Coaxial connectors are one of the main contributors to passive intermodulation (PIM) in radio frequency systems. Such systems exhibit nonlinear characteristics, especially as the transmission power is increased. In this paper, microscopic surface analysis and macroscopic nonlinear models are introduced to provide explanations for PIM characteristics and to make more precise predictions for the third-order and fifth-order intermodulation products (IM3 and IM5) power resulting from n-type connectors. The equivalent circuit models are presented to provide insight into the effects of degradation at the microscopic level. Simulation calculations are performed to explore the resistance and capacitance in the circuit models and the relative contribution of various physical parameters. A full discussion of nonlinear current-voltage models coupled with an original method for solving polynomial coefficients is provided. A series of experiments based on two-tone testing is conducted to measure IM products with the input power from 30 to 44 dBm. The experimental results verify the predictions both in the un-degraded and the degraded conditions. The power-dependence of the PIM features and the effect of contact surface degradation on connectors' performance are observed from the measurements, which are consistent with the theoretical predictions.

This paper investigates the energy-efficient power allocation strategy for multi-user mmWave non-orthogonal multiple access (NOMA) system with different hybrid precoding (HP) structures. Particularly, we consider the fully-access HP structure and the subarray HP structure, respectively. For these two structures, the finite resolution analog precoder is realized through a low-power switches and inverters (SI) network. In the NOMA system, multiple users are first paired according to their channel correlation and gain difference. Following this, we propose hybrid precoding schemes for the low-power SI-based HP structures. Then, a power allocation (PA) problem is formulated to maximize the energy efficiency of the system, subject to per-cluster’ power constraints and per-user’ quality of service constraints. To solve the non-convex PA optimization problem, we devise a suboptimal solution with two-stage PA strategies. Furthermore, the PA problem aiming at conditionally maximizing the spectrum efficiency is also analyzed. Simulation results show that the proposed mmWave-NOMA can achieve higher energy efficiency than the existing mmWave-NOMA scheme and the conventional mmWave orthogonal multiple access scheme.

High-speed interconnected channels, including printed circuit boards (PCB) and high-speed connectors, are widely used in digital baseband communication systems. Connector degradation may lead to deterioration of the integrity of digital signals and is one of the major causes of low communication quality. In the present work, the effect of electrical contact degradation on signal integrity was investigated using model analysis and experimental testing. A 3D electromagnetic field model of a high-speed channel with a degraded contact surface was developed to evaluate transmission loss, signal reflection, and crosstalk. Using multi-conductor transmission line theory and contact physics, a distributed parameter circuit model of a high-speed channel with a degraded contact surface was also developed. The electromagnetic field model results are in good agreements with those obtained from the distributed parameter circuit model. Both the electromagnetic field model and the circuit model results are validated using experimental tests. The results of this investigation provide a better understanding of the characteristics of signal transmission through a degraded contact surface in a high-speed channel and theoretical support for identifying failure features in fault diagnosis.

Coaxial connectors play an important role in communication systems. However, passive intermodulation (PIM) and cross modulation resulting from slight nonlinear characteristics in coaxial connectors may negatively impact signal transmission quality. In addition, degradation of coaxial connectors tends to exacerbate such effects. In the current work, the nonlinear characteristics of pristine coaxial connectors are analyzed and modeled. From these results, a new polynomial behavior model is developed to describe the nonlinear characteristics for connectors with various levels of degradation for the first time. A series of two-tone PIM tests on pristine connectors and degraded connectors are conducted with the input power from 35 dBm to 44 dBm. The test results validate the model for pristine connectors and the model for connectors with various levels of degradation. The error vector magnitude (EVM) is selected as the index to quantify the level of signal distortion. The power of PIM and cross modulation interference, and the impacts of PIM and cross modulation on EVM are theoretically calculated and simulated. This work serves to provide a behavior model that describes the nonlinear characteristics of pristine and degraded connectors, and a theoretical basis for evaluating the impacts of PIM and cross modulation on signal distortion.