Lte Cell Planning

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LTE CELL Planning

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Frequency Planning PCI Planning PRACH Planning TA Planning Neighbor Planning

Contents

HUAWEI TECHNOLOGIES CO., LTD. Huawei Confidential 4

Process for Planning the LTE Network

Detailed Planning

X2 Plannin

g

Cell Planning

Pre-Planning

Information Collection

NB Cell Planning

PCI Plannin

g

TA Plannin

g

ID and Name Planning

Coverage area, Radio environmentUser Number, Traffic Model, Service QoSAvailable frequency and bandwidth

Link BudgetNetwork DimensioningOutput: site number, ideal site location

Simulation based on surveyed site parameterOutput: Engineering parameter table, Coverage prediction, etc

General Process

Frequency

Planning

PRACH Planning


Frequency Planning1x1 frequency Planning

LTE system works on the same frequency band Frequency bandwidth utilizing is highX Interference occurs between the UEs on the edge of a cell

(use same resource)

1x3 frequency Planning LTE system works on the three frequency bandX Frequency bandwidth utilizing is Low Interference can be decreased (the three sector of one site working on three different

frequency band)


Frequency PlanningExample at Band 40 TDD


Frequency Planning

PCI Planning PRACH Planning TA Planning Neighbor Planning

Contents


PCI Planning In LTE systems, each cell has a physical cell identifier (PCI), enabling UE to

differentiate radio signals of different cells. In LTE systems, cells are grouped. primary synchronization code (PSC) and secondary

synchronization code (SSC), where the PSC has three values and SSC has 168 values, totaling

504 PCIs. The secondary synchronization sequence on the secondary synchronization

channel (SSCH) determines the cell group ID ( ) The primary synchronization sequence on the primary synchronization channel

(PSCH) determines the cell ID in a cell group. ( )


PCI PlanningPlanning principles

• Availability: The PCI planning must ensure minimum reuse layers and minimum reuse distance to avoid

possible conflict.

• Extensibility: The initial planning must consider the future capacity expansion to avoid frequent adjustment

of the initial planning result. Some PCI groups and some PCIs of in-use PCI groups can be reserved for future

capacity expansion.

Criteria for assigning the PCIs

• Reuse distance: The distance of two cells using the same PCI must meet the minimum reuse distance.

• Reuse layers: The number of reuse layers refers to the number of eNodeBs separating the two cells using the

same PCI.

• Under normal dual-antenna configuration, separating the PCIs of neighboring cells by modulo 3 of the PCIs

can separate the downlink RS symbols in the frequency domain, improving the accuracy of channel

estimation.


PCI Mod 3 – RS shift among neighbor cells

Frequency domain location of the RS is determined by value of PCI mod 3 If RS is shifted, then it will help for better performance under low load

RS location vs PCI mod 3:


PCI Mod 3 – RS shift among neighbor cells

RS pattern for different Antenna

configuration1 A

nte

nn

a

Po

rt

2 A

nte

nn

a

po

rts

4 A

nte

nn

a

po

rts

Antenna Port 0 Antenna Port 1 Antenna Port 2 Antenna Port 3

RE

No RS transmit for this antenna portRS transmitted or this antenna port

R1: RS transmitted by ant 1R2: RS transmitted by ant 2R3: RS transmitted by ant 3R4: RS transmitted by ant 4

For 4*4 MIMO, the RS of Antenna 3, 4 are

transmitted on OFDM symbols different to that of

Antenna 1, 2

No. of Antenna

port

No. of RS per Ant port per RB within

one Symbol

No. of RS for all Ant ports per RB

within one Symbol

No. of RS for all Ant ports in all RBs within

one Symbol

1 2 2 2* Total No. of RB2 2 4 4* Total No. of RB4 2 4 4* Total No. of RB


PCI Mod 3 Planning

We need to check again about PCI Mod3 result, prevent co-channel interference from same Mod3 result.

Before

After


PCI Conflict

PCI Collision PCI conflict is classified into PCI collision and PCI confusion

• A PCI collision occurs between two or more intra-frequency cells that use an identical PCI but are insufficiently isolated.

• In this case, UEs in the overlapping area of the two cells cannot implement signal synchronization or decoding.

PCI Confusion A PCI confusion occurs between a detected cell and a neighboring cell if the two cells have the same frequency and PCI and if the reference signal received power (RSRP) of the two cells reaches the handover threshold. The PCI confusion may lead to UE handover failures or service drops.

Case : eNodeB mistakenly considers that the detected cell is cell C and then initiates a handover to cell C. If the spot that the UE is on is not covered by cell C but cell B, a handover failure may occur. If two or more neighboring cells of a cell have the same frequency and PCI, there is a PCI conflict between these neighboring cells


PCI Conflict Detection Example


PCI Planning Example PCI group code from 120 to 167 for IBC eNodeB

PCI 360 to 503

Propose 25% buffer for future expansion (468 to 503 reserved for future)

PCI group code from 0 to 119 for Outdoor eNodeB

PCI 0 to 359

Propose 25% buffer for future expansion (270 to 359 reserved for future)

Planning rule To reduce PCI mod 3 result competition among neighboring cells to get better

performance under low load situation (referring to following 2 slides) To avoid PCI mod 30 result competition among neighboring cells to avoid SRS

interfere neighbor cell PRACH


How to Plan PCI ManuallyAssume there is a new site insert into existing areaStep 1. Mark the PCI Mod 3 results of existing cells on the map.

Step 2. Decide the PCI Mod 3 result for the new site on the map. Try the best to avoid same result cover same area.

Step 3. Choose un-used PCI for the new site following the PCI mod 3 result. New PCI shall not same to any neighbor cell.


Frequency Planning PCI Planning

PRACH Planning TA Planning Neighbor Planning

Contents


PRACH Planning – Basic Concept PRACH ( Physical Random Access Channel)

The channel used for transmitting the preamble sequence which is needed during UE

random access

ZC root Sequence a Zadoff Chu sequence has good self-correlation and cross correlation. There are 838 ZC root sequences, each 838 ZC root sequence is 839 bit The ZC sequence is used as the PRACH root sequence

Preamble sequence Preamble sequences of cells are generated through the cyclic shift of the ZC root

sequence. The number of cyclic shift is Ncs


Purpose of PRACH Planning Through the PRACH Planning, engineer allocate ZC root sequence indexes and specify Ncs

Values for cells according to the cell feature.

Different ZC root sequence indexes are allocated to generate different preamble sequence for

neighboring cells. In this way, the interference caused by the same preamble sequence of

neighboring cells is reduced.

There are 64 preamble for each cell. After logical allocation of ZC root sequence, the generated

64 preamble of neighboring cell will be different, so the interference will be reduced


Factor Affecting the Access Radius

Preamble format

Ncs 100 km329.5 km277.3 km114.5 km0

Maximum Cell RadiusPreamble Format

)267.6(04875.1 MDCS TrN

MDT CSNThe unit of r is km. The unit of is sec. The value of is subject to the cell radius and maximum delay extension.


PRACH Planning Example Preambles are generated from root sequence (Zadoff-Chu sequence) and its cyclic shift step (Ncs)

Cell Radius (r) 10 km for low speed cells

TMD indicates the maximum multi-path delay spread. For Huawei LTE products, TMD equals to 5 milliseconds

UE timing deviation is 2 milliseconds Ncs > 1.04875(6.67*10 +5+2) = 77. 03 According to the table Ncs for preamble format 0 to 3

~ The Ncs value is 93 , the Ncs configuration number 11


PRACH Planning Example The number of preamble that can be generated is calculated as follow :

That is each index can generate 9 preamble sequences, The number of ZC sequences is calculated as follows:

- -> in this case, 8 root sequence index are required to generate 64 preamble sequence . So the number of available root sequence index is 104 ( 0,8,16, …824) The available root sequence indexes are assigned to cells. The assignment principal is similar to those

PCI.

993

839

Num

89

64

m


PRACH Planning Example


Frequency Planning PCI Planning

PRACH Planning TA Planning Neighbor Planning

Contents


Tracking Area Planning Principles

A Tracking Area corresponds to the Routing Area (RA) used in UMTS and GSM/Edge

Radio Access Network (URAN and GERAN). The TA consists of a cluster of eNodeBs

having the same Tracking Area Code (TAC) The TA provides a way to track UE location in idle mode. UE will initials TAL update

once cross the TAL barder in idle mode and will not when cross TA boarder TAL information is used by the MME when paging idle UE to notify them of incoming

data connections One TAL can support up to 16 TAs, each TA supports maximum 100 eNodeB in one

MMETAC = Tracking Area Code (1~65533, and 65535) (0 and 65534 are reserved by 3GPP)

TAI = Tracking Area ID = MCC + MNC + TAC

TAL = Tracking Area List

1 TAL = up to 16 TAC

TAL value range: 0~ 65534

Max number of TALs per USN = 20000


TA Planning Principle A TA should be medium. The limitations by the EPC must be considered. When the suburban area and urban area are covered discontinuously, an independent

TA is used for the suburban area. TA should be planned for a continuous geographical area to avoid TA discrete

distribution. The paging area cannot be located in different MMEs. The mountain or river in the planned area can be used as TA boundary to reduce the

overlapping depth of two TAs. In this way, fewer location updates are performed on the

edge of TA. The LAC planning in the existing 2G/3G networks can serve as a reference for planning

TAC


TA Network Design

One TAL contains multiple TAC, with this design when UE in idle condition move to different TAC under one TAL there is no TAU. When MME want to deliver downlink packet data for that UE MME will send to latest TAC where the UE located. If the UE is unreachable MME will try to paging another TAC under one TAL until found. This design will take a time compare with the previous design.

TAL 1

S-GWInternet MME

TAC 1

TAC 2

TAC 3

TAC 4

TAL 2

TAC 5

TAC 6

TAC 7

TAC 8

Under One TAL no need

TAU

UE move to new TAL need

TAU

Last TAC is 8 but UE move

to TAC 7, MME will try paging another TAC under TAL2


Frequency Planning PCI Planning PRACH Planning TA Planning

Neighbor Planning

Contents


Neighbor Cell Planning LTE Network require quick hard handover, so the Neighboring cell Planning

is very important

LTE Neighboring cell planning content : Intra-Freq Neighboring cell, Inter-

freq neighboring cell, Inter-RAT neighboring Cell

LTE neighboring cell Planning principle : Geographically adjacent cell are used as neighboring cell in common scenario, bidirectional neighboring relationship is configured The distance between eNB is small (0.3 – 1km ) in urban areas, and therefore a large

number of neighboring cell are recommended If the adjacent cell of a cell in front of a lake, sea, or a wide road is also in front of the

lake, sea or a wide road, the adjacent cell is configured as its neighboring cell.


Neighbor Cell Planning The method of LTE neighbor cell planning is similar to neighbor planning of GSM/WCDMA/CDMA.

Currently, the planning method and tool for LTE are available.

The configuration is different from GSM/WCDMA/CDMA . There is no BSC/RNC in the LTE system.

When an eNB cell is configured as neighbor cells of other eNBs, external cells must be added first,

which is similar to the scenario where inter-BSC/RNC neighbor cells are configured on the BSC.

That is, neighbor cells can be configured only after the corresponding cell information is added.Site A

Site B

Site B

Site A

A1

A2

A3

B1

B2

B3

A1

A2

A3

B1

B2

B3

Neighbor Cell List(NCL)

Source TargetA B1A B2A B3B A1B A2B A3

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Copyright©2011 Huawei Technologies Co., Ltd. All Rights Reserved.The information in this document may contain predictive statements including, without limitation, statements regarding the future financial and operating results, future product portfolio, new technology, etc. There are a number of factors that could cause actual results and developments to differ materially from those expressed or implied in the predictive statements. Therefore, such information is provided for reference purpose only and constitutes neither an offer nor an acceptance. Huawei may change the information at any time without notice.

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