Channel Recovery In TDMA Systems

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Channel Recovery In TDMA Systems

• By
• Anjaneya Datla

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What are TDMA Systems?

• Time division multiple access (TDMA) is a channel
  access method for shared medium networks.
• Several users can share the same frequency
  channel by dividing the signal into different
  time slots.

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TDMA Frame Structure
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Introduction (continued)

• The users transmit in rapid succession, one after
  the other, each using its own time slot.
• Multiple stations can share the same transmission
  medium (e.g. radio frequency channel) while using
  only a part of its channel capacity with this
  technique.
• TDMA is implemented in
• 2G cellular systems like GSM,IS-136,Personal
  digital cellular, etc.

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Scenario in a TDMA System

• A single base station failure in TDMA wireless
  systems causes all active calls on this base
  station to be dropped.
• In order to increase system end-to-end
  availability ,a multiple channel recovery method
  for TDMA wireless systems is required.
• when a base repeater fails, the channels of
  active calls carried by the base station are
  replaced by working channels in the channel pool
  of the base site.

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Continued

• The method deals not only with the failure and
  recovery of base stations, but also with the
  channel failure recovery in handoffprocesses,
  transient channel failures, and new call setup
  processes.
• All the active calls continue without the
  intervention of end users.

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Description of the process

• In wireless communications systems, the base site
  controller (BSC) handles radio channel allocation
  and many other functions.
• Whenever a channel fails, the call carried by the
  channel will be dropped.
• There different reasons for a channel failure.
• We classify these into 2 types
• Permanent and transient channel failures.

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Description(Continued)

• The permanent channel failures are caused by
  equipment failures of base stations, such as
  power failure or RF amplifier failure, etc.
• For example
• While there are some ongoing calls on the BR, the
  BR is down.
• The transient channel failures are caused by many
  factors in the RF transmission, such as fading,
  shadowing and interference.

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Things Involved

• The channel recovery method is mainly composed of
  three processes
• 1.Monitoring process,
• 2.Channel allocation process,
• 3.BS failure handling process.
• In order to detect and handle base repeater
  failures, a base repeater monitoring process is
  developed.
• The following slide shows the picture of it.

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Monitoring Process Flow Diagram
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Channel Allocation Process

• The Radio Frequency Channel Allocation consists
  of various steps.
• 1. Handling a New Call Requirement.
• 2. Handling a Hand-off Call.
• 3. Handling Base-Station Failure.
• 4. Handling transient failures.
• 5. Updating Base Station repair status.

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Channel Allocation Process Flow Diagram
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Base Station Failure Handling Process

• It involves 2 steps
• Procedure to update system parameters when a BR
  repair is completed.
• Procedure to handle a BR failure handling
  requirement.

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Base Station Failure Handling Process Flow
Diagram
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Final Comments

• The major advantage that we get is reduced
  percentage of Dropped calls.
• Using this method we get increased system end
  to-end availability.

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• Thank You