We consider the use of the Fisher-Snedecor F distribution, which is defined as the ratio of two chi-squared variates, to model composite fading channels. In this context, the root-mean-square power of a Nakagami-m signal is assumed to be subject to variations induced by an inverse Nakagamim random variable. Comparisons with physical channel data demonstrate that the proposed composite fading model provides as good, and in most cases better, fit to the data compared to the generalized-K composite fading model. Motivated by this result, simple novel expressions are derived for the key statistical metrics and performance measures of interest.

The F composite fading model was recently proposed as an accurate and tractable statistical model for the characterization of the composite fading conditions encountered in realistic wireless communication scenarios. In the present contribution we capitalize on the distinct properties of this composite model to derive an analytical framework to evaluate the achievable channel capacity over F composite fading channels under different channel state information (CSI) assumptions. To this end, we first consider that CSI is known only at the receiver, for which we derive novel analytic expressions for the channel capacity under optimum rate adaptation as well as for the corresponding effective capacity. Then, by considering that CSI is known both at the transmitter and at the receiver, we derive novel analytic expressions for the channel capacity under optimum power and rate adaptation, channel inversion with fixed rate and truncated channel inversion with fixed rate. The derived analytic expressions for the considered scenarios are provided in closed-form and benefit from being tractable both analytically and numerically. This enables the derivation of simple bounds as well as approximate and asymptotic expressions which are shown to be useful as they provide meaningful insights on the effect of fading conditions and/or latency on the overall system performance.

Emerging cellular technologies such as those proposed for use in 5G communications will accommodate a wide range of usage scenarios with diverse link requirements. This will necessitate operation over a versatile set of wireless channels ranging from indoor to outdoor, from line-of-sight (LOS) to non-LOS, and from circularly symmetric scattering to environments which promote the clustering of scattered multipath waves. Unfortunately, many of the conventional fading models lack the flexibility to account for such disparate signal propagation mechanisms. To bridge the gap between theory and practical channels, we consider κ-μ shadowed fading, which contains as special cases the majority of the linear fading models proposed in the open literature. In particular, we propose an analytic framework to evaluate the average of an arbitrary function of the signal-to-noise-plus-interference ratio (SINR) over κ-μ shadowed fading channels by using an orthogonal expansion with tools from stochastic geometry. Using the proposed method, we evaluate the spectral efficiency, moments of the SINR, and outage probability of a K-tier heterogeneous cellular network with K classes of base stations (BSs), differing in terms of the transmit power, BS density, shadowing, and fading characteristics. Building upon these results, we provide important new insights into the network performance of these emerging wireless applications while considering a diverse range of fading conditions and link qualities.

This paper investigates the characteristics of the shadowed fading observed in off-body communications channels at 5.8 GHz. This is realized with the aid of the κ-μ/gamma composite fading model, which assumes that the transmitted signal undergoes κ-μ fading, which is subject to multiplicative shadowing. Based on this, the total power of the multipath components, including both the dominant and scattered components, is subject to non-negligible variations that follow the gamma distribution. For this model, we present an integral form of the probability density function (PDF) as well as important analytic expressions for the PDF, cumulative distribution function, moments, and moment generating function. In the case of indoor off-body communications, the corresponding measurements were carried out in the context of four explicit individual scenarios, namely: line of sight (LOS), non-LOS walking, rotational, and random movements. The measurements were repeated within three different indoor environments and considered three different hypothetical body worn node locations. With the aid of these results, the parameters for the κ-μ/gamma composite fading model were estimated and analyzed extensively. Interestingly, for the majority of the indoor environments and movement scenarios, the parameter estimates suggested that dominant signal components existed even when the direct signal path was obscured by the test subject's body. In addition, it is shown that the κ-μ/gamma composite fading model provides an adequate fit to the fading effects involved in off-body communications channels. Using the Kullback-Leibler divergence, we have also compared our results with another recently proposed shadowed fading model, namely, the κ-μ/lognormal LOS shadowed fading model. It was found that the κ-μ/gamma composite fading model provided a better fit for the majority of the scenarios considered in this paper.

In this paper, we investigate the performance of energy detection-based spectrum sensing over F composite fading channels. To this end, an analytical expression for the average detection probability is firstly derived. This expression is then extended to account for collaborative spectrum sensing, squarelaw selection diversity reception and noise power uncertainty. The corresponding receiver operating characteristics (ROC) are analyzed for different conditions of the average signal-to-noise ratio (SNR), noise power uncertainty, time-bandwidth product, multipath fading, shadowing, number of diversity branches and number of collaborating users. It is shown that the energy detection performance is sensitive to the severity of the multipath fading and amount of shadowing, whereby even small variations in either of these physical phenomena can significantly impact the detection probability. As a figure of merit to evaluate the detection performance, the area under the ROC curve (AUC) is derived and evaluated for different multipath fading and shadowing conditions. Closed-form expressions for the differential entropy and cross entropy are also formulated and assessed for different average SNR, multipath fading and shadowing conditions. Then the relationship between the differential entropy of F composite fading channels and the corresponding ROC/AUC is examined where it is found that the average number of bits required for encoding a signal becomes small (i.e., low differential entropy) when the detection probability is high or when the AUC is large. The difference between composite fading and traditional smallscale fading is emphasized by comparing the cross entropy for Rayleigh and Nakagami-m fading. A validation of the analytical results is provided through a careful comparison with the results of some simulations.

In this letter, we report the results of a series of experiments which were performed to examine the impact of terminal handling and movement upon the user equipment (UE) to evolved NodeB (eNB) communications channel at 60 GHz. Three key utilization scenarios, in which a user imitated making a voice call, sending a text message or simply carrying the device in a pocket, are investigated. Each of these three user cases were studied under line of sight (LOS) and non-LOS (NLOS) channel conditions when the user was mobile in a range of different indoor and outdoor small cell scenarios. It is shown that the mode of UE operation (i.e., how the device is handled) will be important for future 60 GHz cellular applications. In particular, for short-range UE to eNB links which are in true NLOS, body shadowing is the dominating factor. To allow our results to be readily incorporated into network simulations, we have characterized the channel by decomposing the received signal into its constituent path loss, shadowed and small-scale fading components. In particular, we have had good success modeling the shadowed fading using the gamma distribution, whereas the small-scale fading observed in the LOS and NLOS channels has been appropriately modeled using the Rice and Nakagami-m distributions, respectively.