Lab. 13 Handoff and Power Control in CDMA systems

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Lab. 13 Handoff and Power Control in CDMA
systems

• 28 Apr, 2008
• Su Ha Yoon (TA)
• shyoon_at_cnr.kaist.ac.kr
• T.5439 (203)

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Contents

• 1. Handoff
• 2. Power Control
• 3. Pre-Lab
• 4. Main-Lab
• 5. References

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Handoff

• Systems are designed with some overlap in the
  coverage areas between sites, because of user
  mobility and the need of eliminating shadow areas
  within the service area.
• Handoff process
• When a MS is moving from one cell to another, the
  MS undergoes procedures called handoff.
• Handoff allows the MS to acquire the pilot
  channel transmitted by neighboring base station
  transceiver system (BTS) and to make another
  connection to a new BTS, while maintaining a
  connection to the old BTS.
• To perform a handoff process, every MS measures
  and internally stores the information about
  neighboring Forward Pilot Channels (FPiChs)
  acquired in its current location.

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Handoff Pilot Sets

• Active set
• Pilots of CDMA carriers are being monitored while
  in idle state.
• During a call, these are the pilots associated
  with forward traffic channels assigned to the MS.
• Candidate set
• Pilots not currently in the active set but with
  enough signal power level to become an active
  pilot.
• Neighbor set
• Pilots that do not belong to the active or
  candidate sets but may be also considered
  candidates for a handoff process
• Remaining set
• All remaining pilots that do not belong to any of
  the other sets but exists in the area where the
  MS is located

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Handoff Types

• Soft handoff
• A soft handoff is applied to an MS that starts
  communication with a new BTS while still
  connected to another BTS
• Make-before-break
• Hard handoff
• A MS is disconnected from one BTS and is switched
  to another
• Break-before-make
• Softer handoff
• A special soft handoff between sectors in the
  same BTS
• Idle handoff
• An idle handoff is performed while in idle state
  when the MS is moving from one BTS to another
• Access handoff
• An access handoff occurs in the system access
  state when the MS is performing access attempts.

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Power Control (1/3)

• FER is the most common network quality parameter
  to execute power control
• Ec/Io (ratio of chip energy, Ec, to interference
  noise spectral density)
• Eb/Io (ratio of bit energy, Eb, to interference
  noise spectral density)
• Power control aims to quickly and efficiently
  estimate the minimum MS transmission power to
  achieve the required communication quality (based
  on FER statistics)
• Benefits of power control in CDMA systems
• Increase in system capacity
• Minimization of near-far effect
• Increase in battery lifetime

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Power Control (2/3)

• Open loop power control
• Usually implemented as the initial power control
  to give an estimate of minimum transmission power
  used for access channels, such as Reverse Access
  Channels (RAChs), Enhanced Access Channels
  (EAChs), and Reverse Common Control Channels
  (RCCChs), during system access state.
• Closed loop power control
• Usually implemented for traffic channels, which
  need a more sophisticated power control system.
  cdma2000 systems can also employ this type of
  power control even during the system access state.

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Power Control (3/3)

• Procedure of the closed loop power control
• An MS initially uses the transmission power
  defined in the last message from last access
  probe transmitted on the system access state.
• The BTS determines a set point power level,
  which is considered ideal for receiving signals
  within a certain QoS.
• The set point is periodically adjusted.
• The BTS performs power control by transmitting
  power control bits, which instruct MSs
  individually to increase or reduce transmission
  power according to the estimated set point value.

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Pre-Lab (1/2)

• Explain the roles of PN code, rake receiver,
  searcher, and finger briefly.
• Explain the active/candidate/neighbor set in the
  handoff process briefly.
• Fig. 7 shows the procedure of soft handoff.
  Explain the procedure of soft handoff using the
  figure.
• The handoff process consists of 4-steps
  initialization, resource reservation, execution,
  and completion. Explain each step briefly.
• What is the near/far problem in CDMA systems and
  how to solve this near/far problem in the CDMA
  system?
• Both open-loop power control and closed-loop
  power control are used in the CDMA systems.
  Explain the difference between open-loop power
  control and closed-loop power control briefly.

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Pre-Lab (2/2)
Due date Before the experiment
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Main-Lab (1/2)Handoff

• Handoff
• Fill the following table and record the data
• PN offset
• Ec/Io
• RSSI
• Finger State
• Active / Candidate / Neighbor
• Varying the location slowly, fill the following
  table and record the data
• Explain the difference before and after handoff
  using the recoded data
• Analyze collected data
• Using the recorded data pilot set status,
  temporal analyzer graph, PN history graph, and
  finger graph, explain the handoff procedure.

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Main-Lab (2/2)Power Control

• Power Control
• Power control during call processing
• Record data during idle mode
• Record data during call origination / active
  phase
• Record data during call delivery / clearing
• Power control of moving users
• Varying the location slowly, fill the following
  table and record the data
• PN offset, RSSI
• Tx./Rx. Power, Tx. Adjust
• Ec/Io, FER
• Analyze collected data
• Using the recorded data pilot set status,
  temporal analyzer graph, PN history graph, finger
  graph, and IS-95 signal graph, explain the power
  control procedure.

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References

• Korowajczuk, et al., Designing cdma2000 systems
  
• Garg, Wilkes, Wireless and personal
  communications systems
• Lee, Miller, CDMA systems engineering handbook
• CC Inst., ANYPA-IMT2000 Protocol Analyzer
  Operation Manual
• http//www.3gpp.org
• http//www.3gpp2.org