Free-space optical (FSO) links are considered as cost-effective, non-invasive alternative to fiber optic cables for 5G cellular backhaul networking. For FSO based backhaul networks we propose an additional millimeter-wavelength (MMW) radio-frequency (RF)-FSO link, used as a backup. Uninterrupted and reliable network connection is possible by switching between primary FSO link and the secondary RF-FSO link; when the primary link is under atmospheric turbulence, the secondary link maintains connectivity as the MMW RF link exhibits complementary characteristics to atmospheric effects. In order to analytically assess the improvement, we also derive concise mathematical expressions for different performance metrics like outage probability, average bit error rate (BER) and capacity. Our results demonstrate that FSO/RF-FSO topology performs better than a single FSO link in terms of outage probability and BER. The dual-hop mixed RF-FSO link is realized with an amplify and forward (AF) relay that adapts an average power scaling (APS) strategy. The irradiance fluctuations in the FSO links are modeled by gamma-gamma distribution assuming strong atmospheric turbulence while it is assumed that the RF link experiences multipath Rayleigh fading. For switching between links a single FSO threshold is considered first, followed by a dual FSO threshold to prevent unnecessary switching.

The availability of free space optics (FSO) systems in dependence on weather conditions and on FSO link parameters, such as transmitted optical power, beam divergence, receiver sensitivity or link path distance, is discussed. A number of phenomena in the atmosphere, such as absorption, scattering, and turbulence, can affect beam attenuation, but in the case of wavelengths typical of FSO systems operation, only scattering and turbulence are appropriate to be taken into consideration. We model the power loss caused by turbulence by using the Rytov scintillation theory. Attenuation due to scattering, which can be expressed as a function of the link distance, wavelength, and meteorological visibility, is calculated from visibility data collected at several airports in Europe. Statistical evaluation of the attenuation caused by scattering and the power link margin calculated from FSO link parameters are used for calculating the link availability.

In this paper, we investigate the detection performance of cooperative spectrum sensing (CSS) using energy detector in several fading scenarios. The fading environments comprise relatively less-studied Hoyt and Weibull channels in addition to the conventional Rayleigh, Rician, Nakagami-m and log-normal shadowing channels. We have presented an analytical framework for evaluating different probabilities related to spectrum sensing, i.e. missed detection, false alarm and total error due to both of them, for all the fading/shadowing models mentioned. The major theoretical contribution is, however, the derivation of closed-form expressions for probability of detection. Based on our developed framework, we present performance results of CSS under various hard decision fusion strategies such as OR rule, AND rule and Majority rule. Effects of sensing channel signal-to-noise ratio, detection threshold, fusion rules, number of cooperating cognitive radios (CRs) and fading/shadowing parameters on the sensing performance have been illustrated. The performance improvement achieved with CSS over a single CR-based sensing is depicted in terms of total error probability. Further, an optimal threshold that minimises total error probability has been indicated for all the fading/shadowing channels.

The paper provides real-word wireless measurement data of the intravehicular channel for both the 3-11 GHz and the 55-65 GHz frequency bands under similar conditions. By spatially averaging channel impulse response realizations within a 10 × 10 grid, we obtain the power-delay profile (PDP). The data measured at 3-11 GHz and 55-65 GHz exhibit significant differences in terms of root mean square (RMS) delay spread, number of resolvable clusters, and variance of the maximal excess delay. Moreover, we evaluate the spatial stationarity via the Pearson correlation coefficient and via the PDP collinearity, depending on the distance in the grid. The measured and calculated results indicate that a strong reverberation inside the vehicle produces similar PDPs within the range of approximately ten wavelengths. We also provide a linear piecewise model of the PDP in logarithmic scale and a generalized extreme value model of a small-scale signal fading. Our channel model is validated utilizing the Kolmogorov-Smirnov test.

This paper aims to present a simple but robust model characterizing the frequency-dependent transfer function of an in-vehicle ultrawideband (UWB) channel. A large number of transfer functions spanning the UWB (3–11 GHz) are recorded inside the passenger compartment of a four-seated sedan. It is found that the complex transfer function can be decomposed into two terms, the first term being a real-valued long-term trend that characterizes frequency dependence with a power law and the second term forming a complex correlative discrete series that may be represented via an autoregressive (AR) model. An exhaustive simulation framework is laid out based on empirical equations characterizing trend parameters and AR process coefficients. The simulation of the transfer function is straightforward as it involves only a handful of variables; however, it is in good agreement with the actual measured data. The proposed model is further validated by comparing different channel parameters, such as coherence bandwidth, power delay profile, and root-mean-square delay spread, obtained from raw and synthetic data sets. It is also shown how the model can be compared with existing time-domain Saleh–Valenzuela-influenced models and related IEEE standards.