ltePRACHInfo
PRACH resource information
Description
returns info
= ltePRACHInfo(ue
,chs
)info
, a structure containing PRACH resource information
given UEspecific settings, ue
, and channel transmission
configuration, chs
. For more information, see PRACH Information.
Examples
Find Root ZadoffChu Sequences from PRACH Information
Find the set of root ZadoffChu sequences required for all preamble indices (0,...,63) in a cell.
ue.NULRB = 6; config.Format = 0; config.CyclicShiftIdx = 8; config.PreambleIdx = (0:63); prachInfo = ltePRACHInfo(ue,config); unique(prachInfo.RootSeq)
ans = 1×4
129 140 699 710
Input Arguments
ue
— UEspecific settings
structure array
UEspecific settings, specified as a structure array that can contain these parameter fields.
Parameter Field  Required or Optional  Values  Description 

NULRB  Required  6, 9, 11, 15, 25, 27, 45, 50, 64, 75, 91, 100  Number of uplink resource blocks. ($${N}_{\text{RB}}^{\text{UL}}$$) 
DuplexMode  Optional 
 Duplexing mode, specified as:

The following parameters
are dependent upon the condition that  
TDDConfig  Optional  0, 1 (default), 2, 3, 4, 5, 6  Uplink–downlink configuration 
SSC  Optional  0 (default), 1, 2, 3, 4, 5, 6, 7, 8, 9  Special subframe configuration (SSC) 
The following parameter
fields are dependent upon the condition that  
NSubframe  Optional  0 (default), Nonnegative scalar integer  Subframe number 
NFrame  Optional  0 (default), nonnegative scalar integer  Frame number 
The following parameter
fields are dependent upon the condition that the Preamble Format,  
CyclicPrefix  Optional 
 Cyclic prefix length 
Data Types: struct
chs
— Channel transmission configuration
scalar structure
Channel transmission configuration, specified as a scalar structure that can contain these parameter fields.
Parameter Field  Required or Optional  Values  Description 

Format  Optional  0, 1, 2, 3, 4 (default is determined by 
Preamble format See Note. 
SeqIdx  Optional  Scalar integer from 0 to 837. The default value is 0.  Logical root sequence index (RACH_ROOT_SEQUENCE) 
ConfigIdx  Optional  Scalar integer from 0 to 63. The default value is determined by

PRACH Configuration Index (prachConfigurationIndex) See Note. 
PreambleIdx  Optional  Scalar integer or vector of integers from 0 to 63. The default value is 0.  Preamble index within cell (raPreambleIndex) 
CyclicShiftIdx  Optional  Scalar integer from 0 to 15. The default value is 0.  Cyclic shift configuration index (zeroCorrelationZoneConfig, yields N_{CS}) 
HighSpeed  Optional  0 (default) or 1  High Speed flag (highSpeedFlag). A value of 1 signifies a restricted set. A value of 0 signifies an unrestricted set. 
The following parameters
are dependent upon the condition that  
FreqIdx  Optional  0 (default), 0, 1, 2, 3, 4, 5  Frequency resource index (f_{RA}).
Only required for 
The following parameter
fields are dependent upon the condition that the Preamble Format,  
FreqOffset  Optional  Scalar integer from 0 to 94. The default value is 0.  PRACH frequency offset (n_{PRBoffset}). Only required for Preamble format 0–3. 
Note Although the parameters 
Data Types: struct
Output Arguments
info
— PRACH resource information
scalar structure
PRACH resource information, returned as a scalar structure. info
contains
the following fields.
NZC
— ZadoffChu sequence length
positive integer
ZadoffChu sequence length, returned as a positive integer. (N_ZC)
Data Types: double
SubcarrierSpacing
— Subcarrier spacing of PRACH preamble
positive integer
Subcarrier spacing of PRACH preamble, in Hz, returned as a positive integer. (deltaf_RA)
Data Types: double
Phi
— Frequencydomain location offset
positive integer
Frequencydomain location offset, returned as a positive integer. (phi)
Data Types: double
K
— Ratio of uplink data to PRACH subcarrier spacing
numeric scalar
Ratio of uplink data to PRACH subcarrier spacing, returned as a numeric scalar. (K)
Data Types: double
TotSubframes
— Number of subframes duration of PRACH
numeric scalar
Number of subframes duration of the PRACH, returned as a numeric
scalar. Each subframe lasts 30720 fundamental periods, therefore TotSubframes
is ceil(sum(Fields)/30720)
,
the number of subframes required to hold the entire PRACH waveform.
The duration of the PRACH is a function of the Preamble Format as
described in TS 36.211, Table 5.7.11 [2].
Data Types: double
Fields
— PRACH field lengths
1by4 numeric vector
PRACH field lengths, returned as a 1by4 numeric vector. The elements are [OFFSET T_CP T_SEQ GUARD]. T_CP and T_SEQ are the lengths in fundamental time periods (T_s), of cyclic prefix and PRACH sequence, respectively. OFFSET is the number of fundamental time periods from the start of configured subframe to the start of the cyclic prefix, and is nonzero only for TDD special subframes. GUARD is the number of fundamental time periods from the end of the PRACH sequence to the end of the number of subframes spanned by the PRACH.
Data Types: double
PRBSet
— PRBs occupied by PRACH preamble
nonnegative integer column vector
PRBs occupied by PRACH preamble, returned as a nonnegative integer column vector. (starts at n_PRB, zerobased).
Note
The PRACH uses a different SCFDMA symbol construction from
the other channels, PUCCH, PUSCH, and SRS. Specifically, the PRACH
does not occupy the set of 12 subcarriers in each RB in the same fashion
as other channels. Therefore, the PRBSet
indicates
the frequency range, 180 kHz per RB, occupied by the PRACH. The PRACH
occupies a bandwidth approximately equal to 1.08 MHz, or 6RBs.
Data Types: uint32
NCS
— Length of zero correlation zone plus 1
positive integer
Length of zero correlation zone plus 1, specified as a positive
integer (N_{CS}). NCS
corresponds
to the complete extent of autocorrelation lags (0 and N_{CS}–1
nonzero) that exhibit perfect correlation properties (1 at 0 lag,
0 at nonzero lags). NCS
is expressed directly,
as in the standard, related to the fundamental ZadoffChu sequence
construction. The actual sample span of the zero correlation zone
in the waveform generated by ltePRACH
is
a function of the sampling rate.
Data Types: double
CyclicShift
— Cyclic shift or shifts of ZadoffChu sequence
numeric row vector
Cyclic shift or shifts of ZadoffChu sequence, returned as a numeric row vector. (C_v).
For High Speed mode, any element of CyclicShift
equal
to –1 indicates that there are no cyclic shifts in the restricted
set for the corresponding preamble index.
Data Types: double
RootSeq
— Physical root ZadoffChu sequence index or indices
numeric row vector
Physical root ZadoffChu sequence index or indices, required
to generate the PRACH for each of the configured set of preamble indices
returned as a numeric row vector. (u) RootSeq
is
either a vector or a scalar aligned with the configuration of chs.PreambleIdx
Data Types: double
CyclicOffset
— Cyclic shift or shifts corresponding to Doppler Shift
vector
CyclicOffset
values are cyclic shifts corresponding
to a Doppler Shift of 1/T_SEQ (d_u).
For High Speed mode, the field CyclicOffset
is present. It contains cyclic
offset values for each of the configured set of preamble
indices. CyclicOffset
is either a vector or a
scalar aligned with the configuration of
chs.PreambleIdx
.
Data Types: double
SamplingRate
— Sampling rate of PRACH modulator
numeric scalar
Sampling rate of the PRACH modulator, returned as a numeric scalar. The function computes the
sampling rate using the following equation:
SamplingRate = 30720000
/ 2048
×N_{fft} where
N_{fft} is a function
of the Number of Resource Blocks given by
ue
.
NULRB
.
NRB  N_{fft} 

6  128 
15  256 
25  512 
50  1024 
75  2048 
100  2048 
In general, N_{fft} is the smallest power of 2 greater than or equal to 12×NRB/0.85
. It is the smallest FFT that spans all subcarriers and results in a bandwidth occupancy (12×NRB/N_{fft}) of no more than 85%.
Data Types: double
BaseOffset
— Base timing offset
numeric scalar
Base timing offset, in microseconds. This field is used for the detection test in TS 36.104 [1]. (duration of N_{CS}/2)
Data Types: double
Data Types: struct
More About
PRACH Information
The parameters “PRACH Mask Index”
and “PRACH Resource Index,” described in TS 36.321 [3], are not explicit in the configuration,
but are implicit in the choice of ue
.NSubframe
and ue
.NFrame
.
The PRACH is always be generated provided it fits with the overall
duplexing arrangement. For FDD, the PRACH is generated in any subframe.
For TDD, the PRACH is generated only in special subframes for Preamble
Format 4, and in uplink subframes for Preamble Format 03, provided
there are info
.
TotSubframes
consecutive
uplink subframes for the chosen TDD configuration starting from the
current subframe.
If chs
.ConfigIdx
is
present, further validation is used to comply with TS 36.211 [2], Table 5.7.12 for FDD and
Table 5.7.14 for TDD. Specifically, chs
.Format
,
if present, is validated against chs
.ConfigIdx
and
a preamble is only generated in appropriate frames and subframes.
If chs
.Format
is absent, the
format is inferred, if possible, from chs
.ConfigIdx
.
If the entry in TS 36.211 [2],
Table 5.7.12 for FDD or Table 5.7.14 for TDD indicates “N/A”
for the preamble format, an error is issued.
For TDD, chs
.FreqIdx
corresponds
to the first entry in the quadruples in TS 36.211 [2], Table 5.7.14. The other three
entries ($${t}_{RA}^{\text{(0)}}$$, $${t}_{RA}^{\text{(1)}}$$, $${t}_{RA}^{\text{(2)}}$$)
in the quadruple are specified by ue
.NSubframe
and ue
.NFrame
.
The PRACH is generated if a combination of chs
.ConfigIdx
, ue
.TDDConfig
, $${t}_{RA}^{\text{(0)}}$$, $${t}_{RA}^{\text{(1)}}$$,
and $${t}_{RA}^{\text{(2)}}$$ given
by ue
.NSubframe
, ue
.NFrame
,
and chs
.FreqIdx
appears in
TS 36.211 [2], Table 5.7.14.
Note
In accordance with this logic,
if
chs
.ConfigIdx
is absent,ue
.NSubframe
andue
.NFrame
are not required at all for FDD.In the case that a preamble is not generated under these rules,
info
.
PRBSet
is empty and the waveform generated byltePRACH
consists of all zeros.
References
[1] 3GPP TS 36.104. “Evolved Universal Terrestrial Radio Access (EUTRA); Base Station (BS) Radio Transmission and Reception.” 3rd Generation Partnership Project; Technical Specification Group Radio Access Network. URL: https://www.3gpp.org.
[2] 3GPP TS 36.211. “Evolved Universal Terrestrial Radio Access (EUTRA); Physical Channels and Modulation.” 3rd Generation Partnership Project; Technical Specification Group Radio Access Network. URL: https://www.3gpp.org.
[3] 3GPP TS 36.214. “Evolved Universal Terrestrial Radio Access (EUTRA); Physical layer; Measurements.” 3rd Generation Partnership Project; Technical Specification Group Radio Access Network. URL: https://www.3gpp.org.
Version History
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