Orthogonal Frequency-division Multiple Access Passive Optical Network Research Articles

Multiple-Noise-Tolerant CO-OFDMA-PON Uplink Multiple Access Using AM-DAPSK-OFDM With Reflective ONUs

A reflective coherent orthogonal frequency-division multiple-access (OFDMA) passive optical network (PON) based on differential amplitude and phase-shift keying (DAPSK) OFDM is proposed herein. In the conventional OFDMA–PON uplink transmission, each optical network unit (ONU) signal has different channel and phase-noise characteristics. In addition, each ONU has an independent laser source; therefore, the carrier frequency offset (CFO) differs among the ONUs. These multiple noises worsen as the number of ONUs increases and adversely affect the spectral bandwidth and system complexity. The proposed system using reflective-type ONUs avoids multiple CFOs because every ONU shares the same laser source, which is transmitted from an optical line terminator. Moreover, by applying a differential modulation scheme to OFDM, we resolve the multiple channel and phase noises without spectral efficiency loss and system complexity increase. The spectral efficiency is maximized using an adaptive modulation technique. The proposed system is experimentally demonstrated in a 20-km OFDMA–PON uplink transmission link with two reflective ONUs. The results confirm the possibility of uplink multiple access without multiple-noise compensation processes. The optimal spectral efficiency in terms of bandwidth size and number of subcarriers is analyzed.

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.

Fairness-Aware Dynamic Sub-Carrier Allocation in Distance-Adaptive Modulation OFDMA-PON for Elastic Lambda Aggregation Networks

In this paper, fairness-aware dynamic subcarrier allocation (DSA) in a distance-adaptive modulation orthogonal frequency division multiple access passive optical network (OFDMA-PON) is proposed and experimentally demonstrated for elastic lambda aggregation networks (EXANs). By applying the distance-adaptive modulation function to OFDMA-PONs, the system can change the transmission parameters (modulation level and symbol rate) for each user according to the user's end-to-end optical loss, which will yield additional bits. Meanwhile, by applying our proposed DSA algorithm, which allocates sub-carriers to users based on transmission parameters and traffic demands, the additional bits can be shared by all users in a fair manner regardless of a user's end-to-end optical loss. This paper conducts a real-time demonstration using an optical coherent OFDMA transceiver and a medium-access control board. The experiments confirm that our algorithm can greatly improve fairness in terms of frame loss rate among users compared to fixed sub-carrier allocation.

Single Subcarrier Gold Sequences Modulated Timing Synchronization for Upstream OFDMA-PON

In this paper, we propose a timing synchronization scheme based on Gold sequences modulated on a single subcarrier for the orthogonal frequency-division multiple access passive optical network (OFDMA-PON). The intensity-modulation and direct-detection real-time experimental demonstrations are carried out over 25-km standard SMF, the performance of the synchronization is investigated by using two optical network units (ONUs) and one optical line terminal based on field-programmable gate array. The results show that the accurate timing symbol synchronization can be achieved at received optical power as low as −21 dBm on the condition of sampling frequency offset range from 0 to 70 ppm between two ONUs. The measured bit error rate is below the forward error correction threshold for both ONUs at received optical power of −18 dBm.

An effective sampling clock synchronization method for continuous- and burst-mode transmission in OFDMA-PONs

A sampling frequency offset (SFO) estimation and compensation method based on frequency domain correlation of long training symbols for orthogonal frequency division multiple access passive optical network (OFDMA-PON) is experimentally demonstrated, which shows excellent performances in transmissions of continuous- and burst-mode. For continuous-mode transmission under a certain SFO, the proposed scheme can perform effectively in a wide received optical power (RoP) range from −8dBm to −2dBm and has high estimation veracity and a large applicable range as large as 100ppm at a certain RoP. Similar behavior is also demonstrated under burst-mode transmission with tiny performance degradation caused by the fact that the algorithm needs time to reach a stable status of synchronization.

Optical-Beat-Induced Multi-User-Interference Reduction in Single Wavelength OFDMA PON Upstream Multiple Access Systems With Self-Homodyne Coherent Detection

We propose a novel technique for mitigating the optical-beat-induced multi-user-interference (MUI) between the upstream multiple access signals in an orthogonal frequency division multiple access (OFDMA) passive optical network (PON). To provide upstream multiple access on a single-wavelength orthogonal frequency division multiplexing optical access network, optical beating interference and polarization diverseness are critical issues that severely degrade system performance. By using the proposed total intensity aggregation with self-homodyne coherent detection, we experimentally demonstrated stable transmission performance by reducing MUI in OFDMA PON upstream multiple access transmission.

Determination of Number of Upstream Subcarriers to Minimize Cycle Time in OFDMA-PON Using Interleaved Polling Method

In an orthogonal frequency-division multiple access passive optical network (OFDMAPON) using an interleaved polling method, delay is increased by long cycle time, where the cycle time is the time duration between the current and next upstream transmissions. The cycle time is affected by the number of upstream subcarriers for an optical network unit (ONU). Available subcarriers are limited due to the system implementation cost, but the small number of upstream subcarriers increases the cycle time in sending the same amount of data. In this paper, we determine the number of upstream subcarriers to guarantee low delay under a gated service discipline.

Staged optimization algorithms based MAC dynamic bandwidth allocation for OFDMA-PON

Orthogonal frequency division multiple access passive optical network (OFDMA-PON) has being considered as a promising solution for next generation PONs due to its high spectral efficiency and flexible bandwidth allocation scheme. In order to take full advantage of these merits of OFDMA-PON, a high-efficiency medium access control (MAC) dynamic bandwidth allocation (DBA) scheme is needed. In this paper, we propose two DBA algorithms which can act on two different stages of a resource allocation process. To achieve higher bandwidth utilization and ensure the equity of ONUs, we propose a DBA algorithm based on frame structure for the stage of physical layer mapping. Targeting the global quality of service (QoS) of OFDMA-PON, we propose a full-range DBA algorithm with service level agreement (SLA) and class of service (CoS) for the stage of bandwidth allocation arbitration. The performance of the proposed MAC DBA scheme containing these two algorithms is evaluated using numerical simulations. Simulations of a 15Gbps network with 1024 sub-carriers and 32 ONUs demonstrate the maximum network throughput of 14.87Gbps and the maximum packet delay of 1.45ms for the highest priority CoS under high load condition.

Analysis of Modulation Order to Guarantee Real-Time Service Throughputs in OFDMA-PON

In an orthogonal frequency-division multiple access passive optical network (OFDMA-PON), each optical network unit (ONU) chooses a modulation format based on the signal-to-noise ratio (SNR) at its receiver. An ONU with a high SNR can use a high-order modulation format to increase its transmission efficiency. When upstream resources are fully utilized, this increases an aggregated upstream throughput by ONUs, but the throughput is varied by ONUs' modulation orders. To guarantee upstream throughputs of real-time services, we first estimate the network throughout in a case that a total upstream resource is fully and fairly distributed to ONUs. By using the estimation, then, we present the lowest order of available modulation formats for the throughput guarantee. We investigate how the modulation order affects the number of ONUs that can be serviced in the OFDMA-PON.

Analysis of optical beat interference noise suppression using RF‐clipping tone in OFDMA‐PON uplink transmission

ABSTRACTIn orthogonal frequency division multiple access‐passive optical network (OFDMA‐PON) uplink transmission with a direct detection system, the optical beat interference (OBI) noise is a very critical issue in regard to channel performance degradation. We have proposed a novel technique to suppress the OBI noise in intensity modulation and direct detection OFDMA‐PON links by using an optical spectrum broadening method using the RF‐clipping tone to improve the SNR of the discrete multitone modulation (DMT) signal with OBI noise suppression. We also experimentally analyzed the dependency of the RF clipping tone on the OBI noise suppression and dither effect. The results show that the received DMT signal in the optical line terminal can achieve 3 Gb/s over a 23 km SSMF with a BER of 2.3×10−4. © 2014 Wiley Periodicals, Inc. Microwave Opt Technol Lett 56:2706–2711, 2014

Suppression of optical beat interference-noise in orthogonal frequency division multiple access-passive optical network link using self-homodyne balanced detection

A new technique, which reduces optical beat interference (OBI) noise in orthogonal frequency division multiple access-passive optical network (OFDMA-PON) links, is proposed. A self-homodyne balanced detection, which uses a single laser for the optical line terminal (OLT) as well as for the optical network unit (ONU), reduces OBI noise and also improves the signal to noise ratio (SNR) of the discrete multi-tone (DMT) signal. The proposed scheme is verified by transmitting quadrature phase shift keying (QPSK)-modulated DMT signal over a 20-km single mode fiber. The optical signal to noise ratio (OSNR), that is required for BER of 10−5, is reduced by 2dB in the balanced detection compared with a single channel due to the cancellation of OBI noise in conjunction with the local laser.

基于光环路正交频分多址无源光网络的光拍频噪声避免方案及性能仿真

In Orthogonal Frequency Division Multiple Access Passive Optical Network(OFDMA-PON)upstream transmission,the Optical Beating Interference(OBI)will be produced if each ONU uses different lasers with the same wavelength.The colorless ONU is hard to achieve with the presence of OBI.The OFDMA-PON system structure was studied and the related formulas were derived to analyze the generation and avoidance of OBI.The OBI avoidance scheme that sending optical carrier used in upstream by downstream transmission combined with coherent detection in optical line terminal was simulated.Via simulation,the anti-dispersion scheme and the effects of dispersion accumulation and the length of training sequence on system performance were studied,and the parameter configuration was optimized to provide a theory reference for practical application.

Design and Analysis of IPACT-Based Bandwidth Allocation for Delay Guarantee in OFDMA-PON

To guarantee delay performances for time-sensitive services in an orthogonal frequency-division multiple access passive optical network (OFDMA-PON), we propose a two-dimensional (i.e., subcarriers and time) upstream bandwidth allocation method based on interleaved polling with adaptive cycle time (IPACT). We first analyze its delay performance in terms of cycle time, i.e., the length of a polling cycle. Then, by setting the maximum polling cycle so as to guarantee timely transmissions for time-sensitive services, we identify the requirements, i.e., the maximum bandwidth allocation, the maximum number of allowed optical network units, and the optimum number of subcarriers, for upstream bandwidth allocation with delay guarantees. The proposed scheme is evaluated both numerically and via simulation.

Bidirectional Radio Frequency Up-Converted Orthogonal Frequency-Division Multiple Access Passive Optical Network With Novel Source-Free Optical Network Units Using Four-Wave Mixing in Semiconductor Optical Amplifier

We propose and demonstrate a bidirectional radio-frequency (RF) up-converted orthogonal frequency-division multiple access passive optical network (OFDMA-PON) system. Novel source-free optical network units (ONUs) are configured in the proposed OFDMA-PON system, which can support simultaneous and interference-free upstream transmission from multiple ONUs over a single wavelength in a single-fiber topology. The four-wave mixing effect in a semiconductor optical amplifier is utilized in the optical line terminal to enable its configuration. Experimental results successfully verify the feasibility of our proposed system.

Tunable optical frequency comb enabled scalable and cost-effective multiuser orthogonal frequency-division multiple access passive optical network with source-free optical network units

We propose and experimentally demonstrate a multiuser orthogonal frequency-division multiple access passive optical network (OFDMA-PON) with source-free optical network units (ONUs), enabled by tunable optical frequency comb generation technology. By cascading a phase modulator (PM) and an intensity modulator and dynamically controlling the peak-to-peak voltage of a PM driven signal, a tunable optical frequency comb source can be generated. It is utilized to assist the configuration of a multiple source-free ONUs enhanced OFDMA-PON where simultaneous and interference-free multiuser upstream transmission over a single wavelength can be efficiently supported. The proposed multiuser OFDMA-PON is scalable and cost effective, and its feasibility is successfully verified by experiment.

A High-Performance OFDMA PON System Architecture and Medium Access Control

Orthogonal frequency-division multiplexing (OFDM) passive optical network (PON) has been considered to be a promising next-generation broadband wired access solution. However, based on the current tree-based architecture, existing OFDM PON systems face severe challenges when increasing the scalability and data-rate performance. In this paper, we propose a high-performance virtual-tree orthogonal frequency-division multiple access PON system (VTOPS). With the virtual-tree architecture and coupled with the use of inexpensive direct modulation, VTOPS features high reliability, scalability, spectrum efficiency, and cost effectiveness all at once. For governing the flexible/fair access and dynamic allocation of bandwidth, VTOPS incorporates a rate-based medium access control (MAC) scheme. The MAC scheme performs dynamic rate adjustment using a neural-fuzzy system. By adjusting the system parameters, the MAC scheme can achieve a wide range of delay and fairness performance under a variety of traffic patterns. Finally, we show both theoretical and experimental results to demonstrate that, by applying the power pre-emphasis algorithm and adaptive subchannel modulation, VTOPS achieves 40 Gb/s downlink and 40 Gb/s uplink transmissions, using low-cost 10 GHz directly modulated lasers.