In this paper, we investigate the potential benefits of deploying relays in outdoor millimeter-wave (mmWave) networks. We study the coverage probability from sources to a destination for such systems aided by relays. The sources and the relays are modeled as independent homogeneous poisson point processes (PPPs). We present a relay modeling technique for mmWave networks considering blockages and compute the density of active relays that aid the transmission. Two relay selection techniques are discussed, namely best path selection and best relay selection. For the first technique, we provide a closed form expression for end-to-end signal to noise ratio (SNR) and compute the best random relay path in a mmWave network using order statistics. Moreover, the maximum end-to-end SNR of random relay paths is investigated asymptotically by using extreme value theory. For the second technique, we provide a closed form expression for the best relay node having the maximum path gain. Finally, we analyze the coverage probability and transmission capacity of the network and validate them with simulation results. Our results show that deploying relays in mmWave networks can increase the coverage probability and transmission capacity of such systems.

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The secrecy outage of millimeter wave (mmWave) overlaid micro wave (µWave) networks under the impact of blockages is analyzed, and closed form as well as integral expressions are provided. Specifically, using a network model that accounts for uncertainties both in node locations and blockages, we characterize the conditional connection outage probability and the secrecy outage probability of hybrid networks with multiple eavesdroppers under basic factors such as density of eavesdropping nodes, antenna gain and blockage density. Upper and lower bounds of the conditional secrecy outage probability for both line-of-sight and non line-of-sight links are derived. As a desirable side effect, certain factors such as blockages and reduced antenna gain can decrease the secrecy outage probability in mmWave networks. This can be considered as a tradeoff between outage capacity and secrecy outage capacity with respect to blockages. Hence, blockages which have been proved to be detrimental for achieving higher data rates in mmWave systems, can be helpful for systems with secrecy constraints. Finally, we have shown the coexistence of mmWave and µWave networks from a secrecy perspective. Index Terms-Secrecy outage, random networks, blockages, millimeter wave I. INTRODUCTION In recent years, the explosive growth of mobile data traffic has led to an ever-growing demand for much higher capacity and lower latency in wireless networks. It has culminated in the development of the fifth generation (5G) wireless communication systems, expected to be deployed by the year 2020, with key goals of data rates in the range of Gbps, billions of connected devices, lower latency, improved coverage and reliability, and low-cost, energy efficient and environmentfriendly operation. To meet the ever-increasing demands, and keeping in mind that the current wireless spectrum is almost saturated, it is imperative to shift the paradigm of cellular spectrum to a new range of frequencies. In this regard, millimeter wave (mmWave) bands with significant amounts of unused or lightly used bandwidths appear to be a viable way to move forward. With bands of 20-100 GHz available for communication, mmWave can be the cornerstone in the design of 5G networks. MmWave bands are weak and cannot penetrate through obstacles like buildings, concrete walls, vehicles, trees etc. Due to these limitations, such bands were not considered

We consider a K link multiple-input multiple-output (MIMO) interference channel where each link consists of two full-duplex (FD) nodes. Two transmit beamforming design problems are solved, i) sum-power minimization problem subject to rate constraints, and ii) energy-efficiency maximization problem subject to individual power constraints. To tackle the sumpower minimization problem, we first generalize the well-known relationship between weighted-sum-rate (WSR) and weighted minimum-mean-squared-error (WMMSE) problems, originally used to solve the sum-rate maximization problems, and then propose a low complexity centralized algorithm which converges to a stationary point. To decrease the exchange of a huge amount of data and excessive signaling traffic among the nodes, a distributed algorithm is also proposed. For the energy-efficiency maximization problem, the original fractional form optimization problem is first transformed into an equivalent subtractiveform optimization problem by exploiting the properties of fractional programming, and then perform a dual-layer optimization scheme. In the outer layer, the energy-efficiency parameter is searched using a simple one-dimensional search, and in the inner layer, the relationship between WSR and WMMSE is exploited to solve the subtractive form optimization problem. Since the proposed algorithms require perfect channel-state-information (CSI), which is difficult to acquire in practice, we also propose a robust design, by taking the imperfect channel knowledge into consideration. It is shown in the simulations that the sum-power achieved in FD mode depends heavily on the transmitter/receiver distortion. Also the energy-efficiency of FD systems is lower than that of half-duplex (HD) systems, as FD nodes need to overcome self-interference and increased inter-user interference which leads to high power consumption.

We investigate the performance of a multi-beam cog-AQ1 1 nitive satellite terrestrial network in which a secondary network 2 (mobile terrestrial system) shares resources with a primary satel-3 lite network given that the interference temperature constraint 4 is satisfied. The terrestrial base stations (BSs) and satellite users 5 are modeled as independent homogeneous Poisson point pro-6 cesses. Utilizing tools from stochastic geometry, we study and 7 compare the outage performance of three secondary transmis-8 sion schemes: first is the power constraint (PCI) scheme where 9 the transmit power at the terrestrial BS is limited by the interfer-10 ence temperature constraint. In the second scheme, the terrestrial 11 BSs employ directional beamforming to focus the signal intended 12 for the terrestrial user, and in the third, BSs that do not satisfy 13 the interference temperature constraint are thinned out (BTPI). 14 Analytical approximations of all three schemes are derived and 15 validated through numerical simulations. It is shown that for the 16 least interference to the satellite user, BTPI is the best scheme. 17 However, when thinning is not feasible, PCI scheme is the viable 18 alternative. In addition, the gains of directional beamforming are 19 optimal when the terrestrial system employs massive multiple-20 input-multiple-output transceivers or by the use of millimeter 21 wave links between terrestrial BSs and users. 22 Index Terms-Cognitive radio, interference, multi-beam satel-23 lite, poisson point processes, satellite-terrestrial networks. 24 AQ2 The associate editor coordinating the review of this paper and approving it for publication was N. Devroye.

Abstract-Recent research prove that device-to-device (D2D) communications offer substantial gain through enhancing throughput and spectral efficiency as well as widening coverage area of cellular network. However, from security perspective, performance of such network has not been well investigated. With this motive and inspired by stochastic geometry approach, we provide secrecy rate analysis for D2D-enabled cellular network under Rayleigh fading channels. The minimum distance among mobile users is used to characterise the retention probability and hence, density of D2D nodes. Moreover, a fraction of the total transmitted power from D2D nodes is allocated to radiate artificial noise (AN) to degrade the eavesdroppers channel. Under such conditions, the closed-form expressions for the probability of achieving non-zero secrecy capacity for the uplink channel between user-equipment and cellular base-station in the presence of D2D nodes and eavesdropper(s). Throughout the paper, we consider the following eavesdropping strategies: (a) a single eavesdropper case; (b) multiple eavesdroppers that can cooperatively cancel the interference; (c) multiple cooperative eavesdroppers that can cooperatively cancel both the interference and AN; and (d) the case of cooperative colluding eavesdroppers. The derived expressions are validated via simulation as a function of antenna gain, eavesdropper density, D2D hard-core distance and D2D node density.

In this paper, we consider a hybrid millimeter wave (mmWave) and micro wave (µWave) network from the perspective of wireless caching and study the optimal probabilistic content/file caching placement at desirable base stations (BSs) using a stochastic geometric framework. Considering the average success probability (ASP) of file delivery as the performance metric, we derive expressions for the association probability of the typical user to the mmWave and µWave networks. Accordingly, we provide an upper bound for the ASP of file delivery and formulate the content caching placement scheme as an optimization problem with respect to caching probabilities, that jointly optimizes the ASP of file delivery considering both content placement and delivery phases. In particular, we consider the caching placement strategy under both noise-limited and interference-limited environments. We numerically evaluate the performance of the proposed caching schemes under essential factors, such as blockages in the mmWave network, cluster radius, BS density, and path loss and compare it with uniform caching placement, caching M most popular contents, and random caching placement. Numerical results demonstrate the superiority of the proposed caching scheme over others, albeit certain trade-offs. Index TermsWireless caching, millimeter-wave networks, micro wave networks, Poison point processes.

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