https://deim.urv.cat/~alexandre.arenas/publicacions/pdf/review.pdf

Synchronization in complex networks

Power Aware Routing in Mobile Ad Hoc Networks

Cognitive radio (CR) technology is envisaged to solve the problems in wireless networks resulting from the limited available spectrum and the inefficiency in the spectrum usage by exploiting the existing wireless spectrum opportunistically. CR networks, equipped with the intrinsic capabilities of the cognitive radio, will provide an ultimate spectrum-aware communication paradigm in wireless communications. CR networks, however, impose unique challenges due to the high fluctuation in the available spectrum as well as diverse quality-of-service (QoS) requirements. Specifically, in cognitive radio ad hoc networks (CRAHNs), the distributed multi-hop architecture, the dynamic network topology, and the time and location varying spectrum availability are some of the key distinguishing factors. In this paper, intrinsic properties and current research challenges of the CRAHNs are presented. First, novel spectrum management functionalities such as spectrum sensing, spectrum sharing, and spectrum decision, and spectrum mobility are introduced from the viewpoint of a network requiring distributed coordination. A particular emphasis is given to distributed coordination between CR users through the establishment of a common control channel. Moreover, the influence of these functions on the performance of the upper layer protocols, such as the network layer, and transport layer protocols are investigated and open research issues in these areas are also outlined. Finally, a new direction called the commons model is explained, where CRAHN users may independently regulate their own operation based on pre-decided spectrum etiquette.

/pdf/crahns-cognitive-radio-ad-hoc-networks-1odtmohw8e.pdf

CRAHNs: Cognitive radio ad hoc networks

With the explosive growth of mobile data demand, the fifth generation (5G) mobile network would exploit the enormous amount of spectrum in the millimeter wave (mmWave) bands to greatly increase communication capacity. There are fundamental differences between mmWave communications and existing other communication systems, in terms of high propagation loss, directivity, and sensitivity to blockage. These characteristics of mmWave communications pose several challenges to fully exploit the potential of mmWave communications, including integrated circuits and system design, interference management, spatial reuse, anti-blockage, and dynamics control. To address these challenges, we carry out a survey of existing solutions and standards, and propose design guidelines in architectures and protocols for mmWave communications. We also discuss the potential applications of mmWave communications in the 5G network, including the small cell access, the cellular access, and the wireless backhaul. Finally, we discuss relevant open research issues including the new physical layer technology, software-defined network architecture, measurements of network state information, efficient control mechanisms, and heterogeneous networking, which should be further investigated to facilitate the deployment of mmWave communication systems in the future 5G networks.

A survey of millimeter wave communications (mmWave) for 5G: opportunities and challenges

The remarkable growth of wireless data traffic in recent times has driven the need to explore suitable regions in the radio spectrum to meet the projected requirements. In pursuance of this, millimeter wave communications have received considerable attention in the research fraternity. Due to the high path and penetration losses at millimeter wavelengths, antenna beamforming assumes a pivotal role in establishing and maintaining a robust communication link. Beamforming for millimeter wave communications poses a multitude of diverse challenges due to the large channel bandwidth, unique channel characteristics, and hardware constraints. In this paper, we track the evolution and advancements in antenna beamforming for millimeter wave communications in the context of the distinct requirements for indoor and outdoor communication scenarios. We expand the scope of discussion by including the developments in radio frequency system design and implementation for millimeter wave beamforming. We explore the suitability of millimeter wave beamforming methods, both, existing and proposed till midyear 2015, and identify the exciting new prospects unfolding in this domain.

Beamforming for Millimeter Wave Communications: An Inclusive Survey

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Ad-hoc Networks: Fundamental Properties and Network Topologies

In this paper we study connectivity in wireless ad-hoc networks by modeling the network as an undirected geometric random graph. The novel aspect in our study is that for finding the link probability between nodes we use a radio model that takes into account statistical variations of the radio signal power around its mean value. We show that these variations, that are unavoidably caused by the obstructions and irregularities in the surroundings of the transmitting and the receiving antennas, have two distinct effects on the network. Firstly, they reduce the amount of correlation between links causing the geometric random graph tend to behave like a random graph with uncorrelated links. Secondly, these variations increase the probability of long links, which enhances the probability of connectivity for the network.Another new result in our paper is an equation found for the calculation of the giant component size in wireless ad-hoc networks, that takes into account the level of radio signal power variations. With simulations we show that for the planning and design of wireless ad-hoc networks or sensor networks the giant component size is a good measure for "connectivity".

/pdf/connectivity-in-wireless-ad-hoc-networks-with-a-log-normal-2oiw0d4knr.pdf

Connectivity in wireless ad-hoc networks with a log-normal radio model

In this paper we propose a new model to calculate interference levels in wireless multi-hop ad-hoc networks. This model computes the expected value of Carrier to Interference ratio (C/I) by taking into account the number of nodes, density of nodes, radio propagation aspects, multi-hop characteristics of the network, and the amount of relay traffic. Our model uses a regular lattice for possible locations of mobile nodes. This enables us to calculate the expected values of C/I , without having detailed information about movement patterns and exact location of all nodes at any moment. Based on this model we have evaluated effects of variations in the network size, network density and traffic load on C/I , and consequently throughput of the network. Our calculations suggest that interference is upper-bounded in wireless ad-hoc networks that use carrier sensing for medium access. Further, our calculations indicate that in large networks traffic increase due to routing overhead does not have a significant impact on network throughput.

/pdf/interference-in-wireless-multi-hop-ad-hoc-networks-2n2e88h4mo.pdf

Interference in Wireless Multi-hop Ad-hoc Networks

This article is a contribution to mathematical modeling and better understanding of fundamental properties of wireless ad-hoc networks. Our focus in this article is on the degree distribution and hopcount in these networks. The results presented here are useful in the study of connectivity and estimation of the capacity in ad-hoc networks. We model a wireless ad-hoc network as an undirected geometric random graph. For the calculation of the link probability between nodes we have suggested to use a realistic radio model; the socalled log-normal shadowing model. Through a combination of mathematical modeling and simulations we have shown that the degree distribution in wireless ad-hoc networks is binomial for low values of the mean degree. Further, we have investigated the hopcount and have shown that the hopcount in wireless adhoc networks can vary between the expected values for lattice networks and random graphs, depending on radio propagation conditions.

/pdf/degree-distribution-and-hopcount-in-wireless-ad-hoc-networks-133jkn7j5f.pdf

Degree distribution and hopcount in wireless ad-hoc networks

In this paper we propose a new model to calculate interference levels in wireless multi-hop ad-hoc networks. This model computes the expected value of Carrier to Interference ratio (C/I) by taking into account the number of nodes, density of nodes, radio propagation aspects, multi-hop characteristics of the network, and the amount of relay traffic. The expected values of C/I are used to determine network capacity and data throughput per node. Our model uses a regular lattice for possible locations of mobile nodes. This enables us to calculate the expected values of C/I, without having detailed information about movement patterns and exact location of all nodes at any moment. Based on this model we have evaluated effects of variations in the network size, network density and traffic load on C/I, and consequently throughput of the network. Our calculations suggest that interference is upper-bounded in wireless ad-hoc networks that use carrier sensing for medium access control. Further, from the point of view of throughput optimization, our calculations show limits on the network size and input data rates per node.

/pdf/interference-in-wireless-multi-hop-ad-hoc-networks-and-its-dz169eu3yu.pdf

R. Hekmat

Papers

Ad-hoc Networks: Fundamental Properties and Network Topologies

Connectivity in wireless ad-hoc networks with a log-normal radio model

Interference in Wireless Multi-hop Ad-hoc Networks

Degree distribution and hopcount in wireless ad-hoc networks

Interference in wireless multi-hop ad-hoc networks and its effect on network capacity