We propose a novel formulation for joint maximization of total weighted sum-spectral efficiency and weighted sum-harvested energy to study Simultaneous Wireless Information and Power Transfer (SWIPT) from a pricing perspective. Specifically, we consider that a transmit source communicates with multiple destinations using Orthogonal Frequency Division Multiplexing (OFDM) system within a dual-hop relay-assisted network, where the destination nodes are capable of jointly decoding information and harvesting energy from the same radiofrequency (RF) signal using either the time-switching (TS) or power-splitting (PS) based SWIPT receiver architectures. Computation of the optimal solution for the aforementioned problem is an extremely challenging task as joint optimization of several network resources introduce intractability at high numeric values of relays, destination nodes and OFDM sub-carriers. Therefore, we present a suitable algorithm with sub-optimal results and good performance to compute the performance of joint data processing and harvesting energy under fixed pricing methods by adjusting the respective weight factors, motivated by practical statistics. Furthermore, by exploiting the binary options of the weights, we show that the proposed formulation can be regulated purely as a sum-spectral efficiency maximization or solely as a sum-harvested energy maximization problem. Numerical results illustrate the benefits of the proposed design under several operating conditions and parameter values.

In this paper, we investigate the feasibility of wireless edge caching in a hybrid millimeter-wave (mmWave)- micro-wave (μWave) network. 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 using stochastic geometric tools. Accordingly, we provide an upper bound on the ASP of file delivery and formulate the content caching placement scheme as an optimization problem with respect to caching probabilities, which jointly optimizes the ASP of file delivery considering both content placement and delivery phases. To simplify the non-convex problem and obtain design insights, we split it into two scenarios: 1) noise-limited and 2) interference-limited, and then propose optimal caching placement algorithms for both. We numerically evaluate the performance of the proposed schemes under several essential factors, such as content popularity, cache size, target data rate, blockages in the mmWave network, BS density, and path loss and also compare it with other common proactive caching schemes, namely uniform caching, caching M most popular files, and random caching. Numerical results demonstrate the superiority of the proposed caching scheme over others, albeit certain trade-offs.

Edge-caching has received much attention as an efficient technique to reduce delivery latency and network congestion during peak-traffic times by bringing data closer to end users. In this paper, we investigate the latency performance of content delivery networks with the aid of edge-caching, in which a data centre is serving the users via a shared wireless medium. Firstly, we derive a cache placement design which minimizes the average (buffering) latency during the delivery phase. It is found that the derived placement solution differs from the conventional placement method for throughput minimization. Secondly, for a given cache placement scheme, we optimize the signal transmission in the delivery phase taking into consideration the cached content to minimize the average user latency. Particularly, two optimization problems based on zero-forcing (ZF) and minimum mean square error (MMSE) designs are formulated subject to requesting rate and transmit power constraints. To deal with the non-convexity of the MMSE problem, an iterative algorithm is proposed that approximates the non-convex constraint by its first-order approximation. Finally, numerical results are presented to demonstrate the effectiveness of the proposed designs.

In this paper, we Investigate the performance of cache enabled millimeter wave (mmWave) ad-hoc network, where randomly distributed nodes are supported by a cache memory. Specifically, we study the optimal caching placement at the desirable mmWave node using a network model that accounts for the uncertainties in node locations and blockages. We then characterize the average success probability of content delivery. As a desirable side effect, certain factors like the density of nodes and increased antenna gain, can significantly increase the cache hit ratio in mmWave networks. However, a trade-off between the cache hit probability and the average successful content delivery probability with respect to the density of nodes is presented.

To cope up with the explosive growth of mobile data demand, the fifth-generation mobile network intents to exploit the available spectrum in millimeter-wave (mmWave) band to boost the communication capacity. However, for a potential mmWave communication to happen, challenges, as propagation losses and blockages, have to be dealt with. Abundant literature illustrating techniques to circumvent these challenges and increase the cellular capacity can be found. Among the approaches used to overcome the challenges in mmWave networks, optimal transmit precoding design, spatial reuse of mmWave base stations (BSs), and mmWave-overlaid microwave (μWave) cellular networks are employed. This paper focuses on the performance analysis of mmWave-overlaid microwave cellular networks, from security perspective. We particularly developed a mathematical framework to analyze the connection outage probability, the secrecy outage probability, and the achievable average secrecy rate of the hybrid mmWave network, while taking fading and the impact of blockages into consideration. Moreover, based on the received signal strength, we formulated a scheme for a generic mobile user to be associated with either the mmWave or μWave network. The exact average secrecy rate of mmWave networks is also formulated using moment generating and Laplace functions as a tool. The derived analytic expressions are validated via simulation results; for different antenna gain, eavesdropper density, BS, and blockage density.

The narrow-beam operation in millimeter wave (mmWave) networks minimizes the network interference leading to noise-limited networks in contrast with interference-limited ones. The medium access control (MAC) layer throughput and interference management strategies heavily depend on the noise-limited or interference-limited regime. Yet, these regimes are not considered in recent mmWave MAC layer designs, which can potentially have disastrous consequences on the communication performance. In this paper, we investigate the performance of cache-enabled MAC-based mmWave ad hoc networks, where randomly distributed nodes are supported by a cache. The ad hoc nodes are modeled as homogenous Poisson point processes. Specifically, we study the optimal content placement (or caching placement) at desirable mmWave nodes using a network model that accounts for uncertainties both in node locations and blockages. We propose a contention-based multimedia delivery protocol to avoid collisions among the concurrent transmissions. Subsequently, only the node with smallest back-off timer among its contenders is allowed to transmit. We then characterize the average success probability of content delivery. We also characterize the cache hit ratio probability, and transmission probability of this system under essential factors, such as blockages, node density, path loss, and caching parameters.

In this paper, we analyze the performance of a millimetre wave (mmWave) network where the base stations (BSs) equipped with very large uniform circular arrays (UCA) serve spatially distributed users. Due to its capability of scanning through both the azimuth as well as elevation dimensions, a 3D UCA is considered at the BSs to characterize the signal-to-interference-plus-noise ratio (SINR) of the network. Furthermore, stochastic geometric tools are employed while modelling the interference associated with a particular user. Thereby, expressions for coverage probability of the network is derived and validated in the numerical section. In particular, with the help of simulation results, we show the effect of the number of BS antennas, radius of the circular coverage area and different network parameters such as BS density, blockage density, path loss exponent, and SINR threshold on the coverage probability of the mmWave network.

We consider the beamforming design to maximize the energy-efficiency (EE) of a K link multiple-input multiple-output (MIMO) interference channel, where each link consists of two full-duplex (FD) nodes. We first transform the original fractional form optimization problem into an equivalent subtractive-form optimization problem by exploiting the properties of fractional programming, and then perform a two-layer optimization scheme. In the outer layer, the EE parameter is searched using a simple one-dimensional search, and in the inner layer, the relationship between Weighted-Sum-Rate (WSR) and Weighted Minimum-Mean-Squared-Error (WMMSE) problems is exploited to solve the subtractive form optimization problem. Simulation results show that the EE of FD systems is lower than that of half-duplex (HD) systems, as FD nodes need to overcome self-interference (SI) which leads to high power consumption.

In this paper, we investigate the secrecy outage probability of random wireless networks from the perspective of the k-th best source, which has still not been well characterized. We consider the artificial noise (AN) transmission strategy at source nodes to confuse the eavesdropper. Furthermore, we use a concept of security-region based on the k-th best source index. This is pragmatic in creating a protected communication zone for the typical destination and also in bounding the number of sources that can cooperate in a Coordinated Multi-point transmission (CoMP) network. We further derive the secrecy outage probability for these CoMP sources based on the security-region. We also provide a closed-form expression for the maximum number of eavesdroppers for a given secrecy outage constraint, which can effect the secure communication. Tractable numerical results are presented under various assumptions of densities, antenna gains, AN transmission factors and path loss exponents.

This paper presents an investigation of the secrecy capacity in device-to-device (D2D) enabled cellular network under the collusion of eavesdroppers. We provide the closed-form expressions for the probability of achieving non-zero secrecy capacity of the downlink channel between cellular base-station (BS) and user in the presence of D2D nodes and eavesdroppers. Furthermore, two techniques are used for the simple yet exact evaluation of the average secrecy rate using moment generating functions with and without interference. The impact of transmission factors, path loss exponents, and node density is analysed in numerical results. In contrast to the general notion of interference-aided secure communication, it has been shown that the interference does not impact the secrecy rate under the collusion of eavesdroppers.

The explosion of cellular users and high demand for data has evolved the single-tier cellular network to multi-tier network. This paper analyses the gain of non-orthogonal multiple access (NOMA), an enabling technique for 5G, in a heterogeneous cellular network (HCN) consisting of a macro base station (MBS) tier and femto base station (FBS) tier. Offloading users to the FBS tier is performed to relieve the MBS tier of over congestion. In order to support offloaded user, the FBS tier employs NOMA. The results are plotted for different channel conditions while offloading the user to FBS tier. Benefits of NOMA (for e.g., higher ergodic rate, user fairness, performance enhancement at cell edge user) are observed for different channel conditions for the offloaded user. It is also observed that offloading to FBS tier with NOMA gives better performance as compared to offloading without NOMA.

We consider the relay selection problem in large-scale energy harvesting (EH) networks. It is known that if channel state information (CSI) is available at EH relays, a diversity order equal to the number of relays can be obtained, however, at the penalty of a feedback overhead (necessary to obtain accurate CSI) which is not suitable for energy-limited devices intended, e.g., for Internet-of-Things applications. In this paper, we therefore propose a new EH relay selection scheme which is based on the residual energy at each relay's battery, and on information on the distribution of the channels between relays and the destination. The method thus minimizes both the outage probability and the feedback cost. Where previous work relay selection based on channel distribution information consider only small-scale fading distribution, we employ a stochastic geometry approach to consider jointly the geometrical distribution (i.e., large-scale fading) and small-scale fading yielding a simple relay selection criterion that furthermore utilizes only rough information on the relay's location, i.e., an ordinal number from the destination. The outage probability of the proposed relay selection scheme is analytically derived, and the achievable diversity order of the proposed approach is investigated. Computer simulations confirm our theoretical analyses and show that our approach is robust against errors in the estimation of the distances between nodes.

In this paper, the secrecy-rate characteristics of multitier downlink heterogeneous networks under generalized fading model is investigated for two types of base-station (BS)-user(s) association scenarios. Each tier within the network has a single multiantenna BS that intends to serve multiple single-antenna mobile users. These users are assumed to be distributed according to homogeneous Poisson point process (PPP) with particular density parameter. Single-antenna eavesdroppers which intend to wiretap the communication between the chosen BS and intended mobile user are also assumed to coexist within the network distributed as PPP with different intensity parameter. We have adopted the maximum received path gain, rather than distance, as a metric to describe the association scenario between a BS and typical user. Therefore, a typical user associates itself with: 1) a BS that provides the user with the maximum path gain or 2) any potential BS that provides the kth maximum path gain to the user. Using stochastic geometry as a tool, the received path gain distributions and the achievable average secrecy rate expressions from the perspective of association with the “best” and the kth best BS are analyzed analytically. Tractable numerical and simulation results are presented under various assumptions of fading scenario, path loss exponent, eavesdropper density, and antenna figures to support the lemmas and propositions stated within this paper.

In this paper, we analyze the secrecy characteristics of random wireless networks using stochastic geometric tools. The locations of the source and eavesdropper nodes are modeled as independent 2-D Poisson point processes. We investigate the secrecy outage probability of such networks from the perspective of the k th best source, which has still not been well characterized. In particular, we derive the received path gain distributions of the typical destination and the eavesdropper from the k th best source. Furthermore, we introduce a novel concept of security-region based on the k th best source index. This is pragmatic in creating a protected communication zone for the typical destination and also to bind the number of sources that can coordinate in a coordinated multi-point transmission (CoMP) network. We further derive the secrecy outage probability for these CoMP sources based on the security-region. We also provide a closed-form expression for the maximum number of eavesdroppers for a given secrecy outage constraint, which can effect the secure communication. Tractable numerical, and simulation results are presented under various assumptions of densities, path loss exponents, and antenna figures.

The secrecy outage of millimeter wave (mmWave) networks under the impact of blockages is derived. Specifically, using a network model that accounts for uncertainties both in node locations and blockages, we characterize the connection outage probability and the secrecy outage probability of mmWave networks with multiple eavesdroppers under basic factors such as density of eavesdropping nodes, antenna gain and blockage density. As a desirable side effect, certain factors such as blockages and reduced antenna gain can decrease the secrecy outage probability. This however is in contrast to general mmWave systems where it has been shown that reduced blockages and high antenna gains provide higher capacities.

The potential benefits of deploying relays in outdoor millimeter-wave (mmWave) networks are investigated. We derive the coverage probability from sources to a typical destination for such systems aided by relays. The sources and the relays are modeled as independent homogeneous Poisson point processes. We present a relay modeling technique for mmWave networks considering blockages and compute the density of active relays that aid the transmission. Closed form expressions for end-to-end signal to noise ratio for two relay selection techniques, namely best path selection and best relay selection are derived. Finally, we analyze the coverage probability and transmission capacity of the network and validate them with simulation results. Our results show that the coverage probability and transmission capacity of mmWave systems, which are often affected by extensive blockages can be increased considerably with the aid of relays.

The secrecy characteristics of random wireless networks considering a generalized fading model, where the communication nodes are equipped with multiple antennas is analyzed. Using stochastic geometric tools, we investigate the secrecy outage probability of such networks from the perspective of the kth best source, which has still not been well characterized in the literature. In particular, we derive the received path gain distributions of the typical destination and the eavesdropper from the k-th best source. Using these results, we derive the secrecy outage probability for two scenarios with respect to the received path gain from any best source and the k-th best source. Furthermore, we introduce a novel concept of security-region based on the k-th best source index. This is pragmatic in creating a protected communication zone for the typical destination. Tractable numerical and simulation results are presented under various assumptions of fading, path loss exponents and antenna figures.

In this paper, we investigate the secrecy performance of the multiple-input multiple-output (MIMO) wiretap channels in the presence of an active full-duplex eavesdropper with consideration of channel estimation error at the legitimate destination and eavesdropper. For this purpose, the probability density functions (PDFs) and cumulative density functions (CDFs) of the receive signal-to-interference-plus-noise ratio (SINR) at the destination and eavesdropper are given by conducting the singular value decomposition (SVD) on the estimated channel coefficient matrices. Consequently, the closed- form expressions for the probability of positive secrecy capacity and secrecy outage probability over Rayleigh fading channels are derived. Finally, the Monte-Carlo simulation results are presented to validate the accuracy of our theoretical analysis.

We consider a K link multiple-input multiple-output interference channel where each link consists of two full-duplex (FD) nodes. Two transmit beamforming design problems are solved: 1) sum-power minimization problem subject to rate constraints and 2) energy-efficiency maximization problem subject to individual power constraints. To tackle the sum-power 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 subtractive-form optimization problem by exploiting the properties of fractional programming, and then performs a dual-layer optimization scheme. In the outer layer, the energy-efficiency parameter is searched using a simple 1-D 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, 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 systems, as FD nodes need to overcome self-interference and increased inter-user interference, which leads to high power consumption.

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. The upper and lower bounds of the conditional secrecy outage probability for both the 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 that have been proved to be detrimental to 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.

We perform an analysis of the secrecy outage of random networks under Nakagami-m fading with multiple transmit antennas. Specifically, using a network model that accounts for uncertainties both in node locations (distances) and channel coefficients (fading), we derive the distribution of the best path gain of eavesdroppers using Probability Generating Functional property of Poisson Point Process (PPP). Using this result, the secrecy outage probability and the conditional secrecy outage probability of random networks with multiple eavesdroppers are obtained, with basic factors such as the density of eavesdropping nodes, the number of transmit antennas and the fading coefficient all accounted for by explicit parameters. The impact of transmission factors, including number of transmit antennas, fading figure, legitimate node distance and node density are studied and analysed in numerical results.

The majority of recent literature characterizes the secrecy capacity of wireless random networks by relying on Poison Point Processes which model the spatial distribution of devices. However, the realistic topologies are distinct from uniform and random assumption of the base stations or users. It has been recently demonstrated that Matérn Hard-core Point Processes (MHCPP) - rather than Poison Point Processes - are better suited to characterize such random location of users and base-stations of cellular systems. In this paper, we perform an analysis of the Secrecy Outage probability of cellular random networks under fading channel by employing the modified MHCPP model. It is also shown that the base station deployment has a significant impact on the secrecy outage.

Correlation between the legitimate receiver and the eavesdropper has been seldom considered in the literature when evaluating secrecy metrics in stochastic wireless networks. In practice, however, poor scattering conditions may lead to spatially correlated channels, which can be exploited by eavesdroppers. In this paper we investigate the connection outage and secrecy outage in Poisson-distributed random networks under Nakagami-m fading and mutually correlated legitimate and eavesdropping channels. Numerical results show that correlated fading has an important effect on security, which may be either beneficial or harmful, depending on the secrecy outage constraints.

We analyze the effect of fading onto the probability of non-zero secrecy capacity, denoted Pr{Cs:i> 0}, in stochastic wireless random networks modeled as Secrecy-Graphs. Specifically, we derive expressions to characterize the probability that the secrecy capacity of a unicast channel to a legitimate node is non-zero, in the case when the channel is affected by Nakagami-m fading, and in the presence of a random (unknown) number of eavesdroppers. The results show that fading can increase the probability of finding information-theoretic secure channels in such conditions, depending on the relative density of legitimate nodes and eavesdroppers.

We investigated the secrecy outage of unicast channels in random networks exposed to unknown numbers of randomly located eavesdroppers, obtaining original expressions which include uncertainty in terms of the location of legitimate nodes relative to eavesdroppers, the number of eavesdroppers, and fading. Under such conditions, we derive the path gain distributions of legitimate and eavesdropper nodes, as well as the corresponding secrecy non-outage. Two interesting conclusions can be drawn from our analysis. The first is that the uncertainty on the number of eavesdropper does not play a significant role in quantifying secrecy outage; and the second is that secret communication at a given rate is possible (albeit subjected to outage), with very low power. Specifically, it is found that the for a given fading figure and network density (which fundamentally determines the secrecy outage) similar secrecy outage is experience by the k-th furthest legitimate node, independent on the source's transmit power.

We consider the secrecy capacity of unicast channels of ad hoc networks exposed to randomly located eavesdroppers, as modeled by S-Graphs. Expressions that quantify the impact of fading and of the density of legitimate nodes relative to that of eavesdroppers are obtained, in terms of the probability that secrecy capacities of unicast channels are nonzero. The results indicate that depending on the relative density of eavesdroppers and the fading intensity, the secrecy capacity of unicast channels subject to fading may be higher than under additive white Gaussian noise (AWGN).