Residual Interference Research Articles

The Residual ISI for Which the Convolutional Noise Probability Density Function Associated with the Blind Adaptive Deconvolution Problem Turns Approximately Gaussian.

In a blind adaptive deconvolution problem, the convolutional noise observed at the output of the deconvolution process, in addition to the required source signal, is—according to the literature—assumed to be a Gaussian process when the deconvolution process (the blind adaptive equalizer) is deep in its convergence state. Namely, when the convolutional noise sequence or, equivalently, the residual inter-symbol interference (ISI) is considered small. Up to now, no closed-form approximated expression is given for the residual ISI, where the Gaussian model can be used to describe the convolutional noise probability density function (pdf). In this paper, we use the Maximum Entropy density technique, Lagrange’s Integral method, and quasi-moment truncation technique to obtain an approximated closed-form equation for the residual ISI where the Gaussian model can be used to approximately describe the convolutional noise pdf. We will show, based on this approximated closed-form equation for the residual ISI, that the Gaussian model can be used to approximately describe the convolutional noise pdf just before the equalizer has converged, even at a residual ISI level where the “eye diagram” is still very closed, namely, where the residual ISI can not be considered as small.

4-bit DAC based 6.9Gb/s PAM-8 UOWC system using single-pixel mini-LED and digital pre-compensation.

Low-cost underwater wireless optical communication (UOWC) systems are attractive for high-speed connections among unmanned vehicles or devices in various underwater applications. Here we demonstrate a high-speed and low-cost UOWC system using a low-resolution digital to analog converter (DAC), a single-pixel mini-sized light-emitting diode (mini-LED), and digital pre-compensation (DPC). The enabled DPC scheme comprises digital pre-distortion (DPD), digital pre-emphasis (DPE), and digital resolution enhancer (DRE), which pre-compensate for mini-LED nonlinearity, the bandwidth limitation of the mini-LED and avalanche photodiode detector, and DAC resolution limitation, respectively. The simulation results show that the in-band signal-to-quantization noise ratio can be increased by 6.8 dB using DRE based on a 4-bit DAC. To further improve the system capacity, we tune the level of DPE in order to optimize the trade-off between the residual inter-symbol interference and signal-to-noise ratio. With the combination of optimized DPE and DRE, we obtain a 21.1% higher data rate compared with full DPE only and demonstrate the transmission of 6.9 Gb/s PAM-8 signal over a 2-m distance underwater based on a single-pixel mini-LED and 4-bit DAC. This paper reports a cost-effective UOWC system first using a low-resolution DAC and DPC, which offers a promising path toward low-cost underwater optical wireless networks.

Energy Efficiency Maximization of Full-Duplex NOMA Systems With Improper Gaussian Signaling Under Imperfect Self-Interference Cancellation

This work addresses the energy efficiency maximization for a downlink cooperative full-duplex non-orthogonal multiple access (FD-NOMA) system in the presence of imperfect self-interference cancellation. We consider the case where users adopt improper Gaussian signaling (IGS) for their transmission and consequently derive the achievable rate of each link in the cooperative system. We jointly optimize the power allocation at the base-station and the IGS circularity coefficients of the cooperative IGS-based FD-NOMA system to maximize its energy efficiency subject to quality-of-service (QoS) requirements. Furthermore, improper constellation diagrams are designed using the predefined optimized IGS coefficients to study the impact of IGS on bit error rate performance. Simulation results demonstrate considerable energy efficiency performance gain of IGS-based FD-NOMA system over its proper Gaussian signaling (PGS)-based FD-NOMA counterpart under residual interference from imperfect self interference cancellation.

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.

Multipoint Overlapping Optical Networks

Coherent transmission has drastically evolved in the last decade to provide high flexibility to improve spectral efficiency. This yields a point-to-point capacity close to Shannon's limit. In this work, we present the multipoint overlapping optical network architecture in a multi-transmitter to single-receiver context to boost the network capacity. It overlaps two optical signals, partly reusing network resources, here frequency slots of 12.5 GHz width. We show that a joint digital signal processing, based on multi-stage parallel interference cancellation efficiently compensates inter-channel interference up to 39% spectrum overlap with a 1 dB SNR penalty for PDM-QPSK signals. To investigate the impact of the residual interference penalty, we model the proposed solution as an additional power-independent Gaussian-noise term introduced in the transmission. Experiments and simulations have successfully validated the model and the extra penalty is shown to be dependent only on the chosen overlapping given factor. Finally, with such a model, we study the network gains brought by the proposed architecture. We investigate different networking scenarios assuming either 2-slot and 3-slot of overlapping, resulting in ∼20% and ∼40% of overlapping. We demonstrate a network capacity gain of up to 17%.

On the Performance of the Unified NOMA Framework for Satellite-Terrestrial Networks with Hardware Impairments

A unified nonorthogonal multiple access (NOMA) framework for satellite-terrestrial network is investigated over Shadowed-Rician fading channels, which can be applied to both power domain NOMA (PD-NOMA) and code domain NOMA (CD-NOMA). Under the realistic assumption of hardware impairments (HIs) and imperfect successive interference cancellation (SIC), the achievable outage probability of the paired users is analyzed first, and the closed-form expressions of exact and asymptotic outage probability are derived. Next, the ergodic sum rate is investigated in different levels of HIs and residual interference. In addition, the energy efficiency in the delay-tolerant transmission mode is studied to characterize the performance of the satellite-terrestrial network. Finally, the Monte Carlo simulation results demonstrate the accuracy of theoretical derivation and showcase the effects of a wide range of satellite channel parameters and the realistic assumption on outage probability, ergodic rate, and energy efficiency.

Effect of mixed plastic hardening on the cyclic contact between a sphere and a rigid flat

This paper studies the effect of mixed plasticity mode (combined with isotropic and kinematic hardening law) on the cyclic contact between an elastic-plastic sphere and a rigid flat. Assuming power-law hardening with different levels of mixed plasticity for the sphere, we derived a semi-analytical expression of load versus interference during the first loading and unloading process. During cyclic loading, our results indicate that the isotropic plasticity model shows no variation of residual interference, while kinematic plasticity has the cyclic effect on the residual interference, and this effect is bigger for the material with a higher hardening exponent. In addition, we provided the semi-analytical expression for the evolution of residual interference, which is accurate for the strain hardening exponent from 0.1 to 0.5.

Theoretical model and digital extraction of subsurface damage in ground fused silica.

Based on the fracture mechanics and grinding kinematics, a theoretical model is developed to determine various subsurface damage (SSD) parameters and roughness Rz of the ground brittle material with consideration of the material removal mode and spring back. Based on the image processing, a digital method is proposed to extract various SSD parameters from the cross-section micrograph of the ground sample. To verify the model and method, many fused silica samples are ground under different processing parameters, and their SSD depth and roughness Rz are measured. The research results show the average SSD depth (SSDa) can be expressed as SSDa = χ1Rz4/3 + χ2Rz (χ1 and χ2 are coefficients). The SSDa is closer to half of the maximum SSD depth (SSDm) as the wheel speed decreases or the grinding depth, feed speed, or abrasive diameter increases. The SSD length or density basically increases linearly with the increase of the SSDm. The digital method is reliable with a largest relative error of 6.65% in SSD depth, extraction speed of about 1.63s per micrograph, and good robustness to the micrograph size and small-scale residue interference. The research will contribute to the evaluation of SSDs and the optimization of the grinding process of fused silica.

Considering the Parameters of Pulse Width Modulation Voltage to Improve the Signal-to-Noise Ratio of Partial Discharge Tests for Inverter-Fed Motors

The improvements in signal-to-noise ratio (SNR) are indispensable to obtain the desired output signal of partial discharge (PD) under square wave pulsewidth modulation (PWM) voltage. In this article, the effect of complex PWM voltage parameters (rise time, fall time, frequency, duty cycle) on the SNR of PD tests is investigated. The results revealed that the sensor's high-frequency gain should be increased to improve the SNR under faster switching. PD impulses are more likely to be submerged in the residual interference under high-frequency voltage. The SNR can be improved by only detecting the PD at the rising front because the PD signal overlaps with commutation noise at the falling front of short duty cycle voltage, such as 0.03% duty cycle. The above results can reference the PWM parameters and improve the SNR in PD tests for rotating machines controlled by power electronics.

Facing the SNR Wall Detection in Full Duplex Cognitive Radio Networks Using a GLRT Multipath-Based Detector

Recently, with the advances in self-interference cancellation, full-duplex (FD) techniques have become a feasible approach to improve the spectrum usage in new generation wireless systems. In particular, in cognitive radio networks, FD allows a secondary user to simultaneously sense the spectrum and transmit, improving the network efficiency. However, the residual self interference (RSI) arising from an imperfect cancellation, represents a bottleneck for the spectrum sensing performance. This paper analytically demonstrates that RSI represents a colored noise which leads to the SNR Wall phenomenon making the typical OFDM signal detectors no longer robust. To overcome this drawback, we propose a generalized likelihood ratio test detector exploiting the multipath correlation due to the primary user’s (PU) channel. It is proven that the proposed method is not affected by the SNR Wall, hence it is robust w.r.t an imperfect self-interference cancellation. Specifically, best detection performance is achieved when an approximated knowledge of the maximum delay spread of the PU channel is available, otherwise it is shown that a limited performance degradation occurs. Moreover, provided results highlight that our approach outperforms the classical alternatives in different scenarios, including when PU employs a mixed numerology OFDM signal, which characterizes the 5G New Radio waveform.

Analysis of relay selection schemes in underlay cognitive radio non-orthogonal multiple access networks

This article investigates the impacts of relay selection schemes on cooperative underlay cognitive radio non-orthogonal multiple access networks, where the partial relay selection scheme, the max–min relay selection scheme and the two-stage relay selection scheme are applied in the network. Moreover, decode-and-forward protocol is used at the transmission relays. What’s more, in order to show the effect of the schemes on the considered network, the closed-form expressions and asymptotic expressions for the outage probability of the system are derived. Furthermore, the outage performance under the effect of perfect and imperfect successive interference cancellation is analysed. Numerical results are given to illustrate the impacts of the relay selection schemes, the number of relays, the residual interference factor and the power allocation factor on the outage performance. Finally, Monte Carlo simulations are presented to validate the accuracy of the numerical results.

Bringing mass spectrometry into the care of patients with multiple myeloma.

Serum protein electrophoresis methods are widely employed to detect, quantify and isotype M-proteins for multiple myeloma patients. Increasing clinical demands to detect residual disease and interferences from new therapeutic monoclonal antibody treatments have stretched electrophoretic methods to their analytical limits. Newer techniques to detect M-proteins using mass spectrometry (MS) are emerging with improved clinical and analytical performance. These techniques are beginning to gain traction within the routine clinical lab testing. This review describes these MS methods with attention to the current and future roles such testing could play in the care of multiple myeloma patients.

Chirp-Like Polyphase Sequence Based Discrete Circulant Transform Spread OFDM for Bandwidth-Limited IM/DD Systems

We propose and investigate chirp-like polyphase sequence (CLPS) based discrete circulant transform spread (DCrT-S) OFDM in bandwidth-limited intensity-modulation and direct-detection systems. This scheme can control the distribution of residual inter-symbol interference (ISI) and inter-carrier interference (ICI) across subcarriers by adjusting the CLPS's parameters. We also propose a sparse CLPS (SCLPS) scheme, by inserting zeros between the elements of the CLPS, to further balance the effects of the ISI/ICI and the noise and improve the performance by optimizing both the CLPS's parameters and the sparsity. We reveal the optimal design rule of CLPS/SCLPS analytically and investigate the performance of the proposed schemes using two-parameter CLPS in ∼110-Gbit/s simulations and experiments. It is shown that the optimal parameter vector of the CLPS is a Zadoff-Chu sequence that spreads the ISI/ICI more evenly over subcarriers. The performance is further improved by optimizing the sparsity. The optimal CLPS and sparsity are insensitive to the received optical power, the system bandwidth, the length of cyclic prefix, the chirp parameter and the signal data rate, and so can be pre-set without channel information. Both CLPS- and SCLPS-based DCrT-S-OFDM outperform Nyquist PAM, conventional OFDM, discrete-Fourier-transform spread (DFT-S) OFDM, and orthogonal-circulant-transform precoded (OCT-P) OFDM. By using the proposed scheme, the data rate is enhanced by 6.7% and 3.2% compared to DFT-S-OFDM and OCT-P-OFDM at a bit error rate (BER) of 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">−3</sup> , while the complexity is reduced to 57.9% of OCT-P-OFDM.

Performance analysis of full‐duplex device‐to‐device transmitter aided non‐orthogonal multiple access

In this paper, a three-user non-orthogonal multiple access (NOMA) system based on device-to-device (D2D) communication and full-duplex (FD) transmission is proposed, in which the D2D user acts as a decode-and-forward (DF) relay to forward the signal from the base station (BS) to the far user, forming a system termed the FD D2D transmitter aided NOMA (FD-D2D-NOMA). In practical NOMA systems, due to the limitation of decoding ability, the near user cannot always perform successive interference cancellation (SIC) successfully. By considering perfect SIC (pSIC) and imperfect SIC (ipSIC), the close-form expressions for the ergodic sum capacity and outage probability of the proposed FD-D2D-NOMA scheme are derived, which match well with the simulation ones. The ergotic sum capacity and outage probability under different levels of residual self-interference at the FD user and residual interference at the far/near user due to ipSIC are investigated, and the results show that, such interferences have significant impact on the performance of the proposed scheme. Moreover, the analytical and simulation results illustrate the performance gain of the proposed scheme compared with other ones under both pSIC and ipSIC scenarios. The impacts on performance exerted by channel conditions and design parameters are also discussed in this paper.

Target Detection and DOA Estimation for Passive Bistatic Radar in the Presence of Residual Interference

With the development of radio technology, passive bistatic radar (PBR) will suffer from interferences not only from the base station that is used as the illuminator of opportunity (BS-IoO), but also from the base station with co-frequency or adjacent frequency (BS-CF/AF). It is difficult for clutter cancellation algorithm to suppress all the interferences, especially the interferences from BS-CF/AF. The residual interferences will seriously affect target detection and DOA estimation. To solve this problem, a novel target detection and DOA estimation method for PBR based on compressed sensing sparse reconstruction is proposed. Firstly, clutter cancellation algorithm is used to suppress the interferences from BS-IoO. Secondly, the residual interferences and target echo are separated in spatial domain based on the azimuth sparse reconstruction. Finally, target detection and DOA estimation method are given. The proposed method can achieve not only target detection and DOA estimation in the presence of residual interferences, but also better anti-mainlobe interferences and high-resolution DOA estimation performance. Numerical simulation and experimental results verify the effectiveness of the proposed algorithm.

Accurate Statistical BER Analysis of DFE Error Propagation in the Presence of Residual ISI

This brief discusses the limitation of previously published statistical decision feedback equalizer (DFE) models when residual inter-symbol interference (ISI) is present and proposes a method that overcomes this limitation. The paper presents an accurate closed-form expression for the DFE with residual ISI and additive white Gaussian noise (AWGN). The analysis is extended to 4-level pulse amplitude modulation (PAM-4) to cover serial links of current interest. The results verify that the proposed model estimates an accurate bit error rate (BER).

Limitations due to residual interference in a fiber-based optical frequency reference at 1.55 µm

We present an experimental investigation of the stability limits specific to optical frequency standards using fiber optic architecture and semiconductor lasers. A compact setup composed of a semiconductor laser frequency-locked onto an acetylene transition detected in saturated absorption has been implemented using only fiber optic components. Fiber optic technology allows compact and reliable solutions for various applications. However, for high sensitivity and stability applications such as metrology, residual reflections induced by optical index inhomogeneities in connectors and fiber-coupled components leading to spurious interference significantly limit performance. We have examined the origin of the interference fringes superimposed on the detected signal and the limitations they cause to the frequency stability of the reference. The effects of temperature and beam power fluctuations are also examined. Our results show that the frequency stability is limited in the 10 − 13 range by the effect of interference fringes due to use of fiber components.

Effectiveness Evaluation of Dual-Polarized OAM Multiplexing Employing SC-FDE in Urban Street Canyon Environments

This study investigates the system capacity of dual-polarized orbital angular momentum (OAM) multiplexing that employs single-carrier with frequency domain equalization (FDE) in urban street canyon environments. To overcome the impact of multipaths, two types of FDE, designed with and without the consideration of the cross-polarization interference (XPI), are introduced. We derive the effects of the residual inter-mode interference (IMI), inter-symbol interference (ISI), and XPI when applying such FDE and incorporate their impacts into the system capacity analysis. Moreover, we adopt the urban street canyon model based on a ray-tracing simulation, which enables performance evaluation in a realistic multipath environment. The numerical results show that although the computational complexity is increased, the consideration of the XPI in the FDE weight design improves the system capacity, and its effectiveness is remarkable in the cases of short link distances.

Error Control on Mobile Station Sides in Collaborative Multiple-Input Multiple-Output Systems

Collaboration between mobile stations (MSs) may lead to a new form of wireless communication. Collaboration on MS sides considerably improves signal detection performance, especially for multiple-input multiple-output (MIMO) transmission systems. In this study, a novel detector collaboration system is proposed to reduce the traffic volume on inter-MS collaboration links. Multiple MSs in the immediate vicinity are used to collaboratively decode the MIMO signals received from a base station. Furthermore, we consider a distributed detection system, in which multiple detection MSs decode the MIMO signals independently. Multiple decision results are exploited to improve the error performance. Residual interference coefficients were used to finalize the decision results. The error ratio performance and the traffic volume over collaboration wireless links were compared with those of two combining schemes through computer simulations and field experiments. The results revealed that the proposed error control scheme on mobile station sides offers a better tradeoff between the error performance and the traffic volume on the collaboration wireless links.

Addressing Residual Interference in Massive MIMO Utilizing Intelligent Reflecting Surfaces

This paper proposes a novel method to address coherent interference (pilot contamination) in Massive MIMO by incorporating control over propagation environment through Intelligent Reflecting Surfaces. In earlier research it was established that each mobile device has unique spatial signature which can be used as identifier even if they are sharing same pilot sequence. However in certain circumstances when their signals are received at BS with same Angle of Arrival their spatial structure become similar thus their individual identity is lost. This situation adds error in acquisition of channel state information, the accuracy of which is the key to benefit from Massive MIMO. This paper present a method to resolve the mentioned accepted gap using mathematical basis and simulation methods. A mathematical model of Massive MIMO is presented which is widely accepted by the subject modeling community. The model is then used to generate the basis for the presented algorithm through further mathematical studies and simulations. The basic algorithm used for the resolution of pilot contamination problem is finally presented in this paper. The algorithm was simulated using MATLAB and simulation results are tabulated to identify the results of pilot de-contamination after incorporating signal propagation control.