This work presents accurate closed-form approximations for the probability density function (PDF) of the sum of independent and identically distributed (i.i.d.) fading envelopes and square fading envelopes, experienced by indoor and outdoor channels operating in the D-band. In order to provide a simple yet accurate analytical expression for these PDFs, we propose the use of the Pearson family of distributions, which are mainly characterized by their skewness and kurtosis. Our analysis has demonstrated that among the seven types of Pearson distributions, the type I Pearson distribution provides the most accurate fit to the exact PDF of envelopes and squared envelopes, for a diverse range of indoor and outdoor wireless propagation scenarios. The distribution parameters are estimated using moments-matching techniques, while the requisite moments are obtained through a measurement campaign conducted in indoor as well as outdoor environments. Specifically, with regard to the indoor scenarios, the following locations have been considered: A mall, an airport, and an entrance hall. With regard to the outdoor scenarios, the following locations have been selected: A university campus, a residential area, and a city center. Our results are further applied to analyze the average bit error rate performance and the ergodic capacity of equal-gain combining (EGC) and maximal-ratio combining (MRC) receivers, the sum rate of rate splitting multiple access (RSMA) systems with EGC diversity reception, as well as the coverage probability of wireless systems employing intelligent reflecting surfaces (IRS). Our analysis is supported by extensive numerical results and Monte Carlo simulations.

Millimeter-wave (mmWave) and D Band (110170 GHz) frequencies are poised to play a pivotal role in the advancement of sixth-generation (6 G) systems and beyond, owing to their ability to enhance performance metrics such as capacity, ultra-low latency, and spectral efficiency. This paper concentrates on deriving statistical insights into power, delay, and the number of paths based on measurements conducted across four distinct locations at a center frequency of 143.1 GHz. The findings underscore the suitability of various distributions in characterizing power behavior in line-of-sight (LOS) scenarios, including lognormal, Nakagami, gamma, and beta distributions, whereas the loglogistic distribution gives the optimal fit for power distribution in non-line-of-sight (NLOS) scenarios. Moreover, the exponential distribution shows to be the most appropriate model for the delay distribution in both LOS and NLOS scenarios. In terms of the number of paths, observations indicate a tendency for the highest concentration within the 10 m to 30 m distance range between the transmitter (Tx) and receiver (Rx). These insights shed light on the statistical nature of D band propagation characteristics, which are vital for informing the design and optimization of future 6 G communication systems.

As the ubiquity of 5G technology permeates various domains, coupled with the introduction of new carrier frequencies under the New Radio (NR) framework, devices employing this advanced technology require stringent and repeatable operational conformance tests. Those tests are essential to ascertain the AUT performance under realistic deployment scenarios, thereby ensuring reliability. Hence emulating realistic channel characteristics is fundamental to reach a reliable evaluation of radio components. Considering small-scale fading phenomena is imperative in evaluating the operational integrity of radio devices, as it pervades everything from vehicular communications to the mobility of user equipment. This work demonstrates implementing and validating the operation of a Rician fading channel emulator which can be integrated in an over-the-air antenna testbed. It provides a real-time cost-effective solution using off-the-shelf software defined radios (SDR). The paper provides an overview on the hardware setup and the software implementation of the Rician fading emulator. The setup is tested in an anechoic chamber and comparative analysis showed a robust correlation between the empirical data and theoretical plots of the Rician fading magnitude statistics.

This contribution aims at experimentally validating the suitability of Gaussian mixture (GM) distributions to capture the stochastic characteristics of outdoor terahertz (THz) wireless channels. In this direction, we employ a machine learning enabled approach, based on the expectation maximization algorithm, in order to identify the suitable number of Gaussian distributions as well as their corresponding parameters that result to an acceptable fit. The fitting accuracy of the GMs to the empirical distributions is evaluated by means of the Kolmogorov-Smirnov (KS), Kullback-Leibler (KL), root-mean-square-error (RMSE) and R2fitting accuracy tests. These tests verify the suitability of GMs to model the small-scale fading channel amplitude of outdoor THz wireless links. In addition, the fitting accuracy results indicate that as the number of mixtures increases the resulting GMs achieve a better fit to the empirical data.

| openaire: EC/H2020/101015956/EU//Hexa-X

This work investigates the suitability of α–µ distribution to model line-of-sight (LoS) and non-line-of-sight (NLoS) multi-path fading in terahertz (THz) wireless systems. The goodness of fit of α–µ to the small-scale fading of the measured channels is evaluated in terms of the Kolmogorov-Smirnov (KS) test. The KS test revealed the capability of α–µ distribution to capture the fading characteristics of THz wireless channels. To highlight the importance of this study and the applicability to the theoretical analysis of THz wireless systems, for indicative values of α and µ, the ergodic capacity of THz wireless systems is assessed.

6G will likely be the first generation of mobile communication that will feature tight integration of localization and sensing with communication functionalities. Among several worldwide initiatives, the Hexa-X flagship project stands out as it brings together 25 key players from adjacent industries and academia, and has among its explicit goals to research fundamentally new radio access technologies and high-resolution localization and sensing. Such features will not only enable novel use cases requiring extreme localization performance, but also provide a means to support and improve communication functionalities. This paper provides an overview of the Hexa-X vision alongside the envisioned use cases. To close the required performance gap of these use cases with respect to 5G, several technical enablers will be discussed, together with the associated research challenges for the coming years.

Communication is essential for coastal and rural areas, and providing an alternative method of communication for isolated coves through maritime communications is a way to cater that need. In order to create a reliable communication system, antenna misalignment attributed to wave motion of the sea must be accounted for because losses in transmission and reception occur. The scope of this study covers the angular variation of wave motion, particularly the roll angle tilting an antenna experiences. In this paper, improvements of using diversity techniques for a 2.4 GHz communication link in the maritime environment were investigated. In particular, spatial diversity, which uses independent multiple antennas to achieve a level of performance one antenna could not, was employed. The use of selection diversity, a type of spatial diversity that selects the antenna branch with the best signal strength, to compensate antenna misalignment is considered and analyzed. A transmitter and receiver front-end incorporating selection diversity were designed and implemented. Results prove that the use of the proposed scheme increase the overall gain of the communication link. There is an average of 1.35 dB and 5.3 dB increase for 2 and 3 antennas respectively, in using receive diversity compared to no diversity, and an average of 2.4 dB increase in using 3 antenna transmit diversity as opposed to no diversity, all of which were exposed to continuous tilting conditions. The presented plots exhibit a general trend showing that selection diversity reduces the received signal strength fluctuations to lower power, and minimizes the losses due to antenna misalignment.

Propagation in maritime environment dynamically change due to the direct impact of ocean wave undulation to the antenna position and orientation. This paper presents an approach in characterizing signal propagation in a maritime environment by replicating ocean wave-induced antenna motions in a semi-anechoic chamber. The proposed setup may also be used to test mismatch and misalignment mitigating techniques in a controlled environment. The effect on the received signal power of angular motions such as roll, and pitch due to ocean wave undulation, which causes polarization mismatch and antenna misalignment, were investigated in this study. Different setup configurations were applied by varying the tilting orientation, tilting period and tilting range of the antenna in order to replicate various sea state conditions. Measurements reveal the extent of signal degradation due to polarization mismatch and antenna misalignment, and how received signal power degrades with the tilting range. Signal power deviation was measured to reach up to 3 dB and signal power was measured to swing up to 10dB.

The antenna input impedance is commonly assumed to be constant but in a real scenario, the impedance value is affected by the environment. This impedance variation affects the performance of the RF power amplifier and its parameters: stability, output power, linearity and efficiency. Among the methods that can mitigate the effects of impedance variation to impedance performance, the tunable matching network (TMN) was used because this technique provides the direct compensation by re-matching the mismatched impedance. A power amplifier was designed first in order to observe the variation of its performance with respect to load impedances which have a VSWR value of less than or equal to four and resulted a PAE variation from 35% to 68%. There was a reduction of 10 percent to the highest achievable PAE mainly due to the loss contributed by the varactors use in the TMN. An improvement up to 10 percent is also seen in various loads especially those near the edge of the VSWR = 4 after integrating the TMN. In addition, the lowest possible output power due to impedance variation was increased from 36 dBm to 38 dBm after integrating the TMN. Another set of simulations was done using ideal varactors in the TMN and resulted to a variation in PAE from 65% to 69% with the lowest output power level of 39.4 dBm recorded.