LTE - RF Configuration Parameters
http://www.linkedin.com/pub/ray-khastur/36/965/b7a
PCI Planning
4G LTE - RF Configuration Parameters| Page 2
Purpose of PCI Planning Cell ID groups are adopted in the cell search procedure of the LTE system.
Specifically, a specific ID within a cell group is determined through the PSCH, and then a cell group ID determined through the SSCH. As specified in 3GPP protocol, the cell ID at the physical layer consists of cell
group ID and the ID within the cell group. There are 168 physical layer cell groups and each group consists of three IDs.
Therefore, totally there are 504 ( 0 to 503 ) PCIs.
4G LTE - RF Configuration Parameters| Page 3
PCI Overview •
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. They are searched based on the primary and secondary synchronization sequences. –
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.
4G LTE - RF Configuration Parameters| Page 4
PCI planning proposed for M LTE project • 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 – Huawei use GENEX U-Net to plan PCI
4G LTE - RF Configuration Parameters| Page 5
Port
1 Antenna
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
ports
2 Antenna
RE
No RS transmit for this antenna port RS transmitted or this antenna port
For 4*4 MIMO, the RS of Antenna 3, 4 are transmitted on OFDM symbols different to that of
ports
4 Antenna
Antenna 1, 2
Antenna Port 0
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 1
Antenna Port 2
Antenna Port 3
4G LTE - RF Configuration Parameters| Page 6
Page
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:
4G LTE - RF Configuration Parameters| Page 7
Page
How to Plan PCI manually Assume there is a new site insert into Cyber Jaya area. It is recommended to plan PCI after neighbor planning.
0
2
1
0 2
2
0
1
1
1 5 2
3 0
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.
4G LTE - RF Configuration Parameters| Page 8
PCI Mod3 Planning BEFORE
AFTER MODIFICATION
We need to check again about PCI Mod3 result, prevent cochannel interference from same Mod3 result.
4G LTE - RF Configuration Parameters| Page 9
What is Antenna Ports?
4G LTE - RF Configuration Parameters| Page 10
What is Antenna Ports?
4G LTE - RF Configuration Parameters| Page 11
PRACH Planning
4G LTE - RF Configuration Parameters| Page 12
PRACH • • • •
Random Access Channel (RACH) RACH procedure begins with a preamble (PRACH) PRACH resources assigned by eNB within PUSCH region PRACH preamble fits into 6 PRBs • Sufficient for timing estimation • Invariant with bandwidth for low complexity • Zadoff Chu sequence • Excellent correlation properties – Zero correlation zone for different cyclic shifts • Flat frequency spectrum • Different sequences provided first by different cyclic shifts, then by different root sequences • Multiple PRACH formats suitable for different cell sizes 4G LTE - RF Configuration Parameters| Page 13
PRACH Planning Principle • • •
There are 64 PRACH preambles in each LTE cell for Radom Access Preambles are generated from root sequence (Zadoff-Chu sequence) and its cyclic shift 838 root sequences are defined by 3GPP with length 839 – For example: for Cyclic Shift step 76, so-call Ncs = 76 • Each root sequence can generate Rounddown(839/76) = 11 sequences • To Generate 64 sequences, number of root sequences needed = Roundup(64/11) = 6 • So available root sequences = Rounddown (838/6) = 139 (Index 0, 6, 12, 18, …)
• • •
Root sequence needs to be reuse in the network Unlike UMTS, there isn’t Cell ID related scramble code used for PRACH in LTE system, collision may occur if same root sequence is planned for PRACH among nearby cells. Thus, we need to plan PRACH root sequence.
4G LTE - RF Configuration Parameters| Page 14
How to decide the cyclic shift step (Ncs) •
Ncs * Ts > TRTD + TMDS + Tdev – Ncs is mainly decided by Cell radius. – TRTD = 2*R/C = 2*R / (3*108 ) seconds = 6.67 * R (us) • TRTD is round trip delay, decided by cell radius R • C is light speed = 3*108 m/s – TMDS is Maximum time delay spread, 5us for Dense Urban and Urban – Tdev is UE timing deviation due to un-ideal synchronization to the downlink • Typically, assume TMDS = 5us, UE timing deviation = 2us – Ts is PRACH sampling period, and Ts = 800/839 [us] If planned cell radius = 9.8Km, then Ncs = 76
4G LTE - RF Configuration Parameters| Page 15
PRACH Ncs Selection •
•
Three dimensions needs to consider: – Cell radius – Margin (over dimensioning for unexpected transmission delay spread) – Root sequence reuse in multi-cell environment Ncs=76 for M project LTE PRACH Planning in KV area – For NLOS case, the transmission delay may be larger than LOS case, i.e., transmit distance larger than cell radius, margin is needed to keep robust – Root sequence is enough for multi-cell reuse: 6 root sequences are needed for each cell, then 838/6 = 139 unique sequences can be assigned for 139 cells – Same setting is just to simplify the network design. Ncs can also be set to different value according to coverage scenario.
4G LTE - RF Configuration Parameters| Page 16
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 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
Huawei will use GENEX U-Net for PRACH planning 4G LTE - RF Configuration Parameters| Page 17
PRACH Planning (I Project) •
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 HLTE 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
4G LTE - RF Configuration Parameters| Page 18
PRACH Planning (I Project) •
•
The number of preamble that can be generated is calculated as follow :
839 Num 9 93
The number of ZC sequences is calculated as follows:
64 m 8 9
4G LTE - RF Configuration Parameters| Page 19
PRACH Planning (I Project)
Input for eNodeB on PRACH Parameter are : 1) Cell Radius 2) Speed Flag 3) Start Root Sequence Index
4G LTE - RF Configuration Parameters| Page 20
