22 rach algo v10
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RACH Algorithm (draft)
Shay Laslo Amit
LTE Research Engineer
Mobility CTO Group
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Research Partners
Shay Laslo Amit RAN Research Engineer, Mobility CTO Group, Cisco System
Dr. Tuvia Apelewicz CEO Muxline Ltd
Ziv Nuss Practical Engineer , Mobility CTO Group, Cisco Systems
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Parameters – high level list
Trigger: Cells with RA Failures / RA Success Rate / Intensity
Sequence of potential diagnose / actions
Root Sequence Issues: RSI Planning, Cell R Not enough opportunities: RA Opportunities, T
Narrow UL interference: RACH Frequency O
High mobility cells: Preamble Format, #
Wide UL interference: RACH power setting
DL interference TBD DL Load (PDCCH) TBD
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Root Cause Analysis
RSI Planning Module (Including Cell Range)
CBRA/CFRA Split Module
RA Opportunities Module (Configuration Index) Interference Module
RACH Frequency Offset
RACH power settings
Preamble Format
RA back-off Module (RA Reattempt delay)
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Algo modules flow
Filter 1
Yes
Time from
last RSI
planning
No
Yes
Yes
Rollback
with logMaintenance window?
SP policy
Wait to maintenance window
If needed according to RAN vendorRB Threshold check & log
Filter 1
still triggered
Yes
Filt
still trig
No
Next cycle
No
RA back-off
Module
Filter 1
still triggered
Yes
No No
Interference
Module
Next
cycle
PDCCH
Utilization > Thr-3
x > t2 days
t1 <x< t2 days Small RSI
planning
Wait to next
bigger RSI
planning
Load
Balancing
Module
Available in all
RAN vendors
x < t1 days
RSI planning time filter (next slide)
CBRA/CFRA
Module
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Filter 1 and 2
Passing Filter 1 only when:
CBRA success rate which is below threshold-1 &
CBRA failures above threshold-2
Or, CFRA success rate is below threshold-4 &CBRA failures above threshold-5
Filter 2
Does success rate and failures of CFRA worse than CBRA
If answer is Yes, go to CFRA/CBRA module
Does success rate and failures of CFRA better than CBRA
If answer is No, go to RSI planning filter
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RSI Planning Time Filter
Last RSI
change
t1 t2
Too close to last
RSI change,
Go to next module
Far enough from last/next
RSI change,
Make small RSI changes
Close enough
RSI chang
Wait to next wide
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RSI Planning – High level
RSI planning should include the following
RSI planning should include clustering abilities
SON will work on separated clusters for control purposes
Motivation is to determine the real required amount of RSI per Amount of RSI according to cell range plus additional RSIs as m
First RSI should be
Between 1 to 419
Odd position, according to physical RSI table
All bank of RSI should be different then it’s 1st tier neighbor
Bank of RSI is recommended to be different than it’s 2nd tier ne If straight RSI separation neighbors isn’t possible due to #neigh
Make separation according to neighbors weights
Trigger neighbors removals to ANR or report on it in a GUI
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Clustering Method
SON has identified triggered cells regarding RACH performance
Those cells will be gathered into clusters for RSI planning
Several clustering methods was identified, still wasn’t chosen - TBD
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CBRA / CFRA Module
Rollback
with logMaintenance window?
SP policy
Wait to maintenance window
If needed according to RAN vendorRB Threshold check & log
Filter 4
CBRA SR < CFRA SR
CBRA Fails >> CFRA Fails
Yes
Main
KPIs OK?
No
RB-3
Yes
No
Yes
2nd cycle
Filter 4
still triggered
No
Filter 5
CBRA SR > CFRA SR
CBRA Fails << CFRA Fails
Yes
No
Main
KPIs OK?
Yes
No
RB-4
Filter 5
still trigge
2nd cycle
In
CFRA enabled?
YesIncrease one step
NumberOfRAPreambles
No
Decrease one stepNumberOfRAPreambles
Available in all
RAN vendors
Input-1
Yes
No
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CBRA / CFRA Module tradeoff
64 signatures separated into two: Contention based RA & Contentio
Contention free are part of handover procedure only
Contention based mainly are for access and reestablishment
Normally more signatures kept for contention based RA
Tradeoff is between mobility and accessibility performance
It depends where the border line should be
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RA Opportunity Module
Rollback
with logMaintenance window?
SP policy
Wait to maintenance window
If needed according to RAN vendorRB Threshold check & log
In OIncrease opportunities
Main
KPIs OK?
No
Yes
Yes
Y1 cycle
Filter 1
still triggered
No
RB-6
Action Time
Window Passed?
YesRB-5
It is possible to increase RA opportunities from 1 to 2,3,5,10 in one r
Tradeoff is between improved access, delay and capacity for UL dat
In some situations even DL throughput could be harmed
Available in all
RAN vendors
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Interference Module
Rollback
with logMaintenance window?
SP policy
Wait to maintenance window
If needed according to RAN vendorRB Threshold check & log
In
Identified as Narrow
Interference?
Yes
No
Main
KPIs OK?
No
RB-7
Yes
Yes
2nd cycle
ncrease PRACH Freq
Offset by x to
cleaner RB
UL RSSI > Threshold
Yes
No
Main
KPIs OK?
No
RB-8
Yes
Ye
Wide Interference Algo
Y2 cycle
Available in all
RAN vendors
Check
RACH
location **
Check Uplink
Interference on
PRB level
** RACH location – On frequency domain (PRB)
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Interference Module tradeoff and Neighbors
Tradeoff is between accessibility and capacity
When moving RACH location to a cleaner RB we’re occupying reso
could be used for data usage and instead we’re using it for better ac
Neighbors - When narrow interference as been identified on RACH
neighboring cells, it’s possible to allocate different frequency shift fo
within those cells
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Identifying Narrow Interference
UL RSSI
Frequency (PRBs)
PUCCH PUCCHACH
ΔY1
PRB
Ref1
ΔY2
PRB
Ref2
The exact location of RACH PRBs on frequency domain is known (configura
The relative UL RSSI in RACH PRBs is compared to other reference PRBs
The reference PRBs shall be part of those in which it’s possible to shift the R
If the relative UL RSSI of RACH is higher than a threshold ΔYi
Then it’s possible to shift RACH PRBs to a cleaner “area”
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Wide Interference Algorithm
TBD
B k Off M d l
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Back-Off Module
Rollback
with logMaintenance window?
SP policy
Wait to maintenance window
If needed according to RAN vendorRB Threshold check & log
In OIncrease raBackOff
Timer x steps
Main
KPIs OK?
No
Yes
Yes
Y3 cycle
Filter 1
still triggered
No
RB-10
Action Time
Window Passed?
YesRB-9
Timer which set a delays for too close RA re-attempts
Tradeoff is between potential increase in delay and overloading RAC
Available in all
RAN vendors
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Thanks
C l
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