Optical Network Unit Research Articles

Demonstration of the high-security 3D-CAP scheme in multi-core fiber transmission

In this paper, the high-security three-dimensional (3D) carrier-less amplitude-phase (CAP) modulation based on 3D space constellation masking in multi-core fiber (MCF) transmission is proposed. Logistic Map model and Four-wing hyper-chaotic systems are employed to implement bit-level encryption, displacement masking, and space masking. This way, we achieved a key space of 1 × 1083 size, which resists violent attacks, and improves the physical layer security of the system. The superposition combined two chaotic models reduces the difficulty of implementation and enables more security for constellation encryption. A 280 Gb/s encrypted 3D-CAP32 signal transmission over 2.5 km MCF is experimentally demonstrated. The experimental results show that the proposed scheme can effectively resist illegal attack from an un-authorized optical network unit (ONU), and compared with an unencrypted 3D-CAP32 signal, the encrypted 3D-CAP32 signal has a receiver sensitivity penalty of 0.38 dB in a back-to-back configuration at a BER of 1 × 10−3. It is a strong candidate for the future highly-secured optical access network.

A Security Detection Scheme Based on TTD for NG-PON2 Fiber Links

For improving the physical layer security of next generation passive optical network (NG-PON2), we propose a security detection scheme by detecting the terminal thermal distribution (TTD) at the optical fiber end face on the optical network unit (ONU), when the fiber link is tapped. The principle of the scheme is given that the thermal energy always exists in fiber links and the TTD at the optical fiber end face can be detected. When the link tapping occurs, the leaking light energy induced by bending converts into the thermal energy, which changes the TTD at the optical fiber end face on ONU of NG-PON2. The TTD models of core and cladding layers at the optical fiber end face owing to bending are built with the double cylindrical coordinate systems, based on the bending loss formula of optical fiber and thermodynamic coupling theory. Then, the simulations for the TTD models are carried out under the different conditions of input power, bending radius and distant of detected point from the center of optical fiber end face, respectively. The simulation results indicate three conditions above are the main factors affecting the TTD changes. Finally, we set up an experimental system in the lab, using a light-emitting diode at 1550nm, and a thermal microscope (Telops-FAST-IR). The experimental results show the TTD of core layer at the optical fiber (G.652D) end face changes 72.5% at the input power of 1dBm with the bending radius from 10mm to 5mm, and are consistent with the simulation ones.

Design and simulation of optical network architecture based on point-to-multipoint direct communication between optical network units for data center

Design and simulation of optical network architecture based on point-to-multipoint direct communication between optical network units for data center

SOA Assisted Wavelength Reusing for 25G Colorless PON With Low-Cost 10G EAM

This paper demonstrates a C-band 25G colorless passive optical network (PON) based on semiconductor optical amplifier (SOA) and 10G electro-absorption modulator (EAM). The experimental results show that the SOA in the optical network unit (ONU) can erase the downlink signal by taking advantage of the gain saturation feature, realizing the reuse of downstream wavelength. Meanwhile, the SOA gain can compensate for the EAM loss by optimizing the current and injection power. Apart from this, equalization algorithms at the optical line terminal are investigated for linear and nonlinear impairments compensation. Besides, the system robustness to the ASE and the maximum transmission speed are also evaluated. Finally, the system capacity can reach up to 25 Gbps with NRZ format at a bit-error ratio threshold of 2 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">−2</sup> , proving that this system is a promising technology for future high-speed colorless 2 × 25G or 4 × 25G Wavelength division Multiplexing (WDM) PON system.

Determination of optimized sleep interval for 10 gigabit-passive optical network using learning intelligence

&lt;span&gt;The overall aim of this project is to investigate the application of a machine learning method in finding the optimized length of asleep time interval (T&lt;sub&gt;AS&lt;/sub&gt;) in a cyclic sleep mechanism (CSM). Since past decade, the implementations of CSM in the optical network unit (ONU) to reduce the energy consumption in 10 gigabit-passive optical network (XG-PON) were extensively researched. However, the newest era sees the emergence of various network traffic with stringent demands that require further improvements on the T&lt;sub&gt;AS&lt;/sub&gt; selection. Since conventional methods utilize complex algorithm, this paper presents the employment of an artificial neural network (ANN) to facilitate ONU to determine the optimized T&lt;sub&gt;AS&lt;/sub&gt; values using learning from past experiences. Prior to simulation, theoretical analysis was done using the M/G/1 queueing system. The ANN was than trained and tested for the XG-PON network for optimal T&lt;sub&gt;AS&lt;/sub&gt; decisions. Results have shown that towards higher network load, a decreasing T&lt;sub&gt;AS&lt;/sub&gt; trend was observed from both methods. A wider T&lt;sub&gt;AS&lt;/sub&gt; range was recorded from the ANN network as compared to the theoretical values. Therefore, these findings will benefit the network operators to have a flexibility measure in determining the optimal T&lt;sub&gt;AS&lt;/sub&gt; values at current network conditions.&lt;/span&gt;

A novel bidirectional entirely passive remote node design for ring topology based NG-PON2 with fiber faults protection capability

The service disruptions in passive optical networks (PONs) due to fiber or node failure is an important issue. In the conventional star topology time and wavelength division multiplexing (TWDM) based next generation passive optical network stage 2 (NG-PON2), there is no provision to restore the service if the fiber between remote node (RN) and optical network unit (ONU) fails. In this paper, we proposed a novel entirely passive node design for ring based NG-PON2 which provides fiber fault protection against any fiber break between RNs. The working of the proposed node is verified by simulating normal conditions and fault conditions. It is observed that in the case of fiber failure, the affected ONUs can still communicate with the optical line terminal (OLT). The performance of the system has been analyzed in terms of bit error rate (BER), and the BER <10−9 confirms the correct working of the system.

A hybrid bandwith allocation algorithm for EPON-WiMAX integrated networks based on auction process

Integration of Ethernet passive optical network and WiMAX technologies is viewed as a great solution for next-generation broadband access networks. In the systems adopting this strategy, weighty bandwidth allocation schemes are fundamental to fulfill the quality of service and fairness requirements of different traffic classes. Existing proposals to overcome the bandwidth allocation problem in EPON/WiMAX networks dismiss collaboration between the self-interested EPON and WiMAX service providers. This study presents a novel EPON-based semi-dynamic bandwidth allocation algorithm to allow the integration process. In the proposed algorithm depending on the auction process, the optical line terminal runs an auction to adequately post the optical network unit bandwidth that distributes the most elevated bidders based on the measurement of the accessible bandwidth. Simulation results demonstrate massive upgrades compared with fair sharing using dual-service-level agreements, limited-service interleaved polling with adaptive cycle time methods, bandwidth allocation strategy using Stackelberg game, and bandwidth allocation strategy using coalition game regarding the quality of service parameters such as throughput and time delay. This will be extremely helpful for optical system upgrading and improvement with minimal effort.

Full-duplex hybrid optical link with 40 Gbit/s 16-QAM signal for wired or wireless selective access based on polarization division multiplexing.

A full-duplex hybrid optical link with 40 Gbit/s 16-ary quadrature amplitude modulation (16-QAM) signal based on polarization division multiplexing (PDM) is proposed, which can provide wired or wireless selective access for the user terminals. The 16-QAM downlink signal for wired and wireless accesses is only modulated onto one of the polarization states of the light wave. Then the generated data-bearing optical tone orthogonally combines with the other polarization state to constitute the downlink optical signal. At the hybrid optical network unit (HONU), an ordinary laser with the fixed wavelength is not only used to provide the optical local oscillator (OLO) for downlink wireless access but also the optical carrier for its uplink, while the OLO and uplink optical carrier for wired access are extracted from the downlink optical signal. Moreover, since the downlink optical signal is a baseband one with two orthogonal polarization states, the spectrum efficiency of our proposed scheme is high. The obtained constellations and eye diagrams of the demodulated 16-QAM downlink and uplink signals for wired and wireless accesses show that our proposed full-duplex hybrid optical link can still maintain a good transmission performance after being transmitted over 20 km standard single mode fiber (SSMF).

OOK-RSOA Modülasyonunu Kullanan Çift Yönlü Karma Optik IM/DD OFDM WDM-PON Sisteminin Performansının İncelenmesi

In this paper, we have studied and simulated bidirectional hybrid long reach Intensity Modulated and Direct Detected Optical Orthogonal Frequency Division Multiplexing Wavelength Division Multiplexing Passive Optical Network (IM/DD-OFDM-WDM-PON) with 100 Gbps of various M-Quadrature Amplitude Modulation (M-QAM) in transmitted downstream signal and 2.5 Gbps On-Off keying (OOK) upstream signal using wavelength reused technique by Reflective Semiconductor Optical Amplifier (RSOA) at Optical Network Unit (ONU). The simple, low cost and colorless long-haul IM/DD-OFDM-WDM-PON based on RSOA is designed to support extreme data rate signal by utilizing Dispersion Compensating Fiber (DCF). All results prove that IM/DD-OFDM-WDM-PON can achieve good Bit Error Rate (BER) performance over propagation length of (300 km for 4-QAM), (200 km for 16-QAM) and (50 km for 64-QAM). For comparison, the performance of the network is studied in terms of BER, the effect of the propagation length on the constellation diagram, and the relation of BER versus bit energy and noise density ratio (Eb/No).

Bayesian auction game theory-based DBA for XG symmetrical PON.

The next-generation passive optical networks (NG-PONs) (i.e., 50G-PON and Time-division-multiplexing/Wavelength-division-multiplexing, TWDM-PON) offer very high bandwidth with improved quality of service. In these PONs, the role of efficient Dynamic bandwidth allocation (DBA) becomes even more important in reducing the upstream delays, bandwidth waste and reducing the upstream delays and delay variance. These qualities of service metrics lead to improved Quality of Experience (QoE) for the end-users in addition to increased revenue for the service providers. This study introduces the game theory concept in the bandwidth distribution process in PON. Specifically, the Bayesian auction game theory (BAGT) process is used in the DBA process to address the unfair and inefficient distribution of upstream bandwidth to the optical network units (ONUs) in XG symmetrical PON(XGs-PON). The proposed BAGT scheme allocates the excess bandwidth to the entire ONUs in proportion to their demands reported via the bidding process. To validate the performance of the BAGT scheme, we also compare it with other existing DBA schemes namely; proportional allocation schemes (PAS), improved bandwidth utilization (IBU), and optimized round-robin (ORR) methods. The simulation results show that the proposed scheme results in higher system throughput and lower upstream delays than the other schemes. BAGT DBA also improves the bandwidth utilization by up to 38% to 50% compared to IBU, ORR, and PAS schemes and exhibits the minimum frame loss ratio.

Bidirectional colorless WDM-PON RoF system with large spurious free dynamic range

A bidirectional colorless wavelength-division-multiplexed passive optical network radio over fiber system with a large spurious-free dynamic range (SFDR) is proposed. By separating the unmodulated optical carrier from the polarization multiplexed optical signal in the optical network unit, upstream wavelength reuse is realized. By adjusting the angle and phase difference between the orthogonal optical polarization modes, third-order intermodulation distortion (IMD3) suppression of the downstream link is realized. The periodic power fading caused by dispersion in the system is solved through single sideband modulation. Experiments have verified the wavelength reuse effect of the upstream link. Compared with the traditional link based on a Mach–Zehnder modulator, the periodic power fading of the system is suppressed under different radio frequencies (RFs) and fiber lengths. The IMD3 of the downstream link is suppressed, and the SFDR is improved by more than 17 dB. Also, the proposed system is tested with a 16 quadrature amplitude modulation RF signal in the experiment, where a good adjacent channel power ratio and error vector magnitude of the system are obtained.

Cloud‐edge collaboration based peer to peer services redirection strategy for passive optical network

With the increasing number of fibre access users, P2P file sharing download traffic has gradually become one of the enormous bandwidth consumptions for the access network. Localizing traffic could save bandwidth and reduce latency, but it caused optical line terminal (OLT) overload problems. A cloud-edge collaboration technology (IRS-CECT) based P2P redirection strategy is proposed for this problem. OLT assumes the role of the cloud computing centre in the strategy. Optical network unit (ONU) serves as an edge computing node to share traffic load for the cloud computing centre. ONU intercepts the upstream query packets for OLT. This strategy can reduce the problem of OLT overload caused by increasing users. Simulation results indicate that the IRS-CECT strategy can reduce the delay by nearly half and reduce the traffic load on the cloud computing centre OLT.

Channel Characteristics Based Adjustable Fingerprint for Identity Authentication in WDM-PON With Deep Neural Networks

Wavelength-division-multiplexed passive optical network (WDM-PON) has been widely deployed for the high-speed, reliable transmission and low-cost properties. The physical layer identity authentication in WDM-PON becomes increasingly prominent. Recently, many device fingerprint based identity authentication schemes are proposed. However, these schemes only realize constant fingerprint, which will be acquired by illegal ONU after optical spectrum analysis. Therefore, the higher-level security requirement cannot be satisfied. To solve the problem, we propose a physical layer identity authentication method in WDM-PON by exploiting the channel characteristics based adjustable fingerprint with deep neural networks (DNNs). By secretly negotiating with legal optical network units (ONUs) on the lengths of the local fibers applied by them, the optical line terminal (OLT) can acquire the unique channel characteristics fingerprint obtained by each legal ONU. It should be noted that the fingerprint can be adjusted by modifying the length of the local fiber. Moreover, the same number of DNNs as legal ONUs are trained for fingerprint identification. Simulation results show 100% identification accuracy for illegal ONU when the length deviation between two fibers applied by legal ONU and illegal ONU is greater than 1.5 km. Meanwhile, the identity of each legal ONU can be recognized with 100% accuracy.

Dynamic Subcarrier Assignment in OFDMA-PONs Based on Deep Reinforcement Learning

Orthogonal Frequency Division Multiplexing Access Passive Optical Networks (OFDMA-PONs), a solution for the next-generation optical access network, allows multiple optical network units (ONUs) to dynamically share subcarriers (SCs) to support efficient bandwidth allocation. In uplink transmission, multiple ONUs can share orthogonal low bit rate SCs to transmit data at different time slots (TSs) during the transmission cycle. In this paper, the dynamic subcarrier allocation (DSA) scheme based on deep reinforcement learning (DRL) is proposed for various ONU bandwidth requests. The novel scheme jointly allocates time slots, subcarriers, and modulation formats in a dynamic and flexible manner. The ONU can save transmit power by using a lower order modulation format while meeting the delay requirement. The simulation part demonstrates how the proposed DRL-based DSA scheme can be adapted to various situations, including 1) variation in the size of ONU bandwidth requests, and 2) variation in the weight of different indicators. The extensive simulation results show that, for the first time, the proposed DRL-based DSA algorithm achieves optimal traffic latency with substantial power saving, compared with the traditional two-dimensional DSA algorithms.

200 Gbps/λ PON Downstream C-Band Direct-Detection Links with ≥29 dB Power Budget

In this paper we present the simulative analysis of a 200 Gbps per wavelength (λ) 8-level pulse amplitude modulation (PAM-8) downstream communication over up to 20 km single mode fiber (SMF) in C-band based on direct detection (DD) achieving at least a 29 dB link power budget in a PON environment. We use chromatic dispersion digital pre-compensation (CD-DPC) and a dual-arm in-phase and quadrature Mach–Zehnder modulator (IQ-MZM) at the optical line termination (OLT) side, while preserving DD in the optical network unit (ONU). Three receiver digital-signal-processing (DSP) options are analyzed and compared: square-root-like technique (SQRT) in combination with a feed forward equalizer (FFE) and a decision feedback equalizer (DFE), the Volterra nonlinear equalizer (VNLE), and the SQRT in combination with the VNLE. The SQRT can be applied in combination with the VNLE to decrease the receiver DSP complexity while maintaining the required system performance. We show that PAM-8 with CD-DPC and the SQRT in combination with the VNLE is a feasible solution for 200 Gbps per λ downstream C-band transmission for PON.

Enhancing Energy Efficiency of the Doze Mode Mechanism in Ethernet Passive Optical Networks Using Support Vector Regression

An Ethernet passive optical network (EPON) is an optical access network that allows a higher data rate with low power consumption. To improve energy savings for an EPON, the sleep and doze modes for the optical network units (ONUs) play a pivotal role. Many prediction schemes have been proposed to control these modes. To increase the prediction accuracy, this study proposes an energy-efficient approach that uses a support vector regression (SVR) model. A dynamic bandwidth allocation (DBA) scheme called SVR-DBA is designed to allocate bandwidth to ONUs more efficiently and fairly. To determine the effectiveness of the proposed scheme, simulations are performed. The simulation results show that the proposed scheme decreases energy consumption for ONUs by up to 47% and fulfills the quality-of-service (QoS) requirements in terms of delay, jitter, and packet loss.

RNN based EPON dynamic bandwidth allocation algorithm for complex network

Abstract In the development of ethernet passive optical networks (EPONs), quality of service (QoS) support and fairness per optical network unit (ONU) are crucial issues. However, making an elaborate analysis of the existing prediction-based bandwidth allocation algorithm, light load penalty, low prediction precision are pointed out. We present an improved dynamic bandwidth pre-allocation algorithm (R-DBA), which employs recurrent neural network (RNN) to predict the high-priority service traffic in EPON. And we introduce mixed integer linear programming (MILP) for optimally building DBA algorithm. This algorithm achieves the prediction of the high-priority service traffic by RNN during the waiting time and supports bandwidth pre-allocation, thus ensuring the fairness of the bandwidth allocation.

Traffic aware cyclic sleep‐based power consumption model for a passive optical network

AbstractFor a network, a power consumption model is an important tool to test the performance of a network process for different traffic loads. In a Passive optical network (PON), the optical network unit (ONU) is responsible for the major power consumption of PON. Both IEEE and ITU have standardized a cyclic sleep process (CSP) for ONU energy conservation. In next‐generation PON; TWDM and XGS PON, the ONU power contribution has increased further due to higher number of ONUs and ONU being tunable. Therefore, an accurate power consumption model of the CSP process for energy efficiency studies under different traffic conditions is of prime importance. The existing CSP power consumption models do not depict the CSP process accurately especially the inactivity of the ONU in the asleep and sleep aware states are not taken into account which reduce the accuracy of the model. The proposed inactivity aware model (IAM) overcomes these gaps and very accurately models the CSP process, as evident from the results, which are better than earlier model results and quite close to earlier published simulation results. The model is also validated through a simulation‐based study and the simulation results are observed to be very close to the model results with only a 5% deviation.

SOA Amplified 100 Gb/s/λ PAM-4 TDM-PON Supporting PR-30 Power Budget with >18 dB Dynamic Range

Semiconductor optical amplifier (SOA) is considered an excellent candidate for power amplification at O-band due to its low cost and small footprint. In passive optical networks (PONs), SOA is popular as a booster and pre-amplifier to improve the link power budget. However, whether as a booster or pre-amplifier, SOA will induce different degrees of nonlinearity when the output power is high, which degrades the transmission performance of the system and leads to a limited receiver dynamic range. In this paper, we experimentally demonstrate the feasibility of using SOA in both transmitter and receiver sides for power budget improvement in 100 Gb/s/λ four-level pulsed amplitude modulation (PAM-4) time division multiplexed PON (TDM-PON) system at O-band. For compensating the linear and nonlinear impairments induced by transceivers and SOA, a look-up-table (LUT) pre-compensation at the optical line terminal (OLT) side and a simple feed-forward equalizer (FFE) at the optical network unit (ONU) side are adopted for downstream transmission. For upstream transmission, a 2nd-order Volterra nonlinear equalizer (VNLE) is utilized at the OLT side, and no pre-compensation is used at the transmitter of the ONU, which releases the digital signal processing (DSP) pressure of ONUs in a multi-user scenario. For the soft-decision FEC (SD-FEC) threshold (1 × 10−2), the IEEE PR-30 power budget requirement is met, and >18 dB dynamic range is achieved in both 25 km downstream and upstream transmission.

Secure SDM–OFDM signal transmission based on memristive neural network

This paper proposes a physical layer security strategy of space division multiplex orthogonal frequency division multiplexing system based on memristive neural network (MNN). Among them, the two-level chaotic control, the application of the memristive chaotic model with conditional symmetry and the encryption of the MNN are all proposed for the first time in the access network. The memristive chaotic model with conditional symmetry generates 8 multiple masking factors and achieves high-security encryption. In the encryption process, the key space is selected by Logistic mapping, and the MNN encryption mechanism disturbances and compresses bits. The proposed encryption strategy has been proved on the experimental platform. The generated OFDM signals are modulated, which transmit data rate of 124.4 Gb/s over the 2 km multi-core fiber (MCF). Bit error rate (BER) and different anti-interference are analyzed in experiments. The key space of this proposed scheme is 2×10399, which is large enough number to effectively resist any brute force or illegal optical network units (ONUs) intrusion in passive optical network (PON). The results show that the proposed SDM–OFDM​ scheme has high sensitivity and security. This scheme has very reliable safety performance and benefit improvement, and is very promising in the future SDM–OFDM system.