Abstract-Recent years have shown a promising progress in understanding geometric underpinnings behind the structure, function, and dynamics of many complex networks in nature and society. However these promises cannot be readily fulfilled and lead to important practical applications, without a simple, reliable, and fast network mapping method to infer the latent geometric coordinates of nodes in a real network. Here we present HyperMap, a simple method to map a given real network to its hyperbolic space. The method utilizes a recent geometric theory of complex networks modeled as random geometric graphs in hyperbolic spaces. The method replays the network's geometric growth, estimating at each time step the hyperbolic coordinates of new nodes in a growing network by maximizing the likelihood of the network snapshot in the model. We apply HyperMap to the AS Internet, and find that: 1) the method produces meaningful results, identifying soft communities of ASs belonging to the same geographic region; 2) the method has a remarkable predictive power: using the resulting map, we can predict missing links in the Internet with high precision, outperforming popular existing methods; and 3) the resulting map is highly navigable, meaning that a vast majority of greedy geometric routing paths are successful and low-stretch. Even though the method is not without limitations, and is open for improvement, it occupies a unique attractive position in the space of trade-offs between simplicity, accuracy, and computational complexity.

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The employment of intelligent reflecting surfaces (IRSs) is a potential and promising solution to increase the spectral and energy efficiency of wireless communication networks. The passive operation of their elements and the fact that they can be deployed on any flat surface, makes them ideal for both indoor and outdoor applications. On the other hand, the capabilities of IRS-aided communications have limitations as they are subject to high propagation losses. To overcome this, the phase rotation at each element needs to be designed in such a way as to increase the channel gain at the destination. However, this increases the system's complexity as well as its power consumption. In this paper, we present an analytical framework for the performance of random rotation-based IRS-aided communications.Under this framework, we propose four low-complexity and energy efficient techniques based on two approaches: a coding-based and a selection-based approach. Both approaches depend on random phase rotations and require no channel state information. In particular, the coding-based schemes use timevarying random phase rotations to produce a time-varying channel, whereas the selection-based schemes, select a partition of the IRS elements at each time slot based on the received signal power at the destination. Analytical expressions for the achieved outage probability and energy efficiency of each scheme are derived. It is demonstrated that all schemes can provide significant performance gains as well as full diversity order.

Abstract-In this paper, we consider two fundamental fullduplex (FD) architectures, two-node and three-node, in the context of cellular networks where the terminals employ directional antennas. The simultaneous transmission and reception of data in non-orthogonal channels makes FD radio a potential solution for the currently limited spectrum. However, its implementation generates high levels of interference either in the form of loopback interference (LI) from the output to the input antenna of a transceiver or in the form of co-channel interference in largescale multicell networks due to the large number of active links. Using a stochastic geometry model, we investigate how directional antennas can control and mitigate the co-channel interference. Furthermore, we provide a model which characterizes the way directional antennas manage the LI in order to passively suppress it. Our results show that both architectures can benefit significantly by the employment of directional antennas. Finally, we consider the case where both architectures are employed in the network and derive the optimal values for the density fraction of each architecture which maximize the success probability and the network throughput.

In this paper, we assess the effect of full-duplex (FD) radio in the context of millimeter-wave (mmWave) communications. Particularly, we propose an analytical framework, based on stochastic geometry, to evaluate the performance of heterogeneous FD-mmWave cellular networks for two user location-based classifications, namely cell-center users (CCUs) and cell-edge users (CEUs). Moreover, we evaluate the performance of the considered networks with successive interference cancellation (SIC) capabilities. Based on the proposed framework, analytical expressions for the coverage and sum-rate performance are derived. We investigate the impact of FD-mmWave communications on the network performance of CCUs/CEUs and quantify the associated performance gains under different network parameter settings. Our results demonstrate the beneficial combination of FD radio with heterogeneous mmWave cellular networks, since it increases the spectral efficiency but also alleviates the effects of the multi-user interference. Furthermore, we present the trade-off between the coverage and sum-rate performance of heterogeneous FD-mmWave cellular networks for the considered user classifications. The results show that half-duplex mode is beneficial for the CEUs to achieve better network performance, as opposed to the CCUs for which FD mode is more efficient. Finally, we show the effectiveness of SIC on the network performance, with significant performance gains for the CEUs. Index TermsFull-duplex, heterogeneous networks, millimeter-wave, successive interference cancellation, stochastic geometry.Christodoulos Skouroumounis, Constantinos Psomas and Ioannis Krikidis are with the communications due to its abundant spectrum resources, which can lead to multi-Gbps rates [14]. As a result of their unique features such as directivity, sensitivity to blockages, and higher path losses, mmWave communications have fundamental differences with the current sub-6 GHz communications [14]. Due to these differences, the unique features of mmWave communications are required to be considered in the design of network architectures and protocols to fully exploit the potentials of mmWave communications. Network densification is proposed to address the large path-loss attenuation of mmWave frequencies, by bringing the transmitter closer to the receiver. This results in increased reliability, improved spectrum efficiency, and increased network capacity. Another important technique to compensate the large path-loss attenuation is the employment of directional antennas, which becomes feasible due to the short wavelength of mmWave signals. In addition to the difficulties caused by the unique features of the mmWave signals, recent studies have shown that these features also cause a positive effect on the network performance, which is the mitigation of the overall interference [15], [16], [18], [19]. Thus, the co-design of FD radio and mmWave networks is of critical importance in order to combat the severe multi-user interference caused by the FD technology by exploiting...