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2022/7/14
LTE Cell Planning
LTE RNP
2010-06
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HUAWEI TECHNOLOGIES CO., LTD.
Huawei Confidential
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, preplanning, detailed planning, and
cell planning. 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.
Frequency Cell ID
Planning Planning
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Information
Collection
TA
Planning
Preplanning
Detailed
Planning
Cell
Planning
PCI
Planning
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NB Cell
X2
PRACH
Planning Planning Planning
Page 3
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. In this case, the performance of the
UEs deteriorates. 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.
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 extent.

For segmental 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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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. The WCDMA cell ID is unique on each RNC, the GSM and
CDMA cell ID also is similar to the WCDMA cell ID.

The eNB involves the local cell ID, sector ID, and cell ID. It is advised to
plan the three IDs starting from 0, which 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, the IDs planned
must be different in principle.
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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.
TAI list

A list of TAIs that identify the tracking areas that the UE can enter without performing
a tracking area updating procedure. The TAIs in a TAI list assigned by an MME to a
UE pertain to the same MME area. Additionally, the TAIs in a TAI list assigned by an
MME to a CS fallback capable UE pertain to the same location area. In this case, the
defining of the relationship between the tracking area(s) and the location area(s) is
operator specific.

In LTE system, if an UE changes the TAs in the TAI list, TA update won’t be triggered.
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TA Planning Principles
A TA should be medium. The limitations by the EPC must be considered.
(Currently, each TA supports a maximum of 30 eNBs in the EPC. The number
may be adjusted later.)
When the suburban area and urban area are covered discontinuously, an
independent TA is used for the suburban area.
A TA should be planned for a continuous geographical area to prevent segmental
networking of eNBs in each TA.
The paging area cannot be located in different MMEs.
The mountain or river in the planned area can be used as the border of a TA to
reduce the overlapping depth 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 to that of scrambling codes in the
WCDMA system. PCI planning also aims to ensure the reuse distance.
Differences between a scrambling code and a PCI: The scrambling code ranges from 0
to 511 whereas the PCI ranges from 0 to 503. In addition, the protocols do not have
specific requirements for scrambling code planning. Therefore, only the reuse distance
needs to be ensured in scrambling code planning. For PCI planning, however, 3GPP
protocols require that the value of PCI/3 should be 0, 1, or 2 in each eNB.
The SCP can be used for PCI planning. The prototype version is available for the tool
specific to PCI planning but the tool needs evaluation.
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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.
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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 of planning LTE neighboring cells is similar to that of planning
GSM/WCDMA/CDMA. Currently, the planning method and tool for LTE
neighboring cells are available.

The actual configuration is different. There is no BSC 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. That is, neighboring cells can be configured only after the
corresponding cell information is added.

Currently, neighboring cells are configured on the eNB based on the local cell ID
instead of the cell ID used in previous systems. Therefore, the local cell ID and cell
ID should be consistent.
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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 the 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, that is, neighboring
cells belonging to different eNBs need to be obtained. In eRAN1.0, each
eNB can be configured with a maximum of 16 X2 interfaces. If there are
more than 16 X2 interfaces, the redundant X2 interfaces with the
remotest distance can be deleted. In eRAN1.1 and eRAN2.0, each eNB
can support 32 X2 interfaces.

The later 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 - Logical Root Sequence
Indexes

What is the logical root sequence index?

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. If less than 64 preamble sequences are
generated, the remaining are generated from the root Zadoff-Chu
sequence corresponding to the
logical index.

The previously mentioned root corresponds to
the logical root sequence index, which is sent
to the UE through the SIB2.
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PRACH Planning - Logical Root Sequence
Indexes

Zadoff-Chu sequence

A Zadoff-Chu sequence has good self-correlation and cross-correlation and is
defined as follows:
xu n  e

j
un( n 1)
N ZC
, 0  n  N ZC  1
N ZC indicates the length of the Zadoff-Chu sequence, and u indicates the
physical root sequence index. The relation between the logical root sequence
index and physical root sequence index is defined in protocols.

The preamble sequences are generated from the
sequence through the following cyclic shift.

The cyclic shift value is defined as follows:
xu ,v (n)  xu (( n  Cv ) mod N ZC )
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vN CS

Cv  0

RA
 RA 
dstart v nshift   (v mod nshift ) N CS
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root Zadoff-Chu
u th
v  0,1,...,  N ZC N CS   1, N CS  0 for unrestricted sets
N CS  0
for unrestricted sets
RA RA
RA
for restricted sets
v  0,1,..., nshift ngroup  nshift  1
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Causes for Planning the Root Sequence
Index
 There are 64 preamble sequences in each cell. The preamble sequence
is selected randomly or 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 Zadoff-Chu sequence index for cells
to ensure that different preamble sequences are generated for
neighboring cells through the index. In this way, interference of preamble
sequences between neighboring cells can be reduced.
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Factors Affecting the Access Radius

Preamble format
Preamble Format

Maximum Cell Radius
0
14.5 km
1
77.3 km
2
29.5 km
3
100 km
Ncs
N CS  1.04875  (6.67r  TMD  2)
The unit of r is km. The unit of TMD is sec. The value of
cell radius and maximum delay extension.
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N CS is subject to the
Page 25
How to Plan (Take a Low Speed Cell as an
Example)

Step 1: The Ncs value is determined by the cell radius. If the cell radius is
10 km, the Ncs value is 76.

Step 2: The value of 839/76 is rounded down to 11, that is, each index
can generate 11 preamble sequences. In this case, six root sequence
indexes are required to generate 64 preamble sequences.

Step 3: The number of available root sequence indexes is 139 (0, 6,
12…828).

Step 4: The available root sequence indexes are assigned to cells. The
assignment principles are similar to those for PCIs.
The planning method of a high speed cell is similar to that of a low
speed cell. The algorithm for determining available root sequence
indexes, however, is more complex.
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Thank you
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