Handoffs and dropped calls
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HANDOFFS AND DROPPED CALLS. Harpinder Kang Khattra. Sub topics. Why Handoff Types of Hand off and their characteristics Dropped call rates and their evaluation. Handoff. Mobiles may move out of coverage area of a cell and into coverage area of a different cell during a call

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HANDOFFS AND DROPPED CALLS

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Handoffs and dropped calls

HANDOFFS AND DROPPEDCALLS

Harpinder Kang Khattra


Sub topics

Sub topics

  • Why Handoff

  • Types of Hand off and their characteristics

  • Dropped call rates and their evaluation


Handoff

Handoff

  • Mobiles may move out of coverage area of a cell and into coverage area of a different cell during a call

  • MSC must identify new BS to handle call

    • MSC must seamlessly transfer control of call to new BS

    • MSC must assign call new forward and reverse channels within the channels of new BS

  • Some important performance metrics in handoff:

    • Seamless – user should not know handoff occurring

    • Minimum unnecessary Handoff due to short time fading

    • Low probability of blocking new calls in the new cell

    • Handoff to a good SNR channel so that an admitted call is not dropped


Handoffs and dropped calls

  • Handoff Main Steps

    • Initiation

    • Resource reservation

    • Execution

    • Completion

  • Important handoff parameter:

    • SNRold to initiate handoff based on minimum acceptable quality

    • SNRnew of the target channel (SNRnew > SNRold )

    • D = SNRnew - SNRold dB

      • If D too small, unnecessary handoffs occur

      • If D too large, may be insufficient time to complete handoff before SNRold becomes too weak and signal is lost


Handoffs and dropped calls

Occurrence of handoff


Handoffs and dropped calls

Types of Handoff

A. Natures of handoff

Hard handoff

2. Soft handoff

3. Softer handoff

B. Purposes of handoff

1. Intracellhandoff:

2. Intercell handoff:

3. Inter BSC/MSC handoff:


Handoffs and dropped calls

4. Intersystem handoff:

5. Intercarrier handoffs:

6. Intermode handoff:

C. Algorithms of handoff

1. MCHO (Mobile Control Handoff)

2. NCHO (Network Control Handoff)

3. NCHO/MAHO (Network Control Handoff/Mobile Assists Handoff)


Dropped call rates

Dropped Call Rates

  • The dropped call is defined as an established call which leaves the system before it is normally terminated

  • The Dropped Call Rate (DCR) parameter represents what percentage of all established calls is dropped during a specified time period

  • The DCR and voice quality are inversely proportional and high DCR may indicate coverage, handoff, or channels accessibility problems


Handoffs and dropped calls

The perception of dropped call rate by the subscribers can be higher due to:

1. The subscriber unit not functioning properly (needs repair).

2. The user operating the portable unit in a vehicle (misused).

3. The user not knowing how to get the best reception from a portable unit (needs education).


Handoffs and dropped calls

Relationship Among Capacity, Voice Quality, Dropped Call Rate

Radio Capacity m is expressed as follows:


Formula of dropped call rate

FORMULA OF DROPPED CALL RATE

  • General Formula of Dropped Call Rate

    The general formula of dropped call rate P in a whole system can be expressed as:

    Where

    And


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