Digital cancellation of multi-band passive inter-modulation based on Wiener-Hammerstein model

Utilizing multi-band and multi-carrier techniques enhances throughput and capacity in Long-Term Evolution(LTE)-Advanced and 5G New Radio(NR)mobile networks.However,these techniques introduce Passive Inter-Modulation(PIM)interference in Frequency-Division Duplexing(FDD)systems.In this paper,a novel multi-band Wiener-Hammerstein model is presented to digitally reconstruct PIM interference signals,thereby achieving effective PIM Cancellation(PIMC)in multi-band scenarios.In the model,transmitted signals are independently processed to simulate Inter-Modulation Distortions(IMDs)and Cross-Modulation Distortions(CMDs).Furthermore,the Finite Impulse Response(FIR)filter,basis function generation,and B-spline function are applied for precise PIM product estimation and generation in multi-band scenarios.Simulations involving 4 carrier components from diverse NR frequency bands at varying transmitting powers validate the feasibility of the model for multi-band PIMC,achieving up to 19 dB in PIMC performance.Compared to other models,this approach offers superior PIMC performance,exceeding them by more than 5 dB in high transmitting power scenarios.Additionally,its lower sampling rate requirement reduces the hardware complexity associated with implementing multi-band PIMC.

Bias-Independent Inter-Modulation Method for Simultaneously Measuring Low-Frequency Modulation and Bias Half-Wave Voltages of Mach-Zehnder Modulators

A bias-independent inter-modulation method is proposed and demonstrated for measuring low-frequency modulation and bias half-wave voltages of Mach-Zehnder modulators(MZMs).The method consists of simultaneous sinusoidal modulation on the modulation and bias ports of the MZM under test.Sinusoidal-modulated sidebands heterodyne with each other and generate the desired inter-modulation products after photodetection,which allows extracting both the modulation depth and half-wave voltage for the modulation and bias ports of the MZM.Our method is independent of bias voltages of the MZM,which can be canceled out by carefully choosing the sinusoidal-modulation frequencies.Moreover,the proposed method enables the low swing voltage for measuring both the modulation depth and half-wave voltage of MZMs.Experiments indicate that the proposed method features the simple setup and high accuracy for low-frequency response measurement ranging from 1 Hz to 1 MHz.

Passive inter-modulation scattering analysis of reflector considering contact nonlinearity

Passive inter-modulation （PIM） is a form of nonlinear distortion caused by the inherent nonlinearities of the passive devices and components in RF/microwave system. It will degenerate the performance of communication system with broad-band channel and high-sensitivity receiver. Therefore, it is necessary to construct a model to simulate this process in order to predict the level of PIM. This paper is aimed at constructing some plate models with one-dimensional and two-dimensional contact nonlinearity sections illuminated by two-tone waves, and calculating the scattered field at a fixed-point in space using time-domain physical optics method. By taking fast Fourier transform （FFT）, we get the spectrum of the scattered field and then analyze the generated PIM products. At the end of this paper, some numerical examples are presented to show the influence rules of the relative factors on PIM. The results indicate the variation of the level of PIM with the number of the nonlinear regions, the nonlinear spacing, and the incident power levels.

Superposition Effect of Passive Intermodulation for Cable Assemblies with Discrete Point-Sources

In order to expand the cell coverage of wireless cellular systems, the number of passive components in wireless systems has been substantially increased. There can be many passive intermodulation(PIM) pointsources even in a device or a radio link, which may add up constructively or destructively. A modified point-source model with lossy components is proposed to evaluate the superposition effect of the forward and refl ected PIM in case of series connection. The index of the series connection factor(SCF) is employed for systems that incorporate multiple PIM sources to predict the important characteristics of the cumulative PIM, such as the maximum and minimum values and the limit form. Furthermore, some initial experimental results are given out and the deviation in the above-mentioned prediction is also analyzed.

Multiplexing modulation design optimization and quality evaluation of BDS-3 PPP service signal

The Precise Point Positioning(PPP)service of BeiDou-3 Navigation Satellite System(BDS-3)is implemented on its Geostationary Earth Orbit(GEO)satellites.However,its signal design is limited by the actual power of satellite and other conditions.Furthermore,the design needs to fully consider the compatibility of diferent service phases.Starting from the actual state of the BDS-3 GEO satellite,this paper studies the multiplexing modulation of the BDS PPP service signal that is based on the Asymmetric Constant Envelope Binary Ofset Carrier(ACE-BOC)technique and proposes several feasible schemes for this signal.Comparison and optimization of these techniques are made from the aspects of transmission efciency,multiplexing efciency,and service forward compatibility.Based on the Type-III ACE-BOC multiplexing modulation technique,phase rotation and intermodulation reconstruction techniques are proposed to suppress the intermodulation interference issue.Finally,a signal based on improved ACE-BOC multiplexing is designed.The quality of the proposed signal was continuously monitored and tested using large-diameter antennas.The evaluation results show that the power spectrum deviation of the signal is 0.228 dB,the correlation loss is 0.110 dB,the S-curve slope deviation is 1.558%on average,the average length diference between the positive/negative chip and the ideal chip is only 0.0006 ns,and the coherence between the carrier and the pseudo code is 0.082°.All quality indicators are satisfactory,indicating that the proposed signal multiplexing modulation technique is an ideal solution that meets all the requirements of the design constraints,and can achieve efcient information broadcasting and forward compatibility of the BDS PPP service.