Interference Rejection Research Articles

Beamformer With Constant-Gm Vector Modulators and Its Spatial Intermodulation Distortion

Spatial interference rejection in analog adaptive beamforming receivers can improve the distortion performance of the circuits following the beamforming network, but is susceptible to the nonlinearity of the beamforming network itself. This paper presents an analysis of intermodulation product cancellation in analog active phased array receivers and verifies the distortion improvement in a four-element adaptive beamforming receiver for low-power applications in the 1.0-2.5-GHz frequency band. In this architecture, a constant-Gm vector modulator is proposed that produces an accurate equidistance square constellation, leading to a sliced frontend design that is duplicated for each antenna element. By moving the transconductances to RF, a fourfold reduction in power is achieved, while simultaneously providing input impedance matching. The 65-nm implementation consumes between 6.5 and 9 mW per antenna element and shows a +1 to +20 dBm in-band and out-of-beam third-order intercept point due to intermodulation distortion reduction.

Resistance‐to‐digital converter designed for high power‐line interference rejection capability

A novel resistance-to-digital converter (RDC), based on the integrating type analogue-to-digital converter principle, is presented in this study. The conversion time of the proposed scheme is not a function of the current value of the parameter being measured. Thus, by suitably setting this parameter, the converter can be made to reject the effects of interference at a particular frequency, such as, that due to power-line at 50/60 Hz. Error analysis was conducted to ascertain the effects of non-idealities of various components of the circuit, on its output. Simulation studies were carried out in LTSPICE to verify the linearity and the interference rejection capability of the converter. Further, a prototype RDC was developed in the laboratory and tested to confirm the results of the simulation.

SDMF based interference rejection and PD interpretation for simulated defects in HV cable diagnostics

Partial Discharge (PD) in cable systems causes deterioration and failure, identifying the presence of PD is crucial to Asset Management. This paper presents methods for interference signals rejection and for PD interpretation for five types of artificial defect in 11 kV ethylene-propylene rubber (EPR) cable. Firstly, the physical parameters of the artificial defects used for PD signal generation are introduced. Thereafter, the sample stress regime, PD testing and detection systems, including IEC 60270 measurement system and High Frequency Current Transformer (HFCT), are outlined. Following on, a novel Synchronous Detection and Multi-information Fusion (SDMF) based signal identification method is developed, to separate PD and interference signals within raw data. Finally, a comparative PD analysis of two detection systems is carried out and several characteristics of insulation related PD signals of EPR cables are reported. The SDMF based data pre-processing and the comparative PD activity analysis contribute to improvement of PD pattern recognition and assist in on-line PD monitoring systems.

Single-use nonenzymatic glucose biosensor based on CuO nanoparticles ink printed on thin film gold electrode by micro-plotter technology

We reported a single-use non-enzymatic glucose biosensor based on a printed CuO nanoparticles film on thin gold film electrode. This three-electrode configuration biosensor consisted of a thin gold film (10nm) working and counter electrodes and a thick-film printed Ag/AgCl reference electrode. The biosensor was fabricated on a polyethylene terephthalate (PET) substrate. CuO nanoparticles with an average particle size of ~7nm were synthesized by a one-step precipitation approach, formulating an aqueous-based nanoparticles ink. A CuO nanoparticles square area of 0.9×0.9mm2 was printed on thin film Au working electrode (φ=1.4mm) of the biosensor by micro-plotter technology. The remarkable resolution and dimensional accuracy of micro-plotter printing technology resulted in a better development of nano-catalyst biosensors compared to conventional ink-jet printing or other techniques. X-ray Photoelectron Spectroscopy (XPS) and Transmission Electron Microscopy (TEM) were used to characterize the printed biosensor. Field Emission Scanning Electron Microscopy (FESEM) characterizations of the copper oxide printed features showed a nano-porous morphology together with high printing resolution. Cyclic Voltammetry (CV) and chronoamperometry (CA) measurements revealed the considerable electro-catalytic performance of the printed biosensor having high sensitivity (2419.8μAmM−1cm−2), acceptable stability and excellent interference rejection against ascorbic acid (AA), uric acid (UA), dopamine (DA), lactose, mannose and maltose. Interference rejection studies were performed in undiluted human serum to verify the functionality of the sensor for real samples. The developed biosensor showed a linear response toward glucose in the range of 0.1 to 6.5mM. The lower detection limit of the biosensor was measured as 0.5μM glucose. This study suggested a high performance robust glucose biosensor not only suitable for biomedical single-use in-vitro application but also for long-term glucose monitoring in industrial processes.

FPGA realisation-based architecture for direction-of-arrival in wireless communication

A signal processing technique used in sensor arrays for directional signal transmission or reception is known as beamforming. By combining elements in a phased array beamforming is achieved. This is done in such a way that, signals at particular angles experience constructive interference while others experience destructive interference. To detect and calculate the signal-of-interest at the output of a sensor array by means of the most desirable spatial filtering and interference rejection, adaptive beamforming is used. But, before beamforming technique, the directions of desired users and undesired users or interferes must be prevailed using a direction-of-arrival (DOA) estimation algorithm. This paper presents FPGA realisation-based design of a smart antenna system based on DOA estimation algorithm using Xilinx system generator (XSG). MUSIC algorithm is considered in this paper to identify the DOA of the input signals incident on the sensor array comprising the smart antenna system. The MUSIC algorithm is a simple and effective eigen structure method of DOA estimation. With this approach, the results of proposed simulated FPGA design of a smart antenna system shows effective hardware utilisation.

FPGA realisation-based architecture for direction-of-arrival in wireless communication

A signal processing technique used in sensor arrays for directional signal transmission or reception is known as beamforming. By combining elements in a phased array beamforming is achieved. This is done in such a way that, signals at particular angles experience constructive interference while others experience destructive interference. To detect and calculate the signal-of-interest at the output of a sensor array by means of the most desirable spatial filtering and interference rejection, adaptive beamforming is used. But, before beamforming technique, the directions of desired users and undesired users or interferes must be prevailed using a direction-of-arrival (DOA) estimation algorithm. This paper presents FPGA realisation-based design of a smart antenna system based on DOA estimation algorithm using Xilinx system generator (XSG). MUSIC algorithm is considered in this paper to identify the DOA of the input signals incident on the sensor array comprising the smart antenna system. The MUSIC algorithm is a simple and effective eigen structure method of DOA estimation. With this approach, the results of proposed simulated FPGA design of a smart antenna system shows effective hardware utilisation.

Toward high value sensing: monolayer-protected metal nanoparticles in multivariable gas and vapor sensors.

For detection of gases and vapors in complex backgrounds, "classic" analytical instruments are an unavoidable alternative to existing sensors. Recently a new generation of sensors, known as multivariable sensors, emerged with a fundamentally different perspective for sensing to eliminate limitations of existing sensors. In multivariable sensors, a sensing material is designed to have diverse responses to different gases and vapors and is coupled to a multivariable transducer that provides independent outputs to recognize these diverse responses. Data analytics tools provide rejection of interferences and multi-analyte quantitation. This review critically analyses advances of multivariable sensors based on ligand-functionalized metal nanoparticles also known as monolayer-protected nanoparticles (MPNs). These MPN sensing materials distinctively stand out from other sensing materials for multivariable sensors due to their diversity of gas- and vapor-response mechanisms as provided by organic and biological ligands, applicability of these sensing materials for broad classes of gas-phase compounds such as condensable vapors and non-condensable gases, and for several principles of signal transduction in multivariable sensors that result in non-resonant and resonant electrical sensors as well as material- and structure-based photonic sensors. Such features should allow MPN multivariable sensors to be an attractive high value addition to existing analytical instrumentation.

Macrocell Protection Interference Alignment in Two-Tier Downlink Heterogeneous Networks

Conventional interference alignment (IA) has been developed to mitigate interference problems for the coexistence of picocells and macrocells. This paper proposes a macrocell protection interference alignment (MCP-IA) in two-tier MIMO downlink heterogeneous networks. The proposed method aligns the interference of the macro user equipment (UE) and mitigates the interference of the pico-UEs with a minimum mean squared error interference rejection combining (MMSE-IRC) receiver. Compared to the conventional IA, the proposed MCP-IA provides an additional array gain obtained by the precoder design of the macro BS and a diversity gain achieved by signal space selections. The degrees of freedom (DoF) of the proposed MCP-IA are equal to or greater than that of the conventional IA and are derived theoretically. Link level simulations show the link capacity and the DoF of the macro UE, and also exhibit the proposed MCP-IA attaining additional array gain and diversity gain. The system level simulation illustrates that the proposed method prevents the interference of the macro UE completely and preserves the throughput of the pico-UE irrespective of the number of picocells. For 4×2 antenna configuration, the system level simulation demonstrates that the proposed MCP-IA throughput of the macro UE is not affected by the number of picocells and that the proposed MCP-IA throughput of the picocells approaches that of single-user MIMO (SU-MIMO) with a 3% loss.

大规模MIMO系统的干扰抑制合并技术研究

为了解决大规模MIMO系统中由于导频污染引起的严重的小区间干扰，对大规模MIMO系统中的干扰抑制合并(IRC)技术进行研究。该技术可利用小区间干扰和信道估计的相关性来抑制干扰。在非理想信道状态信息(CSI)情况下，分别分析了基站天线数、功率收缩因子和干扰因子对IRC方法系统性能的影响，并和最大比合并(MRC)和最小均方误差(MMSE)方法进行仿真对比。仿真结果表明，IRC系统性能明显优于MRC和MMSE，并且在基站天线数低于500时，功率收缩因子可以大于1/2。 In order to solve the serious inter-cell interference caused by the pilot contamination in massive MIMO, the interference rejection combining (IRC) technique is studied. The IRC technique can exploit the correlation between channel estimates and interference to suppress interference. In the case with imperfect channel state information (CSI), the IRC system performance is separately analyzed in the regimes of different numbers of base station (BS) antennas, power scaling factors and interference factors, and simulation comparison with maximum ratio combining (MRC) and minimum mean-square-error (MMSE) methods is made. Simulation results show that IRC has obviously better performance than MMSE and MRC, and the power scaling factor can be greater than 1/2 when the number of BS antennas is less than 500.

A 5.5 mW ADPLL-Based Receiver With a Hybrid Loop Interference Rejection for BLE Application in 65 nm CMOS

This paper presents a low-power hybrid-loop receiver (RX) with high-interference tolerance for Bluetooth low energy (BLE). The hybrid-loop structure based on an all-digital phase-locked loop enables the RX to both enhance the interference tolerance and digitize the frequency-modulated signal without an ADC. A novel single channel receiving method, which enables the conversion of the constellation from frequency shift keying to differential binary phase shift keying signal, is adopted to eliminate the Q-channel signal processing to reduce the power consumption. The prototype RX fabricated in a 65 nm CMOS technology consumes only 5.5 mW and fulfills the BLE requirements of the adjacent channel rejection and out-of-band blocker tolerance without exception. The sensitivity level is −90 dBm.

Constrained Null Space Component Analysis for Semiblind Source Separation Problem.

The blind source separation (BSS) problem extracts unknown sources from observations of their unknown mixtures. A current trend in BSS is the semiblind approach, which incorporates prior information on sources or how the sources are mixed. The constrained independent component analysis (ICA) approach has been studied to impose constraints on the famous ICA framework. We introduced an alternative approach based on the null space component (NCA) framework and referred to the approach as the c-NCA approach. We also presented the c-NCA algorithm that uses signal-dependent semidefinite operators, which is a bilinear mapping, as signatures for operator design in the c-NCA approach. Theoretically, we showed that the source estimation of the c-NCA algorithm converges with a convergence rate dependent on the decay of the sequence, obtained by applying the estimated operators on corresponding sources. The c-NCA can be formulated as a deterministic constrained optimization method, and thus, it can take advantage of solvers developed in optimization society for solving the BSS problem. As examples, we demonstrated electroencephalogram interference rejection problems can be solved by the c-NCA with proximal splitting algorithms by incorporating a sparsity-enforcing separation model and considering the case when reference signals are available.

Development of a microelectrochemical biosensor for the real-time detection of choline

Here we describe the development of a first generation biosensor for the detection of brain extracellular choline, investigating important considerations for in-vivo monitoring such as sensor sensitivity, O2 interference and selectivity. Extensive optimisation of choline biosensor designs resulted in a biosensor with excellent sensitivity towards choline (0.54±0.03nA/μM). Oxygen interference studies demonstrate a 1% reduction in current at 50μM O2 when compared to atmospheric O2 levels (200μM), indicating that the sensor can be used for reliable choline monitoring, free from changes in current associated with physiological O2 fluctuations. A negligible sensitivity of 0.0021±0.0002nA/μM n=8 was achieved utilising poly-phenylenediamine (PPD) as a permselective membrane for interference rejection of ascorbic acid (AA), the most physiologically important endogenous electroactive species present in the brain. The optimised biosensor when implanted into the striatum of a freely moving rat successfully detected local perfusions of choline demonstrating the sensors ability to detect choline in-vivo.

Integrated Synthetic Bandstop Filters for Blocker Rejection at RF and Microwave Frequency Bands

In this paper, active synthetic band-stop filter (BSF) for interference rejection at 2–4, 4–8, and 8–16 GHz are presented. In the designs, a sharp notch, typically less than −50 dB for the entire frequency bands, is synthesized by subtracting the bandpass filter output from the all-pass (AP) output. The proposed synthetic notch filters allow optimization of filter dynamic range (DR) in the AP amplifier and frequency selectivity in the BPF independently, breaking the tradeoff between selectivity and DR ingrained in passive filters. In addition, the notch attenuation can be controlled independently of the filter bandwidth and center frequency tuning, providing more operational flexibility in suppressing blocker under a dynamic interference environment. The notch filters are fabricated in a 0.13- $\mu \text{m}$ SiGe BiCMOS technology. The measured gain is 0–1 dB for all three filters. The 2–4 GHz notch filter shows a 12–13 dB noise figure (NF) and a $- 2\sim -1.5$ dBm input 1-dB compression point (IP $_{{-1\text {dB}}}$ ) in the passband while drawing 20–30 mA from a 3.3-V supply. For the 4–8-GHz design, the measurement shows a 8–10-dB NF and a −1–1 dBm IP $_{-1\text {dB}}$ in the passband at the expense of 20–27.6 mA from a 3.3 V supply. For the 8–16 GHz filter, the measured NF is 14–17 dB and the IP $_{-1\text {dB}}$ is 0–4 dBm with a 70–90 mW dc power dissipation. The die areas are $0.68 \times 0.72$ mm2, $0.63 \times 0.63$ mm2, and $0.62\times 0.57$ mm2 for the S-band, C-band, and X-/Ku-band filters, respectively.

Class-specific discriminant time-frequency analysis using novel jointly learnt non-negative matrix factorization

Time-frequency (TF) representation has found wide use in many challenging signal processing tasks including classification, interference rejection, and retrieval. Advances in TF analysis methods have led to the development of powerful techniques, which use non-negative matrix factorization (NMF) to adaptively decompose the TF data into TF basis components and coefficients. In this paper, standard NMF is modified for TF data, such that the improved TF bases can be used for signal classification applications with overlapping classes and data retrieval. The new method, called jointly learnt NMF (JLNMF) method, identifies both distinct and shared TF bases and is able to use the decomposed bases to successfully retrieve and separate the class-specific information from data. The paper provides the framework of the proposed JLNMF cost function and proposes a projected gradient framework to solve for limit point stationarity solutions. The developed algorithm has been applied to a synthetic data retrieval experiment and epileptic spikes in EEG signals of infantile spasms and discrimination of pathological voice disorder. The experimental results verified that JLNMF successfully identified the class-specific information, thus enhancing data separation performance.

Cross-Layer Optimization for Multi-Hop Wireless Networks With Successive Interference Cancellation

The classical approach to interference management in wireless medium access is based on avoidance. Recently, there is a growing interest in exploiting interference (rather than avoiding it) to increase network throughput. This was made possible by a number of advances at the physical layer. In particular, the so-called successive interference cancellation (SIC) scheme appears very promising, due to its ability to enable concurrent receptions from multiple transmitters as well as interference rejection. Although SIC has been extensively studied as a physical layer technology, its research and advances in the context of multi-hop wireless network remain limited. In this paper, we aim to close this gap by offering a systematic study of SIC in a multi-hop wireless network. After gaining a fundamental understanding of SIC’s capability and limitation, we propose a cross-layer optimization framework for SIC that incorporates variables at physical, link, and network layers. We use numerical results to affirm the validity of our optimization framework and give insights on how SIC behaves in a multi-hop wireless network.

Design considerations for neural amplifiers.

The initial amplification stage is a critical element of a neural signal acquisition system, and the design of low-noise, low-power amplifiers has received a great deal of attention in recent publications. In this paper we discuss practical considerations for the design of amplifiers intended for neural interfaces. Noise is a major issue due to the low amplitude of neural signals. Practical system deployments also require adequate rejection of common-mode interference, such as that due to line power noise or muscle artifacts, and supply noise. This paper attempts to provide some guideance for system and circuit designers and point out opportunities for potential future exploration.

Large Array Null Steering Using Compressed Sensing

In this letter, array null steering is formulated as a sparse recovery problem. In addition, a novel null steering scheme for large arrays by perturbing only a few elements is presented. To achieve this goal, compressed sensing (CS) is used to exploit the sparsity of the perturbed elements. The advantages of the proposed scheme are a significant reduction in hardware cost and lower power consumption, as well as less aging of the elements and faster response. Simulation results show that the CS-based method could be efficiently used to generate wide nulls using at least two elements. The interference rejection ratio achieved by the proposed method is 10–20 dB better than the existing solutions. The performance of different null generation methods in terms of peak-to-sidelobe ratio, pointing error, and beam-width is compared as well. The proposed algorithm is a prominent solution for the future 5G base stations, where a fast and low-cost beam shaping algorithm is required.

An Efficient Sensor-Node Selection Algorithm for Sidelobe Control in Collaborative Beamforming

Collaborative beamforming (CB), which forms a virtual antenna array from a number of distributed wireless nodes in wireless sensor networks (WSNs), can increase the transmission range, enhance energy efficiency, and prolong network lifetime. With perfect carrier phase synchronization, it has been revealed that CB guarantees a stable main lobe, regardless of the locations of the collaborative nodes. However, the sidelobe locations and the level of CB cannot be predicted due to random deployment of the nodes. A high-order sidelobe will cause severe interference to unintended receivers and degrade network capacity. Known sidelobe control methods suffer from exponential complexity with the number of unintended receivers. We tackle this by a novel algorithm that uses decentralized cross-entropy optimization (CEO) to search over different node combinations, which is proven to find the optimal solution with probability one. Simulation results verify the effectiveness of the proposed scheme and illustrate that the proposed scheme can achieve greater interference rejection at much lower complexity compared with a conventional method.

Method of compensating the active component of combined interference in coherent pulse radar

The combined impact of active and passive interferences on coherent pulse radar was investigated. A mathematical model was developed implementing a new method for compensating the active component of combined interference in coherent pulse radar employing spectral differences in the structure of active and passive interferences. The results of simulation reveal that the polarization-time signal processing involving the use of rejection filters for suppression of passive interferences in circuits of forming the weight coefficients of automatic compensator make it possible to significantly enhance the quality of active interference compensation under conditions of exposure to combined interferences. The rejection of passive interference in circuits of forming the weight coefficients is shown to eliminate the distortion of passive spectrum distortion at the output of adaptive polarization filter.

Eigen Domain Interference Rejection Combining Algorithm for MIMO Systems

In this letter, we investigate an eigen domain interference rejection combining (E-IRC) algorithm for multiple-input–multiple-output (MIMO) systems suffering from narrowband interference (NBI). The received signals are transformed into the eigen domain, which is obtained by eigenvalue decomposition of the time domain autocorrelation matrix of the NBI, and the interference is rejected in the eigen domain via multiple antennas. V-BLAST and Alamouti schemes are considered in this letter. For the V-BLAST scheme, the E-IRC algorithm is an extension of the one for SIMO system. For the Alamouti scheme, we redesign the transmission codeword, which can preserve the orthogonality in the eigen domain, and propose an NBI rejection algorithm based on the spatial whitening filter.