Energy Efficient Relay-Assisted Cellular Network Model using Base Station Switching

Cellular network planning strategies have tended to focus on peak traffic scenarios rather than energy efficiency. By exploiting the dynamic nature of traffic load profiles, the prospect for greener communications in cellular access networks is evolving. For example, powering down base stations (BS) and applying cell zooming can significantly reduce energy consumption, with the overriding design priority still being to uphold a minimum quality of service (QoS). Switching off cells completely can lead to both coverage holes and performance degradation in terms of increased outage probability, greater transmit power dissipation in the up and downlinks, and complex interference management, even at low traffic loads. In this paper, a cellular network model is presented where certain BS rather than being turned off, are switched to low-powered relay stations (RS) during zero-to-medium traffic periods. Neighbouring BS still retain all the baseband signal processing and transmit signals to corresponding RS via backhaul connections, under the assumption that the RS covers the whole cell. Experimental results demonstrate the efficacy of this new BS-RS Switching technique from both an energy saving and QoS perspective, in the up and downlinks

Traffic Sensitive and Traffic Load Aware Path Selection Algorithm For MMR WIMAX Networks

The recent developments in the broadband wireless access (BWA) communication systems have introduced several major changes to the existing systems. Legacy IEEE 802.16j is one such amendment to the existing IEEE 802.16 WiMAX family. The key modification introduced by 802.16j system is the concept of relay station (RS), which may be used to enhance the system coverage or to make system throughput optimal. The end terminals, subscriber stations (SS) are unchanged in the standard. The overall change pertinent to the system has raised many unresolved issues related to RS and multi-hop relay base station (MR-BS). The selection of path from a SS to MR-BS via a RS is also one of the issues, need to be addressed. The path selection of a SS in both uplink and downlink directions is left open in the standard. It is very significant to satisfy the traffics of stringent quality of service (QoS) requirements and to appropriately manage the resources of a cell under different circumstances. This paper proposes a path selection algorithm to achieve the aforementioned qualities in the network. The path selection metrics include traffic load of the transparent relay station and traffic sensitivity factor of the SS. An extensive simulation work discusses the performance evaluation of the proposed work using QualNet simulator

Radio resource allocation in relay based OFDMA cellular networks

PhDAdding relay stations (RS) between the base station (BS) and the mobile stations (MS) in a cellular system can extend network coverage, overcome multi-path fading and increase the capacity of the system. This thesis considers the radio resource allocation scheme in relay based cellular networks to ensure high-speed and reliable communication. The goal of this research is to investigate user fairness, system throughput and power consumption in wireless relay networks through considering how best to manage the radio resource. This thesis proposes a two-hop proportional fairness (THPF) scheduling scheme fair allocation, which is considered both in the first time subslot between direct link users and relay stations, and the second time subslot among relay link users. A load based relay selection algorithm is also proposed for a fair resource allocation. The transmission mode (direct transmission mode or relay transmission mode) of each user will be adjusted based on the load of the transmission node. Power allocation is very important for resource efficiency and system performance improvement and this thesis proposes a two-hop power allocation algorithm for energy efficiency, which adjusts the transmission power of the BS and RSs to make the data rate on the two hop links of one RS match each other. The power allocation problem of multiple cells with inter-cell interference is studied. A new multi-cell power allocation scheme is proposed from non-cooperative game theory; this coordinates the inter-cell interference and operates in a distributed manner. The utility function can be designed for throughput improvement and user fairness respectively. Finally, the proposed algorithms in this thesis are combined, and the system performance is evaluated. The joint radio resource allocation algorithm can achieve a very good tradeoff between throughput and user fairness, and also can significantly improve energy efficiency

Multihop Relay Station and 3 sector Cell Zooming usage for Base Station Energy Saving

Projecte final de carrera fet en col.laboració amb Tsinghua UniversityEnglish: A new approach for energy saving in wireless communications is defined. Two different methods to cover a turned off Base Station area in case of low traffic loads are combined; Cell Zooming, in which the other base stations are used to increase the coverage and serve the turned off area. And multihop Relay coverage, which uses relays in multihop relay communications to cover the off zone. The results show that, while keeping the quality of service for the users, the combination of both methods prove a better performance in terms of energy saving than the separate usage of each method.Castellano: Se explica un nuevo método de ahorro energético en comunicaciones wireless formada mediante la combinación de otros dos métodos ya estudiados; por un lado la utilización de relays en comunicaciones multihop cuando, buscando ahorrar energía, una estación base en condiciones de poca carga es parada; "Multihop Relay Coverage". Y, por otro lado, la utilización del resto de estaciones base para ampliar la cobertura a la región donde ha sido parada la estación base; "Cell Zooming". Se demuestra que la combinación de ambos métodos permite obtener un rendimiento óptimo de la red y, al mismo tiempo, conlleva un ahorro energético superior al obtenido utilizando los dos métodos por separado.Català: S'explica una nova tècnica d'estalvi energètic en comunicacions wireless formada mitjançant la combinació de dues tècniques ja estudiades; la utilització de relays en comunicacions multihop quan, per tal d'estalviar energia, s'atura una estació base en condicions de baixa carrega; "Multihop Relay Coverage". I la utilització de la resta d'estacions base per tal d'ampliar la cobertura a la zona que ha estat aturada; "Cell Zooming". Es demostra que la combinació d'aquestes dues tècniques permet mantenir un rendiment òptim i oferir un estalvi energètic superior al que pot oferir la utilització d'aquestes tècniques per separat. Se explica un nuevo método de ahorro energético en comunicaciones wireless formada mediante la combinación de otros dos métodos ya estudiados; la utilización de relays en comunicaciones multihop cuando, buscando ahorrar energía, una estación base en condiciones de poca carga es parada; "Multihop Relay Coverage". Y la utilización del resto de estaciones base para ampliar la cobertura a la región donde ha sido parada la estación base; Cell Zooming. Se demuestra que la combinación de ambos métodos permite obtener un rendimiento óptimo de la red y, al mismo tiempo, conlleva un ahorro energético superior al obtenido utilizando los dos métodos por separado

Optimal Placement of Relay Stations in Wireless Sensor Networks

Wireless sensor networks (WSNs) are a collection of nodes organized into a cooperative network with sensing, processing and transmitting capabilities. WSNs are becoming an increasingly prominent technology that can be used in diverse application areas. In WSNs, cooperative relay stations are projected as one of the most cost effective solutions to meet the demanding requirement of capacity enhancement. In this paper, major concerns of the wireless sensor networks addressed are optimizing the number of relay stations required for covering the desired percentage of sensor nodes by optimal placement of relay stations and optimal assignment of the sensors to the relay stations. The joint problem of relay station placement and coverage is formulated into a mixed integer program which is solvable by commercial GAMS software with Xpress-MP Solver. Sensitivity analysis is carried out, along with a case study to demonstrate the performance gain of the model

Mathematical modelling of end-to-end packet delay in multi-hop wireless networks and their applications to qos provisioning

This thesis addresses the mathematical modelling of end-to-end packet delay for Quality of Service (QoS) provisioning in multi-hop wireless networks. The multi-hop wireless technology increases capacity and coverage in a cost-effective way and it has been standardised in the Fourth-Generation (4G) standards. The effective capacity model approximates end-to-end delay performances, including Complementary Cumulative Density Function (CCDF) of delay, average delay and jitter. This model is first tested using Internet traffic trace from a real gigabit Ethernet gateway. The effective capacity model is developed based on single-hop and continuous-time communication systems but a multi-hop wireless system is better described to be multi-hop and time-slotted. The thesis extends the effective capacity model by taking multi-hop and time-slotted concepts into account, resulting in two new mathematical models: the multi-hop effective capacity model for multi-hop networks and the mixed continuous/discrete-time effective capacity model for time-slotted networks. Two scenarios are considered to validate these two effective capacity-based models based on ideal wireless communications (the physical-layer instantaneous transmission rate is the Shannon channel capacity): 1) packets traverse multiple wireless network devices and 2) packets are transmitted to or received from a wireless network device every Transmission Time Interval (TTI). The results from these two scenarios consistently show that the new mathematical models developed in the thesis characterise end-to-end delay performances accurately. Accurate and efficient estimators for end-to-end packet delay play a key role in QoS provisioning in modern communication systems. The estimators from the new effective capacity-based models are directly tested in two systems, faithfully created using realistic simulation techniques: 1) the IEEE 802.16-2004 networks and 2) wireless tele-ultrasonography medical systems. The results show that the estimation and simulation results are in good agreement in terms of end-to-end delay performances

Performance evaluation of a WiMAX system with relay-assisted scheduling

Työssä tutkitaan IEEE 802.16j standardin määrittelemän järjestelmän suorituskykyä ja keskitytään ei-raaliaikaisiin palveluihin ja verkkoon, jossa verkon topologiaan kuuluu tukiasemien lisäksi välittimiä. Päätelaitteet ryhmitellään kahteen luokkaan sen mukaan, ovatko ne suoraan yhteydessä tukiasemaan, vai onko yhteys muodostettu välittimen avulla. Tukiasemassa toimiva skedulointialgoritmi jakaa lähetysresursseja eri käyttäjien kesken hetkellisen kanavatiedon perusteella. Työssä on rakennettu simulaattori, jonka avulla voidaan tutkia erilaisten järjestelmäparametrien, skedulointialgoritmien ja välittimien vaikutusta järjestelmän suorituskykyyn.An IEEE 802.16j based system with relay-assisted scheduling performance is evaluated in terms of the requirements set by the standard. We focus on the non-real-time (NRT) services in the downlink of a cellular network with two-hop relay transmission. Mobile stations (MSs) are grouped into the base station (BS) region and the relay station (RS) region according to their mean path losses. MSs in the BS region are connected directly to BS while MSs in the RS region receive packet from BS directly or indirectly via RS based on the CSI (Channel State Information). The RS operates in either the amplify-and-forward (AF) mode or decode-and-forward (DF) mode. We propose two relay-assisted scheduling schemes, in which the RS assists the BS in its scheduling decision and therefore we make it possible for the BS to exploit CSI on the access links without those of the relay links from all the users directly. A large amount of feedback overhead is avoided. Our objective is to explore the performance of DF and AF relays in these two different scheduling schemes. Moreover, we consider a friendly graphical user interface to realize user interaction and facilitate the investigation of the effect of different parameters to the system performance

Power-Aware Planning and Design for Next Generation Wireless Networks

Mobile network operators have witnessed a transition from being voice dominated to video/data domination, which leads to a dramatic traffic growth over the past decade. With the 4G wireless communication systems being deployed in the world most recently, the fifth generation (5G) mobile and wireless communica- tion technologies are emerging into research fields. The fast growing data traffic volume and dramatic expansion of network infrastructures will inevitably trigger tremendous escalation of energy consumption in wireless networks, which will re- sult in the increase of greenhouse gas emission and pose ever increasing urgency on the environmental protection and sustainable network development. Thus, energy-efficiency is one of the most important rules that 5G network planning and design should follow. This dissertation presents power-aware planning and design for next generation wireless networks. We study network planning and design problems in both offline planning and online resource allocation. We propose approximation algo- rithms and effective heuristics for various network design scenarios, with different wireless network setups and different power saving optimization objectives. We aim to save power consumption on both base stations (BSs) and user equipments (UEs) by leveraging wireless relay placement, small cell deployment, device-to- device communications and base station consolidation. We first study a joint signal-aware relay station placement and power alloca- tion problem with consideration for multiple related physical constraints such as channel capacity, signal to noise ratio requirement of subscribers, relay power and network topology in multihop wireless relay networks. We present approximation schemes which first find a minimum number of relay stations, using maximum transmit power, to cover all the subscribers meeting each SNR requirement, and then ensure communications between any subscriber and a base station by ad- justing the transmit power of each relay station. In order to save power on BS, we propose a practical solution and offer a new perspective on implementing green wireless networks by embracing small cell networks. Many existing works have proposed to schedule base station into sleep to save energy. However, in reality, it is very difficult to shut down and reboot BSs frequently due to nu- merous technical issues and performance requirements. Instead of putting BSs into sleep, we tactically reduce the coverage of each base station, and strategi- cally place microcells to offload the traffic transmitted to/from BSs to save total power consumption. In online resource allocation, we aim to save tranmit power of UEs by en- abling device-to-device (D2D) communications in OFDMA-based wireless net- works. Most existing works on D2D communications either targeted CDMA- based single-channel networks or aimed at maximizing network throughput. We formally define an optimization problem based on a practical link data rate model, whose objective is to minimize total power consumption while meeting user data rate requirements. We propose to solve it using a joint optimization approach by presenting two effective and efficient algorithms, which both jointly determine mode selection, channel allocation and power assignment. In the last part of this dissertation, we propose to leverage load migration and base station consolidation for green communications and consider a power- efficient network planning problem in virtualized cognitive radio networks with the objective of minimizing total power consumption while meeting traffic load demand of each Mobile Virtual Network Operator (MVNO). First we present a Mixed Integer Linear Programming (MILP) to provide optimal solutions. Then we present a general optimization framework to guide algorithm design, which solves two subproblems, channel assignment and load allocation, in sequence. In addition, we present an effective heuristic algorithm that jointly solves the two subproblems. Numerical results are presented to confirm the theoretical analysis of our schemes, and to show strong performances of our solutions, compared to several baseline methods