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 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

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

Occurrence of handoff

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:

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)

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

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).

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

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