WPO-10 WCDMA Neighbor Cell, Scrambling Code and LAC Planning-47

WCDMA Neighbor Cell, Scrambling Code and LAC Planning

ZTE University

Content

Neighbor Cell Planning

Scrambling Code Planning

LAC Planning

Intra-system Neighbor Cell Planning

Neighbor cell configuration is closely related to system handoverThe following factors should be taken into consideration for neighbor cell configuration:

Neighbor cell countGeography topology structureCoverage scrambling, etc.

According to the principle of protocol, the maximum count of neighbor cell list is 31. So the amount of neighbor cells had better to be less than 20 (consider the affection of neighbor cell combination at the moment of soft handover).Neighbor cell should be inter configuration.After the system launches formally, optimization neighbor cell list can be counted according to soft handover counts.

Method of Intra-system Neighbor Cell Planning

196

200

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4

8

12

100104

108

124

128

132

16

20

24

88

92

96

220

224

228

76

80

84

112

116

120

208

212

216

64

68

72

160

164

168

148

152

156

52

56

60172

176

180

40

44

48

28

32

36

136

140

144

184

188

192Different cells under the same station must be neighbor cell for each other.

The two layers of cells towards current sector should be set to be neighbor cells.

The cell on the first layer back towards current sector can be set to be neighbor cell.

The neighbor cell of current cell (scrambling code 4) can be set to (8, 12, 32, 48, 88, 92, 100, 108, 112, 128, 140, 144, 156, 196, 200, 204, 208, 220)

Inter-system Neighbor Cell Planning

For inter-system neighbor cell planning, the common method aimed 2G is:

Neighbor cell configuration can be set according to the different interoperation policy for 2/3G.When the internal coverage of WCDMA network is discontinuous, the interoperation between the whole network and 2G system should be taken into consideration. The method of 2G neighbor cell configuration in the whole network is the same as the method of intra-system neighbor cell configuration. Besides, the traffic congestion of neighbor cell also should be taken into consideration.When the coverage of WCDMA network is continuous, the system handover only occurs at the edge of WCDMA system and 2G system. Neighbor cell configuration is only needed by border station. The following principles should be taken into consideration:

The cells under the same station with same direction should be set to neighbor cells.Prefer to chooseGSM900.Not distributing neighbor cell for congestible GSM cells as far as possible.

Aircom Realization of Neighbor Cell Planning - 1

The Possible Problem of Neighbor Cell Planning

Content



LAC Planning

OVSF Code Scrambling Code

Data Bits

After-frequency-spreading

chip

The Relationship Between Frequency-spreading and Scrambling Code

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Q

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1 0

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Principle of WCDMA Downlink Scrambling Code

The WCDMA system adopts the CDMA technology, and different BSs or different sectors of a BS are differentiated by scrambling.The length of downlink scrambling code sequence is 3,840,000 chips, with a total of 218 – 1 = 262,143 scrambling sequences. However, the system only uses these scrambling sequences numbered from 0 to 24,575. The normal mode uses the previous 8192 scambling code.

Downlink Scrambling Code Grouping

The 8,192 scrambling code that are commonly used fall into 512 sets, with each set including one primary scrambling code and 15 secondary scrambling code. 512 primary scrambling codes are used for real network planning. Each cell assigns only one primary scrambling code. P-CCPCH, P-CPICH, PICH, AICH, AP-AICH, CD/CA-ICH, CSICH and S_CCPCH (carrying PCH) in one cell always use the same primary scrambling code to transmit. The other downlink physical channel can use primary scrambling code or secondary scrambling code in the same set with primary scrambling code.Totally 512 codes can be divided into 64 groups, each group contain 8 primary codes. This can be used for cell searching.

Scrambling Code and Cell Searching

UE is turned on and starts searching network;Synchronizing with SCH of the cell which UE locates in;

Through Primary Synchronous Code (PSC) of P-SCH, slot synchronization can be realized;Through S-SCH, frame synchronous can be realized. And the scrambling code group of cell can be identified.

Through calculating with P-CPICH, downlink scrambling code can be obtained;Through primary scrambling code of cell, detecting BCH (P-CCPCH) and reading system message, the basic information of cell can be obtained.Listening the paging information on PICH and PCH (S-CCPCH);UE enters the state of IDLE;UE prepares to make location update;After completing location update, the location information of UEis registered to network. And then UE enters the state of standby and can make callings and be called.

Step 1: Cell Search and Slot synchronization

…

Numbering Rule of Downlink Scrambling Code

Downlink scrambling codetotals 218-1 (0..262142)

No. 511 scrambling code group

81768177

8191

8176 : primary scrambling code8177 : secondary scrambling code…8191 : secondary scrambling code

No. 510 scrambling group

81608161

8175


No. 504 scrambling group

80648065

8079


…


112113

127

8176: primary scrambling code8177: secondary scrambling code…8191 : secondary scrambling code


1617

31



01

15


No.0 scrambling code cluster

No. 63 scrambling code cluster… …

Step 2: Frame synchronization and code-group identification

Step 3: Confirm Scrambling Code Number

CPICH is pre-defined symbol sequence. Frequency spreading factor is 256 (Cch,256,0).Use primary scrambling code to scramble.UE decodes CPICH according to the eight primary scrambling codes in the definitizedscrambling code cluster. The primary scrambling code decoded correctly is the scrambling code of the cell.

Obtain Broadcast Message by Decoding P-CCPCH

P-CCPCH includes current SFN and system broadcast message.Frequency spreading factor of P-CCPCH is 256 (Cch,256,1).P-CCPCH uses primary scrambling code to scramble.UE can decodes BCH bone by P-CCPCH through primary scrambling code to obtain system broadcast.

Principle of Scrambling Code Planning

Scrambling code multiplexing needs to guarantee the cells with the same primary scrambling code have an adequate distance to make the coverage of received signals in another cell with the same primary scrambling code lower than the threshold level.

10log( max( , ))ij i jL R R α−

基站 i 基站 jLij

Ri Rj

小区i

小区j

passloss10log( max( , )) 10log(max( , )) ij i j i jL R R R Rα α− − > Δ

passloss

10max (1 10 )reuseL R α

Δ

> ⋅ +

Where, α is the path loss coefficient, Δpassloss is the pass loss difference. indicates the minimum pass loss of the remote BS signal and indicates themaximum pass loss of the main BS signal. Through the above, the formula of scrambling code multiplexing minimum distance is:

10log(max( , ))i jR R α

Cluster-Based Scrambling Multiplexing Method

NRLreuse 3min=

22 jijiN ++=

2

102min

2max 101

3 ⎟⎟⎠

⎞⎜⎜⎝

⎛+≥

Δ

αpassloss

RR

N

The number of station, N, in one scrambling multiplexing cluster is:

Scrambling Multiplexing Distance of Typical Conditions

Typical base station radius in dense urban area is 300 to 600 meters. The typical value of path loss coefficient is 4. Pilot frequency strength of cell border, Ec, is -85dbm. Considering that the path loss difference is 30db, so the pilot frequency strength (Ec) from the same scrambling code cell to the border of this cell is -115dbm. So N is equal to 61 and the minimum multiplexing distance is 4km. Typical base station radius in general urban area is 600 to 1200 meters. The typical value of path loss coefficient is 3.5. Pilot frequency strength of cell border, Ec, is -90dbm. Considering that the path loss difference is 25db, so thepilot frequency strength (Ec) from the same scrambling code cell to the border of this cell is -115dbm. So N is equal to 61 and the minimum multiplexing distance is 8.12km.Typical base station radius in suburb is 1200 to 3000 meters. The typical value of path loss coefficient is 3. Pilot frequency strength of cell border, Ec, is -95dbm. Considering that the path loss difference is 20db, so the pilot frequency strength (Ec) from the same scrambling code cell to the border of this cell is -115dbm. So N is equal to 75 and the minimum multiplexing distance is 18km.Typical base station radius in rural is 5000 to 10000 meters. The typical value of path loss coefficient is 2.5. Pilot frequency strength of cell border, Ec, is -100dbm. Considering that the path loss difference is 20db, so the pilot frequency strength (Ec) from the same scrambling code cell to the border of this cell is -120dbm. So N is equal to 75 and the minimum multiplexing distance is 75km.

Recommended Values of Scrambling Multiplexing DistanceArea BS Radius

(km)Scrambling Multiplexing Distance (km)

Maximum BS Number in a Cluster

4 61

52

6773

8.12

1875

Maximum Number of Scrambling Codes in Use (Take the 3-Sector BS as an Example)

Dense urban area

0.3～0.6 183

Common urban area

0.6～1.2 156

Suburb 1.2～3 201Rural area 5～10 219

For a 3-sector BS, two sectors within the scrambling multiplexing distance may

have no joint coverage scope due to the sector coverage direction, so one

scrambling code can be multiplexed. Therefore, in the case of three sectors,

the actual number of distributed scrambling codes within the scrambling

multiplexing distance can be smaller than the total sector number.

Scrambling Code Planning Principle

To multiplex the same scrambling code, the multiplexing BSs should have an adequate physical distance between them.Scrambling planning should take the features of stepwise networkconstruction into full consideration, and reserve a certain number of scrambling codes, to satisfy demands of indoor distributed systems and network capacity expansion.It is necessary to reserve a certain number of scrambling codes for border BS coordination.

Common Scrambling Distribution

Scrambling Distribution for Micro Cells and Indoor Distributed Systems

Border BS Scrambling Distribution

Example of distribution planning

0~218 219~318 319~511

Scrambling Code Planning – Create Scrambling Code Schemas

Set the scrambling code group and scrambling code in the scrambling code planning. Click Add button to create a new scrambling code schema. Choose the needed scrambling code group and scrambling code and then click OK button to save the schema.

Scrambling Code Planning – Choose Base Station Set

Choose the base station filter in the scrambling code planning

Scrambling Code Planning –Set Scrambling Code Planning Parameters

Scrambling Code Planning –Set Scrambling Code Planning Parameters

Neighbouring cells: This parameter indicates whether to choose considering neighbor cells and 2nd neighbor cells. The default value is to choose check all of them.Adjacent cells: This parameter indicates whether to choose considering adjacent cells, confirms the maximum number of adjacent cells involved in the algorithm calculating. The principle of judgment according to which Aircom judges whether a cell is adjacent cell is that all the cells in the prediction radius of the cell are the adjacent cells. The default value is Consider Adjacent cells. And the maximum number of adjacent cells is 14.Code reuse distance: This parameter indicates whether to choose considering scrambling code multiplexing distance and minimum scrambling code multiplexing distance. Nearby cells is a parameter of Aircom scrambling code planning algorithm. The principle of judgment is that all the cells within the minimum scrambling code multiplexing distance are the Nearby cells. The default value is Consider code reuse distance. The setting of minimum scrambling code multiplexing distance has relationship with radio environment.Select carriers for planning: choose carrier wave of scrambling code planningResolution(m): The precision of this parameter is usually identical with the precision of the map.Consider other cells under the same NodeB: This parameter indicates whether to assign the unique scrambling code to all the cells in the same NodeB. This parameter can insure the scrambling codes of different cells under the same station are different on condition that the multiplexing distance hasn’t been set or the cells under the same station are on the different physical location such as RRH.

Scrambling Code Planning –Scrambling Code Assignment Policy

Scrambling Code Planning –Scrambling Code Assignment Policy

Filter: This parameter lists the station set of scrambling code planningState: This parameter sets the state of every base station set in the scrambling code planning. There are three kinds of states. Plan means all the base stations in the set are involved in the scrambling code assignment; Read Only means the assigned cell scrambling code in the set will be taken into consideration, but won’t be changed; Ignore means the cell scrambling code in the set will not be taken into consideration.# Code Groups: This parameter appoints the scrambling code group count which can be assigned to the cell and its neighbor cells.# Code: This parameter appoints the scrambling code count which can be assigned to the cell and its neighbor cells in the scrambling code group.Minimise: When the numbers of scrambling code group and scrambling code of the cell and its neighbor cells are beyond the value of # Code Groups and # Code, the scrambling code planning tool will choose the scrambling code assignment principle of minimizing the number of # Code or #Code Groups according to the value of #Code or #Code Groups.Code Schema: Choose the scrambling code schema which can be assigned.Cell Property: This parameter can set scrambling code assignment principle for each cell.

Scrambling Code Planning –Scrambling Code Reporting

Scrambling Code Planning –Scrambling Code Reports

The reports include the following contents:The scrambling code group and scrambling code assigned to each cell.The scrambling code group and scrambling code assigned to neighbor cells of each cell.The scrambling code group and scrambling code assigned to adjacent cells of each cell.The scrambling code group and scrambling code assigned to nearby cells of each cell.The scrambling code group and scrambling code assigned to the other cells which are under the same NodeB with the cell.

Content



LAC Planning

LAC Planning

LAC, RAC and URA are an area composed by one or a certain amount of cells. Each cell only belongs to an unique LAC and RAC. RAC is the subset of LAC. CS and PS domain of CN locating UE’s location according to LAC and RAC. CS and PS domain of CN paging the appointed UE by sending paging message to LAC registered to UE and all the cells in RAC. The optimization of LAC and RAC involves a large number of database updating which certainly affects network operation. So LAC and RAC are usually optimized and adjusted based on the technical characteristics, service model and production performance of WCDMA before the network commercial. However, it is not suitable for adjusting frequently. The updateof LAC, RAC an URA, paging strength and system capacity is the reference index to define the size of LAC and RAC.

RNC Planning

The principle of RNC setting is shown below:RNC setting follows the principle of high-capacity, high processing performance and high-reliability;RNC setting should overall consider the factors of the base station number, cell number, sector number, bandwidth of lub interface, BHCA and traffic flow. It should also reserve proper transmission interfaces and capacity of base station number, cell number, sector number and traffic flow for convenience of base station expansion.The site address of RNC is better to be deployed with switch bureau in order to simplify the connection of lu interface.The geographical position of each RNC’s base stations should be relatively centralized to avoid the multiple geographical cross with the other RNC’s base stations and decrease unnecessary handover between two different RNCs.Try to make the total traffic volume of each RNC to be somethingeven and the load to be something balanced;Properly choose the border area between RNCs and try to make the switch area avoid dense areas and main traffic roads.The lur connection can be established inside the local network inorderto realize the soft handover.

LAC Planning

LAC indicates the area where user can move in and need not update the data in VLR. For a location CS service, CN can use location area to launch CS service within one or more cells. Forthe paging of services, TMSI can be assigned to mobile phone. TMSI is unique in a certain LAC. LAC is the abbreviation of Location Area Code. The identifier of LA (Location Area) is LAI which is composed with MCC, MNC and LAC.RA indicates the area where user can move in and need not update the data in SGSN. RA can include one or more cells. RA is usually in an LA. For PS service, CN uses RA to generate the paging of PS services. The identification related to PS, P-TMSI, is used to assign the unique mobile phone in the RA. RAC is the abbreviation of Route Area Code. The identifier of RA (Routing Area) is RAI. RA is in LA and RAI is composed with MCC, MNC, LAC and RAC.

LAC Planning

Take the CS paging as the example. When a mobile phone is paged, CN will send paging requests to all the base stations in the range of LAC through RNC. One LAC may cover tens of or hundreds of cells. So the amount of paging information messages sent to RNC may be surprisingly large. Because NodeB must send paging request to mobile phone through the limited PCH channel, too large range of LAC may bring the paging over loading of NodeB which causes signal congestion and paging information loss. However, too small range of LAC brings large amount of LAC area borders. UE in the borders are easy to make location update between different LACsfrequently. When paging arrives and UE just moves rapidly into another LAC and makes location update, UE cannot receive the paging message sent to the original LAC. This may cause that called can not be connected.

LAC Planning

The division of LAC/RAC should follow these principles:Take the geographical border as the border of LAC/RAC;The border of LAC/RAC should locate in the area with low trafficflow;The traffic flow of each LAC/RAC is balanced.Try to avoid that the borders of several LAC/RAC are in the samesmaller area in order to avoid that MS makes location update continuously between the LACs in a smaller area. The amount of cells in an LAC depends on the paging capacity, frequency of update and traffic flow distrubution. Setting the range of LAC too large causes the incensement of paging load, signal congestion and paging information loss .Setting the range of LAC too small causes the incensement of LAC area borders and call completion rate because of frequent location updates.RAC is usually the subset of LAC. Because the paging of PS domain is generated from network, the load of paging is smaller than in CS domain. Under normal conditions, the planning of RAC and LAC are the same. With the incensement of network data flow,the RAC planning can be adjusted flexibly.

LAC Planning

Setting of location update cell should take the followings into consideration:

During the setting procedure of LAC range, the upper limitmainly depends on the paging capacity of each cell and the lower limit mainly depends on the frequency of location updates; Choosing the LAC border should consider the geographical characteristic and terminal distribution. The purpose is to reduce the frequency of location update. We usually choose the area with minimum handover probability. The effects of load increasing should be considered for LAC and RAC planning. The base station using multiple carrier should belong to the same LAC.

LAC >= RAC. RAC may be reduced along with the increase of PS service.

LAC Planning

In 3G network, paging occurs on PCCH. Logic channel, PCCH, is mapped to PCH. At last, the transmission occurs on SCCPCH. The protocol, 34.108, specifies the parameters of PCCH. There two kinds of transmission format on PCCH, 240bit/10ms and 80bit/10ms. The general format is 240bit/10ms. According to the definition in the protocol, the length of IMSI-GSM-MAP is 60bits. Considering of choosing bits and paging reason, etc. we can conclude that one PCCH can support the information of three IMSIs. The length of TMSI-GSM-MAP or PTMSI-GSM-MAP is 32bit. One PCCH frame of 10ms can include five TMSI or PTMSI paging at most .

LAC Planning

According to the format of PCCH/PCH, one PCCH/PCH can bear 240bit every 10ms. 5TMSI calling messages are supported in 10ms frame. One PCH can send 500 calling messages per second and 1800000 per hour. To reduce calling blocking rate, we set the value of calling capacity of the LAC as 50% of the theoretical value.

Example of Current Network Load Statistics

Take the current network statistics as the example to research whether the LAC division can meet the request of paging. The following figure shows the paging number of every RNC.

ZTE RNCID ZTE LACID RNC/Total 3G Traffic Ratio Paging load(number)

ZRNC101 1011 20.00% 161996

ZRNC102 1021 16.90% 136886.6

ZRNC103 1031 14.28% 115665.1

ZRNC201 2011 17.76% 143852.4

ZRNC202 2021 16.11% 130487.8

ZRNC203 2031 14.95% 121092

Total paging messages(number) 809980 100.00% 809980

Different Paging Times of RNC Corresponding to Paging Load

RAN paging times 1 2 3 4

Paging capability of one LAC in BH 900000 450000 300000 225000

ZTE LACID Paging load (number) Paging load (ratio)

1011 161996.0 18.00% 36.00% 54.00% 72.00%

1021 136886.6 15.21% 30.42% 45.63% 60.84%

1031 115665.1 12.85% 25.70% 38.56% 51.41%

2011 143852.4 15.98% 31.97% 47.95% 63.93%

2021 130487.8 14.50% 29.00% 43.50% 57.99%

2031 121092.0 13.45% 26.91% 40.36% 53.82%

Capacity Expansion Planning of LAC During Network Maturity

ZTE RNC ID ZTE LAC ID RNC/Total 3G Traffic Ratio

Paging load(number)

ZRNC101 1011 20.00% 1,600,264

ZRNC102 1021 16.90% 1,352,223

ZRNC103 1031 14.28% 1,142,589

ZRNC201 2011 17.76% 1,421,035

ZRNC202 2021 16.11% 1,289,013

ZRNC203 2031 14.95% 1,196,198

Total paging messages(number) 8,001,322 100.00% 8,001,322

Paging Load on Different RNCs

RAN paging times 1 2 3 4

Paging capability of one LAC in BH 900000 450000 300000 225000

ZTE LACID Paging load (number) Paging load (ratio)

1011 1,600,264 177.81% 355.61% 533.42% 711.23%

1021 1,352,223 150.25% 300.49% 450.74% 600.99%

1031 1,142,589 126.95% 253.91% 380.86% 507.82%

2011 1,421,035 157.89% 315.79% 473.68% 631.57%

2021 1,289,013 143.22% 286.45% 429.67% 572.89%

2031 1,196,198 132.91% 265.82% 398.73% 531.64%

Case

Suppose that the parameter, CN paging number, is set to be 2. So we assign 2 LACs to to each RNC (except ZRNC201). And in order to meet the requirement of service grown, we adjust the parameter, PAC paging number, from 4 to 1 according to call success rate and call blocking rate. As for ZRNC201, considering that the distribution of 2G traffic flow is just the 3G traffic flow in future, we assign 3 LACs for ZRNC201.To reduce the effect of LAC area changes to network, we should divide the network into 13 LACson the initial network construction. For the effect of adjusting paging parameter from 4 to 1 to network, we can research and analyze it by correlative KPI statistics.

WPO-10 WCDMA Neighbor Cell, Scrambling Code and LAC Planning-47

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