Relay selection in mobile multihop relay network

Mobile Multihop Relay (MMR) network is an attractive and low-cost solution for expanding service coverage and enhancing throughput of the conventional single hop network. However, mobility of Mobile Station (MS) in MMR network might lead to performance degradation in terms of Quality of Service (QoS). Selecting an appropriate Relay Station (RS) that can support data transmission for high mobility MS to enhance QoS is one of the challenges in MMR network. The main goal of the work is to develop and enhance relay selection mechanisms that can assure continuous connectivity while ensuring QoS in MMR network using NCTUns simulation tools. The approach is to develop and enhance relay selection that allows cooperative data transmission in transparent relay that guarantees continuous connectivity. The proposed relay selection defined as Co-ReSL depends on weightage of SNR, α and weightage of Link Expiration Time (LET), β. The QoS performances of the proposed relay selections are in terms of throughput and average end-to-end (ETE) delay. The findings for Co-ReSL shows that at heavy traffic load, throughput increases up to 5.7% and average ETE delay reduces by 7.5% compared to Movement Aware Greedy Forwarding (MAGF) due to cooperative data transmission in selective links. The proposed relay selection mechanisms can be applied in any high mobility multi-tier cellular network

Heterogeneous LTE/ Wi-Fi architecture for intelligent transportation systems

Intelligent Transportation Systems (ITS) make use of advanced technologies to enhance road safety and improve traffic efficiency. It is anticipated that ITS will play a vital future role in improving traffic efficiency, safety, comfort and emissions. In order to assist the passengers to travel safely, efficiently and conveniently, several application requirements have to be met simultaneously. In addition to the delivery of regular traffic and safety information, vehicular networks have been recently required to support infotainment services. Previous vehicular network designs and architectures do not satisfy this increasing traffic demand as they are setup for either voice or data traffic, which is not suitable for the transfer of vehicular traffic. This new requirement is one of the key drivers behind the need for new mobile wireless broadband architectures and technologies. For this purpose, this thesis proposes and investigates a heterogeneous IEEE 802.11 and LTE vehicular system that supports both infotainment and ITS traffic control data. IEEE 802.11g is used for V2V communications and as an on-board access network while, LTE is used for V2I communications. A performance simulation-based study is conducted to validate the feasibility of the proposed system in an urban vehicular environment. The system performance is evaluated in terms of data loss, data rate, delay and jitter. Several simulation scenarios are performed and evaluated. In the V2I-only scenario, the delay, jitter and data drops for both ITS and video traffic are within the acceptable limits, as defined by vehicular application requirements. Although a tendency of increase in video packet drops during handover from one eNodeB to another is observed yet, the attainable data loss rate is still below the defined benchmarks. In the integrated V2V-V2I scenario, data loss in uplink ITS traffic was initially observed so, Burst communication technique is applied to prevent packet losses in the critical uplink ITS traffic. A quantitative analysis is performed to determine the number of packets per burst, the inter-packet and inter-burst intervals. It is found that a substantial improvement is achieved using a two-packet Burst, where no packets are lost in the uplink direction. The delay, jitter and data drops for both uplink and downlink ITS traffic, and video traffic are below the benchmarks of vehicular applications. Thus, the results indicate that the proposed heterogeneous system offers acceptable performance that meets the requirements of the different vehicular applications. All simulations are conducted on OPNET Network Modeler and results are subjected to a 95% confidence analysis

Mobile femtocell utilisation in LTE vehicular environment: vehicular penetration loss elimination and performance enhancement

Mobile computing is fast becoming a vital part of everyday life in which User Equipment (UE) demand being reachable anywhere and at anytime, as they spend much time travellingfrom one place to another, often by trains or buses. The ultimate aim of passengers is the ability to be connected to the Internet while they are moving from one place to another with their mobile devices. Providing indoor coverage on trains and buses directly with outdoor Base Stations (BSs) may not be a good solution due to the high density of use and path losses in the LTE network. This limitation can result in poor signal quality inside the train, and offering broadband services is not always possible. Clearly improvement to broadband access on buses and trains could be achieved by installing more BSs close to railway and bus routes and terminals. However, this solution is not ideal for the Internet Service Providers (ISPs) due to the high investment needed to deploy many more BSs. In addition, such a solution will introduce additional complexity by increasing the number of Handovers (HOs). This issue has focused the research community effort on developing solutions that take advantage of the existing wireless infrastructure without increasing the number of BSs. One method being considered is the development of more efficient methods and technologies to manage the UE’s mobility in seamless ways. In this paper we propose adoption of Mobile Femtocell (Mobile-Femto) technology as a solution to mitigate the Vehicular Penetration Loss (VPL) and Path Loss, with consequent improvement to the vehicular UE’s performance in LTE networks. Our results, using a Matlab simulation model, showed a noticeable improvement in the achieved Ergodic capacity by 5% under a VPL of 40dB while 90% of vehicular UEs spectral efficiency has improved by 1.3b/cu under a VPL of 25dB. In addition, 80% of vehicular UEs have improved their throughput and SINR by 300kb/s and 4dB respectively after implementing the Mobile-Femto into the Macrocell in LTE networks

Green Cellular Networks: A Survey, Some Research Issues and Challenges

Energy efficiency in cellular networks is a growing concern for cellular operators to not only maintain profitability, but also to reduce the overall environment effects. This emerging trend of achieving energy efficiency in cellular networks is motivating the standardization authorities and network operators to continuously explore future technologies in order to bring improvements in the entire network infrastructure. In this article, we present a brief survey of methods to improve the power efficiency of cellular networks, explore some research issues and challenges and suggest some techniques to enable an energy efficient or "green" cellular network. Since base stations consume a maximum portion of the total energy used in a cellular system, we will first provide a comprehensive survey on techniques to obtain energy savings in base stations. Next, we discuss how heterogeneous network deployment based on micro, pico and femto-cells can be used to achieve this goal. Since cognitive radio and cooperative relaying are undisputed future technologies in this regard, we propose a research vision to make these technologies more energy efficient. Lastly, we explore some broader perspectives in realizing a "green" cellular network technologyComment: 16 pages, 5 figures, 2 table

Relay Technology in Cellular Networks

Relay technology has been explored and studied for decades, ranging from generic multi-hop mobile ad hoc networks to most recent collaborative multiple-input multiple-output (MIMO) cellular networks. Deploying low cost relays reduces the infrastructure cost of establishing new base stations in order to improve the cell coverage and system capacity of next generation cellular networks. For efficient heterogeneous network planning, fixed relays are considered as one of the main enhancing technologies in 3rd Generation Partnership Project (3GPP) Long Term Evolution Advanced (LTE-A). The function of the relay station can be described simply as a device which assists in transmissions between the local base station and the mobile station. Since the performance of relay transmissions is strongly affected by the collaborative strategy in dense wireless networks, the relay selection always attracts research attentions. In this thesis, the symbol error probability of the selective decode-and-forward (DF) relaying strategy is derived to explore the selection diversity. Furthermore, an effective joint beamforming vector design and relay selection scheme for a MIMO relay system are proposed. In addition, two main relay deployment scenarios are addressed in this thesis: the fixed relay and the mobile relay. The LTE relay is a fixed relay which is located near the cell edge. A dynamic system level simulator is developed to evaluate the downlink transmission performance of fixed relay-enhanced LTE-A systems. With deployment of a high number of relay nodes inter-cell interference and resource management problems increase. An adaptive beamforming strategy with limited feedback is proposed to reduce inter-cell interference. The proposed algorithm has been applied in relay-enhanced LTE-A cellular networks to show its advantage. Furthermore, we study the concept of shared relays, in which a relay station is deployed at the intersection of neighboring macro cells. An efficient resource allocation and scheduling scheme based on the sub-frame structure of LTE-A is proposed to maximize the benefit of shared relays. As the penetration rate of mobile phones, especially smart phones keeps increasing, users in public transportation expect high speed wireless services. Recently, the mobile relay for high speed railways has gained significant interest. A system level simulator is developed to investigate the capacity and handover performance of the mobile relay in a high speed railway scenario. Furthermore, a coordinated mobile relay node (MRN) strategy is proposed to combat co-channel interference and handover delay problems in a conventional mobile relay system.Die Relaistechnik für Funksysteme wurde seit Jahrzehnten erforscht und untersucht, angefangen von generischen mobilen Multi-Hop Ad-hoc-Netzwerken bis hin zu kollaborativen multiple-input multiple-output (MIMO) Mobilfunknetzen. Das Aufstellen kostengünstiger Relais reduziert die Infrastrukturkosten für den Aufbau neuer Basisstationen, um die Zellabdeckung und die Systemkapazität von Mobilfunknetzen der nächsten Generation zu verbessern. Für eine effiziente heterogene Netzwerkplanung werden ''fixed relays'' (Festrelais) als eine der Technologien in 3GPP LTE-Advanced betrachtet, welche die größten Verbesserungen aufweisen. Die Funktion der Relaisstation kann beschrieben werden als eine Vorrichtung, welche bei der Übertragung zwischen der lokalen Basisstation und der Mobilstation unterstützend wirkt. Da die Leistung von Relaisübertragungen stark von der Kooperationsstragie in dichten Funknetzwerken abhängt, erregt die Relaisauswahl stets die Aufmerksamkeit der Forschung. In dieser Arbeit wird die Symbolfehlerwahrscheinlichkeit der selektiven decode-and-forward (DF) Relais-Strategie abgeleitet, um den Diversitätsgewinn Auswahldiversität zu untersuchen. Weiterhin wurde ein gemeinsames Strahlformungsvektor-Design und Relais-auswahlschema für ein MIMO-Relais-System vorgestellt. Des Weiteren werden in dieser Arbeit zwei wesentliche Relais-Verteilungsszenarien untersucht: das Festrelais-Szenario und das Mobilrelais-Szenario. Das LTE Relais ist ein Festrelais, welches nah an dem Zellenrand liegt. Ein dynamischer System-Level-Simulator wurde entwickelt, um die Downlink-Übertragungsleistung von mit Festrelais erweiterten LTE-A-Systemen zu evaluieren. Bei der Verwendung einer hohen Anzahl von Relaisknoten steigt zum einem die Interzellinterferenz und zum anderen die Problematik des Ressourcenmanagements. Es wird eine adaptive Strahlformungsstrategie mit wenig zurückgekoppelte Information vorgestellt, um Zellinterferenzprobleme zu reduzieren. Der vorgestellte Algorithmus wird auf ein mit Relaisstationen erweitertes LTE-A-Mobilfunknetz angewendet, um seine Vorteile aufzuzeigen. Weiterhin wird das Konzept eines gemeinsam genutzten Relais untersucht, in welchem eine Relaisstation an der Grenze von benachbarten Makrozellen aufgestellt wird. Es wird ein effizientes Ressourcenzuweisungs- und Zeitplanungsschema, basierend auf der Sub-Rahmenstruktur, vorgestellt, um den Vorteil von gemeinsam genutzten Relais zu maximieren. Da die Verbreitungsrate von Mobiltelefonen, besonders von Smartphones, weiter ansteigt, werden Benutzer auch in öffentlichen Verkehrsmitteln drahtlose Hochgeschwindigkeitsdienste erwarten. In letzter Zeit hat das Mobilrelais für Hochgeschwindigkeitszüge große Bedeutung gewonnen. Es wurde daher ein System-Level-Simulator entwickelt, um die Kapazität und Übergabgeleistungsfähigkeit von Mobilrelais in Hochgeschwindigkeitszug-Szenarios zu untersuchen. Zusätzlich wird eine koordinierte Mobilrelais-Strategie zur Bekämpfung von Gleichkanalinterferenz und Übergabeverzögerungsproblemen in herkömmlichen Mobilrelaissystemen vorgestellt

Cooperative and coordinated Mobile Femtocells technology in high-speed vehicular environments: mobility and interference management

In future networks, most users who will be accessing wireless broadband will be vehicular. Serving those users cost-effectively and improving their signal quality has been the main concern of many studies. Thus, the deployment of Mobile Femtocell (Mobile-Femto) technology on public transportation is seen to be one of the promising solutions. Mobile-Femto comes with its mobility and interference challenges. Therefore, eliminating the Vehicular Penetration Loss (VPL) and interference while improving signal quality and mobility for train passengers is the main concern of this paper. The initial system-level evaluation showed that the dedicated Mobile-Femto deployment has great potential in improving users’ experience inside public transportation. The Downlink (DL) results of the Proposed Interference Management Scheme (PIMS) showed significant improvement in Mobile-Femto User Equipment (UE) gains (up to 50%) without impacting the performance of macro UEs. In contrast, the Uplink (UL) results showed noticeable gains for both macro UEs and Mobile-Femto UEs