Design, analysis and simulations of medium access control protocols for high and low data rate applications

Abstract The past two decades have witnessed an unprecedented proliferation of mobile devices equipped with extremely innovative wireless technologies. Short range networks, such as wireless personal area networks (WPANs), wireless sensor networks (WSNs) and wireless body area networks (WBANs) have been defined and researched to deliver high speed home connectivity, environment and health monitoring. This thesis tackles design, analysis and simulation of medium access control (MAC) protocols tailored for short range networks. These have in common the use of battery operated devices but also certain design challenges connected with MAC protocols are common upon selecting the physical layer technology. Ultra wideband (UWB) technology and 60 GHz technology (which is referred to also as millimeter wave communications) are two valid examples of the wireless revolution of the past decade. Several existing standards, such as IEEE 802.15.3, ECMA-368, IEEE 802.15.4 and its amendment IEEE 802.15.4a, are considered in this thesis for MAC analysis in conjunction with UWB technology. With regard to millimeter wave communications the characteristics of the IEEE 802.15.3c standard are taken into account. Apart for the IEEE 802.15.3c all the MAC protocols have been modeled in the network simulator Opnet. One contribution of this thesis is to produce an innovative and in-depth analysis of the management aspects (e.g. ECMA-368 distributed beaconing) stemming from the above mentioned standards by means of analytical and simulation models. This study approach allows selecting the MAC features suitable for the applications and the technologies of interest. The key performance metric used to analyze all the protocols is energy efficiency, but also throughput is investigated. Another contribution brought by this thesis consists in the innovative way of studying slotted-based MAC protocols as an integrated concept connected with the type of network, the type of application and the selected physical technologies. This thesis also shows MAC performance in conjunction with UWB when false alarm, miss-detection and receiver capture (capture is modeled by means of an existing interference model) are taken into consideration. Most of the unrealistic, though common, assumptions in MAC analysis are removed and the performance of selected medical applications is evaluated through Opnet simulations. The well known binary exponential backoff is analyzed with an innovative though simplified one-dimensional Markov chain approach in the context of directional MAC for 60 GHz communications. As shown in the remainder of this thesis, the simplification introduced does not hinder the accuracy of the results, but rather allows accounting even for a finite number of retransmissions with a simple chain extension.Tiivistelmä Kahden viime vuosikymmenen aikana innovatiivisella langattomalla tekniikalla varustettujen viestintälaiteiden määrä on kasvanut räjähdysmäisesti. Lyhyen kantaman verkkoja kuten langattomia henkilökohtaisen alueen verkkoja (WPAN), langattomia anturiverkkoja (WSN) ja langattomia vartaloalueen verkkoja (WBAN) on määritelty ja tutkittu, jotta voitaisiin tuottaa korkeanopeuksisia kotiyhteyksiä sekä välineitä ympäristön ja terveydentilan seurantaan. Tämä väitöskirja käsittelee lyhyen kantaman viestintään suunniteltujen linkinohjauskerroksen MAC-protokollien suunnittelua, analysointia ja simulointia. Näissä kaikissa käytetään akkukäyttöisiä laitteita, mutta myös tietyt MAC-protokollien suunnittelun haasteet ovat tavallisia fyysisen kerroksen teknologiaa valittaessa. Ultra-laajakaistainen (UWB) teknologia ja 60 GHz teknologia (eli millimetriaallonpituusalueen tietoliikenne) ovat hyviä esimerkkejä kuluneen vuosikymmenen langattomasta vallankumouksesta. Tässä väitöskirjassa huomioidaan UWB teknologiaan liittyvää MAC-kerroksen analyysiä tehtäessä useat olemassa olevat standardit, kuten IEEE 802.15.3, ECMA-368, IEEE 802.15.4 ja sen lisäys IEEE 802.15.4a. Millimetriaallonpituusalueen tietoliikenteessä huomioidaan myös IEEE 802.15.3c standardin erityispiirteet. IEEE 802.15.3c:tä lukuun ottamatta kaikki MAC-protokollat on mallinnettu Opnet verkkosimulaattorilla. Tämä tutkimus tarjoaa innovatiivisen ja syväluotaavan tutkimuksen näiden standardien pohjalta ja analyyttisten ja simuloitujen mallien avulla kehitetyistä hallinnallisista lähestymistavoista (esim. ECMA-368 hajautettu majakkasignaali). Näiden avulla voidaan valita kohteena oleviin sovelluksiin ja teknologioihin parhaiten soveltuvia MAC-ominaisuuksia. Kaikkien protokollien analysointiin käytetty ensisijainen suorituskykymittari on energiatehokkuus, mutta myös datanopeuksia on tarkasteltu. Tässä tutkimuksessa esitellään myös innovatiivinen tapa tutkia MAC protokollia integroituina konsepteina suhteessa verkon ja sovellusten tyyppiin sekä fyysisen kerroksen teknologiaan. Lisäksi tämä väitöskirja esittelee MAC suorituskykyä UWB verkossa silloin, kun siinä otetaan huomioon väärät hälytykset, väärä havainnointi ja vastaanottimen signaalinkaappaus (vastaanoton mallintamiseksi käytetään olemassa olevaa interferenssimallia). MAC analyysistä poistetaan useimmat epärealistiset, vaikkakin tavalliset, olettamukset, ja verkkojen suorituskykyä tarkastellaan valittujen kriittisten parametrien monitoroinnissa Opnet-simulaatioiden avulla. Tunnettua binäärijakoinen eksponentiaalinen perääntyminen -algoritmia analysoidaan innovatiivisella, yksinkertaistetulla yksiulotteisella Markov-ketju -mallilla 60 GHz:n suunta-antenni MAC:n yhteydessä. Kuten tässä tutkimuksessa tullaan osoittamaan, esitelty yksinkertaistus ei rajoita tulosten tarkkuutta, vaan mukaan voidaan lukea jopa rajallinen määrä uudelleenlähetyksiä yksinkertaisen Markovin ketjun laajennuksen avulla

REM: Revisiting a cognitive tool for virtualized 5G networks

Abstract: The evidence that mobile data traffic is enormously increasing is forcing the whole telecommunications industry to rethink most of the paradigms which have driven until now the design of mobile networks, traditionally very efficient for voice and limited data communications. It is foreseen that 5G technology will introduce disruptive changes with respect to how radio resources are managed and consumed. In past years cognitive radio made its way to enable more intelligent and autonomous wireless networks but it has encountered several practical problems which have slowed down the massive adoption of this technology. Recently, an apparent turnaround has risen from the adoption of Software-Defined Network (SDN) and Network Functions Virtualization (NFV) principles. In this work we shall restart from known cognitive radio concepts which have been innovative in terms spectrum management in past years, paying particular attention to the concept of Radio Environment Maps (REMs). The main contribution of this work is hence to propose a high-level architecture in which SDN and NFV are the enablers that will facilitate the adoption of REM as the tool for spectrum management, since 5G will exhibit unprecedented levels of flexibility in managing different types of resources

FME: A Flexible Management Entity for Virtualizing LTE Evolved Packet Core (EPC)

The 4G Evolved Packet Core (EPC) is the pillar of the Long Term Evolution (LTE) mobile networks. Inspired by the current trend of designing distributed and more autonomous systems, we can notice that the complexity of the existing EPC seriously limits this possibility. We principally consider a reshaping of cellular networks in order to move towards virtual-distributed architectures allowing dynamic deployments of commercial/noncommercial, temporary or local networks. In this paper, we present Flexible Management Entity (FME), a distributed entity which leverages on virtualized EPC functionalities in 4G-LTE cellular systems. We highlight several conceptual and engineering trade-offs in realizing such a system. We also analyze the behavior and benefits of FME in various simulation settings that expose the dynamic deployment scenarios for 4G networks

Enabling disaster-resilient 4G mobile communication networks

4G Long Term Evolution is the cellular technology expected to outperform previous generations and to some extent revolutionize the experience of users by taking advantage of the most advanced radio access techniques. However, the strong dependencies between user equipment, base stations, and the Evolved Packet Core limit the flexibility, manageability, and resilience of such networks. If the communication links between UE-eNB or eNB-EPC are disrupted, mobile terminals are unable to communicate. In this article, we reshape the 4G mobile network to move toward more virtual and distributed architectures to improve disaster resilience and drastically reduce the dependency between UE, eNBs, and EPC. First, we present the flexible management entity, a distributed entity that leverages on virtualized EPC functionalities in 4G cellular systems. Second, we introduce a novel device-to-device communication scheme allowing the UE in physical proximity to communicate directly without resorting to coordination with an eNB or EPC entity

A Novel Geometric Handover Model for Aerial 4G Networks with WiFi-based X2 Interface

Given the temporary nature of radio communications for mission critical scenarios, the existing dedicated public safety network lacks the flexibility of cutting edge technologies to leverage on packet data services. In this context, new challenges arise such as high-capacity demand and low-latency flexible backhaul connection for public safety users. In this paper, we consider a scenario in which 4G LTE radio coverage is provisioned by aerial eNodeBs installed on low-altitude platforms raised in the sky and interconnected through WiFi links. We focus our attention on the critical aspect of the Third Generation Partnership Project handover mechanism studying the handover performance using a X2 interfaces over WiFi links. We develop a novel eometric model of the handover in the context of public safety communications but extensible also to other contexts. Relying on such a model, the handover failure probability is computed taking into account the different handover phases. The coverage area of an aerial eNodeB is studied using a suitable air-to-ground propagation model, while the average handover duration is computed taking into account the delay introduced by the WiFi communication dynamics

NACRP: A Connectivity Protocol for Star Topology Wireless Sensor Networks

Wireless sensor networks (WSNs) are an ever growing field of applications and one constituent of the future Internet-of-Things (IoT). In this work, we investigate star topology sensor networks compliant with the recent IEEE 802.15.4k standard in which sensors could fail to report sensing information to the access point (AP) due to temporary obstructions that clutter the link with the AP. The contribution of this work is twofold. First, we study general connectivity requirements in relay networks. Second, to restore connectivity and to recover from information loss, we propose the neighbor-assisted connectivity recovery protocol (NACRP), which automatically selects a subset of sensor nodes to act as relays for those which lack connectivity with the AP. In our study, we rely on the tool of stochastic geometry and in particular, on Poisson point processes to seek the tradeoff, which arises from the selection of a subset of relay nodes and the necessary transmitted power that relays need to use to restore network connectivity

A Novel Device-to-Device Communication Protocol for Public Safety Applications

The UMTS Long Term Evolution (LTE) is the latest and most advanced cellular technology that is coming to market. As LTE and its advanced version promise unprecedented peak data rates both in uplink and downlink, they seem to represent a striking solution for many fields requiring mobile broadband access. Nowadays, one area that is strongly emerging is represented by public safety communications. In this field, users not only need to communicate in traditional cellular fashion but they also need to communicate directly in case the network infrastructure is temporary unavailable or if the operating conditions prevent reliable links. In the the literature this is referred to as device-todevice (D2D) communication mode. This paper investigates D2D communications where beacon-enabled and simple LTE terminals are scattered over the area of a major event according to two homogeneous Poisson Point Processes. The contribution of this paper is twofold: we first devise an innovative D2D protocol and then we investigate the probability of LTE mobile terminals to form in D2D networks using a stochastic geometry approach

Distributed Load Balancing for Future 5G Systems On-board High-Speed Trains

The surge of mobile broadband Internet access has nowadays reached the critical point that traffic is projected to increase dramatically in the next years and even the 4G UMTS Long term Evolution (LTE) cellular technology and its advanced version LTE-A might lack enough flexibility and system reconfiguration capability. For these reasons, the quest for the Fifth Generation (5G) of cellular technology has started. In the context of users that require high Quality of Experience (QoE) anytime and anywhere, users on-board of fast moving vehicles such as high-speed trains represent an important market segment for both telecom operators and transportation companies. In particular, people who are moving for business everyday require low latency and high throughput Internet connectivity even when moving at hundreds of kilometers per hour. In this landscape, novel algorithms can find their space in future 5G systems to cope with fast resource (re)allocation in the presence of large Doppler spread and high handover frequency. Focusing on a high-speed train (HST), in this paper we propose a simple but effective distributed load balancing algorithm to relieve service interruption caused by frequent handovers in high mobility scenarios. Our results show the effectiveness of the solution while leveraging on the concept of cell edge intelligence. © 2014 ICST