5,057 research outputs found
Modelling of the Terahertz Communication Channel for In-vivo Nano-networks in the Presence of Noise
This paper focuses on the modelling of communication channel noise inside human tissues at the THz band (0.1-10THz). A novel model is put forward based on the study of the physical mechanism of the channel noise in the medium, which takes into account both the radiation of the medium and the molecular absorption from the transmitted signal. The derivation and the general concepts of the noise modelling is detailed in the paper. The results show that the channel noise power spectral density at the scale of several micrometres is at acceptable levels and the value tends to decrease with the increase of both distance and frequency. In addition, the channel noise is also related to the composition of the human tissues, with the result of higher channel noise in tissues with higher water concentration. The conclusion drawn from the conducted study and analysis paves the way for more comprehensive characterisation of the electromagnetic channel within in-vivo nano-networks
Analytical modelling of the effect of noise on the terahertz in-vivo communication channel for body-centric nano-networks
The paper presents an analytical model of the terahertz (THz) communication channel (0.1 - 10 THz) for in-vivo nano-networks by considering the effect of noise on link quality and information rate. The molecular absorption noise model for in-vivo nano-networks is developed based on the physical mechanisms of the noise present in the medium, which takes into account both the radiation of the medium and the molecular absorption from the transmitted signal. The signal-to-noise ratio (SNR) of the communication channel is investigated for different power allocation schemes and the maximum achievable information rate is studied to explore the potential of THz communication inside the human body. The obtained results show that the information rate is inversely proportional to the transmission distance. Based on the studies on channel performance, it can be concluded that the achievable transmission distance of in-vivo THz nano-networks should be restrained to approximately 2 mm maximum, while the operation band of in-vivo THz nano-networks should be limited to the lower band of the THz band. This motivates the utilisation of hierarchical/cooperative networking concepts and hybrid communication techniques using molecular and electromagnetic methods for future body-centric nano-networks
Multiple Antenna Techniques for Terahertz Nano-Bio Communication
Using higher frequency bands becomes an essential demand resulting from the explosive wireless traffic needs and the spectrum shortage of the currently used bands. This paper presents an overview on the terahertz technology and its application in the area of multi-input multi-output antenna system and in-vivo nano-communication. In addition, it presents a preliminary study on applying multiple input-single output (MISO) antenna technique to investigate the signal propagation and antenna diversity techniques inside the human skin tissues, which is represented by three layers: stratum corneum (SC), epidermis, and dermis layers, in the terahertz (THz) frequency range (0.8-1.2) THz. The spatial antenna diversity is investigated in this study to understand MISO system performance for two different in-vivo channels resulting from the signal propagation between two transmitting antennas, located at the dermis layer, and one receiving antenna, located at epidermis layer. Three techniques are investigated: selection combining (SC), equal-gain combing (EGC), and maximum-ratio combining (MRC). The initial study indicates that using multiple antenna technique with THz might be not useful for in-vivo nano-communication
Single- versus Multi-Carrier Terahertz-Band Communications: A Comparative Study
The prospects of utilizing single-carrier (SC) and multi-carrier (MC)
waveforms in future terahertz (THz)-band communication systems remain
unresolved. On the one hand, the limited multi-path components at high
frequencies result in frequency-flat channels that favor low-complexity
wideband SC systems. On the other hand, frequency-dependent molecular
absorption and transceiver characteristics and the existence of multi-path
components in indoor sub-THz systems can still result in frequency-selective
channels, favoring off-the-shelf MC schemes such as orthogonal
frequency-division multiplexing (OFDM). Variations of SC/MC designs result in
different THz spectrum utilization, but spectral efficiency is not the primary
concern with substantial available bandwidths; baseband complexity, power
efficiency, and hardware impairment constraints are predominant. This paper
presents a comprehensive study of SC/MC modulations for THz communications,
utilizing an accurate wideband THz channel model and highlighting the various
performance and complexity trade-offs of the candidate schemes. Simulations
demonstrate that discrete-Fourier-transform spread orthogonal time-frequency
space (DFT-s-OTFS) achieves a lower peak-to-average power ratio (PAPR) than
OFDM and OTFS and enhances immunity to THz impairments and Doppler spreads, but
at an increased complexity cost. Moreover, DFT-s-OFDM is a promising candidate
that increases robustness to THz impairments and phase noise (PHN) at a low
PAPR and overall complexity.Comment: 18 pages, 12 figures, journa
The Primordial Inflation Explorer (PIXIE): A Nulling Polarimeter for Cosmic Microwave Background Observations
The Primordial Inflation Explorer (PIXIE) is an Explorer-class mission to
measure the gravity-wave signature of primordial inflation through its
distinctive imprint on the linear polarization of the cosmic microwave
background. The instrument consists of a polarizing Michelson interferometer
configured as a nulling polarimeter to measure the difference spectrum between
orthogonal linear polarizations from two co-aligned beams. Either input can
view the sky or a temperature-controlled absolute reference blackbody
calibrator. PIXIE will map the absolute intensity and linear polarization
(Stokes I, Q, and U parameters) over the full sky in 400 spectral channels
spanning 2.5 decades in frequency from 30 GHz to 6 THz (1 cm to 50 um
wavelength). Multi-moded optics provide background-limited sensitivity using
only 4 detectors, while the highly symmetric design and multiple signal
modulations provide robust rejection of potential systematic errors. The
principal science goal is the detection and characterization of linear
polarization from an inflationary epoch in the early universe, with
tensor-to-scalar ratio r < 10^{-3} at 5 standard deviations. The rich PIXIE
data set will also constrain physical processes ranging from Big Bang cosmology
to the nature of the first stars to physical conditions within the interstellar
medium of the Galaxy.Comment: 37 pages including 17 figures. Submitted to the Journal of Cosmology
and Astroparticle Physic
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