In-band Interference Research Articles

Erratum to “A Nonlinear Receiver Leveraging Cascaded Inverter-Based Envelope-Biased LNAs for In-Band Interference Suppression in the Amplitude Domain” [Nov 21 3360-3374

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Coherent Radar Target Detection With In-Band Cyclostationary Wireless Interference

Spectral congestion necessitates the in-band operation or the spectrum-sharing of legacy radar and communication systems. Since these systems operate in the same band in spectrum-sharing mode, they interfere with one another. To address this problem from the radar&#x2019;s perspective, this paper considers the coherent detection of target-reflected radar signals in the presence of interference from an in-band cyclostationary digital modulated wireless communication signal. Three different cases of target-reflected radar signals, namely, deterministic signals, signals with random phase, and completely random signals, are considered in this paper. The optimum detection rules are derived for these three cases and the corresponding receiver structures for the equalization of the interfering signal are presented. Sub-optimum detection structures are also derived with the assumption that the in-band interference is a white stationary time-invariant Gaussian process. Further, considering the equalization, modified CFAR receiver structures are also presented. By considering the mathematical models for cyclostationary or periodic in-band interference, the performances of the optimum, sub-optimum detectors, and modified CFAR detectors are quantified analytically in terms of detection probability and false alarm probability, and the resulting receiver operating characteristic (ROC) curves are analyzed as a function of the signal-to-interference ratio. It is demonstrated that improper equalization of the interfering signal significantly affects the performance of the optimum detector and this impact is analyzed in detail. As spectrum-sharing becomes more prevalent due to spectrum congestion, the proposed optimal, sub-optimal, and modified CFAR detection rules and receiver structures can be incorporated into existing systems with substantial savings.

Novel Successive Interference Cancellation (SIC) With Low-Complexity for GFDM Systems

Generalized frequency-division multiplexing (GFDM) is one of the promising multi-carrier modulation schemes suitable for next-generation wireless communication systems. The main characteristic of GFDM is the flexible time-frequency structure of data blocks. However, this degree of freedom is obtained at the cost of loss of sub-carrier orthogonality, which leads to self-interference. In this paper, we propose a new model that classifies the GFDM self-interferences into two independent categories as inband and adjacent sub-carriers interferences and show their corresponding mathematical formulations. Building on this model, we propose a successive interference cancellation (SIC) technique with low complexity to eliminate these self-interference effectively. The main distinct feature of our proposed technique is its low computational complexity compared to similar interference cancellation techniques. Our analytical findings and numerical experiments indicate that the proposed model and SIC technique considerably improve the system performance in terms of bit error rate (BER) and signal to interference ratio (SIR). We also show that the results of our analytical findings are in good agreement with those of computer simulations.

An Interference-Tolerant Synchronization Scheme for Wireless Communication Systems Based on Direct Sequence Spread Spectrum

In this paper, an interference-tolerant three-level synchronization scheme for wireless communication systems based on Direct Sequence Spread Spectrum (DSSS) is presented. Although the proposed synchronization scheme is demonstrated in a mixed signal IC solution, it is exportable to fully digital realizations. The proposed technique synchronizes the received pseudo-random sequence (PRS) modulated signal with the receiver (RX) reference PRS by making use of its autocorrelation properties. The proposed scheme employs 3 levels that make the proposed scheme tolerant to strong in-band interferences. Experimental results for the prototype demonstrate the capabilities of the proposed approach to achieve over 50% of clock cycle tracking even in the presence of interferences with a power of 5dB higher than the desired signal power. Fabricated in a mainstream 40nm CMOS technology, the synchronization scheme employs 100MHz PRS at TX and RX; the proposed solution consumes 18.7mW power and around 0.087mm² silicon area.

Detection of radio interference in the UHF amateur radio band with the Serpens satellite

High packet losses when uplinking commands to small satellites have been reported in the UHF amateur band (430–440 MHz) since late 2013. Measurements of the uplink radio environment have shown high levels of in-band interference in previous works, but public measurement results are limited. Average interference levels are usually measured over some time to build heat maps. In this paper, the analysis is focused on sustained interference over a 24 ms time window using a maximum-minimum method. New heat maps and interference power distributions over Europe, Africa, the Middle East and the Americas were obtained using this method on measurements from the Serpens satellite. One of the missions of Serpens was to test an in orbit store-and-forward communication system to exchange short messages with ground sensors for disaster monitoring. The satellite operators had difficulties commanding the satellite due to interference, causing bit errors in uplink packets. Interference power of up to −70 dBm was detected during in-orbit measurements over Europe and North America, while expected received power from the ground stations was not more than −80 dBm. High power space-object tracking radars on the ground operating in the 420–450 MHz band could be the cause, but further measurements are required to verify this. Characterizing this interference can help develop mitigation techniques for future satellite communication systems.

A Nonlinear Receiver Leveraging Cascaded Inverter-Based Envelope-Biased LNAs for In-Band Interference Suppression in the Amplitude Domain

This article presents a 2.4-GHz 65-nm CMOS fully integrated nonlinear mixer-first receiver (RX) for the Internet of Things (IoT). To power efficiently improve the in-band interference resilience, we propose an inverter-based envelope-biased low noise amplifier (IBEB-LNA), which exploits dynamic biasing voltage generated from its input signal envelope to suppress the interferer in the amplitude domain. The achievable carrier-to-interference ratio (CIR) at ±3 and ±5 MHz is −45/−59 and −66/−65 dB, respectively. The proposed RX is suitable for ON–OFF keying (OOK) modulation with a 307-kb/s data rate, and the corresponding sensitivity is −83 dBm for keeping 0.1% bit error ratio (BER). The total power consumption is 2.05 mW.

Bandpass Filter With Tunable/Switchable In-Band Interference Rejection

This letter presents a wideband bandpass filter (BPF) with a tunable and switchable in-band notch. This allows the RF front end to pass the signal of interest uninterrupted in the absence of an in-band interferer and reject part of the passband in case a narrowband interferer exists. The BPF is based on a two-path architecture, loaded with resonators on one of the paths to deliver an absorptive notch. The resonators are tuned with varactor diodes and are deactivated when the diodes are in forward bias. The implemented proof-of-concept hardware operates in the 4.8–7.8-GHz frequency range, with an in-band notch tunable between 5 and 6.25 GHz, when activated. The transmission lines were implemented as striplines, resulting in a measured insertion loss of 0.6 dB.

Investigation on In-band Interference Effect and Out-of-band Interference Mechanism of B1I Navigation Receiver

Investigation on In-band Interference Effect and Out-of-band Interference Mechanism of B1I Navigation Receiver

Single Feed Dual-Band RHCP Dielectric Resonator Antenna for GNSS Applications

A single-fed right-handed circularly polarized (RHCP) dielectric resonator antenna (DRA) with in-band filtering for Global Navigation Satellite Systems (GNSS) application is proposed. The design is implemented by placing rectangular DR material above feeding slots through which, two sets of degenerate orthogonal modes, the $TE^{111}$ and higher order $TE^{112}$ mode, are simultaneously excited to achieve circular polarization. The proposed antenna employed simplified structure and feed network to filter antenna radiation between 1.30 and 1.5 GHz to reject in-band interference from L-band satellite and terrestrial communication signals. An antenna prototype is fabricated and tested to validate performance of proposed design with a total antenna size of 103×87.5×50mm3. The measured −10 dB impedance and axial ratio bandwidth are approximately 11.03% (1.164 – 1.3 GHz) and 3.21% (1.559–1.61 GHz) in lower and higher band of GNSS respectively. The gain is found to be of 4 dBi within passband with maximum value of 5.5 dBi at 1.56 GHz.

Performance Analysis of Underwater Acoustic Communications in Barrow Strait

The Arctic Ocean and its various shallow passages are rapidly changing due to global warming. The development of a large-scale wireless network that collects and distributes oceanographic data remotely would be an extremely valuable asset to researchers. This concept, however, is completely dependent upon the ability to acoustically transmit digital information under water over long ranges, which is not currently available. In this work, we investigate the performance of four transceivers that are based on frequency-hopping binary frequency-shift keying and multilevel phase-shift keying (M-PSK) signaling in the 300 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$-$</tex-math></inline-formula> 400-Hz acoustic band. The transceivers use low-rate coding that provides bit rates from 1.8 to 13.3 b/s (bits per second). Their bit error rates are computed based on real data recorded in Barrow Strait (NU). During the 2019 experimental activities, the transmitter was towed by a supporting vessel at an average speed of 4 kn. The receiver, a vertical hydrophone array, was at distance between 14 and 33 km. Additionally, the received signals experienced extended multipath propagation and strong in-band impulsive interferences. For a single-hydrophone receiver, our postprocessing analysis shows reliable bit rates up to 6.7 b/s. When processing uses the array and performs multichannel decision feedback equalization (DFE), the maximum designed rate, i.e., 13.3 b/s, is confirmed. Further analysis reveals that the experimental links could support higher data rates. Our results demonstrate that 2-PSK signaling combined with single-channel DFE and 4-PSK signaling combined with multichannel DFE could reliably achieve 100 and 200 b/s, respectively.

Performance analysis of in-band collision detection for dense wireless networks

With the massive growth of wireless networks comes a bigger impact of collisions and interference, which has a negative effect on throughput and energy efficiency. To deal with this problem, we propose an in-band wireless collision and interference detection scheme based on full-duplex technology. To study its performance, we compare its throughput and energy efficiency with the performance of traditional half-duplex and symmetric in-band full-duplex transmissions. Our analysis considers a realistic protocol and overhead modeling, and a measurement-based self-interference model. Our results indicate that our proposed collision detection scheme can provide significant gains in terms of throughput and energy efficiency in large wireless networks. Moreover, when compared to half-duplex and symmetric full-duplex, our analysis shows that this scheme allows up to 45% more nodes in the network for the same energy consumption per bit. These results suggest that this could be an enabling technology towards efficient, dense wireless networks.

Planar UWB-bandpass filter with multiple passband transmission zeros

A planar ultra-wideband (UWB) bandpass filter (BPF) with multiple passband transmission zeros (TZs) and wide stopband is reported in this manuscript. The basic architecture of the BPF consists of two microstrip-to-coplanar waveguide (CPW) transition arranged on either sides of the substrate. A 3rd order BPF hence developed displays good frequency characteristics with two TZs on either passband edges. Later, defected ground structures (DGS) in the form of complementary split ring resonator (CSRR) and complementary folded split ring resonator (CFSRR) are utilized to place three TZs in the passband so as to cut off in-band interferences. Upon optimized simulation, a prototype is eventually developed and measured for compatible frequency characteristics.

Efficient design approach of triple notched UWB filter

In this article, a triple notched bands (TNB) utra-wideband (UWB) bandpass filter (BPF) is designed based on accurate analytical approach. This study has led to a simple structure composed of an uniform transmission line (UTL) loaded by four stepped-impedance open stubs (SIOS). The proposed design approach allows to accurately define two transmission zeros (TZ) at the cut-off frequencies of the UWB spectrum (3.1 and 10.6 GHz) and three narrow notched bands at 5.18 GHz, 5.86 GHz and 7.92 GHz. The notched band bandwidths could also be controlled as well as the out of band rejection. The simulated and measured results of the designed filter are in good agreement. Interesting performances are obtained satisfying the UWB applications requirements, i.e. insertion loss<1.5 dB, return loss better than 15 dB, high cancellation of the unwanted in-band interferences.

Complex scale feature extraction for gearbox via adaptive multi-mode manifold learning

The transient impacts with sideband modulation caused by some fault of gearbox are the technical basis for fault diagnosis, which will be inevitably interfered by heavy background noise distributed in complex modulation frequency bands. Generally, only the principle components under the selected scale is remained and analyzed as the evidence of fault diagnosis, while some crucial features spread in other scales are ignored. Specially, the selected signal still has lots of in-band noise interference. Motivated by these issues, a new adaptive multi-mode manifold learning (AM2ML) method is proposed to enhance the useful gearbox features distributed complex scales with the in-band noise suppressed. Firstly, a series of mode components are obtained by adaptive variational mode decomposition, where the optimal decomposition level is automatically achieved by the k-value. Time-frequency manifold learning is then respectively employed to mine their corresponding potential structural characteristics. And a reconstructed signal contained multi-scale features are represented via the proportion weights of the correlation coefficients. Therefore, the denoised signal of each manifold mode will be rebuilt by phase preserving and a series of inverse transform while the in-band noise is suppressed. With the weight coefficients of each mode, the final multi-scale features are synthesized. As the result shows, the sub-band energy ratio is introduced to evaluate the effectiveness of the method. The sub-band energy ratio of AM2ML method is about 3 times of VMD method, and about 2 times of fast-kurtogram method. It can be seen that the multiple modes can be adaptively decomposed with the complex scale structural characteristics enhanced by manifold learning, and the expected characteristics distributed in all scales can be well rebuilt via a dynamic weight reconstruction in a self-learning way. The effectiveness of the proposed AM2ML method is verified by the self-made gearbox.

Enhanced tolerance against optical background noise in VLC link by using line coded signal with receiver filter

The performance of visible light communication (VLC) link is significantly affected by optical background noises generated by fluorescent light or AC driven light emitting diode (LED) and eventually degrades the data rate due to the in-band interference between signal and noise. Here, bandwidth efficient 8b10b dc-balanced line coding and post-detection electrical filter based VLC link is demonstrated to improve the system tolerance against the optical background noises. The 8b10b coded signal with low frequency components near DC ensure that the crosstalk noise is effectively minimized by spectral separation of signal and noise contributions. Moreover, the use of post detection filter for 8b10b coded signal gives an additional attenuation of noise frequency to further improve the system tolerance against optical background noise. The proposed VLC link is investigated thoroughly in several noise power levels as well as different noise frequencies, where the results indicate improved system tolerance against noise power by about 6.5 dB in compare to conventional data signal. The demonstration also shows that the proposed scheme maintains a low BER for the noise frequency up to 500 kHz for 10 Mb/s data modulation having a good eye opening.

An Efficient Sinusoid-Like Pseudo Random Sequence Modulator/Demodulator System With Reduced Adjacent Channel Leakage and High Rejection to Random and Systematic Interference

Emerging wireless communication services require the efficient use of available spectrum and improved co-existence of different standards placed in adjacent frequency bands. Co-existence with leakage from primary users in adjacent channels, which falls in the band of interest, is a primary concern for existing and emerging technologies. In this paper, a mixed signal IC technique based on direct sequence spread spectrum is proposed to improve co-existence of radar systems with commercial wireless communication systems. A sinusoid-like pseudo-random sequence is introduced to reduce leakage from radar systems into adjacent channels. The proposed approach reduces the radar signal leakage on adjacent channels by about 22dB when compared with the conventional binary pseudo-random sequence. The proposed technique randomizes narrow and wideband systematic in-band interference, after which interference power can be effectively attenuated through averaging techniques. Experimental results from a 40nm CMOS technology modulator/demodulator prototype demonstrates the feasibility of the proposed architecture. The modulator and demodulator system requires a silicon area of 0.0459mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> and consumes 4.33mW in total.

Efficient Detectors for Telegram Splitting-Based Transmission in Low Power Wide Area Networks With Bursty Interference

Low Power Wide Area (LPWA) networks are known to be highly vulnerable to external in-band interference in terms of packet collisions which may substantially degrade the system performance. In order to enhance the performance in such cases, the telegram splitting (TS) method has been proposed recently. This approach exploits the typical burstiness of the interference via forward error correction (FEC) and offers a substantial performance improvement compared to other methods for packet transmissions in LPWA networks. While it has been already demonstrated that the TS method benefits from knowledge on the current interference state at the receiver side, corresponding practical receiver algorithms of high performance are still missing. The modeling of the bursty interference via Markov chains leads to the optimal detector in terms of a-posteriori symbol error probability. However, this solution requires a high computational complexity, assumes an a-priori knowledge on the interference characteristics and lacks flexibility. We propose a further developed scheme with increased flexibility and introduce an approach to reduce its complexity while maintaining a close-to-optimum performance. In particular, the proposed low-complexity solution substantially outperforms existing practical methods in terms of packet error rate and therefore is highly beneficial for practical LPWA network scenarios.

Design of an S-Band Nanowatt-Level Wakeup Receiver With Envelope Detector-First Architecture

This article presents the first demonstration of a sub-100 nW CMOS wakeup receiver (WuRx) with envelope detector (ED)-first architecture that operates at multigigahertz frequencies. The 2.2 GHz S-band WuRx can operate in two modes that show a tradeoff between power consumption and RF sensitivity. In the low-power mode, the WuRx consumes 11.3 nW and achieves an RF sensitivity of -65 dBm. In the high-sensitivity mode, the WuRx consumes 28.2 nW and achieves a sensitivity of -68 dBm. Measurement results indicate that the WuRx architecture is robust to continuous-wave in-band interferers, with as large as -20 dB carrier-to-interferer ratio.

A novel coordinated detection method for transmissive/reflective sensors against strong in-band interference

Accuracy of transmissive/reflective sensors is usually degraded by strong in-band interference, especially those with frequencies very close or even equal to that of the measured signal. To tackle this challenge, this paper proposes a novel detection method including three units: a coordinated modulator (CM), a high-performance analog narrow-band filter (ANBF), and a smart digital filtering algorithm (SDFA). The CM performs a mixed function of amplitude modulation and phase modulation, and is used to control the sensor’s transmitter to circularly transmit the signal modulated according to the coordinated time-sequence requirement from the SDFA. The ANBF has a very narrow passband to make the analog signal sampled by the SDFA only include the measured signal and an in-band interfering component. The SDFA utilizes the properties of odd/even functions and the definitions of power in A.C. circuit to filter out the in-band interfering component, with the coordination of the CM and ANBF. Effectiveness of the proposed method is validated via simulations and laboratory tests setting up based on a real application case of electromagnetic mold level detection under mold-electromagnetic stirring operating condition. Test results show that the proposed method can effectively deal with strong in-band interfering signal with the frequency very close or even equal to that of the measured signal. In the total of 20000 simulation cases, attenuations of in-band interference can exceed −76 dB. Moreover, in the experimental tests under a condition of −40 dB signal-to-noise ratio, measurement errors of the amplitude of the measured signal can be achieved less than 1.88%.

Mutual interferences in frequency-modulated continuous-wave (FMCW) LiDARs

This paper investigates mutual interferences between FMCW LiDARs both experimentally and theoretically. We show that the FMCW LiDARs have mutual interference problems as those of the FMCW radars. The transient interference degrades the signal-to-noise ratio and the in-band interference generates ghost images. Finally, we discuss their impacts to the autonomous vehicles, and mitigation methods.