Frequency-division Multiplexing Passive Optical Network Research Articles

Pilot-Tone Assisted Successive Interference Cancellation for Uplink Power- and Frequency-Division Multiplexing Passive Optical Network

Frequency division multiplexing (FDM) passive optical network (PON) is considered as a competitive solution for 5G-advanced and 6G mobile fronthaul (MFH) to support multiple radio units (RUs) with shared trunk fiber and distributed unit (DU). However, it is likely to cause uplink signal overlapping by laser wavelength drift, and guard bands should be reserved between FDM channels, which limits the spectral efficiency (SE). In this work, we propose to aggregate multiple uplink FDM channels using power division multiplexing and jointly adopt successive interference cancellation (SIC) at the receiver to improve the uplink SE. We first theoretically derive the SE of such power- and frequency-division multiplexing (PFDM) PON with both guard band and SIC together, and reveal that PFDM PON can achieve higher SE than the pure FDM PON with guard band only. Focusing on the case of two overlapped uplink signals, we propose a pilot-tone assisted SIC to improve the estimation accuracy of frequency offset and phase noise in heavily overlapped uplink signals. In the proof-of-concept experiments, compared to the orthogonal case without considering the guard band, 0.29 bit/s/Hz SE penalty due to the residual interference after SIC is observed when two uplink signals are completely overlapped. The results showed that, in the presence of laser drift, PFDM PON becomes more spectrally-efficient than FDM PON when the relative wavelength drift exceeds 20% of the signal bandwidth.

Identify the Device Fingerprint of OFDM-PONs With a Noise-Model-Assisted CNN for Enhancing Security

Device fingerprint can be utilized in optical communication system to strengthen the physical layer security for its uniqueness and unforgeability. In this letter, we propose and demonstrate a noise-model-assisted feature extraction method to reveal the device fingerprint hidden in the transmitted signal. Our scheme is verified in orthogonal frequency division multiplexing-passive optical network (OFDM-PON). First, the additive and multiplicative noise in normal data signal is extracted and two-dimensional feature matrix is formed. Then, a trained convolutional neural network (CNN) is used as a classifier to identify the fingerprint from the feature matrix. Experimental results show that our method achieves a high identification accuracy up to 99.25%. In the meanwhile, the loss function and training accuracy have an excellent performance. The ability of identifying rogue optical network unit (ONU) is also tested and the identification accuracy is 100%. With the noise-model-assisted CNN, the physical layer security of the system is adequately enhanced under the comprehensive consideration of the ability of identifying legal ONU and resisting illegal ONU.

High-Precision and Low-Complexity Symbol Synchronization Algorithm Based on Dual-Threshold Amplitude Decision for Real-Time IMDD OFDM-PON

We propose a low-complexity and high-precision symbol synchronization algorithm based on dual-threshold amplitude decision for field programmable gate array-based real-time intensity modulation direct detection orthogonal frequency division multiplexing-passive optical network (OFDM-PON) system. In addition, a new criterion to judge symbol synchronization accuracy is proposed first based on bipolar non-return-to-zero codes in time domain. Experimental results show that 95% synchronization precision rate can be achieved after 25 km standard single-mode fiber transmission with the received optical power as low as –21 dBm. Compared with the previously proposed one threshold symbol synchronization algorithm, the synchronization performance has been greatly improved, which brings a maximum signal bit rate gain of 35% when the received optical power is lower than –16 dBm. Furthermore, it is verified that the proposed algorithm is robust. It has wide transmission range which is applicable for OFDM-PON optical access networks within 100 km and has good sampling frequency offset (SFO) tolerance, which can cover the SFO up to 500 ppm without any discard on synchronization precision rate. Finally, complexity analysis shows that our algorithm has the lowest computational complexity and hardware resource consumption, which account for only 0.9% of system resources without any multipliers.

基于光梳状波的相干光正交频分复用-无源光网系统的算法

基于光梳状波的相干光正交频分复用-无源光网系统的算法

Performance analysis of long reach colorless wavelength division multiplexed-orthogonal frequency division multiplexing-passive optical network with broadcast capability

A colorless wavelength division multiplexed-orthogonal frequency division multiplexing-passive optical network (WDM-OFDM-PON) is presented, which is capable of supporting symmetric 10 Gbps downlink direct detection (DD) OFDM unicast signal, broadcast signal, and uplink on–off keying (OOK) signal up to 60 km that includes both single mode and dispersion compensation fiber. At each optical network unit (ONU), DD has been used to receive downlink unicast and broadcast OFDM data. A delay interferometer (DI) has been used at a central office to achieve 10 Gbps uplink signal transmission over 60 km distance utilizing a reflective semiconductor optical amplifier (bandwidth=1.5 GHz) at the ONU because DI works as a vestigial sideband filter and an optical equalizer. Broadcast channel does not affect the system performance because it generates a limited interference of the order of 0.1 to 0.28 dB to downlink and uplink channels, and this interference is distributed to every ONU. For bit error rate of 10−9, the receiver sensitivity of −24, −23.1, and −20.14 dBm is achieved by simulating downlink OFDM unicast channels, OFDM broadcast channel, and uplink OOK unicast channels, respectively, for a symmetric data rate of 10 Gbps over 60 km.

Physically secured orthogonal frequency division multiplexing–passive optical network employing noise-based encryption and signal recovery process

We propose a physically enhanced secure scheme for direct detection–orthogonal frequency division multiplexing–passive optical network (DD-OFDM-PON) and long reach coherent detection–orthogonal frequency division multiplexing–passive optical network (LRCO-OFDM-PON), by employing noise-based encryption and channel/phase estimation. The noise data generated by chaos mapping are used to substitute training sequences in preamble to realize channel estimation and frame synchronization, and also to be embedded on variable number of key-selected randomly spaced pilot subcarriers to implement phase estimation. Consequently, the information used for signal recovery is totally hidden as unpredictable noise information in OFDM frames to mask useful information and to prevent illegal users from correctly realizing OFDM demodulation, and thereby enhancing resistance to attackers. The levels of illegal-decryption complexity and implementation complexity are theoretically discussed. Through extensive simulations, the performances of the proposed channel/phase estimation and the security introduced by encrypted pilot carriers have been investigated in both DD-OFDM and LRCO-OFDM systems. In addition, in the proposed secure DD-OFDM/LRCO-OFDM PON models, both legal and illegal receiving scenarios have been considered. These results show that, by utilizing the proposed scheme, the resistance to attackers can be significantly enhanced in DD-OFDM-PON and LRCO-OFDM-PON systems without performance degradations.

Novel multi-band DFT-spread OFDM-PON systems based on intensity modulation and direct detection for cloud computing

Passive optical network (PON) has become a preferable access technique for cloud computing due to its elastic bandwidth capacity and transmission stability. In particular, the orthogonal frequency division multiplexing PON based on intensity modulation and direct detection (IM/DD OFDM-PON) has gained extensive attention since it is a cost- and spectral-efficient system, while for the traditional IM/DD OFDM-PON, the use of OFDM could lead to the high peak-to-average power ratio (PAPR), and it is impossible to satisfy the different QoS degrees required by ONUs under a cloud environment. Thus in this paper, we design a novel multi-band discrete Fourier transform (DFT)-spread IM/DD OFDM-PON. The DFT-spread is utilized to reduce the PAPR; meanwhile, a multi-band power allocation and bit loading are achieved to satisfy the different degrees of QoS requirement owned by ONUs. The simulation results show that our system has the better performance of PAPR reduction compared with the traditional IM/DD OFDM-PON; meanwhile, the different QoS degrees of all ONUs are guaranteed.

The application of cost-effective lasers in coherent UDWDM-OFDM-PON aided by effective phase noise suppression methods

Digital coherent passive optical network (PON), especially the coherent orthogonal frequency division multiplexing PON (OFDM-PON), is a strong candidate for the 2nd-stage-next-generation PON (NG-PON2). As is known, OFDM is very sensitive to the laser phase noise which severely limits the application of the cost-effective distributed feedback (DFB) lasers and more energy-efficient vertical cavity surface emitting lasers (VCSEL) in the coherent OFDM-PON. The current long-reach coherent OFDM-PON experiments always choose the expensive external cavity laser (ECL) as the optical source for its narrow linewidth (usually<100 KHz). To solve this problem, we introduce the orthogonal basis expansion based (OBE) phase noise suppression method to the coherent OFDM-PON and study the possibility of the application of the DFB lasers and VCSEL in coherent OFDM-PON. A typical long-reach coherent ultra dense wavelength division multiplexing (UDWDM) OFDM-PON has been set up. The numerical results prove that the OBE method can stand severe phase noise of the lasers in this architecture and the DFB lasers as well as VCSEL can be used in coherent OFDM-PON. In this paper, we have also analyzed the performance of the RF-pilot-aided (RFP) phase noise suppression method in coherent OFDM-PON.

Real-time upstream services demonstration in orthogonal frequency division multiplexing-passive optical network system

Real-time digital service and multimedia service upstream transmission in Digital Signal Processing (DSP)-based Orthogonal Frequency Division Multiplexing-Passive Optical Network (OFDM-PON) is experimentally demonstrated with Centralised Light Source (CLS) configuration in this paper. After transmitted over 25 km Standard Single Mode Fibre (SSMF) with −16.5 dBm optical power at receiver, the Bit Error Rate (BER) is 9.5 × 10−11. The implementations of digital domain up-conversion and down-conversion based on Field Programmable Gate Array (FPGA) are introduced, which can reduce the cost of In-ph-ase and Quadrature (IQ) radio frequency mixers utilised at transmitter and receiver. A carrier synchronization algorithm is implemented for compensating carrier offset. A channel equalization algorithm is adopted for compensating the damage of channel. A new structure of Frequency Synchronization Unit (FSU) designed in FPGA is also proposed to cope with the frequency shifting at receiver.

Optical MIMO transmission for SCFDM-PON based on polarization interleaving

Orthogonal frequency division multiplexing-passive optical network (OFDM-PON) and single-carrier frequency division multiplexing (SCFDM)-PON are promising solutions for future high-speed PON-based access. A polarization division multiplexing scheme with direct detection is proposed for OFDM-PON to effectively reduce bandwidth requirements for components. However, the scheme strictly requires spectrum overlapping of two orthogonal sidebands and the 4×4 multi-input-multi-output (MIMO) algorithm to eliminate complex cross-polarization interference. In this letter, we propose a polarization interleaving (PI) approach that significantly reduces bandwidth requirements for optical and electrical components while achieving a high-flexibility and low-complexity MIMO algorithm. Downstream single sideband PI-SCFDM transmission is experimentally demonstrated.

A 40-Gb/s OFDM PON System Based on 10-GHz EAM and 10-GHz Direct-Detection PIN

This letter demonstrates a 40-Gb/s optical double-sideband (ODSB) orthogonal frequency-division multiplexing passive optical network (OFDM-PON) system using a cost-effective 10-GHz-bandwidth electroabsorption modulator (EAM). By employing a subcarrier-adaptive modulation format and pre-emphasis, we successfully achieve 20-km EAM-based single-mode-fiber (SMF) transmission.