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Presentation By Muhammed Syyid

A Cross-Layer (Layer 2 + 3) Handoff Management Protocol for Next-Generation Wireless Systems By Shantidev Mohanty and Ian F. Akyildiz, Fellow, IEEE. Presentation By Muhammed Syyid. NGWS. Next Generation Wireless System Multiple kinds of wireless systems deployed UMTS (WAN) 802.11 (WLAN)

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Presentation By Muhammed Syyid

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

  2. 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

  3. NGWS

  4. 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

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

  6. Handoff in NGWS

  7. Handoff in NGWS • Horizontal Handoff • Link Layer Handoff • IntraSystem Handoff • Vertical Handoff • InterSystem Handoff

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

  9. Goals for Seamless Handoff • Minimize Handoff Latency • Minimize Packet Loss • Limit Handoff Failure • Minimize False Handoff Initiation

  10. 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

  11. 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

  12. 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 • User’s Speed

  13. 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 MT’s movement •  : Handoff signaling delay

  14. Movement during Handoff

  15. 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 < Sth triggers registration for NFA. • Pre-registration messages sent through OBS to NFA (must be completed before signal drops below Smin)

  16. False Handoff • At point p, it can move in any direction  with equal probability • F()=1/2 where - <  <  • Handoff possible only when • [(- 1, 1)] Where 1=arctan(a/2)/(d)=arctan(a/2d) • Probability of False Handoff Initiation is

  17. Using S=Vt (Distance=Velocity X Time) i.e. • t=S/V or t=d/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

  18. Using S=Vt (Distance=Velocity X Time) i.e. • t=S/V or t=d/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 >  the handoff will succeed • Therefore Pf = 0

  19. 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.

  20. 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

  21. Increasing the value of d/Sth reduces the probability of failure

  22. 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.

  23. Analysis Summary • For Fixed value of d(and Sth) handoff failure probability increases as MT’s 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

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

  25. CHMP Modules • Neighbor Discovery Unit • Determines BS’s neighboring the MT’s current BS

  26. 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

  27. 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

  28. Operation

  29. 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.

  30. Handoff Signaling Delay Estimation • Unknown which BS the MT will move to • Using the neighborhood discovery step, compile list of possible BS/FA’s. • 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.

  31. 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.

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

  33. 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

  34.  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) +  • Sath=10log10[Pr(a-d)]

  35. 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 CoA’s • 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

  36. 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

  37. 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)

  38. 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)

  39. Performance Evaluation • Relationship between Sath and Speed

  40. 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

  41. Relationship between Handoff Failure Probability and Speed • When MT’s 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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