Time And Wavelength Division Multiplexed Passive Optical Network Research Articles

High-priority first dynamic wavelength and bandwidth allocation algorithm in TWDM-PON

Abstract Time and wavelength division multiplexing passive optical network (TWDM-PON) is the mainstream scheme of the next generation access network, and it possesses a number of unique characteristics such as high-bandwidth, long-distance data transmission, and connecting lots of users. As the difference among user traffic demands increases, in order to effectively decrease the network delay and improve resource utilization, a high-priority first dynamic wavelength and bandwidth allocation (HF-DWBA) algorithm in TWDM-PON system is proposed in this study. According to the service-level agreement (SLA), in order to determine the priority of an optical network unit (ONU), the proposed algorithm ensures the high-level ONU traffic distribution in terms of wavelength assignment and bandwidth allocation, and it can execute five types of transmission containers (T-CONTs) as well as four kinds of bandwidth allocation strategies. The results of simulation show that in comparison with traditional algorithms, the proposed HF-DWBA algorithm can effectively reduce end-to-end time delay and improve bandwidth utilization ratio, while making fairness among different types of bandwidth allocation strategies.

Analysis of energy efficiency in cloud based heterogeneous RAN with large-scale antenna systems

To address the capacity requirements resulting from huge growth in mobile data traffic, the mobile network operators (MNOs) are densifying their networks with more base stations, and with more spectrum layers. The addition of base stations and spectrum layers increases the energy consumption of the access network. Hence the network needs to be optimized to lower the power consumption (e.g.) through cloud, or deployment of spectral and power efficient radio units like Large-Scale Antenna Systems (LSAS) or massive Multiple Input Multiple Output (MIMO) radio units.In this paper, we analyse the network evolution towards Cloud based Radio Access Network (C-RAN) for a mix of base stations with Macro and LSAS Remote Radio Units (RRU). We derive the computational complexity of the base station components using a flexible power model. We evaluate the need for base station architecture split, when C-RAN is used with LSAS radio units and large antenna configurations. We use a combination of simulators viz.NS3 (for LTE radio network simulation) and CloudSIM Plus (for Cloud based base station simulation). For each base station type, we compare the computational complexity of different sub-components. Further, based on the selected power model, we study the effect of base station's scheduling algorithm (viz.) Proportionate-Fair or Round-Robin, on the computational complexity of the various base station sub-components. We consider Time and Wavelength Division Multiplexed Passive Optical Network (TWDM-PON) for the high capacity low latency fronthaul network. Using the overall radio cluster throughput and power consumption information from Cloud base station, Radio site, and fronthaul network, we assess the energy efficiency metrics for the Cloud RAN and LSAS (with different antenna configurations) with Macro RRUs as reference.Through the simulations, we observe that, the computation complexity was relatively higher for RR scheduling (compared to PF scheduling). But the variations of energy efficiency metric were similar for both the scheduling schemes for different base station configurations.We observe that compared to Macro2TR, LSAS variants are highly energy efficient. This gain is mainly associated with higher throughput due to MU-MIMO (where multiple UEs are accommodated in the same set of radio resources) and lower power consuming components in LSAS. Between LSAS32TR, LSAS64TR and LSAS128TR, we find that LSAS32TR had lower energy efficiency. Further, we observe that the energy efficiency of LSAS64TR is almost same as LSAS128TR, though LSAS64TR supports just half the number of MU-MIMO layers. This implies that the additional number of layers that LSAS128TR system supports, is compensated by power consumed to support the higher antenna chains and spatially multiplexed layers.Thus, MNOs interested in deploying high spectral efficiency solution along with high energy efficiency, may prefer to deploy LSAS64 systems for tower-top deployments of Radio unit deployment, since it offers higher energy efficiency with lower wind-load effect due to smaller antenna size.

Single-Fiber Bi-Directional Burst-Mode EDFA for TWDM-PON

In this paper, we propose a single-fiber bi-directional burst-mode erbium-doped fiber amplifier (EDFA) to simultaneously improve upstream and downstream loss budget in time and wavelength division multiplexed–passive optical network (TWDM-PON). Instead of additional light sources for upstream gain clamping, the downstream signal acting as saturation signal effectively suppresses the upstream burst surge, which widens the input dynamic range of upstream burst signal. For potential reflections caused by the absence of optical isolators, experimental results have demonstrated the degradation of receiver sensitivity at bit-error rate of $1 \times 10^{-3}$ is negligible with a reflection power up to −14 dBm, which proves the promising applications in PONs of the proposed single-fiber bi-directional burst-mode EDFA.

Wavelength-Stable Burst-Mode Laser for Next-Generation PONs

We developed a novel wavelength-stable burst-mode (BM) laser based on a multi-electrode distributed-feedback (DFB) laser. Our main use-case for the multi-electrode laser (MEL) is a time- and wavelength-division multiplexed passive optical network (TWDM-PON) (NG-PON2), but the wavelength-stable BM laser might also enable future coherent TDM-PON systems and high-rate PON systems using optical-filter-based chromatic dispersion compensation. Samples of the proposed laser are realized and characterized. The performance of the MEL-based BM transmitter is evaluated in several experiments in a directly modulated (at 10 Gbps) and externally modulated (at 25 Gbps) configuration. It is shown that the proposed laser is suitable for TWDM-PONs using a 100 GHz wavelength grid.

Experimental Demonstration of FTN-NRZ, PAM-4, and Duobinary Based on 10-Gbps Optics in 100G-EPON

This paper presents an experimental demonstration of 100-Gbps timeand wavelength-division multiplexed passive optical network (TWDM-PON) with 4 × 25-Gbps downstream transmission. We take a comparison of faster-than-Nyquist nonreturn-to-zero (FTN-NRZ), four-level pulse amplitude modulation (PAM-4), electrical duobinary (EDB), and optical duobinary (ODB) on the same transmission link. The use of low-cost 10-Gbps optics in combination with digital signal processing (DSP) makes it feasible for a 25-Gb/s per wavelength transmission over 20-km standard single-mode fiber (SSMF) in a cost-effective way. The spectra efficiency and ISI robustness by going to the higher rate are analyzed theoretically. We achieve link budgets of 33.18 dB for FTN-NRZ, and less than 30 dB budgets for PAM-4, ODB, and EDB in downstream transmission. FTN combination with feedforward equalization (FFE) allows FTN-NRZ to have a 4.18 dB margin in power requirement of PR(x) 30 of 10G-EPON, whereas PAM-4 and ODB with FFE also meet PR(x) 30 with 0.25 dB margin. The results indicate that FTN-NRZ, PAM-4, and ODB can be used for 100G-EPON with 10-Gbps optics, and FTN-NRZ has better performance than other modulations, which is more suitable for next-generation 100G-EPON transmission technique with low cost.

Reverse Bias Voltage Controlled Burst-Mode Booster SOA in λ-Tunable ONU Transmitter for High-Split-Number TWDM-PON

This paper presents a λ-tunable optical network unit (ONU) burst-mode transmitter (B-Tx) with high output power and low burst-off-level power for high-splitnumber time and wavelength division multiplexing passive optical networks (TWDM-PONs). The proposed ONU B-Tx utilizes a burst-mode booster semiconductor optical amplifier (SOA) with a control technique for reverse bias voltage that creates an optical power absorption effect in the burstoff- level state. This paper introduces the design of the biasvoltage- state control circuit, simulations of control-circuit operation, evaluations of the static optical power-absorption effect, and burst-mode operation performance in the booster SOA operated by reverse bias voltage. High output power of over +7.4 dBm and low burst-off-level power of under −73.4 dBm∕15 GHz are successfully achieved in all upstream channels. Crosstalk penalty measurements confirm a very low penalty of under 0.1 dB, which leads to a 256 splitnumber TWDM-PON.

Efficient polling cycle adaptive passive optical network for low-latency 5G fronthaul

Under the large and ubiquitous bandwidth requirements of the upcoming 5G era, new common public radio interface (CPRI) solutions (such as eCPRI) characterized by scale flexible, packet-based bandwidth reduction are receiving extensive attention. In this context, applying a passive optical network (PON) into the mobile fronthaul (MFH) has good prospects due to the features of low cost and wide coverage. However, the millisecond-level latency of the dynamic bandwidth allocation (DBA) procedure exceeds the harsh latency constraints of 5G MFH, and the uneven distribution of traffic caused by user mobility brings waste or congestion of MFH bandwidth resources. To meet the latency constraint and simultaneously improve bandwidth utilization, we propose a flexible time- and wavelength-division multiplexed passive optical network (TWDM-PON)-based MFH architecture, in which optical network units (ONUs) can be dynamically grouped to support efficient use of the bandwidth and adaptive polling cycle. Based on this architecture, the influence of the propagation time on latency is analyzed, and a joint bandwidth and latency constraint (JBL) grouping algorithm is proposed to obtain the appropriate ONU group for different network slice scenarios. The simulation results indicate that, in the case satisfying the latency constraint, the bandwidth utilization reaches 94% and above (maximum 99.5%). Simultaneously, within different slicing scenarios, the polling cycle can be increased by 98% on average (maximum 122%) or decreased by a maximum of 36μs. Compared with the non-grouping situation, the adaptive polling cycle lowers the performance requirement of the hardware device (such as a burst mode transmitter), expands the MFH coverage, and improves the channel utilization.

OLT Energy Savings via Software-Defined Dynamic Resource Provisioning in TWDM-PONs

Time and wavelength division multiplexed passive optical network (TWDM-PON) standards dramatically increase the performance of PON systems and address ever-increasing demands for bandwidth. However, these schemes increase the complexity and energy consumption of PON systems because they exploit multiple wavelengths, which requires multiple transceivers in the optical line terminal (OLT). In this paper, we propose to integrate software-defined networking (SDN) into standard PON architectures to facilitate an orchestrated energy-efficient operation in which the SDN controller dynamically provisions the number of wavelengths, link-rates, and timeslot assignments depending on the global traffic conditions. The simulation results show that the proposed architecture and mechanism improves the energy-saving performance of OLTs if the traffic load is less than 80%, while guaranteeing the quality of service requirements in terms of the mean packet delay, jitter, queue length, throughput, and packet loss ratio.

128 Gb/s TWDM PON system using dispersion-supported transmission method

Abstract Time and wavelength division multiplexed passive optical network (TWDM-PON) trend is considered as the most extraordinary trend of the next generation solution to accommodate exponential traffic growth for converged new services. In this paper, we briefly review recent progress on TWDM-PON system through the use of low cost directly modulated lasers (DMLs) transmission for various line rate transmissions to date. Furthermore, through simulation, we propose and evaluate a cost effective way to upgrade TWDM-PON up to a symmetric capacity of 128 Gb/s using fiber Bragg gratings (FBGs) in optical line terminal (OLT) as a paramount dispersion manager in high speed light-wave systems in both upstream and downstream directions. A low cost and potential chirpless directed modulated grating laser (DMGL) is employed for downstream link and DML with a single delay-interferometer (DI) is employed for upstream link. After illustrating the demonstrated system architecture and configuration, we present the results and analysis to prove the system feasibility. The results show that a successful transmission is achieved over 40 km single mode fiber with a power budget of 33.7 dB, which could support 1:256 splitting ratio.

Power budget improvement of symmetric 40 Gb/s TWDM based PON2 system utilizing DMLs and DCF technique

In this paper, we propose to use optical dispersion compensation based on the widely deployed compensating fiber (DCF) employing directly modulated lasers (DMLs) to improve the power budget in a symmetric 40 Gb/s time and wavelength division multiplexed-passive optical network (TWDM-PON) systems. The DML output waveforms in terms of output optical power, bandwidth enhancement factor (α) characteristics are investigated in order to minimize the effect of DML chirp and improve the transmission performance. Simulation results show dispersion compensation of up to 140 km of SMF with power budget of 56.6 dB and less than 2 dB dispersion penalty. The feasibility of bandwidth enhancement factor and power budget is also investigated. The simulation results indicate sufficient dispersion compensation for TWDM-PON based on DML transmission, which may vary considerably in their practical demonstration due to different system characterization.

Game-Assisted Distributed Decision Making to Build Virtual TDM-PONs in C-RANs Adaptively

Although a promising solution for next-generation radio access networks (RANs), cloud RAN (C-RAN) still faces technical challenges due to the separate locations of the cloud-based baseband unit (BBU) pool and remote radio heads (RRHs). Fortunately, time- and wavelength-division multiplexing passive optical networks (TWDM-PONs) can efficiently bridge the communications between the BBU pool and RRHs. In this work, we address the problem of formulating virtual time division multiplexing PONs (vTDM-PONs) adaptively in a TWDM-PON-based C-RAN. However, instead of relying on a centralized approach, we develop algorithms that can work in a distributed manner. Specifically, we consider a scenario in which the optical network unit (ONU) of each RRH has the initiative to choose a proper vTDM-PON to register to based on its knowledge on the C-RAN. We formulate game theoretic models for the vTDM-PON formation for both static and dynamic operation of a C-RAN, then transform the games into weighted potential games and therefore prove the existence of Nash equilibrium (NE) points in the games. Moreover, we propose a distributed algorithm that can converge to the NE point(s) to enable each ONU to choose its vTDM-PON intelligently. As a comparison, we formulate a centralized mixed-integer linear programming model to provide the optimum vTDM-PON formation solution. Simulation results confirm the effectiveness of the design of the proposed game models and distributed algorithm.

Widely Tunable Two-Section Directly Modulated DBR Lasers for TWDM-PON System**Supported by the National Key Project under Grant No 2016YFB0402301, the National High Technology Research and Development Program of China under Grant No 2013AA014502, and the National Natural Science Foundation of China under Grant Nos 61635010, 61320106013, 61474112, 61321063 and 61274071.

Wavelength tunable and directly modulated distributed Bragg reflector (DBR) lasers with butt-joint technology are designed, fabricated and characterized. The DBR laser consists of a gain section and a DBR section. To increase the electrical isolation between the gain section and the DBR section, parts of a p-doped material in the isolation region are etched off selectively. Over 2 kΩ isolation resistance is realized ultimately without the need of ion implantation, which simplifies the fabrication process. The laser exhibits high speed modulation with a large tunable range. The 3 dB direct modulation bandwidth of the device is over 8 GHz in a 12 nm tunable range. This widely tunable DBR laser with the simple structure is promising as a colorless light source for the next-generation time and wavelength division multiplexed passive optical network (TWDM-PON) systems.

Hybrid optical wavelength demultiplexer and power combiner for TWDM PON

In this paper, we have proposed a hybrid optical wavelength demultiplexer and power combiner for a hybrid time- and wavelength-division multiplexing (TWDM) passive optical network (PON), i.e., a single passive optical device that functions as a 1×N wavelength demultiplexer for distributing the downstream signal in multiple wavelengths from the optical line terminal (OLT) to the N optical network units (ONUs), and simultaneously as an N×1 power combiner for collecting the upstream signal in the same wavelength from the N ONUs to the OLT. Through a design example of a 32 channel hybrid optical wavelength demultiplexer and power combiner on the silicon-on-insulator platform, our numerical simulation result shows that the insertion loss and adjacent channel crosstalk of the downstream wavelength demultiplexer are as low as 4.6 and −16.3 dB, respectively, while the insertion loss and channel non-uniformity of the upstream power combiner can reach 3.5 and 2.1 dB, respectively. The proposed structure can readily be extended to other material platforms such as the silica-based planar lightwave circuit. Its fabrication process is fully compatible with standard clean-room technologies such as photo-lithography and etching, without any complicated and/or costly approach involved.

Demonstration of flexible multicasting and aggregation functionality for TWDM-PON

The time- and wavelength-division multiplexed passive optical network (TWDM-PON) has been recognized as an attractive solution to provide broadband access for the next-generation networks. In this paper, we propose flexible service multicasting and aggregation functionality for TWDM-PON utilizing multiple-pump four-wave-mixing (FWM) and cyclic arrayed waveguide grating (AWG). With the proposed scheme, multiple TWDM-PON links share a single optical line terminal (OLT), which can greatly reduce the network deployment expense and achieve efficient network resource utilization by load balancing among different optical distribution networks (ODNs). The proposed scheme is compatible with existing TDM-PON infrastructure with fixed-wavelength OLT transmitter, thus smooth service upgrade can be achieved. Utilizing the proposed scheme, we demonstrate a proof-of-concept experiment with 10-Gb/s OOK and 10-Gb/s QPSK orthogonal frequency division multiplexing (OFDM) signal multicasting and aggregating to seven PON links. Compared with back-to-back (BTB) channel, the newly generated multicasting OOK signal and OFDM signal have power penalty of 1.6dB and 2dB at the BER of 10−3, respectively. For the aggregation of multiple channels, no obvious power penalty is observed. What is more, to verify the flexibility of the proposed scheme, we reconfigure the wavelength selective switch (WSS) and adjust the number of pumps to realize flexible multicasting functionality. One to three, one to seven, one to thirteen and one to twenty-one multicasting are achieved without modifying OLT structure.

Traffic-aware energy saving scheme with modularization supporting in TWDM-PON

Abstract Time and wavelength division multiplexed passive optical network (TWDM-PON) is considered to be a primary solution for next-generation passive optical network stage 2 (NG-PON2). Due to the feature of multi-wavelength transmission of TWDM-PON, some of the transmitters/receivers at the optical line terminal (OLT) could be shut down to reduce the energy consumption. Therefore, a novel scheme called traffic-aware energy saving scheme with modularization supporting is proposed. Through establishing the modular energy consumption model of OLT, the wavelength transmitters/receivers at OLT could be switched on or shut down adaptively depending on sensing the status of network traffic load, thus the energy consumption of OLT will be effectively reduced. Furthermore, exploring the technology of optical network unit (ONU) modularization, each module of ONU could be switched to sleep or active mode independently in order to reduce the energy consumption of ONU. Simultaneously, the polling sequence of ONU could be changed dynamically via sensing the packet arrival time. In order to guarantee the delay performance of network traffic, the sub-cycle division strategy is designed to transmit the real-time traffic preferentially. Finally, simulation results verify that the proposed scheme is able to reduce the energy consumption of the network while maintaining the traffic delay performance.

Novel ring-based architecture for TWDM-PON with high reliability and flexible extensibility

Time and wavelength division multiplexed passive optical network (TWDM-PON) was determined as a primary solution to NG-PON2 by the full service access network (FSAN) in 2012. Since then, TWDM-PON has been applied to a wider set of applications, including those that are outage sensitive and expansion flexible. So the protection techniques with reliability and flexibility should be studied to address the above needs. In this paper, we propose a novel ring-based architecture for TWDM-PON. The architecture can provide reliable ring protection scheme against a fiber fault occurring on main ring (MR), sub-ring (SR) or last mile ring (LMR). In addition, we exploit the extended node (EN) to realize the network expansion conveniently and smoothly for the flexible extensibility. Thus, more remote nodes(RNs) and optical network units (ONUs) could access this architecture through EN. Moreover, in order to further improve reliability of the network, we design the 1:1 protection scheme against the connected fiber fault between RN and EN. The results show that the proposed architecture has a recovery time of 17ms under protection mode and the reliability of the network is also illustrated to be greatly improved compared to the network without protection. As the number of ONUs increases, the average cost of each ONU could be gradually reduced. Finally, the simulations verify the feasibility of the architecture.

Cost-Minimized Design for TWDM-PON-Based 5G Mobile Backhaul Networks

Dense deployment of small cells would be required to provide for high capacity and universal access to future fifth-generation (5G) mobile networks. However, this would require cost-effective and reliable backhaul connectivity between these small cells. Time and wavelength division multiplexed passive optical networks (TWDM-PONs) are considered a promising choice for this purpose. In this paper,we consider the cost-minimized design of a backhaul network for a 5G mobile system using TWDM-PON. For this, equipment and deployment costs are considered, and the design is based on satisfying network constraints such as the maximum number of subscribers per optical line terminal and themaximumnumber of subscribers per wavelength. Considering the fact that many small cell base stations are dispersed over an extensive wireless coverage, a K-means clustering-based algorithm is proposed for the optimal solution. The strategies of using multistage remote nodes and cable conduit sharing are applied to further reduce the labor cost of trenching and laying fibers. Our simulation results show that the proposed approaches can substantially reduce the backhauling cost in comparison with the traditional intuitive random-cut sectoring approach.

Delay fairness in reconfigurable and energy efficient TWDM PON

In Time and Wavelength Division Multiplexed (TWDM) Passive Optical Networks (PONs), dynamically (de)activating Optical Subscriber Units (OSUs) and assigning Optical Network Units (ONUs) to the active OSUs helps improving the OLT energy efficiency and balancing the network load.However, energy efficiency improvement is traded with a delay increase due to the finite ONU tuning speed and the potential increase of the normalized load with respect to the number of active OSUs. Moreover, even though load balance potentially assures delay balance, the scheduling and assignment of ONUs to OSUs might cause ONU delay unbalance (i.e., delay unfairness). Indeed, if an ONU is forced to tune at each reconfiguration it suffers a high delay penalty due to its limited tuning time.In this study, the impact of the ONU scheduling and assignment to OSUs upon network reconfiguration on the average frame delay unbalance is evaluated. Then, a method that balances the average frame delay by swapping the tuning ONU upon reconfiguration is proposed, for some critical scenarios. Simulation and experimental results show that the delay unbalance is large when the number of active ONUs is small (e.g., at network start up or when the majority of the ONUs is inactive/sleeping). In this case, the proposed method effectively balances the delay experienced by ONUs without impacting the OLT energy savings.

Flexible tunable optical transceiver based on field-programmable gate array for time and wavelength-division multiplexed passive optical network systems

Time- and wavelength-division multiplexed passive optical networks (TWDM-PONs) have been selected by the full services access network community as the most suitable technology for next-generation optical access networks. A key technology in TWDM-PON is the colorless optical network unit transceiver. This paper proposes a flexible, tunable optical transceiver that uses directly modulated tunable lasers. Using a field-programmable gate array (FPGA), programmable reconfigurations and testing capabilities can be embedded into the transceiver in order to implement wavelength control, signal generation, pre-emphasis for upstream, and a bit error rate (BER) test for the downstream. To ensure high-quality signal generation at different bitrates, impedance matching between the laser driver circuit and the laser diodes is optimized. Using the proposed transceiver, three-section-distributed Bragg reflector tunable lasers at or below 2.5 Gb/s direct modulation through a 40-km standard mode fiber transmission were successfully implemented.

Bidirectional EDFAs That Support E2-Class Power Budget of TWDM-PON Without Using Gain-Clamped Light Source

This paper introduces an Erbium-doped fiber amplifier (EDFA)-based solution to support the maximum link budget class (E2) of the time- and wavelength-division multiplexed passive optical network (TWDM-PON). Bidirectional EDFAs, each consisting of an L-band EDFA as the downstream WDM signal booster and a C-band EDFA as the upstream WDM signal preamplifier, are utilized to reduce the number of EDFAs required. Technical challenges are how to widen the input dynamic range of upstream burst signal detection using a preamplifier, and how to reduce the number of optical components. To resolve these issues, a novel device configuration is proposed, where a very short C-band EDF is pumped by a high-power pump light and the pump power unused by the C-band EDF is reused to pump the L-band EDF. A prototype integrated in an MSA-size package is developed, and its effectiveness in supporting the E2-class power budget is experimentally confirmed.