PERFORMANCE EVALUATION OF HANDOVER SCENARIOS IN MOBILE WIMAX NETWORKS

ABSTRACT

Achieving seamless homogeneous handover in mobile WiMAX due to its low cost and state of the art technology will enable ubiquitous broadband access to high volume applications especially with the high global increase  in mobile  subscribers.  Extending  this seamless  handover  across network technologies-heterogeneous  handover- like WiFi will further lower cost, improve battery life and enable high productivity for end users. In this project, ways  of optimizing handover in mobile WiMAX network, and the design and evaluation of system-level performance of different select  handover  scenarios  were  analyzed.  Modeled   voice  application  on  a  mobile  node  at pedestrian and vehicular speeds was used for the  analysis with the media independent handover (MIH)  network  simulator  2  (NS-2)  as  simulation  tool.  MATLAB-based   Trace  Graph  and Microsoft excel were used as the MAC  layer packet-level analysis tools. The average handover delay from the simulation  result is found to be 46 msec in all the simulation which fell below the WiMAX forum’s recommended handover delay of 150 msec for VoIP. The average handover jitter of 47msec  also  fell  under  the  standard  value  of  50  msec.  It was determined  that the

heterogeneous  handover  to  WiFi network  has  acceptable  throughput,  delay,  latency  with  no packet   lost   for  voice   packets. However,  there  were significant  drop  in throughput  observed during  WiMAX  handover  periods with  highest  drop  of 5 packets/sec  from 50  packets/sec  at normal operation. This is due to packet loss caused by Doppler spread at vehicular speed and low SINR  (signal-to-interference  noise)  at non overlapping  cells  and  large  base  station  distances. These throughput drops can be mitigated by appropriate channel modelling, adaptive sampling of Orthogonal Frequency Division Multiplexing (OFDM) symbols at high speed, antenna diversity, and also by making sure that all cells overlap during base station deployments.

INTRODUCTION

1.1 Introduction to the Problem

WiMAX  (Worldwide  Interoperability  for  Microwave  Access)  is  a  certification  that  denotes interoperability of equipment built to the IEEE 802.16 or compatibility standard. It is based on the wireless Metropolitan  Area Network technology,  optimized  for the  delivery  of IP centric services over a wide area.

This thesis introduces the IEEE 802.16e-2005 standard, also known as Mobile WiMAX, which defines the physical (PHY) and Medium Access Control (MAC) layers of it. The 802.16e-2005 [1] is the new, mobile version of the older WiMAX specification  known as  802.16-2004  [2], which is a wireless but fixed, data transmission scheme for providing broadband connection to metropolitan areas. The traditional WiMAX has lacked the ability for the user to move during

transmission. The importance of mobile WiMax becomes imperative, due to the need for a mobile user to change from one serving base station to another. The handover should be fast enough, so that the on-going video or voice call is not interrupted long enough for the user to notice. The support for seamless mobility in mobile broadband radio access network,  will give opportunity for  anytime,  anywhere,  any  network  and  any  device  communication,  especially  for  high bandwidth-hungry internet applications like  online  gaming,  video  and  audio  streaming, voice over IP, video conferencing and location based services.

Mobile WiMAX  enjoys  wide support  from telecom  industry leaders such that  by  creating  a common platform, which addresses a wide range of market and business segments, it will be well placed  to  assume  the  global  standard  for  mobile  broadband  wireless.  Achieving  seamless mobility across different wireless technologies like WiFi (wireless  fidelity) or other 3G (third generation)  broadband  networks  like  UMTS  (universal  mobile  telecommunication services) will further have a user advantage of keeping cost  very low and productivity very high while

saving battery life. In December 2005, the 802.16-2004 WiMAX standards was amended to the

802.16e-2005  and ratified by the IEEE (Institute of Electrical and Electronics Engineers). This amendment   added   the   features   and   characteristics   that   makes   it   necessary   to   support mobility in the air interface [2, 3] [3]. The WiMAX Forum, which is pioneering this technology, defined  system  performance   and  certification   profiles  based  on  the  IEEE   802.16e-2005 amendment  to  go  beyond  the  air  interface  and  identify  network  architecture  necessary  for implementing  end-to-end  mobile  architecture  [4].  This  forum  is  making  sure  that  WiMAX standard  have benefits  that cuts across  equipment  vendors,  consumers,  service  providers  and component makers.

1.2. Motivation

The motivation for this thesis is to determine how seamless mobility in WiMAX network can be achieved, keeping in mind the need to maintain  tolerable system throughput,  delay,  jitter and packet  lose  during  homogenous  (horizontal),  and heterogeneous  (vertical)  handover,  between mobile broadband networks at pedestrian and vehicular speeds

1.3. Research Objectives

The aim of this project is to analyze the various mechanisms for optimizing handover in mobile WiMAX so as to achieve seamless handover session of broadband applications.  Also different handover scenarios will be designed in an attempt to demonstrate possible real life deployment of WiMAX base stations, based on site logistics and existing infrastructure constraints. Performance metrics of throughput, delay, jitter and packet loss will be used to evaluate the performance of a mobile subscriber  (MS) on a voice session with a user in a  correspondent  node (CN) during normal (interleaving) and homogenous handover intervals at different speeds using NS-2. Finally, the same performance  metrics will also be used to  analyze  heterogeneous  handover  of voice session  between  a multimode  MS  and  same  user  in the CN  while  traversing  a WiFi and  a WiMAX coverage area at various speeds and trajectory. This is an attempt to demonstrate the

possibility of saving cost, battery life and achieving high productivity by a very busy business executive or telecoms professional that starts a voice session from home and finishes up in the office while communicating with his client or technical manager respectively

1.4. Organization of Thesis

The thesis starts with an overview and background of WiMAX Technology. Chapter two takes a look  at  the  underlying  technology  and  foundation  of mobile  WiMAX.  Chapter  three  discusses handover types in detail, with current and ongoing research for optimizing  handover  techniques. Chapter four discusses different handover scenarios carried out and the  methods used and results achieved,  at the same time testing the performance  of mobile  WiMAX  handovers.  Chapter  five analyses the trace file output from the simulation.  Finally,  chapter six concludes the report with standard comparisons  and possible ways of improving  handover  issues with recommendation  for further work.

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