Multiple Access Passive Optical Network Research Articles

Optimization and analysis of Spectral/Spatial optical code division multiple access passive optical network

The deployment of high-capacity transport networks while maintaining strict cost constraints is a formidable challenge for network operators in the era of networks beyond 5G (B5G) and 6G. This work explores the use of a 2D spectral-spatial optical code division multiple access (OCDMA) passive optical network (PON). It optimizes the conventional architecture to minimize the cost of deployment while maintaining desirable transmission capacity. Optimization is performed by developing a PON architecture with 2D double-weight zero cross-correlation (DW-ZCC) code that is able to support high capacity through ideal auto and cross-correlation properties. Furthermore, time delay units are employed after the spectral and spatial encoding process to minimize the use of long-span parallel optical fiber path and reduce the overall cost of deployment. Simulation analysis demonstrates that the proposed system is able to support 128 subscribers, each communicating at 10 Gbps data over a system sensitivity of approximately −21 dB. Capital expenditure (CapEx) analysis also demonstrates the effectiveness of the system optimization and reports substantial cost cuts in deploying the proposed architecture compared with the conventional counterpart.

A predictive TDM-PON resource allocation using the ANN method based on equilibrium points of discrete dynamical systems

Resource allocation is one of the challenges in the time division multiple access (TDM) passive optical network (PON) area. Much research has been done to find an efficient resource allocation method. Using machine learning (ML) and finding proper ML algorithms in predictive dynamic bandwidth allocation remains an open research question. This paper aims to predict resource allocation accurately and efficiently based on historical requests. Artificial neural networks (ANN) with historically allocated bandwidth from different time series are used to build the prediction model. This model is constructed by the normal equation method. The proposed model needs a small dataset for its training phase, while its accuracy is higher than other models. The discrete dynamical system builds to find an equilibrium point, which is a stable point in the system. The proposed model can be implemented as a pre-training, or it can be dynamically refined when the model is running by using some of its output as feedback. The system evaluation verifies that the proposed DBA (EQ-ANN) elevates the quality of service (QoS) metrics, such as system throughput, packet drop probability, and packet means delay. The results show that the system throughput improves by up to 5%, and packet loss improves by up to 15%. Moreover, the prediction accuracy of the system reached 99.48%.

Feasibility analysis of 2-dimensional permutation vector optical code division multiple access passive optical network

This paper analyzes the feasibility of a 2-dimensional (2D) permutation vector (PV) optical code division multiple access (OCDMA) passive optical network (PON) in terms of transmission capacity, network reliability, power budget, and the number of subscribers. The proposed PON is built with a novel 2D PV-OCDMA code having ideal auto- and cross-correlation properties. Furthermore, a ring-based topology at the feeder level and a tree-based topology at the distribution level are utilized to support ubiquitous computing. The proposed architecture also employs multiple remote nodes at the feeder level to facilitate adequate power budget and cardinality for high-capacity applications. Simulation results indicate that the proposed PON elevates system transmission capacity by eliminating phase-induced intensity noise and multiple access interference. Furthermore, reliability analysis using mathematical formalism demonstrates that the proposed architecture can provide a connection availability of ≈0.099993 (5 nines), which is significantly higher than the conventional tree-based topology. Power budget analysis also determines that the proposed PON can support well above 320 subscribers at adequate receiver sensitivity and optical network terminals (ONTs) per remote node.

Performance analysis of a heterogeneous network employing DAPSK based OFDMA-PON

Recent mobile broadband networks require heterogeneous networks supporting high capacity on demand. A hybrid Fiber-Wireless (Fi-Wi) access network integrating Differential Amplitude and Phase Shift Keying (DAPSK) based — Orthogonal Frequency Division Multiple Access (OFDMA) Passive Optical Network (PON) and 4G wireless network using Radio over Fiber (RoF) technique is proposed. The proposed heterogeneous network is simulated, and the performance is analyzed in terms of Bit Error Rate (BER), Error Vector Magnitude (EVM), Capacity, and Spectral efficiency. The proposed network is simulated considering a higher data rate of 10 and 25 Gbps, and the effect of system parameters like Laser Power, Fiber Length, and Number of users is analyzed. The results show that a higher network capacity of 720 Gbps with an average capacity of about 45 Gbps and a higher spectral efficiency of 4.85 bps/Hz is achieved for the multi-user heterogeneous network link with sixteen users. The minimum value of optical power sufficient to achieve the desired BER is found to be −6 dBm. The suitability of the proposed integrated architecture in supporting multiple services is analyzed by considering different services at each UE. The spectral efficiency of the multi-service link varies from 3 to 4 bps/Hz.

Timing Jitter Analysis and Mitigation in Hybrid OFDM-DFMA PONs

Hybrid orthogonal frequency division multiplexing-digital filter multiple access passive optical networks (OFDM-DFMA PONs) offer a cost-effective solution to the challenging requirements of next-generation optical access networks and 5G and beyond radio access networks. It is crucial to consider the impact of timing jitter in any ADC/DAC-based system, therefore this paper presents an in-depth investigation into the impacts of DAC/ADC timing jitter on the hybrid OFDM-DFMA PON's performance. We introduce improved accuracy white and coloured, DAC and ADC timing jitter models, applicable to any DSP-based transmission system. We prove that DAC and ADC timing jitter effects are virtually identical and investigate the effects of white/coloured timing jitter on upstream performance in hybrid OFDM-DFMA PONs and determine the associated jitter-induced optical power penalties. To mitigate against the timing jitter-induced performance degradations, a simple, but highly effective DSP-based technique is implemented which increases robustness against the timing jitter effects and significantly reduces timing jitter-induced optical power penalties. This consequently relaxes DAC/ADC sampling clock jitter requirements and so reduces implementation costs. White (coloured) timing jitter effects are shown to be independent of (dependent on) ONU operating frequency band and a trade-off between DAC and ADC jitter levels can be exploited to reduce ONU costs.

Nonlinear Quantization for Power-Domain Non-Orthogonal Multiple Access Passive Optical Network

A passive optical network (PON) system is required to accommodate multi-services represented by fifth/sixth (5G/6G) mobile communication systems. While maintaining low cost, to meet these requirements (which are high capacity, low latency, and high reliability), the PON system must accommodate a large number of optical network units (ONUs). The use of power-domain non-orthogonal multiple access (PD-NOMA) for PON has been studied to increase the number of accommodatable ONUs. However, with an increase in the ratio of transmitted power between multiplexed ONUs, the effect of quantization noise in the analog-to-digital converter (ADC) is more significant. This study proposes to apply an optimal quantizer based on the Lloyd-Max algorithm (which is a nonlinear quantization algorithm) to PD-NOMA-PON. In general, the Lloyd-Max algorithm requires continuous probability density function when setting the partitions. We adopt a continuous function estimated from the discrete probability distribution extracted by the low-resolution ADC using an expectation maximization algorithm. We conduct experiments to verify the feasibility of the proposed quantizer for the downlink and confirm the improvement of the optical signal-to-noise ratio penalty for all power ratios.

Time-domain uplink synchronization method for a spectral efficient OFDMA-based PON

The feasibility of a time-domain technique, proposed for uplink synchronization of the bandwidth scalable orthogonal frequency division multiple access passive optical network (BS-OFDMA PON), is experimentally demonstrated. The results show that a delay variation of less than 50% of the cyclic prefix is tolerable, relaxing the thin time synchronization required in the uplink of the evaluated architecture. Moreover, we enhance the spectral efficiency of the BS-OFDMA PON by reducing the guard band ( B g ) between the optical carrier and the signal bandwidth, as well as by eliminating the frequency gap ( Δ f G ) between the optical network units. The downlink results demonstrate that Δ f G can be eliminated with negligible performance penalties, and B g can be reduced to almost half the signal bandwidth. Error-free transmissions were achieved after uplink propagation over 45 km of single-mode fibers with received power of ≈ − 16.8 d B m and B g = 450 M H z , with a signal bandwidth of 1 GHz.

Orthogonal Frequency Division Multiple Access Passive Optical Network for 5G Deployment

Orthogonal Frequency Division Multiple Access Passive Optical Network for 5G Deployment

Investigation of a Flexible Downstream Scheme for Sampling Rate and Bandwidth Reduction in Short Reach Communication Systems

We demonstrate a cost- and spectrum-effective orthogonal frequency-division multiple access passive optical network downstream scheme based on multi-band and modified sub-Nyquist sampling over transmission reach of 20km. The sampling rate and bandwidth of ADC are reduced effectively, and double spectrum efficiency is obtained. The aggregate bit rate achieves 50.4 Gb/s. The influence of bit resolution of ADC/DAC is investigated and 8-bit resolution is regarded as a reasonable choice. The performance of receiver sensitivity and nonlinearity tolerance is studied. A 20km PON downstream transmission with splitter ratio of 1:64 is considered and the FEC limit of $3.8\times 10 ^{-3}$ is met. The research results show that the proposed scheme is suitable for the short reach communication systems and could be regarded as a promising candidate for the system beyond NG-PON2.

An optimized architecture to reduce the impact of fiber strands in spectral/spatial optical code division multiple access passive optical networks (OCDMA-PON)

Abstract Exploitation of the spectral/spatial two dimensional optical code division multiple access (2D-OCDMA) systems in passive optical networks (PONs) is not explored extensively due to the fact spatial encoding requires deployment of multiple star couplers in the topology where each coupler is connected to different ends of either transmitter or receiver nodes. As a result, this scheme is not suitable for PON applications because it requires a significant increase in the amount of fiber deployment within the network along with the complexity of implementation to deploy the required star couplers. To deploy spectral/spatial OCDMA systems at PON and reduce the impact of fiber strands, this work proposes and investigates an optimized architecture of 2D-OCDMA for PONs based on enhanced multi-diagonal (EMD) code. Spectral/spatial encoding technique is used to develop 2D-EMD coding algorithm from the existing 1D-EMD scheme. This operation elevates orthogonality between the adjacent codes and supports high capacity through superior noise mitigation at the receiving end. A complete system architecture is developed and implemented in an excessively used software for optical networks implementation and analysis called Optisystem, for analysis under different performance parameters of PON. It is observed that the proposed system provides better performance in terms of transmission capacity, and cardinality, in comparison with existing 1D-EMD code and other 2D-OCDMA counterparts. Analysis shows that for an agreeable BER of 10 - 9 the proposed system can support 192 subscribers each communicating at 2 Gbps of data over 25 km single mode fiber. In terms of capital expenditure (CAPEX), four times cost saving per user is achieved for proposed architecture (PA) over conventional architecture (CA) for nearly similar performance.

Experimental Demonstration of a Real-Time Digital Filter Multiple Access PON With Low Complexity DSP-Based Interference Cancellation

A four-channel, upstream, digital filter multiple access (DFMA) passive optical network (PON) is experimentally demonstrated for the first time in a 26 km single mode fiber (SMF) intensity modulation and direct detection system employing real-time optical network units (ONUs) and optical line terminal (OLT), which are dynamically reconfigurable in terms of channel spectral allocation and signal modulation parameters. To combat physical channel frequency response-induced cross channel interference (CCI) between spectrally overlaid orthogonal channels, a real-time, reconfigurable CCI cancellation (CCIC) function implemented in the OLT receiver digital signal processing (DSP), is demonstrated to significantly improve the DFMA PON performance and robustness in terms of significant reductions in total channel bit error rates (BERs) and individual subcarrier BERs, substantial increases in channel capacities, considerably reduced sensitivity to ONU synchronization, and excellent transparency to the interfering channel's signal modulation format. The tradeoff between the complexity of the CCIC function's filter, in terms of tap count (multiplier elements) and the DFMA PONs performance is optimized to determine the optimum tradeoff. It is shown that the CCIC filter only requires as few as 42 taps to achieve excellent CCIC performance. We also fully analyze the DSP complexity of the transmit and receive DFMA filters and the CCIC filters for varying DFMA channel counts and varying ratios of AD/DA converter sample rate to digital logic clock rate (parallelization factor). It is shown that DFMA filter complexity is independent of channel count and furthermore that for channel counts ≥ 4 the CCIC filter only needs to process ~10 interference-inducing samples per wanted signal sample, resulting in only ~10 multipliers per parallel filter in the CCIC filter. We have therefore successfully demonstrated an ultra-low complexity, real-time CCIC function, which considerably enhances the performance and robustness of DFMA PONs.

Hybrid DFT-Spread OFDM-Digital Filter Multiple Access PONs for Converged 5G Networks

In this paper, we propose hybrid discrete Fourier transform (DFT)-spread orthogonal frequency division multiplexing (OFDM)-digital filter multiple access (DFMA) passive optical networks (PONs) for the first time to the best of our knowledge. In this case, digital filtering based on digital signal processing is applied to individual DFT-spread OFDM signals from various optical network units, and a single fast Fourier transform operation and its following data recovery processes are implemented in a pipelined approach in the optical line terminal. The proposed networks maintain all salient features associated with previously reported hybrid OFDM–DFMA PONs. More importantly, they additionally reduce the upstream signal peak-to-average power ratios by less than 2 dB. As a direct result, in comparison with the hybrid OFDM–DFMA PONs, the proposed PONs increase the upstream system power budget by more than 3 dB and reduce the minimum required digital-to-analog converter/analog-to-digital converter quantization bits by at least 1 bit.

Design and Implementation of Two-Dimensional Enhanced Multi-diagonal Code for High Cardinality OCDMA-PON

This paper proposes the design of a novel two-dimensional enhanced multi-diagonal (2D-EMD) code along with the implementation of corresponding architecture for incoherent optical code division multiple access passive optical network (OCDMA-PON). The proposed algorithm is derived by using spatial coding as second dimension in the existing 1D-EMD code to elevate orthogonality within adjacent codes and minimize the interference of subscribers simultaneously accessing the medium. Performance of the proposed 2D-EMD OCDMA system is analyzed through Gaussian approximation and simulation analysis for an agreeable bit error rate (BER) of $$10^{-9}$$ . Analytic analysis shows that the proposed 2D-EMD OCDMA system support more subscribers in comparison with existing systems based on 2D diluted-perfect difference (2D-DPD) and diagonal eigenvalue unity (DEU) codes. Cardinality of the proposed setup surpasses 2D-DPD and 2D-DEU by 5 and 1.8 times for an acceptable BER of $$10^{-9}$$ . Moreover, the optimal communication requirement is satisfied by 2D-EMD system with lowest effective source power of $$-27$$ dBm at 622 Mbps of data. Simulation analysis through a highly recognized software called Optisystem also validates the mathematical analysis and shows that the proposed system can accommodate large number of subscribers at high data rates. Both analytical and simulation analysis proves that the proposed system is able to support next generation PONs.

Performance Investigation of a Cost- and Power-Effective High Nonlinearity Tolerance OFDMA-PON Scheme Based on Sub-Nyquist Sampling Rate and DFT-Spread

We investigate the performance of a cost- and power-effective high nonlinearity tolerance orthogonal frequency-division multiple access passive optical network scheme based on sub-Nyquist sampling and discrete Fourier transform spread. The analog-to-digital converter with a sampling rate below the Nyquist sampling rate is used for signal detection for each optical network unit. The complicated pre-process procedure is located in the optical line terminal. Only Low-point FFT and IDFT procedures are required in the ONU, reducing the computational complexity and power consumption in the ONU, and the sampling rate of ADC, and improve the cost- and power-efficiency effectively. Moreover, the peak-to-average power ratio is reduced effectively with the scheme. The simulation results show that the measured bit error ratio of each ONU signal well less than the forward-error correction limit of 3.8 × 10 -3 is obtained after 40-km standard single mode fiber transmission.

Hybrid OFDM-Digital Filter Multiple Access PONs

Hybrid orthogonal frequency division multiplexing (OFDM) digital filter multiple access (DFMA) passive optical networks (PONs) are, for the first time, proposed and extensively investigated, where digital signal processing (DSP) based software-reconfigurable digital filtering is employed for each individual OFDM signal from various optical network units (ONUs), and a single fast Fourier transform operation and its following data recovery processes are implemented in a pipelined approach in the optical line terminal. As a direct result of combining both OFDMA and DFMA PON characteristics, the proposed hybrid OFDM-DFMA PON still maintains highly desirable features associated with DFMA PONs, more importantly, it also offers a number of unique advantages including great relaxation of digital filter DSP complexity and considerable reduction in transceiver cost, significantly enhanced upstream PON performance and its robustness and flexibility, as well as excellent backward compatibility with existing OFDM-based 4G networks. In this paper, an analytical hybrid OFDM-DFMA PON model is developed, and numerical simulations are performed to verify the validity of the proposed technique and also to examine the upstream hybrid OFDM-DFMA PON performance characteristics over representative 25-km standard single mode fibre IMDD PON systems. It is shown that in comparison with the DFMA PONs, the hybrid OFDM-DFMA PON can improve the upstream ONU EVM performance by >10 dB for relatively large received optical powers, and also increases the differential ONU launch power dynamic range by as large as 16 dB.

Power budget of 25-Gb/s digital orthogonal filter multiple access PONs with 10G-class optics

Abstract Power budget is a key factor that should be considered in intensity modulation and direct detection (IM/DD) passive optical networks (PONs). Based on the low-cost 10G-class electro-absorption modulated laser (EML) operating at C-band, we not only experimentally and theoretically investigate the interplay between the chromatic dispersion, the chirp of EML, and the self-phase modulation (SPM), but also explore the influences of the resolution and timing jitter of the analog to digital converter (ADC). Both theoretical and experimental results show that high power budget can be effectively achieved by making full use of the high launch power induced SPM effect and EML-induced frequency chirp. Based on the 10-G transmitter optical sub-assembly (TOSA) and receiver optical sub-assembly (ROSA), we successfully realize 25 Gb/s signal transmission at C-band over 25 km standard single mode fiber (SSMF) in IM/DD PON system. Even the worst performing bands can still achieve 25 dB power budget. The proposed scheme in this work has a potential application in future cost-effective optical access networks.

Individual Stokes-Vector-Based SOP Recovery in CO-OFDMA-PON Uplink Transmission

The state of polarization (SOP) is a critical issue faced by the single-wavelength-based orthogonal frequency division multiple-access passive optical networks, because each optical network unit uses different polarization-sensitive optical devices and paths. To compensate SOP variation, an individual Stokes vector-based SOP recovery (ISVSR) technique is proposed. A single pilot-tone-based SOP compensation was individually applied and experimentally verified the effect of the ISVSR technique in the self-coherent reflective passive optical network uplink transmission. By employing individual SOP recovery, a root-mean-square compensation error and bit error rate close to zero were experimentally achieved. Consequently, the SOP variation can be quickly and accurately compensated without requiring hardware-based complex polarization control or installation of expensive devices.

Multiplicative PIC detection for OCDMA systems with non‐negativity constraints

Non-negativity constraints arise naturally in many applications such as medical and astronomical imaging. These constraints have been recently exploited in the optical communication field where a projected parallel interference cancelation detector has been developed within the context of cancelling multi-access interference in upstream on-off-keying optical code division multiple access passive optical networks; the latter possess the property that the transmitted data symbols are non-negative. The authors build upon these results and propose a new parallel interference cancellation structure with better features and improved performance. This detector is characterised by a multiplicative update equation and it exhibits a number of unique and desirable features such as stability and smooth convergence behaviour even for highly loaded systems. Up to our knowledge, this structure has not been proposed before either in optical or in wireless communication field. Simulation results are promising and further improvements are possible.

Physical-Enhanced Secure Strategy for OFDMA-PON Using Chaos and Deoxyribonucleic Acid Encoding

Due to massive parallelism, huge storage, and ultralow power consumption characteristics of deoxyribonucleic acid (DNA), we propose a secure orthogonal frequency-division multiple access passive optical network (OFDMA-PON), using chaos encryption and DNA encoding. In this scheme, the transmitted bit data are interleaved according to DNA operation rules, and the encoding and operation rules are randomly controlled by using a chaotic map. This DNA encoding can improve the complexity and the random characteristic of the chaotic encrypted sequences. A physical layer secures OFDMA-PON system with 36.77-Gb/s downstream signal, and the 15.45-Gb/s upstream signal is successfully experimentally demonstrated. The experimental results verify that the chaos and DNA encoding based physical layer security enhancement technique can suggest an effective solution for future physically secured OFDMA networks.

All-optical VPN utilizing DSP-based digital orthogonal filters access for PONs

Utilizing digital filtering-enabled signal multiplexing and de-multiplexing, a cost-effective all-optical virtual private network (VPN) system is proposed, for the first time to our best knowledge, in digital filter multiple access passive optical networks (DFMA-PONs). Based on the DFMA technology, the proposed system can be easily designed to meet the requirements of next generation network’s flexibility, elasticity, adaptability and compatibility. Through dynamic digital filter allocation and recycling, the proposed all-optical VPN system can provide dynamic establishments and cancellations of multiple VPN communications with arbitrary traffic volumes. More importantly, due to the employment of DFMA technology, the system is not limited to a fixed signal format and different signal formats such as pulse amplitude modulation (PAM), quadrature amplitude modulation (QAM) and orthogonal frequency division multiplexing (OFDM) can be used. Moreover, one transceiver is sufficient to simultaneously transmit upstream (US)/VPN data to optical line terminal (OLT) or other VPN optical network units (ONUs), thus leading to great reduction in network constructions and operation expenditures. The proposed all-optical VPN system is demonstrated with the transceiver incorporating the formats of QAM and OFDM, which can be made transparent to downstream (DS), US and VPN communications. The bit error rates (BERs) of DS, US and VPN for OFDM signals are below the forward-error-correction (FEC) limit of 3.8×10−3 when the received optical powers are about −16.8 dBm, −14.5 dBm and −15.7 dBm, respectively.