PCI Planning for LTE

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One frame (10 ms)

PSS SSS

6 resource blocks

(72 center sub-carriers)

Two

synchronization signals

synchronization signals

synchronization signals

synchronization signals

transmitted once every 5 ms

Primary Synchronization Signal (PSS)

◦ Subframe #0 and #5

◦ Mapped on 72 subcarriers in the middle of the band

◦ OFDM symbol #6

Secondary Synchronization Signal (SSS)

◦ Subframe #0 and #5

◦ Mapped on 72 subcarriers in the middle of the band

One frame (10 ms)

PSS SSS

6 resource blocks

(72 center sub-carriers)

Two

synchronization signals

synchronization signals

synchronization signals

synchronization signals

transmitted once every 5 ms

Primary Synchronization Signal (PSS)

◦ Subframe #1 and #6

◦ Mapped on 72 subcarriers in the middle of the band

◦ OFDM symbol #2

Secondary Synchronization Signal (SSS)

◦ Subframe #0 and #5

◦ Mapped on 72 subcarriers in the middle of the band

Detection of carrier frequency Detection of SCH symbol timing Identification of cell ID (0-2)

Detection of radio frame timing

PSS

Read System Info & RS

◦

timing

◦

sequence

◦

frequency shift

Detection of radio frame timing

Detection of cell ID group (0-167) ⇒ PCI Detection of MIMO & CP configuration

PSS signal

◦

3 different sequences called Physical-Layer Identities

(0-Group #0 Group #0Group #0 Group #0 PCI PCIPCI PCI₀₀₀₀ PCI PCIPCI PCI₂₂₂₂ PCI PCI PCI PCI₁₁₁₁ Group #1 Group #1 Group #1 Group #1 PCI PCI PCI PCI₃₃₃₃ ID ID ID ID₅₅₅₅ PCI PCI PCI PCI₄₄₄₄ Group #2 Group #2 Group #2 Group #2 PCI PCI PCI PCI₆₆₆₆ PCI PCI PCI PCI₈₈₈₈ PCI PCIPCI PCI₇₇₇₇ Group #167 Group #167Group #167 Group #167 PCI PCI PCI PCI_501501501501 PCI PCI PCI PCI_503503503503 PCI PCIPCI PCI_502502502502

◦

3 different sequences called Physical-Layer Identities

(0-2)

SSS signal

◦

168 different sequences called Physical-Layer

Cell-Identity groups (0-167)

168 Physical-Layer Cell-Identity groups with 3

Physical-Layer Identities per group

For each cell, PCI_i = 3S_j + P_k

◦ i = 0 … 503

◦ j = 0 … 167group

◦ k = 0 … 2 ID

The sequence for the SSS signal is generated as follows:

◦ m₀ = m’ mod 31

◦ m₁ = [m₀+INT(m’/31)+1] mod 31

◦ m’ = S_j+q(q+1)/2

◦ m’ = S_j+q(q+1)/2

◦ q = INT((S_j+q’(q’+1)/2)/30); q’ = INT(S_j/30)

Simulations hint that the following combinations at adjacent cells will

give bad performance, i.e. long synchronization times and high interference:

◦ Same ID, i.e. same k

◦ Same m₀

◦ Same m₁

For example, PCI_i = 0 ⇒ PCI_i = 3, 6, … 498, 501 and 1, 2, 90, 91, 92,

177, 178, 179, 261, 262, 263, 342, 343, 344, 420, 421, 422, 495, 496, 497 are not optimal combinations for adjacent cells

There are six possible frequency shifts of RSs

The frequency shift is given by

ν

= PCI

mod 6

Shift = 0 Shift = 1 Shift = 5

Shift = 0 Shift = 1 Shift = 5

Shift = 0 Shift = 1 Shift = 5

Shift = 0 Shift = 1 Shift = 5

……… ……… ……… ……… shift,i i

mod 6

Different

ν

should be used in adjacent

cells

However, if applying the rule that k should be

different in adjacent cells, this will also lead to

different

ν

in adjacent cells

There are two main strategy options:

Neighboring sites are grouped into clusters, and each cluster

is assigned a limited number of Code Groups. Each site is

assigned a specific Code Group and each sector a specific

Color Group

Random planning i.e. PCI plan that does not consider PCI

grouping and does not follow any specific reuse pattern

The first strategy option is recommended to use in order to

avoid non-optimal PCI combinations for adjacent cells

0 00 0 1111 2222 ............ 162162162162 163163163163 164164164164 165165165165 166166166166 167167167167 0 00 0 0000 3333 6666 ............ 486486486486 489489489489 492492492492 495495495495 498498498498 501501501501 1 11 1 8888 11111111 14141414 494494494494 497497497497 500500500500 503503503503 2222 5555 2 22 2 16161616 19191919 22222222 ............ 502502502502 1111 4444 7777 10101010 13131313 Alt. Alt. Alt. Alt. 1 1 1 1 Alt. Alt. Alt. Alt. 2 2 2 2 0 00 0 1111 2222 ............ 162162162162 163163163163 164164164164 165165165165 166166166166 167167167167 0 0 0 0 0000 3333 6666 ............ 486486486486 489489489489 492492492492 495495495495 498498498498 501501501501 1 1 1 1 4444 7777 10101010 490490490490 493493493493 496496496496 499499499499 502502502502 1111 2 2 2 2 8888 11111111 14141414 ............ 494494494494 497497497497 500500500500 503503503503 2222 5555

PCIs should be split into 3 different color groups and 168 code

groups

Code groups should be reserved for special purposes, e.g.

in-building and PLMN borders or for future expansions

If a color group is assigned per sector and a code group is assigned

per site, this will eliminate the risk of having the same k or frequency shift in the same site, in adjacent cells or pointing at each other

2 22

0 1 2

Assign a color group

to each sector and a

code group per site

0 00 0 1 11 1 2 2 2 2 3 3 3 3 19 1919 19 6 66 6 4 4 4 4 5 5 5 5 7 7 7 7 8 88 8 9 9 9 9 11 11 11 11 10 10 10 10 13 1313 13 14 14 14 14 16 16 16 16 17 1717 17 18 18 18 18 20 20 20 20 12 12 12 12 15 15 15 15 22 2222 22 23 23 23 23 24 24 24 24 2 22 2 1 11 1 35 3535 35 25 2525 25 28 28 28 28 26 2626 26 27 2727 27 0 1 2 0 1 2 0 1 2 0 1 2 0 1 2 0 1 2 0 1 2 0 1 2 0 1 2 0 1 2 0 1 2 0 1 2 0 1 2 0 1 2 0 1 2 0 1 2 P2 P0 P₁ 0 1 2 0 1 2 0 1 2 0 1 2 0 1 2 0 1 2 0 1 2 0 1 2 0 1 2 0 1 2 0 1 2 0 1 2 0 1 2 0 1 2 0 0 1 2 0 1 2 0 1 2 0 1 2 0 1 2 0 0 0 k=0 ⇒ Color group 0 k=1 ⇒ Color group 1 k=2 ⇒ Color group 2 37 3737 37 40 4040 40 39393939 0 1 2 0 1 2 0 1 2 36 36 36 36 38 38 38 38

Typically 10-15 3-sector sites in a cluster

Use a subset of the code groups in each cluster

If there are ~70 code groups available, PCIs may be repeated every

fifth or sixth cluster

Structured planning like this eliminates the risk of having

conflicting k or frequency shift in the same site, in adjacent cells or pointing at each other

Also the risk of having conflicting SSS sequences in adjacent cells

is reduced – although this may appear at cluster borders

28 28 28 28 29 2929 29 30 3030 30 31 31 31 31 33 33 33 33 32 32 32 32 35 35 35 35 34 3434 34 44 44 44 44 45 45 45 45 46 46 46 46 1 2 0 1 2 0 1 2 0 1 2 0 1 2 0 1 2 1 2 0 1 2 1 2 0 1 2 0 1 2 0 1 2 0 1 2 0 1 2 0 1 2 0 1 2 0 1 2 0 1 2 2 42 42 42 42 41 41 41 41 43 43 43 43

Irregular pattern for site-to-site distances and sector angles

3-sector sites, 6-sector sites and Omni sites may be mixed in same area

⇒ It may not be possible to follow a strict planning pattern ⇒ Priority orders need to be followed

When planning PCI:s the following priority orders are

recommended:

1.

The same PCI:s should be avoided within the same site and

as neighbors

2.

PCI:s with conflicting k values should be avoided within the

same site and as neighbors

same site and as neighbors

3.

PCI:s with conflicting m

and m

values should be avoided

within the same site and as neighbors

Reasons for not following these rules strictly:

Will not work in an irregular pattern (see previous slide)

Will cause a lot of limitations on neighbors and neighbor lists

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