305090798 04-basic-parameter-planning-rules-v1-1

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PRACH Planning
PCI Planning
UL DM RS Planning
Key Planning Areas parameters – TD-LTE

PRACH Planning
Principle
PRACH configuration two cells must be different within the PRACH re-use distance to
increase the RACH decoding success rate
PRACH transmission can be separated by:
• Time (prachConfIndex)
– PRACH-PUSCH interference: If PRACH resources are separated in time within eNB
– PRACH-PRACH interference: If same PRACH resources are used for the cells of an
eNodeB.
– PRACH-PRACH interference is preferred to PRACH-PUSCH interference so
prachConfIndex of the cells on one site should be the same
• Frequency (prachFreqOff)
– Allocation of PRACH area should be next to PUCCH area either at upper or lower
border of frequency band, however should not overlap with PUCCH area
– Avoid separation of PUSCH in two areas by PRACH (scheduler can only handle one
PUSCH area)
– For simplicity use same configuration for all cells
• Sequence (PRACH CS and RootSeqIndex)
– Use different sequences for all neighbour cells

Preamble Formats, FDD+TDD common
• 3GPP (TS36.211) specifies 4 random access formats common for both FDD/TDD
• Difference in formats is based in the different durations for the cyclic prefix,
sequence and guard time which have an effect on the maximum cell radius
• Only Formats 0 and 1 are supported in initial releases (up to RL30)
Recommendation:
 Select Format0 for cell
ranges <14.53 km
 Select Format1 for cell
ranges <77.34 km

Preamble Format 4, TDD-only
• 3GPP (TS36.211) specifies a special random access format 4 for TDD
• Is allocated in UpPTS when it is two symbols long
• Maximum cell radius with preamble format 4 is about 1.4km
• NOTE: when using preamble format 4, only root sequences 0-137 are allowed.
• NOTE: when using preamble format 4, allowed value of prachCS is 4...6. Setting
prachCS =6 gives the maximum cell range <1.4km
• NOTE: prachFreqOff must be set to 0 with preamble format 4
• NOTE: prachHsFlag must be set to false with preamble format 4
SequenceCP
sT 5.14CP  sT 133SEQ 

PRACH Configuration Index, prachConfIndex TDD
RL15
prachConfIndex is
restricted to values
3...7 or 51..53 if
tddSpecSubfConf is
set to '7' (ssp7).
prachConfIndex is
restricted to values
3...7, 23..25, 33..35
or 51...53 if
tddSpecSubfConf is
set to '5' (ssp5)
Preamble
format 4
also
supported
PRACH
configuration
Index
Preamble
Format
Density
Per 10 ms
 RAD
Version
 RAr
PRACH
configuration
Index
Preamble
Format
Density
Per 10 ms
 RAD
Version
 RAr
0 0 0.5 0 32 2 0.5 2
1 0 0.5 1 33 2 1 0
2 0 0.5 2 34 2 1 1
3 0 1 0 35 2 2 0
4 0 1 1 36 2 3 0
5 0 1 2 37 2 4 0
6 0 2 0 38 2 5 0
7 0 2 1 39 2 6 0
8 0 2 2 40 3 0.5 0
9 0 3 0 41 3 0.5 1
10 0 3 1 42 3 0.5 2
11 0 3 2 43 3 1 0
12 0 4 0 44 3 1 1
13 0 4 1 45 3 2 0
14 0 4 2 46 3 3 0
15 0 5 0 47 3 4 0
16 0 5 1 48 4 0.5 0
17 0 5 2 49 4 0.5 1
18 0 6 0 50 4 0.5 2
19 0 6 1 51 4 1 0
20 1 0.5 0 52 4 1 1
21 1 0.5 1 53 4 2 0
22 1 0.5 2 54 4 3 0
23 1 1 0 55 4 4 0
24 1 1 1 56 4 5 0
25 1 2 0 57 4 6 0
26 1 3 0 58 N/A N/A N/A
27 1 4 0 59 N/A N/A N/A
28 1 5 0 60 N/A N/A N/A
29 1 6 0 61 N/A N/A N/A
30 2 0.5 0 62 N/A N/A N/A
31 2 0.5 1 63 N/A N/A N/A

RACH Density
• Based on the expected RACH procedures per second and the maximum
collision probability of the RACH preambles it is possible to estimate the
RACH density as follows:
100*
100
1ln*64*)1(
)__(







 UE
collp
LoadRachex
x
UE
collp = maximum collisiion probability [%]
Ex-RACH_Load = expected RACH Procedures per sec
0.5 ≤ x => RACH Density = 0.5
0.5 < x ≤ 1 => RACH Density = 1
1 < x ≤ 2 => RACH Density = 2
5 < x => RACH Density = 10
• Recommendation: use PRACH density 1 for
start
• Since PRACH performance measurement
counters are available (RL15 – M8001- Cell Load)
it will be possible to evaluate the amount of
PRACH / RACH procedures in time and adapt
/optimize the settings
• Future features: PRACH Management (auto-
configuration, future SON feature called PRACH
optimization (an aspect of this feature is to adjust
the PRACH density to the traffic in the cell)

PRACH Frequency Offset
prachFreqOff
• Indicates the first PRB available for PRACH in the UL frequency band
• PRACH area (6 PRBs) should be next to PUCCH area either at upper or lower
border of frequency band to maximize the PUSCH area but not overlap with
PUCCH area
• Parameter is configured based on the PUCCH region (see PUCCH dimensioning)
i.e. its value depends on how many PUCCH resources are available.
• If PRACH area is placed at the lower border of UL frequency band then:
PRACH-Frequency Offset= roundup [PUCCH resources/2]
• If PRACH area is placed at the upper border of the UL frequency band then:
PRACH-Frequency Offset= NRB -6- roundup [PUCCH resources/2]
NRB: Number of Resource Blocks
NOTE: prachFreqOff must be set to 0 if prachConfIndex is set to 51...53 (preamble
4)

PRACH Cyclic Shift for preambles 0-3
PrachCS
• PrachCS defines the configuration used for the preamble generation. i.e. how
many cyclic shifts are needed to generate the preamble
• PrachCS depends on the cell size
– Different cell ranges correspond to different PrachCS
• Simplification: To assume all cells have same size (limited by the prachConfIndex)
Recommendation:
Select PrachCS based on the cell
range E.g. if estimated cell range is
15km then PrachCS: 12
If all cells in the network are assumed
to have same cell range them
PrachCS is the same for the whole
network

PRACH Cyclic Shift for preamble 4
PrachCS
• For preamble 4, prachCs configuration maps to special table of cyclic shifts
• The highlighted configuration indices 4…6 are supported in RL15
CSNCSN
CSN configuration CSN value
0 2
1 4
2 6
3 8
4 10
5 12
6 15
7 N/A
8 N/A
9 N/A
10 N/A
11 N/A
12 N/A
13 N/A
14 N/A
15 N/A

PrachCS and rootSeqIndex
• PrachCS defines the number of cyclic
shifts (in terms of number of samples) used
to generate multiple preamble
sequences from a single root sequence
• Example based on PrachCS=12 -> number
of cyclic shifts: 119
– Root sequence length is 839 so a cyclic shift
of 119 samples allows ROUNDDOWN
(839/119)= 7 cyclic shifts before making a
complete rotation (signatures per root
sequence)
• 64 preambles are transmitted in the PRACH
frame. If one root is not enough to generate
all 64 preambles then more root sequences
are necessary
– To ensure having 64 preamble sequences
within the cell it is necessary to have
ROUNDUP (64/7)= 10 root sequences per
cell
• For preamble format 4, root sequence
length is 137.

PRACH Cyclic Shift
rootSeqIndex
• RootSeqIndex points to the first root
sequence to be used when generating
the set of 64 preamble sequences.
• Each logical rootSeqIndex is
associated with a single physical root
sequence number.
• In case more than one root sequence
is necessary the consecutive number
is selected until the full set is
generated
• NOTE: parameter rootSeqIndex
specifies the logical root sequence
index
Logical
root
sequence
number
Physical root sequence index (in increasing order of
the corresponding logical sequence number)
0–23 129, 710, 140, 699, 120, 719, 210, 629, 168, 671, 84, 755,
105, 734, 93, 746, 70, 769, 60, 779
2, 837, 1, 838
24–29 56, 783, 112, 727, 148, 691
30–35 80, 759, 42, 797, 40, 799
36–41 35, 804, 73, 766, 146, 693
42–51 31, 808, 28, 811, 30, 809, 27, 812, 29, 810
52–63 24, 815, 48, 791, 68, 771, 74, 765, 178, 661, 136, 703
…. …..
64–75 86, 753, 78, 761, 43, 796, 39, 800, 20, 819, 21, 818
810–815 309, 530, 265, 574, 233, 606
816–819 367, 472, 296, 543
820–837 336, 503, 305, 534, 373, 466, 280, 559, 279, 560, 419,
420, 240, 599, 258, 581, 229, 610
Extract from 3GPP TS 36.211 Table 5.7.2.-4 (
Preamble Formats 0-3). Mapping between logical
and physical root sequences.
Recommendation:
Use different rootSeqIndex across
neighbouring cells means to ensure
neighbour cells will use different
preamble sequences

PRACH Planning
Wrap Up
Steps:
- Define the prachConfIndex
• Depends on preamble format (cell range)
• It should be the same for each cell of a site
- Define the prachFreqOff
• Depends on the PUCCH region
• It can be assumed to be the same for all cells of a network (simplification)
- Define the PrachCS
• Depends on the cell range
• If for simplicity same cell range is assumed for all network then prachCS is the
same for all cells
- Define the rootSeqIndex
• It points to the first root sequence
• It needs to be different for neighbour cells
• rootSeqIndex separation between cells depends on how many are necessary
per cell (depends on PrachCS)

PRACH Planning example
Assumptions:
- prachConfIndex=3 for all cells
• preamble format =0
• One PRACH opportunity per 10ms
- prachFreqOff=6 for all cells
• PRACH starts at sixth PRB in frequency domain
- Define the prachCS=8 for all cells
• Max cell range = 5.5km
• Each cell consumes 4 root sequences
{1,2,3,4}
{5,6,7,8}{9,10,11,12}
{13,14,15,16}
{21,22,23,24} {17,18,19,20}
{25,26,27,28}
{33,34,35,36} {29,30,31,32}
{37,38,39,40}
{41,42,43,44}{45,46,47,48}eNB #1
eNB #2
eNB #3
eNB #4
{49,50,51,52}
{53,54,55,56}{57,58,59,60}
eNB #5
root sequence indices
used in the cell

Exercise
• Plan the PRACH Parameters for
the sites attached in the excel
• Assumptions:
– PUCCH resources =6
– Cell range = 12km (all cells
have same range)
– BW:10MHz

PCI Planning
Introduction
• There are 504 unique Physical Cell IDs (PCI)
Physical Layer Cell Identity = (3 × NID1) + NID2
NID1: Physical Layer Cell Identity group. Range 0 to 167
– Defines SSS sequence
NID2: Identity within the group. Range 0 to 2
– Defines PSS sequence
Resource element
allocation to the
Reference Signal
• PCI impacts the allocation of
resource elements to the
reference signal and the set
of physical channels
• Allocation pattern repeats every 6th Physical Layer Cell Identity

PCI Planning
• Analogous to scrambling code planning in UMTS
– Maximum isolation between cells with the same PCI
▪ To ensure that UE never simultaneously receive the same identity from more than
a single cell
• Physical Cell Identity is defined by the parameter phyCellID:
Parameter Object Range Default
phyCellId LNCEL 0 to 503 Not
Applicable
• There should be some level of co-ordination across international borders when
allocating PCIs.
– This will help to avoid operators allocating the same identity to cells on the same RF
carrier and in neighbouring geographic areas

PCI Planning
Recommendations for 2Tx
In priority order, number 1 most important in
FDD (all four should be fulfilled, ideally).
Number 2 important in TDD!
1. Avoid assigning the same PCI to
neighbour cells
2. Avoid assigning the same mod3 (PCI)
to ‘neighbour’ cells
3. Avoid assigning the same mod6(PCI) to
‘neighbour’ cells
4. Avoid assigning the same mod30 (PCI) to
‘neighbour’ cells
Id = 5
Id = 4
Id = 3
Id =
11
Id =
10
Id = 9
Id = 8
Id = 7
Id = 6
Id = 2
Id = 1
Id = 0
Example 1 PCI Identity Plan
Example 2 PCI Identity Plan

PCI Planning example
PCI=0
PCI=1PCI=2
PCI=3
PCI=5 PCI=4
PCI=6
PCI=8 PCI=7
PCI=9
PCI=10PCI=11eNB #1
eNB #2
eNB #3
eNB #4
PCI=12
PCI=13PCI=14
eNB #5
Quiz: how to allocate PCI for a single-cell TD-LTE omni site to be placed at the
red circle?

- UlseqHop
- UlGrpHop
- grpAssigPUSCH
- ulRsCs
- Sequence Group Number (u)
UL Reference Signal Planning

UL Reference Signal
Overview
Types of UL Reference Signals
• Demodulation Reference Signals (DM RS)
– PUSCH/PUCCH data estimation
• Sounding Reference Signals (SRS)
– Mainly UL channel estimation UL (RL40/RL15)
DM RS is characterised by:
• Sequence (Zadoff Chu codes)
• Sequence length: equal to the # of subcarriers
used for PUSCH transmission
• Sequence group:
▪ 30 options
▪ Cell specific parameter
• Cyclic Shift: UE and cell specific parameter
UL DM RS allocation per slot for Normal
Cyclic Prefix

UL DM Reference Signal
Need for Planning
Issue:
• DM RS occupy always the same slot in time
domain
• In frequency domain DM RS of a given UE
occupies the same PRBs as its
PUSCH/PUCCH data transmission
• Possible inter cell interference for RS due to
simultaneous UL allocations on neighbour
cells
– No intra cell interference because users
are separated in frequency
– Possible inter cell interference
Scope of planning:
• DM RS in co-sited cells needs to be
different
UL DM RS allocation per slot for Normal
Cyclic Prefix

• RS sequences for PUSCH have different lengths depending the UL
bandwidth allocated for a UE
• 30 possible sequences for each PRB allocation length of 1-100 PRBs
• Sequences are grouped into 30 groups so they can be assigned to cells
• Sequence group number ‘u’:
RS Sequences and RS Sequence Groups
Sequence Group Id, ‘u’
  30modSCHgrpAssigPU PCIu
grpAssigPUSCH: group
assignment for PUSCH Range
[0…29], step 1

Cyclic Shift
• Additional sequences can be derived from a basic sequence by
applying a cyclic shift
• Cyclic shifts of an extended ZC sequence are not fully orthogonal, but
have low cross-correlation
• The actual UL reference signal cyclic shift ncs used by UE is different
for every 0.5ms time slot
  12mod)( sPRS
)2(
DMRS
)1(
DMRScs nnnnn 
Cell-specific static cyclic shift
defined by LNCEL/ulRsCs
and broadcast on BCCH
TTI-specific cyclic shift
signalled to UE on PDCCH
DCI0 in each uplink
scheduling grant (defined by
scheduler)
Pseudorandom cyclic shift offset that
changes every time slot. Depends
on the PCI, slot number ns and u via
LNCEL/grpAssigPUSCH
ulRsCs ndmrs1
0 0
1 2
2 3
3 4
4 6
5 8
6 9
7 10
DCI0 CS
field
ndmrs2
000 0
001 6
010 3
011 4
100 2
101 8
110 10
111 9
u
N
c 





 32
30
cell
ID
init

UL DM Reference Signal
Hopping Techniques
• Sequence Hopping
– Intra-Subframe hopping between two sequences within a sequence group for
allocations larger than 5PRBs
– Only enabled is Sequence Group hopping in disabled
– Not enabled in RL10/RL20/RL30: ulSeqHop= false
• Sequence Group Hopping
– In each slot, the UL RS sequences to use within a cell are taken from one
specific group
– If group varies between slots: Group hopping
– Group Hopping not enabled in RL10/RL20/RL30: UlGrpHop = false
▪ Group is the same for all slots
• Cyclic Shift Hopping
– Always used
– Cell specific cyclic shift added on top of UE specific cyclic shift

Planning
From Theory to Practice… (1/2)
Theory:
• It should be possible to assign to the cells of one site the same sequence
group ‘u’ and ‘differentiate’ the sequences using different cell specific cyclic shifts
i.e. allocating different ulRsCs
Remember!: Cyclic shifts of an extended ZC
sequence are not fully orthogonal, but have
low cross-correlation

Planning
From Theory to Practice… (2/2)
Practice:
• It doesn’t seem to work
• UL Throughput gets considerably affected if UL traffic in neighbour cell
– From 40 Mbps to ~ 22 Mbps in the example
PCI grpAssigPusch sequence id u ulRsCs cinit
75 0 15 0 79
76 29 15 4 79

Planning
New rule
• Allocate different sequence group u for every cell, including cells of the
same site
– Cross-correlation properties between sequences from two different groups are good
because of sequence grouping in the 3GPP spec
• ulRsCs does not matter (it is only relevant for sequences within one seq group u)

Planning
Results
• UL Throughput still suffers from UL interference in neighbour cell but the effect is
lower
PCI grpAssigPusch sequence id u ulRsCs cinit
75 0 15 0 79
76 0 16 0 80

Pros an cons of the new planning rule
• [+]: Results seem to be better
• [+]: Less parameters to plan, only PCI planning needed
– UlRsCs only relevant when using sequences of the same group
– ‘u’ will be different if PCI module 3 rule is followed. In that case
‘grpAssigPUSCH’ value is not relevant
• [ -]: Reduced group reuse distance compared to the case of assigning the same
group per each site

UL DM RS Planning
Wrap up
– If cells of the site follow the PCImod3 rule, the sequence group number ‘u’ will be
different
– If PCImod3 rule is not followed, check PCImod30 rule
▪ If problems use grpAssigPUSCH to differentiate the ‘u’ - sequence group
number-
– If same ‘u’ has to be used in neighbouring cells and cannot be changed using
grpAssigPUSCH then assign different ulRsCs to the cells of a site. Range [0…7]
• Principle: DM RS needs to be different in cells of the same eNodeB
• Current planning approach:
– Assign different sequence group number ‘u’ to the cells of the same
site. Range: [0…29]. grpAssigPUSCH can be constant =no need for
planning

UL DM RS Planning example, PCI-based
PCI = 1
Dss = 0
u = 1
eNB #1
eNB #2
eNB #3
eNB #4
eNB #5
PCI = 0
Dss = 0
u = 0
PCI = 2
Dss = 0
u = 2
PCI = 3
Dss = 0
u = 3
PCI = 4
Dss = 0
u = 4
PCI = 5
Dss = 0
u = 5
PCI = 9
Dss = 0
u = 6
PCI = 10
Dss = 0
u = 7
PCI = 11
Dss = 0
u = 8
PCI = 12
Dss = 0
u = 6
PCI = 13
Dss = 0
u = 7
PCI = 14
Dss = 0
u = 8
PCI = 6
Dss = 0
u = 6
PCI = 7
Dss = 0
u = 7
PCI = 8
Dss = 0
u = 8

UL DM RS Planning example, how to use
grpAssigPusch to tune PCI-based sequence
allocation in case of PCImod30 collision
PCI = 1
Dss = 0
u = 1
eNB #1
eNB #2
eNB #3
eNB #4
eNB #5
PCI = 0
Dss = 0
u = 0
PCI = 2
Dss = 0
u = 2
PCI = 3
Dss = 0
u = 3
PCI = 4
Dss = 0
u = 4
PCI = 5
Dss = 0
u = 5
PCI = 9
Dss = 0
u = 6
PCI = 10
Dss = 0
u = 7
PCI = 11
Dss = 0
u = 8
PCI = 12
Dss = 0
u = 6
PCI = 13
Dss = 0
u = 7
PCI = 14
Dss = 0
u = 8
PCI = 6
Dss = 0
u = 6
PCI = 7
Dss = 0
u = 7
PCI = 8
Dss = 0
u = 8
indoor eNB
PCI = 30
Dss = 29
u = 29

305090798 04-basic-parameter-planning-rules-v1-1

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