Error Vector Magnitude Performance Research Articles

Power Amplifier Optimization for M2M Node using DPD and Hybrid DFT-s-OFDM with CFR

Power Amplifiers (PAs) play a vital role in mobile communication. However, their inherent nonlinearity can lead to issues such as unwanted radiation, interference with neighboring channels, and distortion within the desired frequency range. To address these problems, PAs are typically operated at a lower power level than their saturation point, sacrificing power efficiency to improve Error Vector Magnitude (EVM) performance. Consequently, more than 70-80% of the DC power is wasted as heat. This inefficiency necessitates the exploration of techniques to enhance PA efficiency while maintaining acceptable linearity and performance. Digital Pre-Distortion (DPD) is a useful technique to linearize PAs. DPD allows affordable nonlinear PAs to function with minimal distortion in their nonlinear operating regions. This results in amplified signals with increased power output and improved power efficiency. Using nonlinear functions, the output signal of the PA can be linearized, mitigate distortions, and be effectively optimized. When using various operating channels and varying time, temperature, and PA nonlinearity, the DPD must adjust. In order to increase the power efficiency of 5G systems, DPD-enabled systems are inculcating with adaptive DFT-s-OFDM employed 5G physical layer along with the Crest Factor Reduction (CFR) algorithm.

Error Vector Magnitude as a Performance Standard for Antennas in the Millimeter-Wave Era: Part 2: Modeling, simulation, and measurement methods

The error vector magnitude (EVM) is a comprehensive measure of the amplitude and phase distortion of digitally modulated signals and a potential tool for characterizing the performance of active beamforming arrays, especially at millimeter-wave frequencies, because of the high level of integration and limited spacing between the radiating elements. A review of the EVM measurement process and fundamental principles for time-domain demodulation with a vector signal analyzer (VSA) and spectral correlation with a vector network analyzer (VNA) was presented in [1]. This article demonstrates how researchers have modeled and measured impairments from antenna and phased array signal transmission to characterize their influence on the EVM of single and multicarrier digital signals. It presents examples of simulation models and measurements of the distortion from ultrawideband (UWB) passive antenna transmission, power amplifier (PA) nonlinearities, and phased array beam squint and beam scan intersymbol interference (ISI). A brief survey of over-the-air (OTA) test ranges for EVM analysis is also provided. This overview of state-of-the-art EVM simulation and measurement methods is intended to help interested readers understand and enhance the EVM performance analysis methods applied to antennas and phased arrays in this new era of millimeter-wave communications.

Monolithic InAs/InP Quantum Dash Mode-Locked Lasers for Millimeter-Wave-Over-Fiber Mobile Fronthaul Systems

Semiconductor monolithic mode-locked lasers (MLLs) are potential solutions for generating high-speed optical pulses in future mobile fronthaul networks in the millimeter-wave (mmW) bands. Our previous studies have investigated using buried heterostructure (BH) quantum dash (QDash) multi-wavelength lasers for photonic mmW applications. Here we present results from monolithic chip-scale ridge waveguide QDash MLLs for generating and transmitting mmW signals. Through optimizing epitaxy growth, waveguide design, and fabrication process, the five-layer ridge waveguide QDash MLL exhibits superior performance with regard to the coherent comb bandwidths, lasing threshold current, output power, and internal quantum efficiency. The generated mmW frequency at 28.36 GHz exhibits excellent frequency stability, with a drift of less than ± 50 kHz. For the first time, we have utilized the free-running five-layer ridge waveguide QDash MLL to implement single- and dual-optical carrier modulation schemes in the millimeter-wave-over-fiber (mmWoF) systems. Both modulation schemes have achieved satisfactory performance achieving error vector magnitude (EVM) performance much lower than the 3GPP requirements (<12.5%) for future networks. In particular, the single-carrier modulation scheme achieves higher conversion efficiency and improved EVM performance. In contrast, the dual-carrier modulation scheme alleviates the path length matching challenges, offering a low-cost and easy-to-implement solution in different usage scenarios.

Enhancing signal quality in dense wavelength division multiplexed systems by eliminating crosstalk with cascaded optical bandpass filters

Non-orthogonal wavelength division multiplexing (WDM) channels are crucial in achieving significantly higher capacity and spectral efficiency than conventional schemes. Additionally, conventional schemes face challenges in electrical processing of wide-bandwidth signals. To suppress crosstalk in non-orthogonal WDM channels, the use of cascaded bandpass filters with suitable transmissivity and bandwidth is investigated for effective channel separation of large-capacity and multiplexed optical signals. This study employs the bandwidth ratio as a parameter, which is defined as the ratio of the channel spacing to the signal bandwidth, to quantify the extent of signal overlapping, and uses optical bandpass filters to filter non-orthogonal signals with a bandwidth ratio ranging from 1.0 to 0.75. The non-overlapping portion is set as the transmission bandwidth of the filter, and the crosstalk is maximally reduced with two-stage filters using Nyquist, super Gaussian, and Butterworth shaped filters. According to the analysis, the combination of Gaussian N = 1 and Gaussian N = 5 exhibits the lowest error vector magnitude (EVM) performance within a bandwidth ratio of 0.8 to 1.0. Simulations showed that a two-stage OBPF with a combination of Gaussian N = 1 and Gaussian N = 5 provides the best EVM performance at a bandwidth ratio between 0.85 to 1.0 within the combination of filter shapes and their orders we used. Additionally, the study includes an analytical investigation of the impact of amplified-spontaneous-emission noise associated with the Erbium-doped fiber amplifier (EDFA) and frequency resolution tolerance of the LCOS filter. The results demonstrate that cascaded EDFAs can be achieved down to OSNR of 10 dB at a minimum resolution of 4 GHz. Finally, the optimal filter shape is analyzed for different bandwidth ratios. The investigation shows that the optimal filter shape is independent of the function used and remains consistent across all bandwidth ratios. The tolerance of the filter is primarily affected by the −0.5 dB transmittance bandwidth between subchannels, which varies depending on the bandwidth ratio. Furthermore, a high tolerance is observed in the −20 dB transmittance bandwidth.

A low‐spur harmonic‐cancelation digital predistortion based on neural network for frequency‐hopping HF transmitters

AbstractHigh frequency (HF) transmitter implemented with the multioctave broadband power amplifier (PA) is always faced with the problem of interfering harmonics because of the nonlinearity of the PA. With the harmonic‐cancelation digital predistortion (HC‐DPD) scheme, the harmonics at lower frequencies can be canceled by the injected components and the harmonics at higher frequencies can be filtered out using a low‐pass filter (LPF). However, the HC‐DPD scheme brings the problem of unwanted spurs while lowering the requirements for sampling rate. In this article, a time‐delay neural network (TDNN) model is used to replace the conventional memory polynomial (MP) model in the forward modeling. Theoretical derivation and simulation results validate the effectiveness of the TDNN model in harmonic cancelation and spur suppression. Further, a frequency‐agile neural network (FANN) model is proposed based on the TDNN model. By adding the carrier frequency to the inputs of the network, the trained model can apply to all the trained carrier frequencies and is more friendly to the frequency‐hopping scenarios. Experiments were carried out on a 2–30 MHz HF transmitter testbench. Measurement results show that the harmonic‐to‐fundamental power ratio, the adjacent channel power ratio (ACPR), and the error vector magnitude (EVM) performances were all improved by more than 20 dB. Compared with the MP model, the unwanted spurs can be suppressed by up to 22 dB. In addition, the number of total model coefficients of the proposed FANN model is only 22% of that of the TDNN model under the frequency‐hopping scenario.

A Digital Frequency-Dependent I/Q Imbalance and Group Delay Estimation and Compensation Modules for mmWave Single Carrier Baseband Transceivers

This paper proposes the estimation and compensation modules of digital frequency-dependent (FD) I/Q imbalance and group delay for single carrier (SC) mode with 15 Gbps throughput rate in the millimeter-wave (mmWave) band. The proposed compensation module of a digital recursive filter can mitigate FD I/Q imbalance effects caused by the -3 dB corner imbalance of the reconstruction and anti-aliasing filters of I/Q branches. The proposed recursive filter with the appropriate initial coefficients based on the result of Golay sequence estimation can shorten the convergence time and precisely acquire the desired coefficients. The average image rejection ratio (IRR) performance after compensating by the proposed module can be improved from 21.97 dB to 47.54 dB. Besides, the group delay distortion in reconstruction and anti-aliasing filters will cause intersymbol interference to distort the in-band signal. We employ a digital equalization filter with the filter coefficients derived from the correlation results based on the Golay sequence to compensate the in-band group delay distortion. After the proposed group delay is pre-compensation at TX, the system-level performance of error vector magnitude (EVM) performance is improved by 6.21 dB to -27.78 dB to satisfy the IEEE 802.11ad/ay requirement in 64-QAM mode. The inner RX BER performance with the FD I/Q imbalance and the group delay compensation modules can achieve 3 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-3</sup> at 23 dB and also satisfy the system requirement at SNR of required 25.52 dB. A four-times parallelism architecture is proposed to work at a clock rate of 625 MHz with 64-QAM mode. The gate count and power consumption of the proposed design are 154.4 K and 16.2 mW, respectively.

Efficient Digital Signal Recovery for Satellite Communications With Active Phased Arrays

In this letter, a transfer learning-assisted (TLA) digital signal recovery (DSR) method is proposed for the linearization of active phased arrays (APAs) for satellite communications to handle the transition to different communication scenarios. The frozen layers of a deep neural network (DNN) are pretrained to extract the main nonlinear characteristics of the APA, and the fine-tuning layers are adopted to achieve prompt update of the regression parameters according to the variations in average input power levels and steering angles. This allows satisfactory reception performance to be maintained in time when the nonlinearity of the APA changes. Experimental results on a <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$4 \times 4$</tex-math> </inline-formula> APA antenna at 28 GHz show that the proposed method improves the adjacent channel power ratio (ACPR) and the error vector magnitude (EVM) performance. Compared with the existing fully relearned DNN-DSR method, the proposed method achieves almost as good performance with only 1/10 of the data.

Automatic turbulence mitigation for coherent free-space optical links using crystal-based phase conjugation and fiber-coupled data modulation.

There are various performance advantages when using temporal phase-based data encoding and coherent detection with a local oscillator (LO) in free-space optical (FSO) links. However, atmospheric turbulence can cause power coupling from the Gaussian mode of the data beam to higher-order modes, resulting in significantly degraded mixing efficiency between the data beam and a Gaussian LO. Photorefractive crystal-based self-pumped phase conjugation has been previously demonstrated to "automatically" mitigate turbulence with limited-rate free-space-coupled data modulation (e.g., <1 Mbit/s). Here, we demonstrate automatic turbulence mitigation in a 2-Gbit/s quadrature-phase-shift-keying (QPSK) coherent FSO link using degenerate four-wave-mixing (DFWM)-based phase conjugation and fiber-coupled data modulation. Specifically, we counter-propagate a Gaussian probe from the receiver (Rx) to the transmitter (Tx) through turbulence. At the Tx, we generate a Gaussian beam carrying QPSK data by a fiber-coupled phase modulator. Subsequently, we create a phase conjugate data beam through a photorefractive crystal-based DFWM involving the Gaussian data beam, the turbulence-distorted probe, and a spatially filtered Gaussian copy of the probe beam. Finally, the phase conjugate beam is transmitted back to the Rx for turbulence mitigation. Compared to a coherent FSO link without mitigation, our approach shows up to ∼14-dB higher LO-data mixing efficiency and achieves error vector magnitude (EVM) performance of <16% under various turbulence realizations.

Digital radio-over-fiber system based on differential pulse code modulation and space division multiplexing.

In this paper, we present and experimentally demonstrate a digital-radio-over-fiber (D-RoF) architecture based on differential pulse code modulation (DPCM) and space division multiplexing (SDM). At low quantization resolution, DPCM can effectively reduce quantization noise and obtain significant signal-to-quantization noise ratio (SQNR) gain. We experimentally study the 7-core and 8-core multicore fiber transmission of 64-ary quadrature amplitude modulation (64QAM) orthogonal frequency division multiplexing (OFDM) signals with a bandwidth of 100 MHz in a fiber-wireless hybrid transmission link. Compared to PCM-based D-RoF, the error vector magnitude (EVM) performance in the DPCM-based D-RoF is effectively improved when the quantization bits (QBs) are 3-5 bits. In particular, when the QB is 3 bits, the EVM of the DPCM-based D-RoF is 6.5% and 7% lower than that of the PCM-based system in 7-core- and 8-core-multicore fiber-wireless hybrid transmission links, respectively.

Out-of-Band Digital Predistortion for Power Amplifiers With Strong Nonlinearity

Conventional full-band digital predistortion (DPD) suppresses the inband (IB) distortion to improve the error vector magnitude (EVM) performance and simultaneously suppresses the out-of-band (OOB) distortion to reduce the adjacent-channel interference. However, its performance is very limited when the nonlinearity is strong, especially in terms of suppressing the OOB distortion. This paper proposes an OOB DPD scheme for strong nonlinearity with a special focus on suppressing the OOB distortion to reduce the adjacent-channel interference. The proposed OOB DPD is featured by specifying an arbitrary OOB-distortion band for linearization and controlling the improvement level of EVM performance. Experiments demonstrate that the proposed OOB DPD can achieve superior performance in suppressing the OOB distortion when the nonlinearity is strong. We also present analyses to show that in strong nonlinearity cases with high compression, focusing on suppressing the OOB distortion at a specific band is an effective way to improve the suppression level of the target distortion. The proposed OOB DPD can further improve the transmission power under the assurance of low adjacent-channel interference. It can be applied in communications with urgent needs in high transmission power, high efficiency, and low adjacent-channel interference, such as military communications that usually adopt low-order modulations with low EVM requirements.

Performance evaluation of a simplified power-domain NOMA for visible light communications.

The performance of a visible light communication (VLC) system based on power-domain nonorthogonal multiple access (PD-NOMA) is experimentally evaluated in this paper. The simplicity of the adopted nonorthogonal scheme is provided by the fixed power allocation method at the transmitter and the single one-tap equalization executed before the successive interference cancellation at the receiver. The experimental results proved the successful transmission of the PD-NOMA scheme with three users in VLC links of up to 2.5m, after a proper choice of the optical modulation index. All users achieved error vector magnitude (EVM) performances below forward error correction limits in all evaluated transmission distances. At 2.5m, the user with the best performance reaches an E V M=2.3%.

High-speed Multi-channel all-optical de-aggregator based on polarization-assisted phase-sensitive amplification in elastic optical networks

An all-optical de-aggregator for four wavelength-multiplexed channels based on polarization-assisted (PA) phase-sensitive amplification (PSA) is proposed, aiming to improve spectral efficiency in elastic optical networks (EONs). Benefiting from a single bi-directional PSA based on the nonlinear-optical loop mirror (NOLM), signals and their conjugates can be extracted and located at two polarization states respectively. To avoid the interference of undesired harmonics sharing the same frequency with input signals, we introduce a spatial dislocation between signal and interference harmonics by sending signals to different input ports of the NOLM. For each channel, the signal and its conjugate are coherently superimposed by PA-PSA. Each of the four 25/50 Gbaud quadrature phase shift keying (QPSK) signals is de-aggregated into two binary phase shift keying (BPSK) signals. We use the same scheme to de-aggregate 25/50 Gbaud 16-ary quadrature amplitude modulation (16-QAM) into 4-level pulse-amplitude-modulation (PAM-4) signals for four channels to verify the tunability of the scheme. The bit-error-rate (BER) and error vector magnitude (EVM) performance of the scheme are investigated and the corresponding OSNRs for error-free signal recovery are obtained respectively.

Spur-Free Harmonic Cancelation Digital Predistortion for HF Transmitters

High frequency (HF) transmitter implemented with the multioctave broadband power amplifier (PA) is always faced with the problem of harmonics because of the nonlinearity of the PA. With the previous harmonic cancellation digital predistortion (HC-DPD) scheme, harmonics and the fundamental components, as a whole, are modeled with a uniform memory polynomial (MP) model. Although the harmonics can be well canceled, unwanted spurs can be generated when the nonlinearity order of the MP model exceeds the critical point because of the limited sampling rate. In this letter, a spur-free HC-DPD (SF-HC-DPD) scheme is proposed to suppress the spurs. Without increasing the sampling rate, a novel anti-aliasing MP (AA-MP) model is proposed. With the energy-saving linearization technique, the signal quality and robustness of HF communication can be greatly improved. Measurement results show that the harmonic-to-fundamental power ratio, the adjacent channel power ratio (ACPR), and the error vector magnitude (EVM) performances were all improved by nearly 20 dB. In addition, the unwanted spurs can be suppressed for being below −80 dBc, which is more than 26 dB better than the HC-DPD scheme with the MP model.

Residual Compensation-Based Extreme Learning Machine for MIMO-NOMA Receiver

Extreme learning machine (ELM) uses a simple machine learning (ML) architecture that allows its implementation for smart IoT network operations. However, some inaccuracy lies between the predicted and the actual data during the ELM training, which can be caused due to the limitation of the modeling representation. This paper thus investigates a residual compensation-based ELM (RC-ELM) for its application in designing a receiver for MIMO-NOMA aided IoT systems. In RC-ELM, the base ELM layers determine the relationship between the transmitted and received data and the additional layers of the RC-ELM attempt to compensate the error introduced during the training mechanism. The analysis of the appropriate number of compensation layers for training error minimization is conducted on the basis of the bit error rate (BER) and the error vector magnitude (EVM) performances of the RC-ELM training. A minimum BER improvement of 5% for user 1 and 18% for user 2 is shown with with the aid of RC-ELM for a two-IoT user instance. The EVM is marginally increased by 0.0008% for user 1 and 1.61% for user 2 in training stage. Besides, the RC-ELM receiver is also compared to the minimum mean square error (MMSE), the classic ELM and the trained multilayer perceptron (MLP) receivers in terms of BER and EVM. Both of the ELM receivers show improved performances with respect to the other receivers.

All-Optical Multi-Channel Aggregator for QPSK to 16QAM Based on Time-Lens and Phase Reloader in Elastic Optical Networks

An all-optical aggregator consisting of time-lens and a phase reloader for two four-channel multiplexed quadrature phase shift keying (QPSK) signals to a wavelength division multiplexed (WDM) 16-ary quadrature amplitude modulation (16QAM) signal is proposed. The feasibility of the scheme is confirmed by the waveforms of the intermediate process and the constellations of input-output signals. The performance of bit error rate (BER) and error vector magnitude (EVM) values under different optical signal-to-noise ratios (OSNR) are analyzed to evaluate the system, and the OSNR penalties of the aggregated signal at the forward error correction (FEC) threshold are between 2.25 dB and 2.45 dB. This scheme potentially enables reconfigurable service and improves compatibility in elastic optical networks (EON).

Analog Mobile Fronthaul Supporting 128 RF Chain With Nonlinear Compensator for B5G and 6G Ma-MIMO Beamforming

These paper details a fronthaul optical link using delay-division-multiplexing (DDM) scheme with Volterra based nonlinear compensator for beyond fifth generation (B5G) and 6G massive multiple-input multiple-output (Ma-MIMO) beamforming. Based on pre-allocated relative time delays, pre-processed signals can be deaggregated to different RF chain signals following spectral aliasing caused by the digital signal processing (DSP) at remote radio units. The Volterra based nonlinear compensator is used to compensate nonlinear distortion and IQ imbalance of the fronthaul link. By combined the DDM scheme and Volterra technique, we can easily deaggregate signals and mitigate the interference caused by nonlinear distortion and IQ imbalance at the same time. In experiments, the DDM scheme support 128 RF chain signals is demonstrated. With the Volterra compensator, the signal input power of Mach-Zehnder modulator (MZM) has 18 dB margin. IQ imbalance caused by phase misalignment can also be compensated by the IQ Volterra. It can keep the acceptable error vector magnitude (EVM) performance within a ±10° range. After 25-km optical link, the EVM of each RF Chain is underneath 8%. And the total received 128 RF chain signals will require CPRI data rate as high as 840 Gb/s.

Constant-Envelope OFDM for Power-Efficient and Nonlinearity-Tolerant Heterodyne MMW-RoF System With Envelope Detection

The radio over fiber (RoF) system using optical heterodyne (OH) for broadband up-conversion and envelope detection (ED) for phase-noise-insensitive down-conversion stands out as a simple, robust, and cost-effective solution for exploiting the abundant bandwidth resource at the millimeter-wave (MMW) band. In this paper, we dedicate efforts to experimentally investigate such an MMW-RoF system based on the constant-envelope orthogonal frequency division multiplexing (OFDM) (CE-OFDM) technique. A critical benefit of employing CE-OFDM is its excellent tolerance to the nonlinear distortions, which are essential for the wide acceptance of analog RoF systems. Also, thanks to the analog angle modulation transforming the OFDM signal to a constant envelope signal, the carrier-suppressed double-sideband (CS-DSB) modulation can be implemented for encoding the CE-OFDM signal onto the optical carrier, leading to significant improvements in power efficiencies of both fiber and radiofrequency (RF) links. In experiments, a 60-GHz OH-ED MMW-RoF system is established, of which the distances of fiber and MMW wireless transmissions are 10 km and 1.2 m respectively. Under the case of 2-GHz 64-quadrature amplitude modulation (QAM) OFDM baseband signal, the achieved experimental results show that the proposed OH-ED MMW-RoF system outperforms its counterpart using the conventional OFDM in terms of nonlinearity insensitivity, RF and optical power efficiency enhancements (indicated by over 11.5-dB and 3.2-dB reductions in the lowest transmit RF and receive optical powers for satisfying the 8% error-vector-magnitude (EVM) limit). In addition, when the QAM order of the 2.5-GHz OFDM baseband signal reaches 256, the CS-DSB CE-OFDM scheme enables an acceptable EVM performance of 4.43%.

Experimental Evaluation of Hybrid Fibre–Wireless System for 5G Networks

This article describes a novel experimental study considering a multiband fibre–wireless system for constructing the transport network for fifth-generation (5G) networks. This study describes the development and testing of a 5G new radio (NR) multi-input multi-output (MIMO) hybrid fibre–wireless (FiWi) system for enhanced mobile broadband (eMBB) using digital pre-distortion (DPD). Analog radio over fibre (A-RoF) technology was used to create the optical fronthaul (OFH) that includes a 3 GHz supercell in a long-range scenario as well as a femtocell scenario using the 20 GHz band. As a proof of concept, a Mach Zehnder modulator with two independent radio frequency waveforms modifies a 1310 nm optical carrier using a distributed feedback laser across 10 km of conventional standard single-mode fibre. It may be inferred that a hybrid FiWi-based MIMO-enabled 5G NR system based on OFH could be a strong competitor for future mobile haul applications. Moreover, a convolutional neural network (CNN)-based DPD is used to improve the performance of the link. The error vector magnitude (EVM) performance for 5G NR bands is predicted to fulfil the Third Generation Partnership Project’s (3GPP) Release 17 standards.

Low-Complexity Adaptive Frequency-Domain Nonlinear Equalization for Analog RoF Mobile Fronthaul Using FFT/IFFT-Assisted Channel Aggregation

Addressing the nonlinearity induced signal degradation is of critical importance for harvesting the transparent benefits of an analog radio over fiber (A-RoF) architecture, to support mobile fronthaul (MFH) with high spectral efficiency and reduced latency. Here, for linearizing the low-latency A-RoF MFH using digital-domain fast Fourier transform /inverse fast Fourier transform (FFT/IFFT) assisted channel aggregation/de-aggregation (CA/DA), we propose and experimentally demonstrate a compatible adaptive frequency-domain (FD) nonlinear equalization scheme. This scheme is characterized by a much lower computational complexity compared with the popular time-domain Volterra nonlinear equalizer while delivering a comparable performance. The proposed equalization scheme is implemented using the FD two-box cascaded Hammerstein structure. It enables simplified coefficients estimation, computationally efficient equalization, FFT/IFFT calculation reusing in channel DA, and shared legacy one-tap FD linear equalization in the OFDM system. Experimental validations of the proposed nonlinear equalization approach are carried out via typical electroabsorption modulator (EAM) and Mach-Zehnder modulator (MZM) based intensity modulation and direct detection (IMDD) A-RoF links. Cost-effective fiber-optic (with EAM) and optical up-conversion enabled V-band millimeter-wave (mm-wave) fiber-wireless (with MZM) transmissions are demonstrated. Experimental results show that the proposed scheme can effectively improve the performances of both EAM and MZM based 10-km fiber-optic A-RoF MFH links, in terms of the (>8 dB) reduction of adjacent channel leakage ratio, (>10 dB) improvement of error-vector magnitude (EVM) and (>5 dB) enhancement of input intermediate-frequency (IF) power range, which retains an acceptable (below 8 %) EVM performance for the 64-QAM modulation. The input IF signal aggregates 8 125-MHz 64-QAM OFDM channels. Furthermore, the proposed scheme enables the transmission of a 5-Gbit/s aggregated IF 64-QAM signal over a 10-km fiber link and 1.2-m 60-GHz wireless channel, wherein a >12 dB improved input power margin is observed.

Experimental demonstration of all-optical aggregation and de-aggregation for a QPSK signal in an elastic optical network.

The aggregation and de-aggregation between one QPSK and two BPSK signals are experimentally demonstrated based on cross-phase modulation (XPM) effects and phase-sensitive amplification (PSA), aiming to improve flexible spectral efficiency in the elastic optical network. Benefiting from the nonlinear-optical loop mirror (NOLM), the two BPSK signals can be extracted without any information redundancy for the de-aggregation scheme. The wavelength of the extracted signals stay the same as the input signal in the NOLM. Moreover, the aggregation from two BPSK signals to one QPSK signal is also successfully achieved. The feasibility of the two schemes can be confirmed by the transfer functions and the input-output constellation. The bit-error-rate (BER) and error vector magnitude(EVM) performance of the two schemes are also investigated and the corresponding OSNRs for error-free signal recovery are obtained respectively. The proposed schemes contribute to the realization of flexible optical networks and can be applied in the future gateway node between optical sub-networks.