12,399 research outputs found
Modulation and Signal Processing for LEO-LEO Optical Inter-satellite Links
We investigate key aspects of coherent optical communications on
inter-satellite links (ISLs) for the next-generation ultra-dense low-Earth
orbit (LEO) constellations. Initially, the suitability of QPSK, 8-QAM, and
16-QAM modulation formats with different symbol rates (28 GBaud, 60 GBaud, and
120 GBaud) and channel coding schemes (oFEC and staircase codes) for intra- and
interorbital connections is evaluated. We provide SNR margins for all
investigated sets and determine unfeasible operating points. We show that sets
with higher-order modulation formats combined with high symbol rates can prove
unfeasible, even for first-neighbor connections. Furthermore, the presence or
absence of optical pre-amplification as well as the choice for a more robust
channel coding technique, such as the oFEC, can be decisive in certain LEO-LEO
links. Next, we characterize the Doppler shift (DS) and its time derivative for
first-neighbor interorbital connections in two different topologies and for
general connections established between any pairs of satellites. Our results
reveal that while the maximum Doppler-generated frequency shift amplitude can
be considerably higher than those typically found in fiber-optic
communications, the time derivative values are significantly lower. Finally, we
address all-digital DS compensation in extreme cases of frequency offset
amplitude and derivative where the typical Mth-power algorithm is not
sufficient. To this end, we propose a filtered version of an existing two-stage
method combining spectral shifts with the Mth-power method. The simulation
results indicate that this approach provides an appropriate solution for all
examined cases.Comment: 13 pages, 7 figures, 6 table
Twenty-five years of sensor array and multichannel signal processing: a review of progress to date and potential research directions
In this article, a general introduction to the area of sensor array and multichannel signal processing is provided, including associated activities of the IEEE Signal Processing Society (SPS) Sensor Array and Multichannel (SAM) Technical Committee (TC). The main technological advances in five SAM subareas made in the past 25 years are then presented in detail, including beamforming, direction-of-arrival (DOA) estimation, sensor location optimization, target/source localization based on sensor arrays, and multiple-input multiple-output (MIMO) arrays. Six recent developments are also provided at the end to indicate possible promising directions for future SAM research, which are graph signal processing (GSP) for sensor networks; tensor-based array signal processing, quaternion-valued array signal processing, 1-bit and noncoherent sensor array signal processing, machine learning and artificial intelligence (AI) for sensor arrays; and array signal processing for next-generation communication systems
Integrated Optical Fiber Sensor for Simultaneous Monitoring of Temperature, Vibration, and Strain in High Temperature Environment
Important high-temperature parts of an aero-engine, especially the power-related fuel system and rotor system, are directly related to the reliability and service life of the engine. The working environment of these parts is extremely harsh, usually overloaded with high temperature, vibration and strain which are the main factors leading to their failure. Therefore, the simultaneous measurement of high temperature, vibration, and strain is essential to monitor and ensure the safe operation of an aero-engine.
In my thesis work, I have focused on the research and development of two new sensors for fuel and rotor systems of an aero-engine that need to withstand the same high temperature condition, typically at 900 °C or above, but with different requirements for vibration and strain measurement.
Firstly, to meet the demand for high temperature operation, high vibration sensitivity, and high strain resolution in fuel systems, an integrated sensor based on two fiber Bragg gratings in series (Bi-FBG sensor) to simultaneously measure temperature, strain, and vibration is proposed and demonstrated. In this sensor, an L-shaped cantilever is introduced to improve the vibration sensitivity. By converting its free end displacement into a stress effect on the FBG, the sensitivity of the L-shaped cantilever is improved by about 400% compared with that of straight cantilevers. To compensate for the strain sensitivity of FBGs, a spring-beam strain sensitization structure is designed and the sensitivity is increased to 5.44 pm/ΌΔ by concentrating strain deformation. A novel decoupling method âSteps Decoupling and Temperature Compensation (SDTC)â is proposed to address the interference between temperature, vibration, and strain. A model of sensing characteristics and interference of different parameters is established to achieve accurate signal decoupling. Experimental tests have been performed and demonstrated the good performance of the sensor.
Secondly, a sensor based on cascaded three fiber Fabry-PĂ©rot interferometers in series (Tri-FFPI sensor) for multiparameter measurement is designed and demonstrated for engine rotor systems that require higher vibration frequencies and greater strain measurement requirements. In this sensor, the cascaded-FFPI structure is introduced to ensure high temperature and large strain simultaneous measurement. An FFPI with a cantilever for high vibration frequency measurement is designed with a miniaturized size and its geometric parameters optimization model is established to investigate the influencing factors of sensing characteristics. A cascaded-FFPI preparation method with chemical etching and offset fusion is proposed to maintain the flatness and high reflectivity of FFPIsâ surface, which contributes to the improvement of measurement accuracy. A new high-precision cavity length demodulation method is developed based on vector matching and clustering-competition particle swarm optimization (CCPSO) to improve the demodulation accuracy of cascaded-FFPI cavity lengths. By investigating the correlation relationship between the cascaded-FFPI spectral and multidimensional space, the cavity length demodulation is transformed into a search for the highest correlation value in space, solving the problem that the cavity length demodulation accuracy is limited by the resolution of spectral wavelengths. Different clustering and competition characteristics are designed in CCPSO to reduce the demodulation error by 87.2% compared with the commonly used particle swarm optimization method. Good performance and multiparameter decoupling have been successfully demonstrated in experimental tests
Antenna Selection With Beam Squint Compensation for Integrated Sensing and Communications
Next-generation wireless networks strive for higher communication rates,
ultra-low latency, seamless connectivity, and high-resolution sensing
capabilities. To meet these demands, terahertz (THz)-band signal processing is
envisioned as a key technology offering wide bandwidth and sub-millimeter
wavelength. Furthermore, THz integrated sensing and communications (ISAC)
paradigm has emerged jointly access spectrum and reduced hardware costs through
a unified platform. To address the challenges in THz propagation, THz-ISAC
systems employ extremely large antenna arrays to improve the beamforming gain
for communications with high data rates and sensing with high resolution.
However, the cost and power consumption of implementing fully digital
beamformers are prohibitive. While hybrid analog/digital beamforming can be a
potential solution, the use of subcarrier-independent analog beamformers leads
to the beam-squint phenomenon where different subcarriers observe distinct
directions because of adopting the same analog beamformer across all
subcarriers. In this paper, we develop a sparse array architecture for THz-ISAC
with hybrid beamforming to provide a cost-effective solution. We analyze the
antenna selection problem under beam-squint influence and introduce a manifold
optimization approach for hybrid beamforming design. To reduce computational
and memory costs, we propose novel algorithms leveraging grouped subarrays,
quantized performance metrics, and sequential optimization. These approaches
yield a significant reduction in the number of possible subarray
configurations, which enables us to devise a neural network with classification
model to accurately perform antenna selection.Comment: 14pages10figures, submitted to IEE
Beam scanning by liquid-crystal biasing in a modified SIW structure
A fixed-frequency beam-scanning 1D antenna based on Liquid Crystals (LCs) is designed for application in 2D scanning with lateral alignment. The 2D array environment imposes full decoupling of adjacent 1D antennas, which often conflicts with the LC requirement of DC biasing: the proposed design accommodates both. The LC medium is placed inside a Substrate Integrated Waveguide (SIW) modified to work as a Groove Gap Waveguide, with radiating slots etched on the upper broad wall, that radiates as a Leaky-Wave Antenna (LWA). This allows effective application of the DC bias voltage needed for tuning the LCs. At the same time, the RF field remains laterally confined, enabling the possibility to lay several antennas in parallel and achieve 2D beam scanning. The design is validated by simulation employing the actual properties of a commercial LC medium
Distributed Sensing, Computing, Communication, and Control Fabric: A Unified Service-Level Architecture for 6G
With the advent of the multimodal immersive communication system, people can
interact with each other using multiple devices for sensing, communication
and/or control either onsite or remotely. As a breakthrough concept, a
distributed sensing, computing, communications, and control (DS3C) fabric is
introduced in this paper for provisioning 6G services in multi-tenant
environments in a unified manner. The DS3C fabric can be further enhanced by
natively incorporating intelligent algorithms for network automation and
managing networking, computing, and sensing resources efficiently to serve
vertical use cases with extreme and/or conflicting requirements. As such, the
paper proposes a novel end-to-end 6G system architecture with enhanced
intelligence spanning across different network, computing, and business
domains, identifies vertical use cases and presents an overview of the relevant
standardization and pre-standardization landscape
Sensing User's Activity, Channel, and Location with Near-Field Extra-Large-Scale MIMO
This paper proposes a grant-free massive access scheme based on the
millimeter wave (mmWave) extra-large-scale multiple-input multiple-output
(XL-MIMO) to support massive Internet-of-Things (IoT) devices with low latency,
high data rate, and high localization accuracy in the upcoming sixth-generation
(6G) networks. The XL-MIMO consists of multiple antenna subarrays that are
widely spaced over the service area to ensure line-of-sight (LoS)
transmissions. First, we establish the XL-MIMO-based massive access model
considering the near-field spatial non-stationary (SNS) property. Then, by
exploiting the block sparsity of subarrays and the SNS property, we propose a
structured block orthogonal matching pursuit algorithm for efficient active
user detection (AUD) and channel estimation (CE). Furthermore, different
sensing matrices are applied in different pilot subcarriers for exploiting the
diversity gains. Additionally, a multi-subarray collaborative localization
algorithm is designed for localization. In particular, the angle of arrival
(AoA) and time difference of arrival (TDoA) of the LoS links between active
users and related subarrays are extracted from the estimated XL-MIMO channels,
and then the coordinates of active users are acquired by jointly utilizing the
AoAs and TDoAs. Simulation results show that the proposed algorithms outperform
existing algorithms in terms of AUD and CE performance and can achieve
centimeter-level localization accuracy.Comment: Submitted to IEEE Transactions on Communications, Major revision.
Codes will be open to all on https://gaozhen16.github.io/ soo
Genetically Synthesized Supergain Broadband Wire-Bundle Antenna
High-gain antennas are essential hardware devices, powering numerous daily
applications, including distant point-to-point communications, safety radars,
and many others. While a common approach to elevate gain is to enlarge an
antenna aperture, highly resonant subwavelength structures can potentially
grant high gain performances. The Chu-Harrington limit is a standard criterion
to assess electrically small structures and those surpassing it are called
superdirective. Supergain is obtained in a case when internal losses are
mitigated, and an antenna is matched to radiation, though typically in a very
narrow frequency band. Here we develop a concept of a spectrally overlapping
resonant cascading, where tailored multipole hierarchy grants both high gain
and sufficient operational bandwidth. Our architecture is based on a near-field
coupled wire bundle. Genetic optimization, constraining both gain and
bandwidth, is applied on a 24-dimensional space and predicts 8.81 dBi realized
gain within a half-wavelength in a cube volume. The experimental gain is 6.15
with 13% fractional bandwidth. Small wire bundle structures are rather
attractive for designing superscattering and superdirective structures, as they
have a sufficient number of degrees of freedom to perform an optimization, and,
at the same time rely on simple fabrication-tolerant layouts, based on low-loss
materials. The developed approach can be applied to low-frequency (e.g.,
kHz-MHz) applications, where miniaturization of wireless devices is highly
demanded
Polymer-Based Micromachining for Scalable and Cost-Effective Fabrication of Gap Waveguide Devices Beyond 100 GHz
The terahertz (THz) frequency bands have gained attention over the past few years due to the growing number of applications in fields like communication, healthcare, imaging, and spectroscopy. Above 100 GHz transmission line losses become dominating, and waveguides are typically used for transmission. As the operating frequency approaches higher frequencies, the dimensions of the waveguide-based components continue to decrease. This makes the traditional machine-based (computer numerical control, CNC) fabrication method increasingly challenging in terms of time, cost, and volume production. Micromachining has the potential of addressing the manufacturing issues of THz waveguide components. However, the current microfabrication techniques either suffer from technological immaturity, are time-consuming, or lack sufficient cost-efficiency. A straightforward, fast, and low-cost fabrication method that can offer batch fabrication of waveguide components operating at THz frequency range is needed to address the requirements.A gap waveguide is a planar waveguide technology which does not suffer from the dielectric loss of planar waveguides, and which does not require any electrical connections between the metal walls. It therefore offers competitive loss performance together with providing several benefits in terms of assembly and integration of active components. This thesis demonstrates the realization of gap waveguide components operating above 100 GHz, in a low-cost and time-efficient way employing the development of new polymer-based fabrication methods.A template-based injection molding process has been designed to realize a high gain antenna operating at D band (110 - 170 GHz). The injection molding of OSTEMER is an uncomplicated and fast device fabrication method. In the proposed method, the time-consuming and complicated parts need to be fabricated only once and can later be reused.A dry film photoresist-based method is also presented for the fabrication of waveguide components operating above 100 GHz. Dry film photoresist offers rapid fabrication of waveguide components without using complex and advanced machinery. For the integration of active circuits and passive waveguides section a straightforward solution has been demonstrated. By utilizing dry film photoresist, a periodic metal pin array has been fabricated and incorporated in a waveguide to microstrip transition that can be an effective and low-cost way of integrating MMIC of arbitrary size to waveguide blocks
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