04 random access gc

1 © Nokia Siemens Networks RA41214EN20GLA1

Random AccessLTE Radio Parameters RL20


1. LTE Functionalities and Overview

2. Channel Configuration

3. General parameter DB structure and System Information Broadcast

4. Random Access

5. Radio Admission Control (RAC)

6. Radio Bearer Control & DRX /DTX Management

7. LTE Mobility Management

8. UL/DL Scheduler

9. MIMO Mode Control (MIMO-MC)

10.Power Control

Presentation / Author / Date

Contents


Module Contents

• Overview

• PRACH Configuration

• RA Procedure

• RA Power Ramping

• Preamble Generation


OverviewRandom access procedure is performed for the following events:• Initial access from RRC_IDLE

• RRC Connection Re-establishment procedure

• Handover

• DL data arrival during RRC_CONNECTED requiring random access procedure

• UL data arrival during RRC_CONNECTED requiring random access procedure

• E.g. when UL synchronisation status is "non-synchronised" or

there are no PUCCH resources for SR available

It takes two distinct forms:

• Contention based (applicable to all five events);

• Non-contention based (applicable to only handover and DL data arrival)

Normal DL/UL transmission can take place after the random access procedure

In total there are 64 preambles per cell (pooled into 2 groups)

Preambles are grouped to indicate the length of the needed resource.

A number of preambles are reserved for contention-free access


Module Contents

• Overview


• RA Procedure




PRACH Types

PreambleCP

DL timing (eNB)

UE Tx

eNB Rx

1 ms

0.1 ms

GT

0.8 ms

PRACH configuration index ( → see next slides)

parameter selects one of the 4 types

Example timing for type 0:


PRACH Types

PRACH types:

• Type 0: 1 ms duration

• Type 1: 2 ms

• Type 2: 2 ms

• Type 3: 3 ms

Format type 0 & type 1 supported in RL20

Recommendation: Select Format0 for cell

ranges <14.53 km Select Format1 for cell

ranges <77.34 km


PRACH Configuration

Type, time and frequency resources are defined by:

.

*3GPP TS 36.211 Table 5.7.1-2

prachConfIndex

LNCEL; 3..24;1; 3

Range is restricted to two different ranges: 3-8 and 19-24 (internal)

PRACH configuration index:

Recommendation:

Configure the same PRACH configuration Indexes at cells belonging to the same site. E.g.:

3 or 4 or 5 if RACH density=1 and 6 or 7or 8 if RACH density=2 (Preamble Format 0)

RACH density – see next slide


RACH Density

• RACH Density indicates how many RACH resources are per 10ms frame. • Only RACH density values of 1 and 2 are supported in RL20.E.g.

– RACH density=1 Only one random access attempt per frame – RACH density=2 Two random access attempts per frame

• 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*1001ln*64*)1(

)__(

UEcollp

LoadRachexx

UEcollp = maximum collisiion probability [%]

Ex-RACH_Load = expected RACH Procedures per sec

0.5 ≤ x => RACH Density = 0.50.5 < x ≤ 1 => RACH Density = 1 1 < x ≤ 2 => RACH Density = 2 2 < x ≤ 3 => RACH Density = 3 3 < x ≤ 5 => RACH Density = 5 5 < x => RACH Density = 10

• Recommendation: use PRACH density 1 for start

• Since PRACH performance measurement counters are available (RL20) it will be possible to evaluate the amount of PRACH / RACH procedures in time and adapt /optimize the settings


PRACH Frequency OffsetprachFreqOff

• 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

prachFreqOff

First PRB available for PRACH in UL

LNCEL; 0...94;1; -

Max. value is ulChBw(in PRB) - 6


Module Contents

• Overview


• RA Procedure




RA Procedure

• Random access procedure handled by MAC and PHY Layer through PRACH (in UL) and PDCCH ( in DL)

• RACH only carries the preambles and occupies 6 resource blocks in a subframe

Process: • UEs selects randomly a preamble from the list of preambles broadcasted in the

BCCH

• UE calculates OLPC parameters ( Initial Tx Power)

• Checks contention parameters (i.e. max. number of retries)

• UE transmits initial RACH and waits for a response before retry. Open loop PC ensures that each retry will be at a higher power level.

• Upon receipt of successful UL RACH preamble, eNB calculates power adjustment and timing advance parameters together with an UL capacity grant ( so UE can send more info )

DL

PUSCH: UE specific data

PRACH response

ULPreamble

Not detected

Preamble

Next PRACH resource

On the resources indicated by PDCCH


RA Procedure

(1) A preamble will be selected by UE and transmitted in the available subframe. Based on correlation the eNB may detect the access and furthermore can measure the timing of the UE transmission.

(2) The eNB answers using the same preamble and at this point a timing advance will be fixed. Information on the scheduled resource will be exchanged and a temporary C-RNTI will be assigned.

(3) The UE sends its id. The type of id depends on the state. In case of idle state NAS info has to be provided (IMSI, TMSI) else the C-RNTI is used.

(4) The contention resolution is performed, i.e. the eNB addresses the UE using the C-RNTI.

UE eNB

Random Access Preamble1

Random Access Response 2

Scheduled Transmission3

Contention Resolution 4

The contention based random access procedure follows these steps:raRespWinSize

Window size for RA response (in TTI)

LNCEL; 2 (0), 3 (1), 4 (2), 5 (3), 6 (4), 7 (5), 8 (6), 10 (7); 10 TTIs (7)

raContResoT

Max. Time for cont. resol.

LNCEL; 8ms (0), 16ms (1), 24ms (2), 32ms (3), 40ms (4), 48ms (5), 56ms (6), 64ms (7); 32ms (3)

ulpcRarespTpc

TPC command indicated in message 2 related to message 3 power

LNCEL; -6...8dB;2dB; 0dB


RA Procedure

The contention free random access procedure

UE eNB

RA Preamble assignment0

Random Access Preamble 1

Random Access Response2

• E.g. during handover a temporary valid preamble will be issued.

• It is (temporarily) dedicated to this UE.

• No contention resolution is needed as the preamble shall not be used by other UEs.


Module Contents

• Overview


• RA Procedure




RA Power Ramping

UE sets the initial transmission power of RACH and send preamble signal

BCH information

Preamble (RACH)

PDCCH

Preamble (RACH)

Random access message (UL-SCH)

Preamble (RACH)

PPRACH = min{ Pmax, PREAMBLE_RECEIVED_TARGET_POWER + PATHLOSS}

prachPwrRamp

Power increment step

LNCEL; 0dB (0), 2dB (1), 4dB (2), 6dB (3); 2dB (1)

preambTxMax

Max. RA transmissions

LNCEL; 3 (0), 4 (1), 5 (2), 6 (3), 7 (4), 8 (5), 10 (6), 20 (7); 8 (5)

Values 50 (8), 100 (9), 200 (10) also defined but should not be used

ulpcIniPrePwr

Initial received target power

LNCEL; -120 dBm (0), -118 dBm (1), -116 dBm (2), -114 dBm (3), -112 dBm (4), -110 dBm (5), -108 dBm (6), -106 dBm (7), -104 dBm (8), -102 dBm (9), -100 dBm (10), -98 dBm (11), -96 dBm (12), -94 dBm (13), -92 dBm (14), -90 dBm (15); -104 dBm (8)


Module Contents

• Overview


• RA Procedure




Preamble Generation

64 preambles made of Zadoff-Chu sequences with zero correlation zone:

• given by the logical index RACH_ROOT_SEQUENCE

• Zadoff Chu sequence u is given by

10, ZC

)1(

ZC

Nnenx N

nunj

u

*3GPP TS 36.211 Table 5.7.2-4

rootSeqIndex

LNCEL;0…837;1; 0

• ZC sequence of length 839 (prime number) is used

• 838 different root sequences available. (PRACH Root Sequence). Also different cyclic shifts can be used depending on cell size

• Sub-carrier spacing is 1.25 kHz

• ZC sequence of length 839 (prime number) is used

• 838 different root sequences available. (PRACH Root Sequence). Also different cyclic shifts can be used depending on cell size

• Sub-carrier spacing is 1.25 kHz

)mod)(()( ZC, NCnxnx vuvu


Preamble Generation

First: take all available cyclic shifts of one root

Zadoff-Chu sequence:

If not enough: take next logical index and so on

CS ZC CS CS

CS

RA RA RA RA RAstart shift shift CS shift group shift

0,1,..., 1, 0 for unrestricted sets

0 0 for unrestricted sets

( mod ) for restricted sets0,1,..., 1

v

vN v N N N

NC

d v n v n N v n n n

• Cyclic shift given by

Root Zadoff-Chu sequence order for preamble formats 0 – 3.:

*3GPP TS 36.211 Table 5.7.2-2

prachCS

Preamble cyclic shift (Ncs configuration)

LNCEL;0…15;1; 0

Restricted set (high speed) NOT in RL20

prachHSFlag

Unrestricted or restricted (high speed) set selection

LNCEL; false; false

Only unrestricted set could be selected in RL20


PRACH Cyclic ShiftPrachCS

• 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 network wise

prachCS


LNCEL;0…15;1; 0


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

rootSeqIndex

LNCEL;0…837;1; 0

prachCS


LNCEL;0…15;1; 0


PRACH Cyclic ShiftrootSeqIndex

• 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

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

rootSeqIndex

LNCEL;0…837;1; 0


PRACH PlanningWrap 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)rootSeqIndex

LNCEL;0…837;1; 0

prachCS


LNCEL;0…15;1; 0

prachFreqOff

First PRB available for PRACH in UL

LNCEL; 0...94;1; -

prachConfIndex

LNCEL; 3..24;1; 3

Range is restricted to two different ranges: 3-8 and 19-24 (internal)


Preamble generation

-Exercise Consider a cell of 37 km radius. Provide a sensitive setting for the cell size dependent parameters


Preambles - Contention and Non-Contention

Non Contention Based

Contention Based

64 preambles per cell

raNondedPreambTotal number of non dedicated RA preamblesLNCEL; 4 (0), 8 (1), 12 (2), 16 (3), 20 (4), 24 (5), 28 (6), 32 (7), 36 (8), 40 (9), 44 (10), 48 (11), 52 (12), 56 (13), 60 (14), 64 (15); 1 ; 40 (9)

Remaining are Non Contention Based

Dedicated

preambles

Non-Dedicated

preambles


Type A and B Grouping of Preambles

The contention based Random Access preambles are grouped into:

• Type A - for requesting a normal UL resource.

• Type B - for requesting a larger resource due to Message Size AND Pathloss (PL) criteria having been met.

raNondedPreamb Contention Based

64 preambles per cell

raPreGrASize Random Access Preambles Group A SizeLNCEL; 4 (0), 8 (1), 12 (2), 16 (3), 20 (4), 24 (5), 28 (6), 32 (7), 36 (8), 40 (9), 44 (10), 48 (11), 52 (12), 56 (13), 60 (14) ; 1 ; 32 (7)

raPreGrASize Type A Preambles

Type B Preambles

raNondedPreamb

raPreGrASize

Remaining are Type B

?

?


Type B Criteria

The Type B Random Access preambles are used if:

• The message size is greater than raSmallVolUl.

AND

• the pathloss is less than:PCMAX – preambleInitialReceivedTargetPower - deltaPreambleMsg3 - messagePowerOffsetGroupB

Where:

PCMAX is the UE maximum output power.

raSmallVolUl Small Size Random Access Data Volume In UplinkLNCEL; 56 bits (0), 144 bits (1), 208 bits (2), 256 bits (3) ;1 ; 144 bits (1)

deltaPreMsg3 Delta Preamble Random Access Message 3LNCEL; -1...6 ;1 ; 0

raMsgPoffGrBRA Message Power Offset For Group B SelectionLNCEL; -infinity (0), 0 dB (1), 5 dB (2), 8 dB (3), 10 dB (4), 12 dB (5), 15 dB (6), 18 dB (7) ;1 ; 10 dB (4)

ulpcIniPrePwr Preamble Initial Received Target PowerLNCEL; -120 dBm (0), -118 dBm (1), -116 dBm (2), -114 dBm (3), -112 dBm (4), -110 dBm (5), -108 dBm (6), -106 dBm (7), -104 dBm (8), -102 dBm (9), -100 dBm (10), -98 dBm (11), -96 dBm (12), -94 dBm (13), -92 dBm (14), -90 dBm (15);1 ; -104 dBm (8)


Feature LTE97 –> Cell Range 77 km

•No parameter enabling/disabling this feature at the moment.

•For the PRACH configuration should be set as follows:– High speed flag should be set to: prachHsFlag = false (cannot be

changed in RL20)

– PRACH configuration Index should be set in the range: prachConfIndex = 19 …. 24 i.e Preamble Format 1 must be used as per 3GPP 36.211

– PRACH Cyclic Shift should be set to: prachCS = 0 (otherwise 77 km is not possible)

– Therefore 64 root sequences are required – so there have to be care about the setting of rootSeqIndex compared to the neighbor cells.

– It is rather good to set the aggregation level for the RACH signals as high as possible therefore set

– pdcchAggMsg4 = pdcchAggPreamb = pdcchAggRaresp = 8

– Besides that the Preamble power settings should be made in accordance to big propagation loss.


Feature LTE97 –> Cell Range 77 km, cont.

•Feature is defined by parameter settings

•The parameter settings is however condition necessary to get such cell range but not sufficient.

•The feature can work under good propagation conditions only like:

– Propagation over water

– Propagation over flat terrain

– Base station suppose to be on very high tower or on the hill in otherwise flat terrain.

– Each such case should be analyzed by network planning tools, and /or propagations measurement.

04 random access gc

Documents