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This article provides a comprehensive overview of calibrating a correlation-based channel sounder designed for the low terahertz (THz) frequency range. The calibration process outlined herein encompasses fundamental aspects, including the calibration of the measured delay and amplitude of the channel impulse response (CIR). Specifically, it discusses the influence of the utilized waveguides during a back-to-back (B2B) calibration, as well as the effects of antennas, and noise floor estimation. Furthermore, the calibration procedure is enhanced through deconvolution to mitigate the impact of the measurement system itself. Specifically, the discussion addresses the windowing technique applied to the deconvolved signal. Lastly, additional considerations such as averaging, interpolation, MIMO configurations, and highresolution measurements are discussed.

Abstract As the need for higher data rates for communication increases, the terahertz (THz) band has drawn considerable attention. This spectral region promises a much wider bandwidth and the transmission of large amounts of data at high speeds. However, there are still challenges that need to be addressed before the THz telecommunications technology hits the consumer market. One of the recurring concerns is that THz radiation is greatly absorbed by atmospheric water-vapor. Although many studies have presented the attenuation of THz signals under different atmospheric conditions, these results analyze specific temperature or humidity values, leaving the need for a more comprehensive analysis over a wider range of climate conditions. In this work, we present the first study of the attenuation of THz radiation over a broad range of temperatures and humidity values. It is worth noticing that all of our measurements have been undertaken at atmospheric pressure unlike many previous studies where the pressure was not kept constant for various temperatures. Furthermore, we extend our analysis beyond the impact of absolute humidity on the bit error rate in THz communications. We also discuss the refractivity of the atmosphere, examining its variations across different temperatures and humidity levels. THz propagation is studied using two different measurement systems, a long-path THz time-domain spectrometer as well as a quasi-optic setup with vector network analyze. We also compare the results with the ITU-R P.676-13 propagation model. We conclude that the attenuation at the absorption peaks increases linearly with water content and has no dependence on the temperature, while the refractive index, away from absorption lines, namely at 300 GHz shows a sub-linear increase with humidity.

Abstract Future wireless communication systems at low terahertz frequencies (0.1–1 THz) suffer from high attenuation losses, and therefore, highly directive antennas are foreseen. As highly directive antennas have narrow beams, the alignment of the transmitter and the receiver is a crucial step in such systems. A device discovery approach using results from ray tracing (RT) combined with an iterative fine tuning is presented by the authors. A summary of previous investigations emphasises the benefits in terms of performance compared to an iterative approach. Furthermore, it indicates strong dependency of the RT output on the accuracy of the input data, that is, the environmental model. The authors extend the previous works by evaluating the impact of antenna characteristics. It is shown that the sidelobes lead to an error in the final alignment due to the superposition of the received power via multipath components, and equations to calculate the maximum error are given. Besides, the impact is evaluated with respect to sidelobe suppression. Here, equations to calculate the maximum error are given and it is shown that the sidelobes do not affect the alignment if the gain of the sidelobe is more than 30 dB lower than that of the mainlobe.

This paper investigates the performance boundaries of a calibrated deterministic indoor channel model. From a propagation modeling point of view, this process allows to assess the weakness of ray tracing and sets the boundary conditions for a such modeling method. The principle of the deterministic model calibration used in this work focuses upon the estimation of optimal material parameters by means of a few pilot measurements and a simulated annealing method. This technique improves the accuracy of the prediction model for all measurement positions including those not considered by the calibration. The performance of the calibrated ray tracing model and the sensitivity of the calibration to the number of pilot measurements have been investigated. For this investigation, a measurement campaign has been conducted within an indoor office building at 2.45 GHz with 100 MHz bandwidth. Furthermore, the model performance has been compared to empirical indoor models.

Mobile communication services are getting more and more important and, in particular, multimedia services have attracted the interest of the users. Mobile TV is one of the most demanded candidates. Powerful and efficient communication systems are needed, which provide high capacities, especially at the downlink. Furthermore, interactivity is essential for supporting the user needs and to extend the service offering. As one possible solution to meet the mentioned requirements, we consider the combination of the cellular network UMTS and the mobile broadcast network DVB-H, which form a hybrid network. We investigate the performance of hybrid networks and develop a system model, which describes the hybrid network and the load switching between both networks. One of the contributions is the definition of the switching bound concept, which represents an efficient tool to assess the necessity and the feasibility of hybrid networks and the amount of load switching. The performance indicators cell load and grade of service are analyzed by using theoretical and realistic scenarios.