On the Benefits of Network-Level Cooperation in Millimeter-Wave Communications

Relaying techniques for millimeter-wave wireless networks represent a powerful solution for improving the transmission performance. In this work, we quantify the benefits in terms of delay and throughput for a random-access multi-user millimeter-wave wireless network, assisted by a full-duplex network cooperative relay. The relay is equipped with a queue for which we analyze the performance characteristics (e.g., arrival rate, service rate, average size, and stability condition). Moreover, we study two possible transmission schemes: fully directional and broadcast. In the former, the source nodes transmit a packet either to the relay or to the destination by using narrow beams, whereas, in the latter, the nodes transmit to both the destination and the relay in the same timeslot by using a wider beam, but with lower beamforming gain. In our analysis, we also take into account the beam alignment phase that occurs every time a transmitter node changes the destination node. We show how the beam alignment duration, as well as position and number of transmitting nodes, significantly affect the network performance. Moreover, we illustrate the optimal transmission scheme (i.e., broadcast or fully directional) for several system parameters and show that a fully directional transmission is not always beneficial, but, in some scenarios, broadcasting and relaying can improve the performance in terms of throughput and delay.Comment: arXiv admin note: text overlap with arXiv:1804.0945

Enabling Millimeter Wave Communications for Use Cases of 5G and Beyond Networks

The wide bandwidth requirements of the fifth generation (5G) and beyond networks are driving the move to millimeter wave (mmWave) bands where it can provide a huge increase in the available bandwidth. Increasing the bandwidth is an effective way to improve the channel capacity with limited power. Moreover, the short wavelengths of such bands enable massive number of antennas to be integrated together in small areas. With such massive number of antennas, narrow beamwidth beams can be obtained which in turn can improve the security. Furthermore, the massive number of antennas can help in mitigating the severe path-loss at mmWave frequencies, and realize high data rate communication at reasonable distances. Nevertheless, one of the main bottlenecks of mmWave communications is the signal blockage. This is due to weak diffraction ability and severe penetration losses by many common building materials such as brick, and mortar as well as the losses due to human bodies. Thus, user mobility and/or small movements of obstacles and reflectors cause rapid channel gain variations which leads to unreliable communication links. The harsh propagation environment at such high frequencies makes it hard to provide a reliable service, hence, maintaining connectivity is one key design challenge in mmWave networks. Relays represent a promising approach to improve mmWave connectivity where they can redirect the signal to avoid the obstacles existing in the propagation environment. However, routing in mmWave networks is known to be a very challenging problem due to the inherent propagation characteristics of mmWave frequencies. Furthermore, inflexible routing technique may worsen network performance and increase scheduling overhead. As such, designing an appropriate transmission routing technique for each service is a crucial issue in mmWave networks. Indeed, multiple factors must be taken into account in the routing process, such as guaranteeing the robustness of network connectivity and providing high data rates. In this thesis, we propose an analytical framework to investigate the network reliability of mmWave relaying systems for multi-hop transmissions. We also propose a flexible routing technique for mmWave networks, namely the $n^{\rm th}$ best routing technique. The performance of the proposed routing technique is investigated using tools from stochastic geometry. The obtained results provide useful insights on adjusting the signal noise ratio (SNR) threshold for decode and forward (DF) relay according to the order of the best relay, blockage and relay densities in order to improve spectral efficiency. We also propose a novel mathematical framework to investigate the performance of two appropriate routing techniques for mmWave networks, namely minimum hop count (MHC) and nearest LoS relay to the destination with MHC (NLR-MHC) to support wide range of use cases for 5G and beyond networks. Analytical models are provided to evaluate the performance of the proposed techniques using tools from stochastic geometry. In doing so, we model the distribution of hop count using phase-type distribution, and then we use this distribution to derive analytical results for the coverage probability and spectral efficiency. Capitalizing on the derived results, we introduce a comprehensive study of the effects of different system parameters on the performance of multi-hop mmWave systems. These findings provide important insights for designing multi-hop mmWave networks with better performance. Furthermore, we adapt the proposed relay selection technique for IoT devices in mmWave relaying systems to prolong the IoT device’s battery life. The obtained results reveal the trade-off between the network connectivity and the energy consumption of IoT devices. Lastly, we have exploited the enormous bandwidth available in the mmWave band to support reliable fronthaul links for cell-free (CF) massive multiple-input multiple-output (MIMO). We provide a comprehensive investigation of different system parameters on the uplink (UL) performance of mmWave fronthaul-based CF mMIMO systems. Results reveal that increasing the access point (AP) density beyond a certain limit would not achieve further improvement in the UL data rates. Also, the higher number of antennas per AP may even cause UL data rates degradation

Modeling and analyzing wireless networks using stochastic geometry

Over the past decade, stochastic geometric models, and most notably the planar Poisson point process (PPP) model, have become popular for the analysis of spectral efficiency in wireless networks, in both the D2D and the cellular contexts [1]. By modeling base station (BS) and user locations as spatial point processes, stochastic geometry has recently been recognized as a tractable and efficient analytical tool to quantify key performance metrics. This tool provides a natural way of defining and computing macroscopic properties of multiuser information theory. These properties are obtained by averaging over all node patterns found in a large random network of the Euclidean plane. For example, some key performance metrics such as signal to interference and noise ratio and data rate depend on the network geometric configurations. This tool has thus been widely adopted for analyzing the network performance and broadening network design. This thesis proposes new models to represent several new scenarios. Three main scenarios are considered: 3-D inbuilding networks, MIMO adhoc networks, and multihop communication under mmWave networks. To do so, mathematical tools such as Poisson point processes, Poisson line processes, Boolean models and Poisson bipolar models are used. Each model is 1) generative in that it has a clear physical interpretation, 2) leads to explicit analytical representations of important wireless performance metrics, and 3) highly parametric, with parameters expressing the geometric characteristic of the elements of networks. Physical interpretations from these models are quite different from previous results. The core of this thesis is focused on the effects of correlated shadowing. Shadowing is the effect that the received signal power fluctuates due to objects obstructing the propagation path. By introducing an independent shadowing term over links, it is possible to model the effect of shadow fading. Most previous papers analyzing urban networks assume that shadowing fields are independent over links. With this assumption, it is possible to derive simple closed-form expressions of important network performance metrics. However, this assumption cannot capture that shadowing fields are spatially correlated. This thesis goes beyond the independent shadowing approximation and analyzes the effects of correlated shadowing on various performance metricsElectrical and Computer Engineerin