Performance Aspects in Millimeter-Wave Wireless  Networks

Sammanfattning: The ever-growing data rate and comunications demand pose more challenges for the upcoming generations of mobile communications, i.e., fifth generation (5G) and beyond. To deal with these challenges, several solutions can be deployed, e.g., the use of massive amount of antennas at the transmitter and receiver nodes, the increase of cell density and the increase of the spectrum resources. More precisely, most of the current mobile networks and telecom operators mainly operate from 800 MHz to 6 GHz, however, this frequency range is probably not enough to face the growing traffic demand. For this reason, in the last years, communications in the millimeterwave (mm-wave) frequency range (30-300 GHz) have attracted the interest of many researchers, who consider mm-wave communications a promising solution to deal with the longstanding problem of spectrum scarcity. However, in comparison to lower frequency communications, the signal propagation in the mm-wave frequency range is subject to more challenging conditions. The latter lead to frequent transmission interruptions when the signal path between the transmitter and the receiver, usually line-of-sight (LOS), is blocked. In this thesis, we present three papers that study several aspects of the mm-wave wireless networks and potential solutions to overcome the blockage issue and increase the reliability for the mm-wave communications. The first work studies the contribution of the reected beams for the communications in non line-of-sight (NLOS). This work provides a stochastic model that is able to evaluate the coverage probability not only considering the direct beam, but also including first order reections, which may contribute to the coverage probability in NLOS.The second paper analyzes a possible solution to overcome the blockage issue that is the multi-connectivity (MC). This technique allows the user equipments (UEs) to establish and maintain connections with multiple cells/access points at the same time and it increases the number of possible available links per UE. In this scenario, we propose a novel link scheduling algorithm for network throughput maximization, and quantify the potential gain of MC for mm-wave cellular networks. The proposed algorithm is able to numerically approach the global optimum and overtakes the single connectivity schema in terms of network throughput.Finally, in the third paper, we study a complementary approach to the multi-connectivity schema, i.e., the relying technique. In this work, we perform a throughput analysis of a relay-aided mm-wave wireless network. We consider two possible transmission strategies, by which the source nodes transmit either a packet to both the destination and the relay in the same timeslot (broadcast) or to only one of these two (destination or relay) by using directional transmissions. We analyze and show the optimal transmission strategy with respect to several system parameters, e.g., positions and number of the nodes, by taking into account the different beamforming gains and interference levels of the possible transmission strategies.