PRACH Demo for Eden-NET Live 2016-10-26

PRACH Optimization Eden-NET 16 SP2 •

Elina Järvelä

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October 2016

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PRACH  – LTE UL cont rol channel Primary Random Access Channel PRACH is used when UE needs to •

send new UL data

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send control information

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RACH setup failure rate

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receive new DL data

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Call setup failure rate

hand over from serving cell to target cell

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Handover failure rate

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Non-optimized PRACH settings lead to increased

transit from RRC_IDLE to RRC Connected state

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PRACH Parameter Plann ing Primary Random Access Channel   s   r   e    t   e   m   a   r   a    P

PRACH configuration is combination of four parameters •

Root Sequence Index (RSI) in Code domain

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Frequency Offset (FO) in Frequency domain

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Configuration Index (CI) in Time domain

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Cyclic Shift (CS) in Code domain

UE should not receive simulaneously multiple PRACH from immediate neighbors with any of the   n following conditions   o    i    t Overlapping RSIs while PRACH being transmitted in same time and frequency   g   a    d   n    i   n Transmitted in overlapping time while similar code and frequency are used   n   e   n Transmitted in overlapping frequency while similar code and time are used   a   m    l   m    P   o   c   e   r In addition, the four PRACH parameters must not be inconsistent with one another  •

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PRACH Planning Challenges Challenges Challenges Manual planning of PRACH parameters is tedious and error prone Quick fine tuning of PRACH parameters to suit changing radio conditions is not feasible manually Improving RACH success rate •

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Vendor support LTE PRACH module •

Nokia -

HetNet support utilizing Nokia eNB functionality: LTE2020 PRACH Management Optimization for HetNet •

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 Automatic calculation of expected cell range

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HetNet neighbor identification

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High speed UE flag

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Huawei

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Ericsson

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Use cases LTE PRACH module •

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Fresh allocation

change all

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When hard to fix conflicts

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When unable to find values for new cells

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If RACH success rate it poor for an area

Conflict resolution

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minimal changes

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When new cells are on air and start serving

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When minimal changes preferred

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If individual cell has poor RACH success rate

Inconsistency resolution -

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within one cell

When cell is having no conflicts but RACH success rate is poor 

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RSI FO CI PUCCH PUSCH

Use cases PRACH Module

Root Sequence Index Frequency Offset Configuration Index Physical Uplink Control Channel Physical Uplink Shared Channel

Fresh allocation

Conflict resolution

Inconsistency resolution

 Allocation is re-planned for all selected cells

PRACH issues detected for 

Detect PRACH parameter inconsistencies within a cell

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Option: HsFlag indicates if the cell serves high speed or low speed users

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Cells on same site Cells within a reuse distance Cells with incoming or outgoing intra LTE neighbor relations, within or out of reuse distance

Checking: −

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Option: FDD LTE cells also time synchronized

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Global and forbidden values Unsupported or out of range values Overlap with PUCCH or masked PUSCH area (interference) Not adjacent to PUCCH area (inefficient utilization of physical resouce blocks, PRBs) Out of band FO (interference and loss of information) Not aligned parameters RSI, CI and FO

Policies LTE PRACH module •

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Neighbor finding strategy -

Coverage overlap: Expected / Fixed cell range or Propagation path loss

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Reuse distance: Fixed / Relative

Parameter planning -

RSI (code domain)

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FO (frequency domain) - optionally planned

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CI (time domain)

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CS (code domain)

always planned

optionally planned  –

optionally planned

Differentiation strategy -

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Code domain and frequency and/or time domain

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RSI FO CI CS

Root Sequence Index Frequency Offset Configuration Index Cyclic Shift

Key principl e & planning rule PRACH Module Key principle •

PRACH configuration must not be identical in the user defined neighborhood of a selected LTE cell

Planning rule •

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First try to differentiate the PRACH by using Root Sequence Index (RSI) Then, if user has chosen one of both of the optional settings, try to differentiate cells based on Time and/or Frequency domain RSI is always planned, optional by user: FO, CI, CS

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RSI FO CI CS

Root Sequence Index Frequency Offset Configuration Index Cyclic Shift

UI parameters 1/3 PRACH Module

Maintenance windo w

No change in HsFlag True False Fresh allocation Use case

Conflict resolution Inconsistency resolution

Modify necessary parameters Use manual selection 10

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UI parameters 2/3 PRACH Module

By expected cell range By fixed cell range By propagation path loss

Coverage overlap Neighbor finding strategy

Reuse distance

Fixed reuse distance

Relative reuse distance 11

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UI parameters 3/3 PRACH Module

Parameters planning

Differentiation strategy

Mod2(PCI) value Use PRFO forbidden list

Skip target cell Skip neighbor cell

Other settings

Open loop Closed loop 12

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Back-end parameters  – configuration.ini PRACH Module configuration.ini file contains the common settings used whenever PRACH module is run [Forbidden.Global] -

Forbidden or reserved PRACH configuration values

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The module must not use any values from the reserved PRACH configuration groups for recommending new PRACH configuration

[FixedCellRange] #cellType_deploymentType (Range in km) = Value (km) -

Cell Type: Macro, Micro, Pico, Femto

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Deployment Type: Urban, SubUrban, Rural

[PropagationPathLoss] #propagationPathLossSetting (Ranges) = Value

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Cell type: Macro, Micro, Pico, Femto

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Cell edge RSRP and UE antenna height © Nokia Solutions and Networks 2014