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The composite multipath/shadowing model is key to accurate modeling of real-world wireless channels, due to the combination of the effects of both fading and shadowing. However, the fundamental limits of spectrum-sharing cognitive radio have not been studied for such propagation conditions, leaving a gap in the analysis of these systems and, hence, the communication strategies that can be built upon toward improving performance. In this paper, we consider a primary/secondary spectrum-sharing network and study the performance of the secondary's multihop link by taking the composite multipath/shadowing model, which is described by the generalized- $K$ distribution, for the radio channels. In the multihop system, communication between secondary users (SUs) is assisted by intermediate relay terminals, under coexistence constraints with the primary users (PUs) . We assess the performance of the multihop system, first by deriving the moment generating function (mgf) and the probability density function (pdf) of the upper bounded end-to-end signal-to-noise ratio in closed form. The result is then used to obtain closed-form expressions of bounds on the ergodic capacity and the average bit error rate (ABER) , under the resource sharing constraints. The theoretical results are assessed with numerical analysis for different operating conditions.

In this paper, the performance of wireless energy transfer (WET) in millimeter wave (mmWave) massive multiple-input multiple-output (MIMO) systems is analyzed. By accounting for rainfall effects, path loss and small-scale fading, a comprehensive MIMO channel model is first developed, which is suitable for modeling the energy propagation in WET mmWave massive MIMO systems operating in rainy or clear conditions. Based on this model, a framework for the channel estimation at the hybrid data-and-energy access point (HAP) is presented. Starting from the law of energy conservation, the downlink energy transferred by the HAP and harvested by the user equipments (UEs) is assessed, for several important scenarios. In particular, the results show that the asymptotic harvested energy increases linearly with the number of HAP antennas and the number of UEs, but decreases exponentially with the raining parameters which monotonically increase with the operating frequency.

In integrated mobile satellite systems (MSSs) with ancillary terrestrial component (ATC), seamless handoff techniques will be fundamental for allowing users to switch between the space segment and the terrestrial component. On the other hand, introducing multiple-input multiple-output (MIMO) antenna technology in next-generation MSS-ATC systems promises the well-known advantages related to the MIMO implementation. For performing handoff analysis, the single-input single-output (SISO) channel model equivalent to the MIMO model needs to be developed, which is challenging in MSS-ATC networks because of the high complexity of the satellite channel, and the vast difference in the nature of the MSS and the ATC links. This challenge is tackled in this paper, where an optimal user-driven handoff algorithm for MSS-ATC systems is presented, with both types of links implementing MIMO. Furthermore, for a better signal prediction, Kalman filtering is proposed, which significantly increases the performance. Notably, the application of multi-antenna technology in MSS-ATC systems reveals significant gains in terms of handoff performance.

This paper analyzes the spectral efficiency of massive multiple-input multiple-output (MIMO) systems in both centralized and distributed configurations, referred to as C-MIMO and D-MIMO, respectively. By accounting for real environmental parameters and antenna characteristics, namely, path loss, shadowing effect, multi-path fading and antenna correlation, a novel comprehensive channel model is first proposed in closed-form, which is applicable to both types of MIMO schemes. Then, based on the proposed model, the asymptotic behavior of the spectral efficiency of the MIMO channel under both the centralized and distributed configurations is analyzed and compared in exact forms, by exploiting the theory of very long random vectors. Afterwards, a case study is performed by applying the obtained results into MIMO networks with circular coverage. In such a case, it is attested that for the D-MIMO of cell radius $r_{\mathrm{c}}$ and circular antenna array of radius~$r_{\mathrm{a}}$, the optimal value of~$r_{\mathrm{a}}$ that maximizes the average spectral efficiency is accurately established by $r_{\mathrm{a}}^{\mathrm{opt}}=r_{\mathrm{c}}/1.31$. Monte Carlo simulation results corroborate the developed spectral-efficiency analysis., IEEE Transactions on Communications, accepted for publication, January 2016; 12 pages, 8 figures

In coverage areas overlapped by the mobile satellite system (MSS) and the ancillary terrestrial component (ATC) of integrated MSS/ATC networks, users can suffer severe co-channel interference (CCI) due to the coexistence of MSS and ATC signals. The vast difference between the characteristics of the desired channels for a user, depending on whether it is connected to the satellite or to the terrestrial station, makes the corresponding performance evaluation very challenging. This paper tackles this issue by using the powerful generalized-K distribution, and offers a unified closed-form analysis for the system performance of both types of connections. In particular, it is revealed that the user's diversity gain depends only upon the minimum between the fading parameter and the shadowing parameter of the desired channel, regardless of the CCI. Also, the coding gain increases with the diversity gain. The effectiveness of the analysis is corroborated by Monte Carlo simulations.

To account for antenna physical parameters and real propagation conditions encountered by large-scale multipleinput multiple-output (MIMO) antenna systems in practical deployment, this paper develops a comprehensive MIMO channel model in an analytical way. In particular, major parameters including path loss, shadowing effect, multi-path fading, channel polarization, channel correlations, antenna cross-polarization discrimination and environmental cross-polar coupling, are integrated in a mathematically tractable way. Then, an upper bound on the ergodic capacity of the comprehensive MIMO channel is derived asymptotically, i.e. as the number of transmit and/or receive antennas of the MIMO system approaches infinity. Finally, Monte Carlo simulation results corroborate the effectiveness of the proposed model and the accuracy of the resulting capacity bound. Thanks to its high generality and compactness, the proposed model can serve as the kernel for the design and performance evaluation of large-scale MIMO in real propagation environments.

This paper develops a general and unified multi-input multi-output (MIMO) channel model applicable to both mobile satellite systems (MSS) and ancillary terrestrial component (ATC) links of integrated MSS with ATC. Major channel parameters pertaining to the MSS and ATC links, such as large-scale path loss, shadowing effect, small-scale multi-path fading, satellite elevation angle, channel polarization and temporal correlations, antenna cross-polarization discrimination and environment cross-polar coupling, are all taken into account in a compact, flexible and fully parameterized way. Moreover, a step-by-step methodology used for Monte-Carlo simulation of the proposed channel model is explicitly provided. Further, numerical results illustrating the effects of several channel parameters are presented. The proposed model is general and constitutes a fundamental kernel for the design and performance evaluation of MSS-ATC networks, and is also suitable for the modeling of other hybrid networks such as heterogeneous networks.