Rach Paramter Nokia and Huawei
Rach Paramter Nokia and Huawei
Rach Paramter Nokia and Huawei
CONFIDENTIAL | www.mobily.com.sa
Contents
• Overview
• RA Procedure
• PRACH Types
• PRACH Configuration
• PRACH Formats
• PRACH FreqOffset
• PRACH Preambles
• Preamble Generation
• Root Sequence Index
• PRCH Cyclic Shift
• Preamble Groups
Overview
• Relevant scenarios in which the RACH is used:
– UE in RRC connected state / not uplink-synchronized need to send new UL
data or control information (e.g. an event-triggered measurement report)
– UE in RRC connected state / not uplink-synchronized need to receive new DL
data and therefore had to transmit ACK/NACK in UL
– UE in RRC connected state / handing over from current serving cell to a target
cell
– Transition from RRC_IDLE to RRC Connected state
(e.g. initial access or tracking area update)
– Recovering from radio link failure
– Exceptional an uplink-synchronized UE is allowed to send a SR if it has no
other UL resource to send the SR.
• Two types of RACH
– Contention-based (implying an inherent risk of collision)
– Contention-free
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.
PRACH
• 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 Not
moredetected
info ) response
DL
Next On the resources indicated by PDCCH
PRACH
resource
UL PUSCH: UE specific data
Preamble Preamble
RACH only carries the preambles ( no additional signalling or user data like in WCDMA Rel 99)
The eNodeB may also schedule data in the resource blocks reserved for random access channel preamble
transmission.
RACH Types
Contention-based: (implying an inherent risk of collision)
Contention-based Radom Access Contention Free Random Access
Procedure Procedure
UE eNB UE eNB
Random Access Preamble (on PRACH) Random Access Preamble
(with embedded 1-bit indication for L2/L3 message size) (on PRACH)
1 1
L2/L3 message
(PUSCH transmission including contentin resolution
identity)
3 For new downlink data or HO eNB has the
option of allocating a dedicated signature to a
UE => contention free access is possible =>
Contention resolution Message faster than contention based and therefore
4
better for time-critical procedures like HO
(1)
RA Procedure
The contention based random access procedure follows these steps:
A preamble will be selected by UE and transmitted in the available subframe. Based
raRespWinSize
on correlation the eNB may detect the access and furthermore can measure the
timing of the UE transmission. Window size for RA response (in TTI)
LNCEL; 2 (0), 3 (1), 4 (2), 5 (3), 6 (4), 7 (5),
(2) The eNB answers using the same preamble and at this point a timing advance will be 8 (6), 10 (7); 10 TTIs (7) [7]
fixed. Information on the scheduled resource will be exchanged and a temporary C-
RNTI will be assigned. UE eNB
(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.
1 Random Access Preamble
(4) The contention resolution is performed, i.e. the eNB addresses the UE using the C-
RNTI.
Random Access Response 2
Name: raRespWinSize
Description: Random Access Response Window Size: Random Access Response Window Size
parameter defines the window size for the random access response in TTIs.
Range/Step: 2 (0), 3 (1), 4 (2), 5 (3), 6 (4), 7 (5), 8 (6), 10 (7)
Default: 10 (7)
Network Setting: 10(7)
Remark: raRespWinSize: The start of this UE timer is the subframe number containing the end
of the preamble + 3 subframes => 2 ms after this subframe. The UE must receive the RAR within
this window otherwise it assumes the RACH procedure as failed.
Name: raContResoT
Description: Maximum Content Resolution Timer: The Maximum Content Resolution Timer parameter
defines the maximum amount of time allowed for contention resolution.
Range/Step: 8ms (0), 16ms (1), 24ms (2), 32ms (3), 40ms (4), 48ms (5), 56ms (6), 64ms (7)
Default: 32ms (3)
Network Setting: 32ms (3) [FDD], 48ms (5) [TDD]
Remark: raContResoT: Trigger for this UE Timer is the transmission of the MSG 3. In case the UE does
not receive the MSG 4 within this time window it assumes that the contention resolution fails. In this
case the UE will restart the RACH procedure.
Huawei parameters:
parameter ID Range unit default comment
ContentionResolutionTimer [40,48,56,64] Subframe 64 From MSG3 to MSG4, expiry means RA failure
RA Procedure
The contention free random access procedure
UE eNB
0 RA Preamble assignment
• The open loop power control is performed by the UE, based on received information transmitted on system information
block in broadcast channel (BCH) and the measured path loss in downlink
• The UE sets the initial transmission power in the first preamble and waits for the UL grant on PDCCH. If not acknowledged,
the MS increases the preamble transmission power by a specified power offset step.
Preamble Initial Received Target Power
Name: ulpcIniPrePwr
Description: Preamble Initial Received Target Power: The Preamble Initial Received Target Power
parameter defines the initial power for Random Access Preamble transmission.
Range/Step: -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):
Default: -104 dBm (8)
Network Setting: -110 dBm (5) and -104 dBm (8) [FDD], -104 dBm (8) [TDD]
Huawei Parameter:
Huawei Parameter:
• Formats
– The length of TCP (Cyclic Prefix),
TPRE (Preamble) and TGT (Guard
Time) depends on the preamble
format
– Length typically one sub-frame
(0.1ms CP + 0.8ms Preamble
sequence + 0.1ms guard period)
– Four different formats available for
different environments (e.g. large
cells..) (5 formats for TDD)
– PRACH reserved PRBs cannot be
used by PUSCH i.e. they are out of
scope for scheduling for data
transmission
PRACH Formats
Preamble Format Burst (µs) TCP(μs) TSEQ(μs) FDD Cell Radius (R) (km)
0 1000 103.1 800 R ≤ 14.5
1 2000 684.4 800 R ≤ 77.3
2 2000 203.1 1600 R ≤ 29.5
3 3000 684.4 1600 R ≤ 100
4 167.9 14.58 133.33 N/A
– Normal 1 ms RA burst with 800 μs preamble sequence, for small-medium cells (up to ~14 km)
– 2 ms RA burst with 800 ìs preamble sequence, for large cells (up to ~77 km) without a link budget problem
– 2 ms RA burst with 1600 μs preamble sequence, for medium cell (up to ~29 km) and increased path loss
– 3 ms RA burst with 1600 μs preamble sequence, for very large cells (up to ~100 km) and increased path loss
– Frame structure type 2 and special subframe configurations with UpPTS lengths 4384 Ts and 5120 Ts only.
[Ts = 1 / 30.72MHz] (up to 1.4 km cell range)
• Name: prachConfIndex:
• Description: PRACH Configuration Index: Defines allowed
System frame and sub-frame numbers for random access
attempts, and the preamble format
• FDD Range/Step: 3...24, step 1
• TDD Range/Step: 3...53, step 1
• Default: 3
• Network Setting: 3
Huawei parameters:
parameter ID Range unit default
PrachConfigIndexCfgInd CFG, NOT_CFG CFG
PrachConfigIndex [0,63] 3
PreambleFmt [0,4] 0
PRACH Frequency Offset
0 nPRBoffset
RA
NRB
UL
6
If PRACH area is placed at the lower border of UL frequency band then:
• Name: prachFreqOff • The PRACH area (6 PRBs) should be next to PUCCH area
either at upper or lower border of frequency band to
• Description: PRACH Frequency Offset: First physical maximize the PUSCH area but not overlap with PUCCH
resource block available for PRACH in the UL system area
frequency band.
• TDD specific: prachFreqOff =0 when preamble
• Range/Step: 0...94, step 1 format 4 is used
• Default: 1
• Network Setting: 3 (FDD), 11(TDD)
Huawei parameters:
parameter ID Range unit default comment
PrachFreqOffset [0,94] 6 Related with PUCCHAlgoSwitch
PRACH Sequences
• Formats
– Zadoff-Chu sequences with length 839 (prime number) for Preamble Format 0-3 and 139 for
Preamble Format 4 are used
Available Sequences.
– 838 for Preamble Format 0-3
– 138 for Preamble Format 4
Cyclic shifts:
– 16 for Preamble Format 0-3
– 6 for Preamble Format 4
Fig: Zadoff-Chu sequence. The real (upper) and imaginary (lower) parts of
the complex-valued output (Wikipedia)
• Detection is sensitive to considerable Doppler shifts => special rules for high speed cells
There are 64 preambles sequences available in each cell. The set of 64 preamble sequences in a cell is
found by including first, in the order of increasing cyclic shift, all the available cyclic shifts of a root
Zadoff-Chu sequence
Fig:
example of
preambles
generation with zero
autocorrelation zone
length equal to 279
(prachCS=14)
Preamble generation
Zero correlation zone and Cyclic shift
• zero correlation zone decode PRACH even if sent on the same time/ frequency
• preamble signals generated based on two different ZC sequences are not correlated
within the geographical range related to prachCS
• the dimensioning of the cyclic shift, must be greater than the maximum round-trip delay
Required number of different root Zadoff–Chu sequences grows with Ncs (Cyclic Shift) and
the cell radius:
Limits due to preamble
premable formats
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
un( n1)
j
xu ,v (n) xu (( n Cv ) mod N ZC )
xu n e N ZC
, 0 n N ZC 1
• 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
rootSeqIndex
LNCEL;0…837;1; 0
Huawei parameters:
prachHSFlag
Unrestricted or restricted (high speed) set selection
LNCEL; true, false; false
Huawei parameters:
Huawei parameters:
Huawei parameters:
Non-Dedicated Dedicated
preambles 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.
raPreGrASize ?
raNondedPreamb ? 64 preambles
per cell
raNondedPreamb
Contention Based
raPreGrASize
Random Access Preambles Group A Size Remaining
LNCEL; 4 (0), 8 (1), 12 (2), 16 (3), 20 (4), are Type B
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 B
Type A Preambles Preambles
Type B Criteria
The Type B Random Access preambles are used if:
• The message size is greater than raSmallVolUl. raSmallVolUl
Small Size Random Access Data Volume
In Uplink
AND LNCEL; 56 bits (0), 144 bits (1), 208 bits
• the pathloss is less than: (2), 256 bits (3) ;1 ; 144 bits (1)
ulpcIniPrePwr deltaPreMsg3
Preamble Initial Received Target Power Delta Preamble Random Access Message
LNCEL; -120 dBm (0), -118 dBm (1), -116 3
dBm (2), -114 dBm (3), -112 dBm (4), -110 LNCEL; -1...6 ;1 ; 0
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) raMsgPoffGrB
RA Message Power Offset For Group B Selection
LNCEL; -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)
Number of RA Preambles
Name: raNondedPreamb
Description: Number Of Random Access Preambles: This parameter determines the total number of
non dedicated RA preambles that UE can select from (i.e. for contention based RA). The minimum
cannot be zero.
Range/Step: 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)
Default: 40 (9)
Network Setting: 40 (9) [FDD], 60 (14) [TDD]
Name: raPreGrASize
Description: Random Access Preambles Group A Size: Defines the size of the Random Access
Preambles Group A.
Range/Step: 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)
Default: 32 (7)
Network Setting: 32 (7)
RA Message Power Offset for Group B selection
Name: raMsgPoffGrB
Description: RA Message Power Offset For Group B Selection: Path loss threshold in dB required for
selecting one of the two groups of Random Access Preambles. The UE will only use preambles from
group B if it needs to send a large Msg3 AND its measured path loss is less than Pmax -
PREAMBLE_INITIAL_RECEIVED_TARGET_POWER - DELTA_PREAMBLE_MSG3 -
messagePowerOffsetGroupB (see 36.321 ch 5.1.2)
Range/Step: -infinity (0), 0 dB (1), 5 dB (2), 8 dB (3), 10 dB (4), 12 dB (5), 15 dB (6), 18 dB (7)
Default: 10 dB (4)
Network Setting: 10 dB (4)
Huawei parameters:
parameter ID Range unit default comment
messagePowerOffsetGroupB not applicable dB 10 GroupB power offset
Message Size Message Coding
Large Size RA MCS in UL:
Name: raLargeMcsUl
Description: Large Size Random Access MCS in Uplink: Defines the modulation and coding scheme
(MCS) to be used for large size Random Access Message 3 in case of initial access or handover
Range/Step: 0...15, step 1
Default: 5
Network Settings: 5
Huawei parameters:
Huawei parameters:
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