Ultra-Wideband Terahertz Channel Propagation Measurements from 500 to 750 GHz

Abstract

This paper presents empirically based ultrawideband and directional channel measurements, performed in the Terahertz (THz) frequency range over 250 GHz bandwidth from 500 GHz to 750 GHz. Measurement setup calibration technique is presented for free-space measurements taken at Line-of-Sight (LoS) between the transmitter (Tx) and receiver (Rx) in an indoor environment. The atmospheric effects on signal propagation in terms of molecular absorption by oxygen and water molecules are calculated and normalized. Channel impulse responses (CIRs) are acquired for the LoS scenario for different antenna separation distances. From the CIRs the Power Delay Profile (PDP) is presented where multiple delay taps can be observed caused due to group delay products and reflections from the measurement bench.

TeraMIMO: A Channel Simulator for Wideband Ultra-Massive MIMO Terahertz Communications

“…The molecular absorption coefficient, K ( 𝑓 ), represents a unique THz fingerprint for each gas, 𝑔, and isotopologue, 𝑖. By analogy with [67], K ( 𝑓 ) is expressed in (26), where 𝑇 is the system temperature (in Kelvin), 𝑇 0 is reference temperature (296.0 Kelvin), 𝑇 STP is a temperature at standard pressure (273.15 Kelvin), 𝑃 is the system pressure (in atm), 𝑃 0 is the reference pressure (1 atm), ℏ is the Planck constant, 𝐾 𝐵 is the Boltzmann constant, 𝑅 is the gas constant, and 𝑁 𝐴 is the Avogadro constant. Furthermore, 𝜉 (𝑖,𝑔) , 𝑆 (𝑖,𝑔) (𝑇), 𝑓 (𝑖,𝑔) 𝑐 , and 𝛼 (𝑖,𝑔) 𝐿 are respectively the mixing ratio, line intensity (in Hz m 2 /molecule), resonant frequency (in Hz), and Lorentz half-width (in Hz) of isotopologue 𝑖 of gas 𝑔.…”

“…Also, threedimensional (3D) end-to-end channel models are developed in [13], [24] by incorporating Graphene-based antennas. Other recently reported indoor LoS THz channel measurements include the works in [25] for three bands of 10 GHz bandwidth over 140 − 220 GHz, and in [26] for ultra-wideband channels of 250 GHz bandwidth over 500 − 750 GHz. Furthermore, sub-THz (142 GHz) outdoor urban (120 m) channel models for both LoS and non line-of-sight (NLoS) scenarios are reported in [27]; the same models are verified for indoor scenarios in [28].…”

Terahertz Channel Propagation Phenomena, Measurement Techniques and Modeling for 6G Wireless Communication Applications: a Survey, Open Challenges and Future Research Directions

“…f) Multi-Path Resolution: High timing accuracy that will enable accurate characterization with high delay resolutions is expected with equipment capable of capturing the characteristics of the rich multipath environment when measuring over large bandwidths where clusters of MPCs would be easily detected by their Time of Arrival (ToA). As an example, in [119] measurements over an ultra-wide frequency range of 250 GHz were conducted using a VNA that allowed for a very high delay resolution of 4 picoseconds given 1600 data points. Clear and similar in shape LoS and specular peaks could be seen, while distorted peaks with different clusters of distinguishable MPCs appeared as a consequence of diffuse particle scattering from rough surfaces of various test materials' placed intentionally as reflectors in the propagating environment.…”

“…The setup consists of a VNA connected at the Tx and Rx sides to frequency extender modules which in turn are connected to a waveguide and horn antenna that must be fixed precisely to avoid causing any signal reflections back to the frequency extender. To realize such a setup practically and enable an accurate measurement campaign and account for system errors in transmission and also due to source mismatches, system directivity and reflection tracking [119], the VNA/ extender heads require lengthy calibration techniques, e.g., Short, Offset-short, Load and Thru (SOLT) [134]. One of the key limitations related to measurements using VNAs is that the frequency extenders have to be connected via physical connections to maintain phase synchronization; thus, the measurements are constrained in terms of Tx-Rx separation distance while at these short distances the VNA must be placed somewhere near the Tx and Rx ends therefore, acting as an unwanted reflector and scatterer.…”

Standard Propagation Channel Models for MIMO Communication Systems

“…25 Wireless Communications and Mobile Computing First, conducting large-scale channel measurements is a major concern. It is still very difficult to carry out large-scale channel measurements, due partly to the complex nature of the dynamic environment, especially for outdoor scenarios, and the sophisticated equipment that is required for such measurements in the mmWave [177,220] and Terahertz (THz) [221] bands. In the case of double-directional channel measurements, switched channel sounders have been used.…”