general IPACT. We confirm a close match between simulation and our theoretical results and show the effectiveness of our method.

Experimental Comparison of FBMC and OFDM for Multiple Access Uplink PON

Filter bank multicarrier (FBMC) is a favourable candidate for next generation optical access networks due to its capability to operate without a cyclic prefix and its high resilience to synchronization errors in the system. In this paper, we analyze the performance of FBMC in upstream passive optical networks (PON), without the employment of inter optical network unit (inter-ONU) frequency guard bands. By using both experimental work and numerical simulations, the impact of relative time offsets on inter-ONU orthogonality is studied. Furthermore, numerical simulations are also used to study the impact of frequency offsets in such systems. Moreover, comparisons are drawn to orthogonal frequency division multiplexing (OFDM)-based upstream PONs. This paper experimentally demonstrates that imperfect time synchronization impacts all subcarriers in an OFDM system, while it affects only the immediately adjacent subcarriers in an FBMC system, which could be corrected for by the restoration of synchronicity between users. A simple feedback mechanism is experimentally demonstrated to automatically restore orthogonality and synchronization between users in order to validate the practical implementation of the scheme.

Demonstration of multi‐channel 80 Gbit/s integrated transmitter and receiver for wavelength‐division multiplexing passive optical network and fronthauling applications

The performance evaluation of a multi-channel transmitter that employs an arrayed reflective electroabsorption modulator-based photonic integrated circuit and a low-power driver array in conjunction with a multi-channel receiver incorporating a pin photodiode array and integrated arrayed waveguide grating is reported. Due to their small footprint, low power consumption and potential low cost, these devices are attractive solutions for future mobile fronthaul and next generation optical access networks. A BER performance of <10(-9) at 10.3 Gbit/s per channel is achieved over 25 km of standard single mode fibre. The transmitter/receiver combination can achieve an aggregate bit rate of 82.4 Gbit/s when eight channels are active.

Assessment methodology of protection schemes for next generation optical access networks

Optical access networks are evolving towards next generation solutions offering much higher bandwidth per end point. Moreover, the uninterrupted access to the network services is becoming crucial and therefore operators are now considering protecting their access networks. However, the cost factor is still very important due to the relatively low cost sharing in access segment. For this purpose, this paper proposes an assessment methodology that can be used to compare different protection schemes and help to identify the suitable solution for a given scenario. The assessment criteria includes some reliability measures such as Failure Impact Factor (FIF) and connection availability, as well as cost parameters such as the investment required in greenfield and brownfield scenarios and the increase in power consumption compared to the unprotected network. The proposed criteria have been used to compare 7 representative protection schemes shown in literature, which differ mainly in the number of protected network elements and the technology used for protection (fiber, wireless, etc.). The considered protection schemes have been applied to a hybrid wavelength division multiplexing/time division multiplexing Passive Optical Network (Hybrid PON) architecture in an urban area. It has been shown that it is difficult to identify the absolute best scheme with respect to all the considered criteria. However, depending on the requirements from the operator regarding the targeted reliability performance in the network, an appropriate protection scheme can be recommended for either a greenfield or a brownfield scenario.

Experimental demonstration of large capacity WSDM optical access network with multicore fibers and advanced modulation formats.

Towards the next generation optical access network supporting large capacity data transmission to enormous number of users covering a wider area, we proposed a hybrid wavelength-space division multiplexing (WSDM) optical access network architecture utilizing multicore fibers with advanced modulation formats. As a proof of concept, we experimentally demonstrated a WSDM optical access network with duplex transmission using our developed and fabricated multicore (7-core) fibers with 58.7km distance. As a cost-effective modulation scheme for access network, the optical OFDM-QPSK signal has been intensity modulated on the downstream transmission in the optical line terminal (OLT) and it was directly detected in the optical network unit (ONU) after MCF transmission. 10 wavelengths with 25GHz channel spacing from an optical comb generator are employed and each wavelength is loaded with 5Gb/s OFDM-QPSK signal. After amplification, power splitting, and fan-in multiplexer, 10-wavelength downstream signal was injected into six outer layer cores simultaneously and the aggregation downstream capacity reaches 300 Gb/s. -16 dBm sensitivity has been achieved for 3.8 × 10-3 bit error ratio (BER) with 7% Forward Error Correction (FEC) limit for all wavelengths in every core. Upstream signal from ONU side has also been generated and the bidirectional transmission in the same core causes negligible performance degradation to the downstream signal. As a universal platform for wired/wireless data access, our proposed architecture provides additional dimension for high speed mobile signal transmission and we hence demonstrated an upstream delivery of 20Gb/s per wavelength with QPSK modulation formats using the inner core of MCF emulating a mobile backhaul service. The IQ modulated data was coherently detected in the OLT side. -19 dBm sensitivity has been achieved under the FEC limit and more than 18 dB power budget is guaranteed.

Demonstration of a novel software-defined Flex PON

Next generation optical access network needs more flexibility and programmable service provisioning to meet the future effective network operation and maintenance requirements. We propose a novel full-service software-defined Flex PON solution that has three innovative features: (a) DSP-enabled flexible transceiver and flexible link, (b) OLT side access network resource virtualization, and (c) software-defined programmable network functions and resource scheduling. We also experimentally demonstrate the three DSP-enabled flexible transceiver/link application scenarios. The first case uses single OFDM-based RF band that delivers 1.6/3.22/4.03/4.7 Gb/s to different ONUs with QPSK, 16QAM, 32QAM, or 64QAM modulations for achieving different optical power budgets of 36, 32, 30, or 28 dB, respectively. The second case uses dual RF bands to deliver wireless/video/data services in different bands dynamically, realizing a service-programmable capability based on the real network deployment requirements and link conditions. The third case demonstrates a multiband wireless signal transmission in a flexible frequency relocation manner to reuse the PON infrastructure.

Dynamic Wavelength and Bandwidth Allocation in Flexible TWDM Optical Access Network

As one of the most promising next generation optical access network (OAN), flexible time and wavelength division multiplexing (TWDM) OAN can increase capacity smoothly and reallocate wavelength and timeslot resource dynamically to cope with variations in traffic pattern. However, the scheduling of both wavelength and timeslot resource becomes a critical problem. In this letter, a dynamic wavelength and bandwidth allocation (DWBA) solution including the DWBA mechanism, mixed integer linear programming (MILP) model, and two heuristic algorithms is proposed to solve the scheduling problem. By comparison of the two algorithms, only one algorithm is selected to support 10-year lifetime. Under different traffic patterns, the selected DWBA algorithm has better bandwidth utilization and lower delay in contrast with the static wavelength allocation (SWA). The backward compatibility and cost efficiency of flexible TWDM OAN are also discussed.

A 10G/1G Dual-rate Burst-mode Receiver for Next Generation Optical Access Networks

A 10G/1G Dual-rate Burst-mode Receiver for Next Generation Optical Access Networks

Energy-Saving Mechanism in WDM/TDM-PON Based on Upstream Network Traffic

One of the main challenges of Passive Optical Networks (PONs) is the resource (bandwidth and wavelength) management. Since it has been shown that access networks consume a significant part of the overall energy of the telecom networks, the resource management schemes should also consider energy minimization strategies. To sustain the increased bandwidth demand of emerging applications in the access section of the network, it is expected that next generation optical access networks will adopt the wavelength division/time division multiplexing (WDM/TDM) technique to increase PONs capacity. Compared with traditional PONs, the architecture of a WDM/TDM-PON requires more transceivers/receivers, hence they are expected to consume more energy. In this paper, we focus on the energy minimization in WDM/TDM-PONs and we propose an energy-efficient Dynamic Bandwidth and Wavelength Allocation mechanism whose objective is to turn off, whenever possible, the unnecessary upstream traffic receivers at the Optical Line Terminal (OLT). We evaluate our mechanism in different scenarios and show that the proper use of upstream channels leads to relevant energy savings. Our proposed energy-saving mechanism is able to save energy at the OLT while maintaining the introduced penalties in terms of packet delay and cycle time within an acceptable range. We might highlight the benefits of our proposal as a mechanism that maximizes the channel utilization. Detailed implementation of the proposed algorithm is presented, and simulation results are reported to quantify energy savings and effects on network performance on different network scenarios.

Study on the energy-efficient scheme based on the interconnection of optical-network-units for next generation optical access network

An energy-efficient scheme based on the interconnection of optical network unit (ONU) is introduced, which can significantly reduce the energy consumption of the low-traffic operation. The energy consumption model for the ONU-interconnected optical access network (OAN) based on the electronic switch (ES) technology is established, and the energy efficiency of the proposed scheme is analyzed and compared with that of the OAN using optical switch (OS). The simulation results demonstrate that the ONU-interconnected scheme can efficiently reduce the energy consumption of OAN, and it shows a good energy consumption performance under daily traffic model.

Influence of optical filtering on transmission capacity in single mode fiber communications

This paper presents the design and analysis of optical filters that are placed at the output of directly modulated vertical cavity surface emitting laser (VCSEL) in the process of inexpensive transmitter’s implementation for upcoming generation optical access network. Generation of non return to zero (NRZ) optical signal from the transmitter for 110 km error-free single mode fiber (SMF) transmission at 10 Gb/s with bit error rate (BER) of 10−30 in the absence of the external modulator and encoder was proposed. Effects of super-Gaussian and Butterworth optical filters at VCSEL output were demonstrated to maximize performance of SMF optical systems without need of any dispersion compensation technique.

Coherent Ultra Dense WDM Technology for Next Generation Optical Metro and Access Networks

Coherent optical communication has been well established as the technology of choice for long haul and high bit rate communication systems since a decade ago. Recent technology advances and ongoing price erosion further open the window of opportunity for the application of coherent optical transmission technology in other domains. This paper describes in detail the capabilities, design and implementation of a coherent ultra dense WDM technology for optical metro and access networks. Its capabilities enable a number of attractive options, such as variable downstream bit rates from 150 Mbit/s up to 10 Gbit/s per user, embedded OTDR and the coexistence with legacy systems such as GPON, EPON, XGPON or RF-Video in optical distribution networks. Due to its flexibility and capacity, it is also suitable for deployments in metropolitan networks, as well as for mobile front-haul and back-haul applications.