Understanding the Effects of Hotspots in Wireless Cellular Networks

1
Understanding the Effects of Hotspots in Wireless
Cellular Networks

• Infocom 2004
• Speaker Bo-Chun Wang
• 2004.7.23

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Outline

• Introduction
• Related Work Motivation
• Modeling Hotspots
• Experimental Results
• A Fluid Flow Model for Modeling Cellular Networks
• Analytical Modeling of Hotspots
• Conclusion

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Introduction

• Hotspots
• occur whenever there is contention among users
  for bandwidth
• lead to blocked and dropped user
• impact the performance of the network

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Previous work

• Consider hotspots with reference to load
  balancing and congestion control
• Focus on algorithms and techniques to improve
  capacity and performance
• Lack of research that studies properties of
  hotspots in detail

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Contributions

• Classify hotspots into three different types
  based on some cause
• Show how the different types of hotspots differ
  in their impact on performance
• Propose a fluid flow model to substantiate of
  experimental observations
• Develop an analytical model to study hotspots

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Related Work

• Sajal K. Das, Sanjoy K. Sen, Rajeev Jayaram. A
  Novel Load Balancing Scheme for the Tele-traffic
  Hot Spot Problem in Cellular Networks. Wireless
  Networks,1998
• Johan Karlson, Berth Eklundh. A Cellular Mobile
  Telephone System with Load Sharing An
  Enhancement of Directed Retry. IEEE Transactions
  on Communications, 1989

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Related Work (contd.)

• Jung-Shyr Wu, Jen-Kung Chung, Chang-Chung Wen.
  Hot-Spot Traffic Relief with a Tilted Antenna in
  CDMA Cellular Networks. IEEE Transactions on
  Vehicular Technology, 1998

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Motivation

• Most of previous works only deals with hotspots
  within the context of other problems
• None of them identify the specific
  characteristics of hotspots
• A better knowledge of hotspots can help in
  designing realistic simulations which can
  facilitate better network design

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Some Questions addressed in work

• How are hotspots created?
• How do they affect network performance?
• Do different types of hotspots impact performance
  in different ways?

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Modeling Hotspots

• Delay based there is an accident which is
  delaying all the users in that cell.
• Capacity based the base station of a cell can
  only support a lower number of users.
• Preferential mobility based there is an event
  and people are moving towards a given location.

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Simulation setup and network model

• Use a square cell for simplicity in the
  implementation and in the analysis.
• Two types of networks
• bounce-back network This network exhibits edge
  effects.
• wrap-around network This network avoids edge
  effects.

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Regions in a bounce-back network
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Implementation details

• Users and cells
• homogeneous users and cells
• the capacity of each cell is 50,000 units
• the bandwidth requirements of each user is 500
  units
• the cell latency are exponentially distributed
• Mobility model
• random walk mobility model except in the case of
  the preferential mobility hotspots

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Implementation details (contd.)

• Performance measures
• network utilization the ratio of the number of
  users in the network to the number of users that
  the network can support
• steady state utilization a networks maximum
  utilization without loss

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Number of hotspots
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Placement of hotspots
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Clustering of hotspots
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Local and global impact
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Local and global impact (contd.)
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A Fluid Flow Model for Modeling Cellular Networks
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One dimensional chain network
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Two dimensional bounce-back network
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Modeling Hotspots Using an Enhanced Fluid Flow
Model
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Modeling Hotspots Using an Enhanced Fluid Flow
Model (contd.)
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Modeling Hotspots Using an Enhanced Fluid Flow
Model (contd.)
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Analytical Modeling of Hotspots

• Consider the network to be a closed network of
  M/M/B/B queues
• Find the marginal probability that there are
  exactly ki k jobs at the ith node in such a
  closed network

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Analytical Modeling of Hotspots (contd.)
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Conclusion

• Present a detailed study of hotspots in wireless
  cellular networks
• Identify three types of hotspots based on
  different causes and study their different
  properties
• Develop two analytical models to substantiate
  simulation results