What are the possible causes for an Access Failure in UMTS?

• Missing Neighbors
• Poor Coverage
• Pilot Pollution / Spillover
• Poor Cell Reselection
• Core Network Issues
• Non – availability of resources. Admission Control denies
• Hardware Issues
• Improper RACH Parameters
• External Interference

LTE The Vision Beyond 3G by Nortel
Ericsson Parameters to make Handover Easier

What is Soft Handover Overhead? What is the typical value in UMTS network?

• Soft Handover Overhead is calculated in two ways. 1) Average Active Set Size – Total Traffic / Primary Traffic. 2) Secondary / Total Traffic
• Typical Values are like 1.7 (Avg Active Set Size) or 35% (Secondary / Total )

How to improve Soft Handover in UMTS Network?
How can we avoide to many Soft Handover attempts?

What is the typical Call Setup Time for a 3G UE to 3G UE Call? What are the possible RF related causes for a delayed CST in this type of call?

• 6 to 9 seconds
• Multiple RRC Attempts (UE is on poor coverage – need more than Access Attempt)
• Delayed Page Responses
• High Load on Paging and/or Access Channel
• Paging / Access Parameters

Download UMTS Radio System Planning and Optimization Guide

What can we try to improve when access failure is high?

When access failure is high we can try the following to improve RACH performance:

• Increase maximum UE transmit power allowed: Max_allowed_UL_TX_Power.
• Increase power quickly: power_Offset_P0.
• Increase number of preambles sent in a given preamble cycle: preamble_Retrans_Max.
• Increase the number of preamble cycles: max_Preamble_Cycle.
• Increase number of RRC Connection Request retries: N300.

Know What are the Possible Reasons for Access Failure in UMTS?

What is Hard Handover in UMTS? When will it happen?

· Hard Handover in UMTS is a break before make type Handover
· It can happen in the inter RNC boundaries where there is no Iur link.

This may Helpful to You

IRAT Handover Guide
Inter System Cell Reselection Optimization Guide
TEMS UMTS Dropped and Block Call Specification 

What are the possible causes for a Drop Call on a UMTS network?

There are several reasons for RAB Drop in WCDMA network.

·         Poor Coverage (DL / UL)

·         Pilot Pollution / Pilot Spillover

·         Missing Neighbor

·         SC Collisions

·         Delayed Handovers

·         No resource availability (Congestion) for Hand in

·         Loss of Synchronization

·         Fast Fading

·         Delayed IRAT Triggers

·         Hardware Issues

·         External Interference

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WCDMA Neighbor Cell, Scrambling Code and LAC Planning
TEMS UMTS Dropped & Blocked Call Specifications

What are the possible causes for a lower PSR?

There are several different reason for low Paging Success Ratio

- Non-continuous RF Coverage – UE going in and out of coverage area frequently
- Very High ‘Periodic Location Update Timer’ – Keeping UEs in VLR long time after it moved out of coverage
- Lower Paging Channel Power
- Access Channel Parameter Issues
- Delayed Location Update when crossing the LA / CN Boundaries

Also Check

E Book on GPRS and EDGE Performance

What is G-RAKE Receiver?