LTE RADIO PLANNING CONCEPT
1. Frequency planning 2. PCI Planning 3. PRACH Planning 4. TAL/TAC Planning 5. Neighbor Planning
Process for Planning the LTE Network Coverage area, Radio environment User Number, Traffic Model, Service QoS Available frequency and bandwidth
Information Collection
Link Budget Network Dimensioning Output: site number, ideal site location
Pre-Planning
General Process Simulation based on surveyed site parameter Output: Engineering parameter table, Coverage prediction, etc
Detailed Planning
Cell Planning
Frequency Planning
ID and Name Planning
TA Planning
PCI Planning
NB Cell Planning
X2 Planning
PRACH Planning
PCI PCI Planning Planning
How to Distinguish Between Different Cells? (1) • 504 possible reference signals: • → 3 various orthogonal sequences – mapped to the physical layer cell ID •
•
→ 168 various pseudo-random sequences – mapped to the cell ID groups
→ 168 x 3 = 504 sequences in total
• → subject to network planning
eNode B
U E
eNode B
PCI Planning - Introduction
Physical Cell identification and Global Cell ID identification Physical Layer Cell ID (PCI) – – – –
The sequence to generate the Reference Signal depends upon the PCI Short repetition cycle of 1 ms Limited to 504 values so not unique Careful assignment needed because a UE shall never receive the same value from 2 different cells
Global Cell ID (ECGI)
• • • •
E-UTRAN Cell Global identifier Part of SIB 1 SIB 1 is sent once every 20ms Unique in the network: constructed from MCC, MNC en E-UTRAN Cell Identifier
ECGI ( E-UTRAN Cell Global Identifier) is used to identify cells globally. It can change (if necessary) once every 80ms but then it is repeated 3 times before it can be changed again, Cell ID = mod(ECI,256)
PCI Plan Sample Sector 1 Sector 2 Sector 3
…. 422 335
376 379
377 380
420 423
421 424
422 425
….
….
375 378
….
….
…. 421 334
….
420 333
….
….
5
480 483
481 484
482 485
….
161 - 167
4
….
141 - 160
3
….
126 - 140
2
….
111 - 125
1
….
1 - 140
0
….
SSS/PSS
501
502
503
Border East
Allocation For
Macro (General) Border Area WEST/NORTH
Border West
Border Area EAST/SOUTH
Id = 0
Indoor (General)
Id = 2
Id = 6
Id = 8
Spare
Id = 1 Id = 3 Id = 5
Id = 7 Id = 9
Id = 11 Id = 4
Id = 10
PCI Macro : 3 – 422, 3 sites out of the range. PCI Indoor : 423 – 482, 10 sites out of the range.
PciConflictAlmSwitch
PCI Conflict PCI conflict is classified into PCI collision and PCI confusion
PCI Collision
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.
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
1 Antenna Port
PCI Mod 3 –Reference Signal RS pattern for different Antenna configuration
No. of Antenna port
No. of RS per Ant port per RB within one Symbol
1 2 4
2 2 2
No. of RS for all Ant No. of RS for all Ant ports ports per RB within in all RBs within one one Symbol Symbol 2 4 4
2* Total No. of RB 4* Total No. of RB 4* Total No. of RB
2 Antenna ports
RE
No RS transmit for this antenna port
For 4*4 MIMO, the RS of Antenna 3, 4 are transmitted on OFDM symbols different to that of Antenna 1, 2
4 Antenna ports
RS transmitted or this antenna port
R1: RS transmitted by ant 1 R2: RS transmitted by ant 2 R3: RS transmitted by ant 3 R4: RS transmitted by ant 4
Antenna Port 0
Antenna Port 1
Antenna Port 2
Antenna Port 3
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:
Conclusion PCI Planning
How to Plan PCI manually Assume there is a new site insert into current LTE network It is recommended to plan PCI after neighbor planning.
0
2 1
0 2
2
0
1
1
1
3 0 5 2
2
0 1
4 1
2
0 1
Note: Please use PowerPoint “Slide Show” mode to see the animation to play the steps.
Step 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. Step 4. Check the PCI mod 30 result with neighboring cell.
Automatic PCI allocation process
PRACH Planning
Intra-Cell Interference CellAlgoSwitch RACHCfg RACHCfg RACHCfg RACHCfg RACHCfg RACHCfg
RachAlgoSwitch PwrRampingStep PreambInitRcvTargetPwr MessageSizeGroupA PrachFreqOffset PrachConfigIndexCfgInd PrachConfigIndex
How can multiple terminals perform random access attempt at the same time without collision?
eNodeB
UE 1
UE 2
UE 3
Solution ?
64 different orthogonal Preambles available in each cell obtained by cyclic shift of a Zadoff-Chu sequence If however collision is happening (2 UEs using the same preamble) -> contention resolution process
Physical Random Acces Channel (PRACH) PRACH •
UE sends the preamble to the network on PRACH:
•
PRACH occupies 6 resource blocks (of 180 kHz) in a subframe (or set of consecutive subframes) reserved for sending random access preamble to the network.
•
PRACH reserved PRBs cannot be used by PUSCH i.e. they are out of scope for scheduling for data transmission
•
Within 1 ms subframe, PRACH divided into Cyclic Prefix, Preamble and Guard that length is depend on preamble format as below
Multiplexing of PRACH with PUSCH and PUCCH PRACH slot Duration( e.g. 1ms)
PRACH Location •
Total UL Bandwidth
PUCCH PRACH
PRACH bandwidth (6 PRBs)
PRACH
PUSCH PRACH slot period
PUCCH
Time
UL PRACH is orthogonal with the data in PUCCH and PUSCH (reserved
resources)
The location of those resource blocks is dynamically defined by 2 RRC Layer Parameters (PRACH Configuration Index and PRACH Frequency offset). The UE may learn the configuration from the system information(SIB2)
PRACH Planning
Step 1: Determine Ncs value by the cell radius. (E.g. Assume the cell radius is 9.8 km, take Ncs value 76)
Step 2: The value of 839/76 is rounded down to 11, that is, each index should generate 11 preamble sequences. In this case, 6 (64/11) root sequence indexes are required to generate 64 preamble sequences.
Step 3: The number of available root sequence indexes is 839/6=139 (0, 6, 12,…,6*n,…, 828)
Step 4: The available root sequence indexes are assigned to cells. The reuse distance shall be as far as possible
CellName TNG219ML_PDKARENLRNGNML1 TNG219ML_PDKARENLRNGNML2 TNG219ML_PDKARENLRNGNML3 JKS276ML_BALAIKARTINIML1 JKS276ML_BALAIKARTINIML2 JKS276ML_BALAIKARTINIML3 BOO063ML_RADARAURIML1 BOO063ML_RADARAURIML2 BOO063ML_RADARAURIML3 JKS103ML_GUNTURML1 JKS103ML_GUNTURML2 JKS103ML_GUNTURML3 L.RA.GrpB.Att L.RA.GrpB.Resp L.RA.GrpA.Att L.RA.GrpA.Resp L.RA.Dedicate.Att L.RA.Dedicate.Resp
PCI 78 79 80 120 121 122 252 253 254 237 238 239
RSI 78 79 80 6 186 186 768 253 254 618 624 616
TAL/TAC Planning
TAC Planning •
When planning borders between TAC and TA lists, the following general rules apply: –
TAC and TA lists should be planned so that areas with frequent TAC update signaling are located in low mobility areas. This makes it easier for the eNodeB to cope with the additional signaling caused by the TAL update procedure.
–
TAC and TA list should be planned so that the need for TAC updates (TAL border) is minimized. This is accomplished by considering how users travel within the network. Busy roads, railways, and so on, should cross as few TA list borders as possible.
–
If operator have 2G/3G network, can consider referring to 2G/3G network LAC border as LTE TAC border due to 2G/3G LAC was optimized. Hence, TAC should align with the GSM/UMTS LAC boundary. Multiple TACs can correspond to one LAC. In fact, one TAC can correspond to one LAC.
–
Otherwise, extra LAUs may be caused by CSFB calls, increasing the CSFB delay. For example, if a TAC corresponds to multiple LACs, a 1s to 2s LAU delay may occur after a CSFB is performed.
–
In project usually TAC correspond to LAC border & TAL correspond to RNC ID border.
TAL and TAC Planning
TAC is designed based on 3G LAC border LAC is referred to ensure the TAC is not overlapped with others 3G LAC border
Tracking Area should be planned relatively large (100 ENodeB, 3 cell/ENodeB. It is proposed to have 40 ENodeB for each Tracking Area
TAC range = 1 ~ 65533, (0 and 65534 is already reserved by 3GPP)
TAL = Tracking Area List TAL range = 0 - 65534 1 TAL = 8 TAC (support up to 16 TAC, TAC size should be reduced if the paging load is high)
TAL would be based on existing RNC border TAI (Tracking Area ID) = MCC – MNC - TAC
MME Paging message
TAC = 1
TAC = 3
TA list TAC 1 TAC 2 TAC 4
TAC ID = 1000 TAC ID = 1002
MNC
TAC
TAI
510
10
1000
510 – 10 – 1000
TAC = 4
TAL ID = 1 TAC ID = 1001
MCC
TAC = 2
RNC Border
TA Network Design S-GW
Internet
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.
MME
UE Under move One to new TAL TAL no need needTAU TAU
TAL 1
TAC 2
TAC 1
TAC 4 TAC 3
TAL 2
Last TAC is 8 but UE move to TAC 7, MME will try paging another TAC under TAL2
TAC 6
TAC 5
TAC 8 TAC 7
Neighbor Planning
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 Neighbor Cell List (NCL)
A1
A3
Site B B3
A2
B1
B2
Site A A1
A3
Site B A2
B3
B1
B2
AnrSwitch
Source A A A B B B
Target B1 B2 B3 A1 A2 A3
EutranExternalCell EutranIntraFreqNCell
