FAJ 121 1350
IMPROVED RACH COVERAGE
WCDMA DOMAIN
introduction
There is need to increase the RACH coverage to improve the WCDMA RAN accessibility.
Improvement in RACH coverage can be seen up to -3 dB by blocking the most sensitive
preamble signatures and lowering the preamble threshold and has the following benefits:
Extend coverage
PS drop call rate can be improved
Reduced Response time.
The feature is license controlled on RNC node level. It can be activated and deactivated on the
cell level, due to a trade-off between coverage & capacity
Feature description
Feature description
RACH Coverage
DCH Coverage
RACH Coverage
DCH Coverage
- Decoding
- Power control
- Softer handover gain
Feature description
› RACH coverage is usually smaller than DCH coverage due to Softer HO, Decoder and P
ower control.
› Even though UE is on DCH coverage, UE can’t make a call out of RACH coverage.
RACH Coverage
DCH Coverage
RACH preamble
Feature description
› By the increasedRachCoverage feature, RACH coverage extend.
› More UEs, especially in poor coverage area, are able to access to the cells.
Increased RACH Coverage
DCH Coverage
RACH preamble
AICH
Feature description
› UEs which establish PS RAB and move out of RACH coverage still can keep the RAB.
› But as soon as UE state moves to Cell_FACH due to inactivity, the UE will drop because
UL doesn’t reach the cell.
RACH Coverage
DCH Coverage
RAB Establish
(Cell_DCH)
Cell_DCH  Cell_FACH due
to inactivity
DROP
Feature description
› After the implementation of increased RACH coverage, the RACH coverage will be close
r to DCH coverage.
› The probability of transition failure from DCH to FACH will become smaller.
Increased RACH Coverage
DCH Coverage
RAB Establish
(Cell_DCH)
Cell_DCH  Cell_FACH due
to inactivity
Success
Controlling parameters
COUNTERS TO MONITOR
› pmRecievedPreambleSIR is expected to improve because of enhanced RACH detection
algorithm
› pmPositiveMessages is expected to increase (Positive Acquisition Indicator Msgs sent on
AICH to the UE with preamble detection)
› pmSuccReceivedMsgs is expected to increase which are Successfully Received Transport
Blocks during PRACH setup
› Propogation Delay might show users accessing to NW with more distance