Term Paper Presentation

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Term Paper Presentation

• By
• Prashanth Busa

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(No Transcript)
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Presentation Sequence

• Abstract
• History and Introduction
• System Model
• Proposed Soft handoff scheme
• Study of Connection reliability
• Numerical Examples
• Conclusion and further research

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Abstract

• A two phase soft handoff scheme
• Power allocation
• Power re-distribution
• The initial power allocation phase includes
  handoff and connection with the BS with best
  link quality independent of BS power
  availability, causing heavily or lightly loaded
  BS
• The power re-distribution phase is to smooth out
  the loading on the system by co-ordinating the
  power allocations among neighboring BSs
• Developing an analytical model for the proposed
  handoff scheme
• Results show that proposed handoff scheme cam
  significantly improve connection reliability and
  increase system capacity in downlink transmissions

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History and Introduction

• Transmission power critical resource in CDMA for
  satisfactory QoS
• Mobile station (MS) closer to the BS experiences
  less path loss and less inter-cell interference
• Optimal power distribution and lower outage
  probability
• are needed
• What is soft handoff and hard handoff??
• Most research on CDMA downlinks was based on hard
  handoff and recent soft handoff schemes doesnot
  emphasize on power re-distribution.
• SSDT saves power resources but doesnot consider
  co-ordiantion among neighboring cells

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System Model

• A cellular CDMA with hexagonal cells
• Center located BS, All BSs controlled by MSC.
• Communication is by FDD, seperate downlink and
  uplink
• Intra and Inter cell interferences and
  non-perfect orthogonality
• Maximum power for each BS Pm, Pilot signal power
  Pp
• Only two BSs can provide connection in soft
  handoff
• Rake receiver is instructed to tune its fingers
  for the two BSs
• Each connection has ON and OFF periods, packets
  transmitted only during the ON period
• Closed loop power control in the downlink to
  satisfy minimum power requirements

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Proposed soft handoff scheme

• Pi0 and Pi1 powers for connection I from BS 0 and
  BS 1
• For (i), link quality is given by
• Link quality for connection from BS 1
• is found similarly

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Soft handoff decisions

• Two possibilities, to move connection jointly
  shared by BS 0 and BS 1 and to completely
  handover to BS1

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Connection reliability analysis

• Unreliable when SIR is not guaranteed due to
  insufficient power resources and measured by
  outage probability
• After initial power allocation, the probability
  that BS 0 does not have sufficient power is
• Worst case all the connections are removed
  from service and Pr represents the upper bound of
  connection unreliability
• After re-distribution, the upper bound for
  connection unreliability is
• Represents that BSs do not have sufficient
  power to serve all connections after one round of
  power re-distribution

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Numerical Examples

• Assumptions for each hexagonal cell,
• normalized distance1
• normalized power1
• 5Mhz bandwidth re-used in each cell
• path loss exponent4
• standard deviation8dB
• transmission rate9.6kbps
• Fig 3, compares the analytical bounds with
  the simulation results when traffic load is low.
• Fig 4,Using only initial power allocation
  and both are close for again low traffic

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Examples (cont.)

• Fig 5, connection unreliability for soft handoff
  and hard handoff
• Fig 6, two phase soft handoff scheme with scheme
  with only power allocation
• As the number of MSs increase power
  re-distribution is more effective

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Examples (cont.)

• Fig7, Comparison with equal power soft handoff
  and proposed soft handoff scheme vs soft handoff
  distance
• As the number of MSs increases equal power scheme
  shows little improvement in connection
  unreliability

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Conclusion

• A soft handoff/power redistribution scheme has
  been proposed for CDMA downlinks and its effect
  on connection reliability is studied.
• Connection reliability is significantly improved
  by power redistribution
• Further research is how the this scheme effects
  packet transmission and connection admission in
  CDMA downlinks