A CrossLayer Layer 2 3 Handoff Management Protocol for NextGeneration Wireless Systems By Shantidev

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A Cross-Layer (Layer 2 3)Handoff Management
Protocol forNext-Generation Wireless
SystemsByShantidev Mohanty and Ian F. Akyildiz,
Fellow, IEEE

• Presentation By
• Muhammed Syyid

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NGWS

• Next Generation Wireless System
• Multiple kinds of wireless systems deployed
• UMTS (WAN)
• 802.11 (WLAN)
• Bluetooth (PAN)
• Satellite (Global)
• Unification of systems to provide optimal data
  availability

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NGWS
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NGWS Design Goals

• Support for the best network selection
• Mechanism to ensure high-quality and security
• Seamless inter-system mobility
• Scalable architecture (any of wireless systems)
• QoS provisioning

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Mobility Management

• Location Management
• Track Location of users between consecutive
  communications
• Handoff Management
• Keep connections active while moving between base
  stations

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Handoff in NGWS
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Handoff in NGWS

• Horizontal Handoff
• Link Layer Handoff
• IntraSystem Handoff
• Vertical Handoff
• InterSystem Handoff

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Current Status

• Link Layer Handoff
• Efficient algorithms available in literature
• InterSystems and IntraSystems Handoff
• Signaling Delay
• Packet Loss

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Goals for Seamless Handoff

• Minimize Handoff Latency
• Minimize Packet Loss
• Limit Handoff Failure
• Minimize False Handoff Initiation

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Handoff Protocols By TCP/IP Layer

• Network Layer
• Mobile IP
• Transport Layer
• TCP-Migrate
• MSOCKS (Split proxy TCP SPLICE)
• Modification of SCTP (Stream Control Transmission
  Protocol)
• SIP

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Mobile IP

• Issues
• Triangular Routing
• High Global Signaling Load
• High Handoff Latency
• Reasons for handoff latency
• Handoff Requirement Detection
• Registration at New Foreign Agent (NFA)
• Proposed Solutions in Literature
• Triangular Routing
• Route Optimization
• High Global Signaling Load / Registration at NFA
• Hierarchical Mobile IP (HMIP)
• Cellular IP
• IDMP
• HAWAII

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• Solution to Handoff Latency due to Requirement
  Detection
• Use Link Layer Information
• Calculate probability of Handoff
• Factors affecting handoff signaling delay
• Traffic Load on the network
• Wireless Link Quality
• Distance between user and home network
• Users Speed

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Analysis of Current Systems

• RSS Received Signal Strength
• BS Base Station
• MT Mobile Terminal
• OBS Old Base Station
• NBS New Base Station
• FA Foreign Agent
• OFA Old Foreign Agent
• NFA New Foreign Agent
• Sth The threshold value of RSS to initiate
  handover
• Sath The Adaptive threshold value of RSS to
  initiate handover
• Smin The minimum value of RSS required for
  successful communication
• a Cell Size
• d Cell Boundary
• v Speed of MTs movement
• ? Handoff signaling delay

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Movement during Handoff
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Handoff Scenario

• MT moves with speed v
• RSS of the OBS decreases continuously
• RSS drops below Sth at the point P marking cell
  boundary d.
• RSS lt Sth triggers registration for NFA.
• Pre-registration messages sent through OBS to NFA
  (must be completed before signal drops below
  Smin)

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False Handoff

• At point p, it can move in any direction ? with
  equal probability
• F(?)1/2? where -? lt ? lt ?
• Handoff possible only when
• ??(- ?1, ?1)
• Where
• ?1arctan(a/2)/(d)arctan(a/2d)
• Probability of False Handoff Initiation is

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• Using SVt (DistanceVelocity X Time) i.e.
• tS/V or td/v
• The largest possible distance to cover while
  travelling to NBS is ?(a/2)2(d)2
• As velocity increases the time to cover distance
  will decrease
• When the time to leave the cell falls below the
  handoff signaling delay, handoff will fail
• Therefore Pf 1

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• Using SVt (DistanceVelocity X Time) i.e.
• tS/V or td/v
• As velocity increases the time to cover distance
  will decrease
• While the time to leave the cell is greater then
  handoff signaling delay, handoff will succed
• When d/v gt ? the handoff will succeed
• Therefore Pf 0

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False Handoff Initiation

• As cell boundary d is increased, the probability
  of false handoff initiation increases (keeping
  cell size a constant)
• As cell size a is decreased the probability of
  false handoff increases (keeping d constant)
• Cell sizes are currently trending towards smaller
  size to cope with capacity and improve data
  rates.
• Hence, value of d must be carefully selected.

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Handoff Failure and Speed

• From the above, handoff failure depends on speed
  (keeping a,d,Sth fixed).
• As speed increases the probability of failure
  increases
• For intersystem handoffs the handoff latency is
  higher making it more susceptible to failure

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• Increasing the value of d/Sth reduces the
  probability of failure

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Handoff Failure Signaling Delay

• The higher the signaling delay the greater the
  probability of failure (over a constant d)
• The higher the value of d the lower the
  probability of failure for a single value for
  signaling delay
• Therefore to optimize and minimize handoff
  failure , the distance (and therefore Sth) must
  be adaptive to signaling delay.

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Analysis Summary

• For Fixed value of d(and Sth) handoff failure
  probability increases as MTs speed increases
• For Fixed value of d(and Sth) handoff failure
  probability increases as handoff signaling delay
  increases
• Large values of d(and Sth) increase the
  probability of false handoff initiation

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CHMP

• Derive information from link layer (2) and
  network layer(3) to create adaptive architecture
• Titled proposed solution as Cross-Layer (Layer
  23) Handoff Management Protocol or CHMP

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CHMP Modules

• Neighbor Discovery Unit
• Determines BSs neighboring the MTs current BS

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• Uses network discovery protocols
• Speed Estimation Unit
• Uses VEPSD (Velocity Estimation using the Power
  Spectral Density of RSS) to estimate speed.
• The doppler frequency is used to determine speed
  v
• V(c/fc)fm
• where c speed of light in free space
• fc carrier frequency of RSS
• fm maximum doppler frequency
• Handoff Signaling Delay Estimation Unit
• Estimates delays associated with
  intra/intersystem handoffs

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• Handoff Trigger Unit
• Collects previously collected and calculated
  information to determine the appropriate time to
  initiate handoff
• Handoff Execution Unit
• Triggers the Actual handoff at the appropriate
  time calculated by the Handoff Trigger Unit

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Operation
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Neighborhood Discovery

• Determine neighbors using the neighbor discovery
  unit.
• If OBS and NBS have common FA link-layer handoff
  occurs (CHMP is not used)
• IF OBS and NBS have different FA (intrasystem) or
  belong to different systems (intersystem) CHMP is
  used.

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Handoff Signaling Delay Estimation

• Unknown which BS the MT will move to
• Using the neighborhood discovery step, compile
  list of possible BS/FAs.
• Send an invalid Authentication Extension message
  to the GFA (for intrasystem) or HA (intersystem).
• GFA/HA respond with an HMIP Registration Reply
  indicating registration failure.
• The round trip response time is used to estimate
  the handoff signaling delay.
• Uses existing HMIP protocol without any extra
  implementation
• Causes extra signaling overhead but solution
  still improves performance significantly.
• Alternative delay estimation algorithms available
  in literature if signaling overhead is not
  tolerable.

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Handoff Anticipation

• When the RSS continuously decreases, a handoff is
  anticipated
• Existing movement prediction techniques used to
  estimate the next BS
• Retrieve estimated signaling delay from the
  Handoff Delay Estimation Unit.

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Handoff Initiation

• Estimate optimal moment to initiate handoff
• Estimate Sath using speed and handoff signaling
  delay estimates.
• Trigger handoff when RSS lt Sath
• Sath for intrasystems is referenced as Sath1
• Sath for intersystems is referenced as Sath2

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• Pr(x) Received power at point x
• Pr depends on various factors, including
  frequency, antenna heights, antenna gains etc
• d0 is known as reference distance
• Typical values for d0 are
• 1 km for macrocells
• 100 m for outdoor microcells
• 1m for indoor picocells

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• ? is the path loss exponent
• Depends on cell size and local terrain
  characteristics
• Typical values range between 3-4 for macro and
  2-8 for microcelluar environments
• ? is a random variable representing variation in
  Pr(x) due to shadowing
• Typical value is 8dB
• Pr(x)Pr(d0)(d0/x)? ?
• Sath10log10Pr(a-d)

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Handoff Execution

• HMIP registration started when the handoff
  trigger is received.
• After registration the MT is switched to the NBS
• Simultaneous Binding preserved for a limited time
  by binding CoA of both OFA and NFA to the GFA for
  intrasystem and HA for intersystem, this avoids
  the ping-pong effect.
• Packets are forwarded to both CoAs
• If the MT returns to the old BS there is no need
  to carry out HMIP handoff again.
• If the MT does not return to the old BS, it
  deregisters from the old BS

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CHMP Location

• Implemented at MT referred to as Mobile Assisted
  network controlled Hand Off (MAHO)
• MT implemented components
• Speed Estimation
• RSS Measurement
• Handoff Signaling Delay Estimation
• Network implemented components
• Handoff Trigger Unit
• Handoff Execution Unit
• Implemented at Network referred to as Network
  Assisted mobile controlled Hand Off (NAHO)
• Network implemented components
• Speed Estimation
• RSS Measurement
• Handoff Signaling Delay Estimation
• MT implemented components
• Handoff Trigger Unit
• Handoff Execution Unit

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Types of Handoffs

• Intersystem
• Macro-Inter Between a macro-cellular system and
  another macro-cellular system (Inter_MA_HO)
• Micro-Inter Between a microcellular system and
  another microcellular system (Inter_MI_HO)
• Macro-Micro-Inter Between a macro-cellular
  system and a micro-cellular system
  (Inter_MAMI_HO)
• Micro-Macro-Inter Between a micro-cellular
  system and a macro-cellular system
  (Inter_MIMA_HO)

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• Usually Microcellular systems are overlapped
  by macrocellular systems. Therefore for
  Inter_MAMI_HO there is no handoff failure
• Intrasystem
• Macro-Intra Between two cells of a
  macro-cellular system (Intra_MA_HO)
• Micro-Intra Between two cells of a microcellular
  system (Intra_MI_HO)

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Performance Evaluation

• Relationship between Sath and Speed

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• Sath increases as speed increases
• That is for a high speed MT handoff should be
  initiated early
• Sath increases as ? increases
• When ? is large the handoff must start earlier to
  allow time for registration/handoff to complete
• In order to compensate for Shadow fading and
  errors in estimation, Sath was increased by 10
  percent

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• Relationship between Handoff Failure Probability
  and Speed
• When MTs speed is known, there is a 70-80
  percent reduction in Handoff Failure Probability
  with CHMP
• With CHMP in use probability of failure becomes
  independent of speed
• Comparing the figures for fixed RSS thresholds,
  failure probabilities are different for intra and
  intersystem handoffs
• This further enhances the case for adaptive
  thresholds

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• Relationship between Handoff Failure Probability
  of CHMP and Handoff Signaling Delay
• There is a 70-80 percent reduction in Handoff
  Failure Probability with CHMP compared to fixed
  RSS schemes.
• With CHMP in use probability of failure becomes
  independent of ?
• Probability of failure is limited to desired
  values irrespective of speed and variation of
  handoff signaling delay

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• Relationship between False Handoff Initiation
  Probability of CHMP and Speed
• Fixed value of RSS Threshold Sth is calculated
  such that a user with highest speed is guaranteed
  the desired value of handoff failure probability.
• Comparatively the adaptive CHMP reduces the false
  handoff initiation probability by 5-15 percent
• CHMP initiates handoff while preventing an early
  handoff (minimizing false handoff initiation) and
  late handoff (minimize probability of failure)

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Conclusions

• When a fixed value of RSS threshold (Sth) is used
  handoff failure probability increases with an
  increase in speed or handoff signaling delays
• The adaptive CHMP Protocol estimates speed and
  handoff signaling delay of possible handoffs
  creating a dynamic RSS threshold (Sath)
• CHMP significantly enhances the performance of
  both intra and intersystem handoffs
• CHMP reduces the cost associated with false
  handoff initiation