2013/10/2
LTE Cell Planning LTE RNP
Content Process for Planning the LTE Network Frequency Planning Cell ID Planning TA Planning PCI Planning Neighboring Cell Planning X2 Planning PRACH Planning
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Process for Planning the LTE Network The general process includes information collection, pre-planning, detailed planning, and cell planning.
Information Collection
In the cell planning, main concerns are frequency planning, cell ID planning, TA planning, PCI planning, neighboring cell planning, X2 interface planning, and PRACH planning.
Preplanning Detailed Planning Cell Planning
Frequency Cell ID Planning Planning
TA Planning
PCI Planning
NB Cell X2 PRACH Planning Planning Planning
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Content Process for Planning the LTE Network Frequency Planning Cell ID Planning TA Planning PCI Planning Neighboring Cell Planning X2 Planning PRACH Planning
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Frequency Planning Why and when perform frequency planning? When the LTE system works on the same frequency band, serious interference occurs between the UEs on the edge of a cell because they are close to each other and use the same resources. The inter-cell interference coordination (ICIC) technology can be used to change interference distribution, thus improving the throughput of the UEs on the edge of a cell.
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Frequency Planning
When static DL ICIC is used, the entire bandwidth is divided into three parts, each of which serves as the edge band of a cell for reuse. In this case, network planning engineers need to perform frequency planning.
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Notes for Frequency Planning In
actual applications, the network structure is quite complex, therefore 1x3 frequency reuse can mitigate interference only to a certain way.
For
expansion, frequent planning adjustments need to be performed. In this case, network performance may deteriorate.
In
scenarios where indoor coverage and outdoor coverage require coordination, frequency reuse cannot be ensured.
If
the DL ICIC function is required, dynamic ICIC is recommended.
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Dynamic ICIC
Serving cell communicate through X2 interface which PRBs are interfered or with poor quality to its neighbors. Neighbor cells do interference-aware scheduling of PRBs to lower or avoid interference Page 8
Content Process for Planning the LTE Network Frequency Planning Cell ID Planning TA Planning PCI Planning Neighboring Cell Planning X2 Planning PRACH Planning
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Cell ID Planning Different
from a WCDMA cell ID, LTE cell ID consists of 20-bit eNB ID and 8-bit cell ID, which ensures that the LTE cell ID is unique in the entire network. If the PLMN (MCC + MNC) is used, the LTE cell ID is unique worldwide.
Usually
is recommended to keep a relationship between eNB ID, the cell name and cellID and ensures that they are consistent.
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Considerations for Actual Planning
› In practice, customers may provide numbering rules for different areas and cities. › If customers have no additional requirements, consistency check of cellID planning should be taken into account.
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Content Process for Planning the LTE Network Frequency Planning Cell ID Planning TA Planning PCI Planning Neighboring Cell Planning X2 Planning PRACH Planning
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TA Planning TA Concept
Similar to the location area and routing area in 2G/3G networks, the tracking area (TA) is used for paging. TA planning aims to reduce location update signaling caused by location changes in the LTE system.
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TA Planning Principles
A TA should be medium. The limitations by the EPC must be considered. (For example the maximum number of eNBs in the EPC that can handle i.e 30avg ).
Take into account the more paging messages the less resources for data, and less throughput due to the paging messages are mapped into the PDSCH.
A TA should be planned for a continuous geographical area to prevent segmental network of eNBs in each TA.
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TA Planning Principles Mountains or rivers in the planned area can be used as border of a TA to reduce the overlapping of different cells in two TAs. In this way, fewer location updates are performed on the edge of a TA.
The LAC planning in the existing 2G/3G networks can serve as a reference for planning TAs.
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Content Process for Planning the LTE Network Frequency Planning Cell ID Planning TA Planning PCI Planning Neighboring Cell Planning X2 Planning PRACH Planning
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PCI Planning › In LTE system, the physical cell identifier (PCI) is used to differentiate radio signals of different cells. That is, the PCI is unique in the coverage of cells.
› Cell IDs are grouped in the cell search procedure. The ID of a cell group is determined through the SSCH, and then a specific cell ID is determined through the PSCH.
› The function of PCIs in the LTE system is similar of scrambling codes in the WCDMA system. PCI planning also aims to ensure the reuse distance.
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PCI Planning › Differences between a scrambling code and a PCI: The scrambling code ranges from 0 to 511 whereas the PCI ranges from 0 to 503.
› Note: Physical Cell id can be any from the range 0-503. In order to manage this huge amount of cells, LTE has divided them in to 168 groups and in each group there can be 3 cells. So Physical Cell ID = Cell Group ID * 3 + Cell ID
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Actual Considerations PCIs need to be reserved for indoor coverage. For multiple cities, PCIs need to be reserved for border coverage. For a high site that may lead to cross-cell coverage, a large reuse distance needs to be set independently. For PCI planning, however, 3GPP protocols require that the value of PCI/3 should be 0, 1, or 2 in each eNB
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Content Process for Planning the LTE Network Frequency Planning Cell ID Planning TA Planning PCI Planning Neighboring Cell Planning X2 Planning PRACH Planning
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Neighboring Cell Planning The
method or criteria of planning LTE neighboring cells is similar to that of planning GSM/WCDMA/CDMA.
The
actual configuration is different. There is no BSC or RNC in the LTE system. When an eNB cell is configured as neighboring cells of other eNBs, external cells must be added first, which is similar to the scenario where inter-BSC neighboring cells are configured on the BSC.
Neighboring
cells can be configured only after the corresponding cell information is
added.
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ANR and Neighboring Cell Planning Automatic Neighbor Relation (ANR) can automatically add and maintain
neighbor relations. The initial network construction, however, should not fully depend on ANR for
the following considerations: a. ANR is closely related to traffic in the entire network. b. ANR is based on UE measurements but the delay is introduced in measurements. After initial neighbor relations configured and the number of UEs increasing,
some neighboring relations may be missing. In this case, ANR can be used to detect missing neighboring cells and add neighbor relations, thus network performance improved.
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Content Process for Planning the LTE Network Frequency Planning Cell ID Planning TA Planning PCI Planning Neighboring Cell Planning X2 Planning PRACH Planning
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X2 Interface Planning X2
interface planning is based on neighbor relations, but this time the eNB relations are the input.
Some vendor releases support a maximum of 16 X2 interfaces and some others can support 32 X2 interfaces.
The
latest version of the ANR can automatically maintain X2 interfaces to solve the problems with missing X2 interfaces or configuration errors.
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Content Process for Planning the LTE Network Frequency Planning Cell ID Planning TA Planning PCI Planning Neighboring Cell Planning X2 Planning PRACH Planning
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PRACH Planning
› Sequence Root Index › Cyclic Shift › Preamble format
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PRACH Planning The random access preambles are generated from Zadoff-Chu sequences with zero correlation zone. There are 64 available preamble sequences in each cell. The 64 preamble sequences are first generated from a root Zadoff-Chu sequence using cyclic shift. The previously mentioned root corresponds to the logical root sequence index, which is sent to the UE through the SIB2 in DL SCH.
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PRACH Planning
The PRACH Bandwitdh is 6 PRBs (1.08Mhz). 72 subcarriers at 15Khz each. RA use 864 at 1.25Khz subcarriers within this Bandwidth , 26subcarriers as a guard to avoid interference with PUCCH/PUSCH The remaining 838 are root Zadoff-Chu sequences available for preamble construction( its is needed the cyclic shift also to generate them).
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Causes for Planning the Root Sequence Index There are 64 preamble sequences in each cell. The preamble sequence is
assigned by the eNB. To reduce interference of preamble sequences between neighboring cells, the root Zadoff-Chu sequence index need to be planned properly. The planning aims to assign the root sequence index for cells to ensure that
different preamble sequences are generated from neighboring cells through this index. In this way, interference of preamble sequences between neighboring cells can be reduced.
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Cyclic Shift
Ncs is related to the cell size, the smaller the Ncs the smaller the cell size. R <= c/2[(Ncs -1)(800us/839)-Delay spread] Assuming Ncs=13 and Delay Spread 5.2us the obtained cell radius is 1.08
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PRACH Planning
Preamble Format
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