Cross-modulation Interference Research Articles

Modeling of Signal Distortion Caused by Passive Intermodulation and Cross Modulation in Coaxial Connectors

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 this 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 is conducted with the input power from 35 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.

Energy detection UWB system based on pulse width modulation

A new energy detection ultra-wideband system based on pulse width modulation is proposed. The bit error rate (BER) performance of this new system is slightly worst than that of a pulse position modulation (PPM) system in additive white Gaussian noise channels. In multipath channels, this system does not suffer from cross-modulation interference as PPM, so it can achieve better BER performance than PPM when cross-modulation interference occurs. In addition, when synchronisation errors occur, this system is more robust than PPM.

Adaptive threshold to mitigate the effect of cross-modulation interference and synchronisation errors in energy detection pulse position modulation ultra-wideband systems

In conventional energy detection (ED) pulse position modulation (PPM) systems, the optimal decision threshold is 0. However, when cross-modulation interference (CMI) or synchronisation errors occur, the optimal threshold deviates from 0 and the bit error rate (BER) performance is degraded greatly. An adaptive threshold is developed to replace 0 threshold to find the optimal threshold. The research results show that this adaptive threshold effectively mitigates the effect of cross modulation interference (CMI) or synchronisation errors and achieves BER improvement.

Cross-Modulation Interference With Lateralization of Mixed-Modulated Waveforms

This study investigated the ability to use spatial information in mixed-modulated (MM) sounds containing concurrent frequency-modulated (FM) and amplitude-modulated (AM) sounds by exploring patterns of interference when different modulation types originated from different loci as may occur in a multisource acoustic field. Interaural delay thresholds were measured from 5 normal-hearing adults for an AM sound in the presence of interfering FM and vice versa as a function of interferer modulation rate. In addition, the effects of near versus remote interferer rates, and fixed versus randomized interferer interaural delay, were investigated. AM interfered with lateralization of FM at all modulation rates. However, the FM interfered with AM lateralization only when the FM rate was higher than the AM rate. This rate asymmetry was surprising given the prevalence of low-frequency dominance in lateralization, but was predicted by a cross-correlation model of binaural interaction. Effects were similar for fixed and randomized interferer interaural delays. The results suggest that in multisource environments, sources containing different modulation types significantly interfere with localization in complex ways that reveal interactions between modulation type and rate. These findings contribute to the understanding of auditory object formation and localization.

Mitigation of cross-modulation interference in UWB energy detector receivers

For ultra-wideband (UWB) pulse position modulation (PPM) signalling, cross-modulation interference (CMI) occurs when the amount of the pulse-position shift is less than the maximum excess delay of the multipath channel. Such CMI severely degrades the bit error rate (BER) performance of energy detector (ED) receivers. To alleviate the adverse effect of CMI, in this letter we propose an enhanced energy detector (E-ED) combined with block-orthogonal-coded PPM (BOC-PPM). Each PPM frame is chopped into several sub-windows and the outputs of sub-windows are combined to form the decision statistic. The optimum combining scheme is derived based on the maximum likelihood (ML) criteria. Through analysis and simulations, we show that E-ED can significantly suppress CMI and thus performs well in the CMI region.

Cross-Modulation Interference and Mitigation Technique for Ultrawideband PPM Signaling

The detection issues of ultrawideband (UWB) signals depend on the type of modulation scheme that is used during the transmission. Cross-modulation interference (CMI) is a problem that is specific to UWB pulse-position-modulation (PPM) signaling. In this paper, the effects of CMI on the performance of noncoherent UWB receivers are analyzed. The probabilities of error for transmitted-reference (TR) and energy detector (ED) receivers in the presence and absence of CMI are derived. Optimal and suboptimal CMI avoidance algorithms, which are based on novel acquisition techniques, are proposed for Rake receivers. The results show that the performance degradation in both receivers, which is due to the CMI effects, can be significant, depending on the modulation index. TR receivers still can be functional in the presence of CMI, and the target performance level determines the modulation index to be used. It is unlikely that effects of CMI on the performance of ED receivers in the presence of CMI are more severe relative to TR receivers, and the performance level is not acceptable. As a result, PPM signaling is not an appropriate modulation technique for ED receivers that are operating in the CMI region, unless CMI mitigation algorithms can be developed. Furthermore, the proposed optimal and suboptimal algorithms are two promising schemes for avoiding the CMI effects and, consequently, for improving the performance of Rake receivers operating in the CMI region.

Perceived Picture Quality in CATV Systems With Impairments

The results of a study of subjective reactions to a variety of impairments in CATV systems is presented. Methods of simulating and measuring random noise, inter-modulation, cross-modulation, co-channel and adjacent channel interference, and hum modulation are described. The effects of some of these impairments on picture quality, as perceived by a group of subjects are shown. The results provide an indication of the continuous relationship between picture quality and impairment level.

Crossmodulation in transistorized TV tuners

This paper describes crossmodulation in transistorized television tuners and develops an analytical method for predicting the crossmodulation of transistors over a wide range of operating biases and frequencies. The paper also evaluates crossmodulation interference in the mixer stage as well as in the rf stage of television tuners under adjacent-channel conditions. Various methods for the reduction of crossmodulation are reviewed. A transistor television tuner modified in accordance with the technique developed in the paper is shown to be substantially improved in crossmodulation performance.

Radio Channel Selection for Interference-Free Operation

A procedure for the selection of mutually-interference-free (MIF) radio communication channels has been devised. Cross-modulation interference and various forms of intermodulation products were considered, as well as other interferences representative of real situations. The channel-selection process consists of the assignment of a priority to all previously-accepted channels over all later trial channels that result in an interference-producing condition. This results in the maximum number of MIF channels that can be obtained by any presently-known practical method from a given available bandwidth. Use of the procedure indicates that a 40-60-per cent increase in the maximum number of MIF channels may be achieved by reallocation of frequencies in the 225-400-mc band. Reassignment would not penalize any of the services entitled to use of the military VHF/UHF band. The use of a slide rule "Radio Interference Calculator," developed specifically for the problem, considerably reduces the computations required for MIF channel selection.