Spatial Interference Nulling Before RF Frontend for Fully Digital Phased Arrays

Irazoqui, Robin; Fulton, Caleb

doi:10.1109/access.2019.2945978

Cited by 12 publications

(5 citation statements)

References 19 publications

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“…Although interesting for our goal, reference [6] assumes that only phase shift control is available in the analog domain and it relies on simulation results only. A recent paper [7] uses a passive block called a Spatial Interference Mitigation Circuit (SMIC) placed before the RF front-end to create an spatial notch for MIMO receiver elements. References [2]- [4], [8]- [19] do demonstrate the design of interference robust techniques using CMOS integrated circuit technologies in sub-GHz bands.…”

Section: Introductionmentioning

confidence: 99%

“…References [2]- [4], [8]- [19] do demonstrate the design of interference robust techniques using CMOS integrated circuit technologies in sub-GHz bands. Only references [7], [10], [12] provide some simple line-of-sight demonstrations. However, an adaptive analog weight calculation is essential to support real-world multi-path scenarios, and this was not addressed.…”

Section: Introductionmentioning

confidence: 99%

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Interference Mitigation by Adaptive Analog Spatial Filtering for MIMO Receivers

Alaei

Golabighezelahmad

Boer

et al. 2021

IEEE Trans. Microwave Theory Techn.

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Exposed to strong co-channel/adjacent channel interference, digital Multiple-Input Multiple-Output (MIMO) receivers require high dynamic range Analog-to-Digital Converters (ADCs). Hybrid analog-digital beamforming featuring spatial filtering before the ADCs can adaptively mitigate interference in both the analog and digital domains; hence, relaxing the required dynamic ranges of the ADCs. This paper demonstrates the effectiveness of hybrid beamforming in this mitigation utilizing adaptive Minimum Mean Square Error (MMSE) and Error Vector Magnitude (EVM) as an optimization criterion. Extensive EVM measurements are carried out with a conductive set-up using a 4-element 22 nm FD-SOI CMOS prototype MIMO receiver chip to verify the performance of the adaptive MMSE algorithm. Over-the-Air (OTA) measurements with a linear 4element dipole antenna array with half-wavelength spacing in the 2.4 GHz ISM-band quantify the improvement for real world scenarios, e.g., having a multipath propagation channel and mutual coupling between the antenna array elements. OTA results show that a rejection of 22.5 dB and 24.5 dB can be achieved on average in an in-door laboratory environment utilizing Vector Modulator (VM) constellations with 16 and 64 points, respectively.

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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Interference Mitigation by Adaptive Analog Spatial Filtering for MIMO Receivers

Alaei

Golabighezelahmad

Boer

et al. 2021

IEEE Trans. Microwave Theory Techn.

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“…In the literature, the interference mitigation (IM) of the FMCW radar systems is generally tackled through two ways: (1) system (i.e., antenna array, waveform, etc) design methods [1]- [8] and (2) signal processing approaches [9]- [22]. The system design related methods generally require that the radar system have the capability for waveform modulation, new radar architecture, or a coordination unit, etc.…”

Section: Introductionmentioning

confidence: 99%

Interference Mitigation for FMCW Radar With Sparse and Low-Rank Hankel Matrix Decomposition

Wang,

Ding,

Yarovoy

2021

Preprint

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In this paper, the interference mitigation for Frequency Modulated Continuous Wave (FMCW) radar system with a dechirping receiver is investigated. After dechirping operation, the scattered signals from targets result in beat signals, i.e., the sum of complex exponentials while the interferences lead to chirp-like short pulses. Taking advantage of these different time and frequency features between the useful signals and the interferences, the interference mitigation is formulated as an optimization problem: a sparse and low-rank decomposition of a Hankel matrix constructed by lifting the measurements. Then, an iterative optimization algorithm is proposed to tackle it by exploiting the Alternating Direction of Multipliers (ADMM) scheme. Compared to the existing methods, the proposed approach does not need to detect the interference and also improves the estimation accuracy of the separated useful signals. Both numerical simulations with point-like targets and experiment results with distributed targets (i.e., raindrops) are presented to demonstrate and verify its performance. The results show that the proposed approach is generally applicable for interference mitigation in both stationary and moving target scenarios.

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“…ADAPTIVE ANALOG SPATIAL FILTERING FOR MIMO RECEIVERS goal, reference [60] assumes that only phase shift control is available in the analog domain and it relies on simulation results only. A recent paper [61] uses a passive block called a Spatial Interference Mitigation Circuit (SIMC) placed before the RF front-end to create an spatial notch for MIMO receiver elements. References [12-18, 28, 29, 37, 40, 44-46] do demonstrate the design of interference robust techniques using CMOS integrated circuit technologies in sub-GHz bands.…”

Section: Introductionmentioning

confidence: 99%

“…References [12-18, 28, 29, 37, 40, 44-46] do demonstrate the design of interference robust techniques using CMOS integrated circuit technologies in sub-GHz bands. Only references [37,45,61] provide some simple line-of-sight demonstrations. However, an adaptive analog weight calculation is essential to support real-world multi-path scenarios, and this was not addressed.…”

Section: Introductionmentioning

confidence: 99%

Interference Mitigation for MIMO Receivers: RF Front-end Featuring Adaptive Analog Spatial Filtering

Golabighezelahmad

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Multiple-Input Multiple-Output (MIMO) and beamforming systems have recently attracted increasing attention, because they allow for spatial multiplexing and diversity gains, improving link throughput and link reliability. As the spectrum becomes heavily utilized in sub-GHz bands that are favored over millimeter-wave frequencies for their propagation characteristics as well as energy-efficiency, strong mutual interference can occur. MIMO systems offer a solution for efficient use of scarce radio spectrum.In analog beamforming phased array receivers, i.e., Multiple-Input Single-Output (MISO) receiver systems, phase-shifting and possibly amplitude weighting is applied to multiple antenna signals before summing into a single output that only requires one ADC per array. Analog beamforming is a favorable method because of SNR improvement, its ability to cancel out interferers before entering the ADC, and its ability to improve the interference robustness of the receiver. However, many analog beamforming receivers lack flexibility to realize adaptive beamforming. On the other hand, digital MIMO systems are capable of advanced signal processing, achieving an improved data capacity and link reliability for realistic channel models that include propagation reflections and multi-path fading. In a digital MIMO receiver, however, element-level analog-to-digital conversion exposes the RF front-ends and following ADCs to strong in-band interferers, limiting the dynamic range of the receiver. Hybrid analog-digital approach, e.g., adding analog spatial filtering before entering the ADCs can relax its dynamic range and hence the number of required ADC bits. Chapter 2 presents a survey of recently published interference mitigation techniques for MISO and MIMO beamforming receivers. Two MIMO receiver architectures exist for interference mitigation in the analog domain: 1) a MIMO receiver featuring analog spatial notch filtering; 2) a multi-beam MIMO receiver architecture implemented using multiple parallel phased arrays.In chapter 3, we propose a new reconfigurable multi-beam architecture supporting both digital MIMO and analog spatial filtering. Spatial interference rejection is achieved using a set of flexible orthogonal beams with a programmable spatial-direction. RF/analog beamforming is realized by an improved constant-Gm vector modulator (VM). In addition to significant linearity enhancement, RF frequency range is extended in a compact and power efficient way, so that the MIMO receiver covers sub-6 GHz vii viii ABSTRACT bands in a software-defined radio fashion. A 0.7-5.7 GHz 22 nm FD-SOI prototype chip achieves >29 dB spatial filtering for a single notch and an ultra-wideband 20 dB notch suppression bandwidth of 2.3 GHz at broadside excitation at an LO frequency of 2.5 GHz. In the notches, an IIP3 of +16 dBm and B1dB of -11.5 dBm at 41 dB gain is achieved, improving IIP3 and B1dB by 35dB and 27dB, respectively, by spatial filtering. A single-element noise figure of 5.5-7 dB is achieved on the vector modulator constellation cor...

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Spatial Interference Nulling Before RF Frontend for Fully Digital Phased Arrays

Cited by 12 publications

References 19 publications

Interference Mitigation by Adaptive Analog Spatial Filtering for MIMO Receivers

Interference Mitigation by Adaptive Analog Spatial Filtering for MIMO Receivers

Interference Mitigation for FMCW Radar With Sparse and Low-Rank Hankel Matrix Decomposition

Interference Mitigation for MIMO Receivers: RF Front-end Featuring Adaptive Analog Spatial Filtering

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