1. HANDOFFS AND DROPPED CALLS
Harpinder Kang Khattra

2. Sub topics Why Handoff Types of Hand off and their characteristics
Dropped call rates and their evaluation

3. 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

4. Important handoff parameter:
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

5. Occurrence of handoff

6. Types of Handoff A. Natures of handoff B. Purposes of handoff
Hard handoff
2. Soft handoff
3. Softer handoff
B. Purposes of handoff
1. Intracell handoff:
2. Intercell handoff:
3. Inter BSC/MSC handoff:

7. C. Algorithms of handoff
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)

8. 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

9. 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).

10. Relationship Among Capacity, Voice Quality, Dropped Call Rate
Radio Capacity m is expressed as follows:

11. 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