ltePRACHInfo

PRACH resource information

Description

example

info = ltePRACHInfo(ue,chs) returns info, a structure containing PRACH resource information given UE-specific settings, ue, and channel transmission configuration, chs. For more information, see PRACH Information.

Examples

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Find the set of root Zadoff-Chu 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

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UE-specific settings, specified as a structure array that can contain these parameter fields.

Parameter FieldRequired or OptionalValuesDescription
NULRBRequired6, 9, 11, 15, 25, 27, 45, 50, 64, 75, 91, 100

Number of uplink resource blocks. (${N}_{\text{RB}}^{\text{UL}}$)

DuplexModeOptional

'FDD' (default), 'TDD'

Duplexing mode, specified as:

• 'FDD' for Frequency Division Duplex or

• 'TDD' for Time Division Duplex

The following parameters are dependent upon the condition that DuplexMode is set to 'TDD'.

TDDConfigOptional

0, 1 (default), 2, 3, 4, 5, 6

SSCOptional

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 DuplexMode is set to 'TDD' or when chs.ConfigIdx is present.

NSubframeOptional

0 (default), Nonnegative scalar integer

Subframe number

NFrameOptional

0 (default), nonnegative scalar integer

Frame number

The following parameter fields are dependent upon the condition that the Preamble Format, chs.Format, is set to '4'.

CyclicPrefixOptional

'Normal' (default), 'Extended'

Cyclic prefix length

Data Types: struct

Channel transmission configuration, specified as a scalar structure that can contain these parameter fields.

Parameter FieldRequired or OptionalValuesDescription
FormatOptional

0, 1, 2, 3, 4 (default is determined by ConfigIdx field if present). However, the Format field must be specified if the ConfigIdx field is not specified.

Preamble format

See Note.

SeqIdxOptional

Scalar integer from 0 to 837. The default value is 0.

Logical root sequence index (RACH_ROOT_SEQUENCE)

ConfigIdxOptional

Scalar integer from 0 to 63. The default value is determined by Format field, if present. However, the ConfigIdx field must be specified if the Format field is not specified.

PRACH Configuration Index (prach-ConfigurationIndex)

See Note.

PreambleIdxOptional

Scalar integer or vector of integers from 0 to 63. The default value is 0.

Preamble index within cell (ra-PreambleIndex)

CyclicShiftIdxOptional

Scalar integer from 0 to 15. The default value is 0.

Cyclic shift configuration index (zeroCorrelationZoneConfig, yields NCS)

HighSpeedOptional

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 ue.DuplexMode is set to 'TDD'.

FreqIdxOptional

0 (default), 0, 1, 2, 3, 4, 5

Frequency resource index (fRA). Only required for 'TDD' duplexing mode.

The following parameter fields are dependent upon the condition that the Preamble Format, chs.Format, is set to 0, 1, 2, or 3.

FreqOffsetOptional

Scalar integer from 0 to 94. The default value is 0.

PRACH frequency offset (nPRBoffset). Only required for Preamble format 0–3.

Note

Although the parameters chs.Format and chs.ConfigIdx are both described as 'Optional', at least one of these parameters must be specified. If both parameters are present, then chs.Format is used and chs.ConfigIdx is ignored.

Data Types: struct

Output Arguments

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PRACH resource information, returned as a scalar structure. info contains the following fields.

Zadoff-Chu sequence length, returned as a positive integer. (N_ZC)

Data Types: double

Subcarrier spacing of PRACH preamble, in Hz, returned as a positive integer. (deltaf_RA)

Data Types: double

Frequency-domain location offset, returned as a positive integer. (phi)

Data Types: double

Ratio of uplink data to PRACH subcarrier spacing, returned as a numeric scalar. (K)

Data Types: double

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 5.7.1-1 [2].

Data Types: double

PRACH field lengths, returned as a 1-by-4 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 non-zero 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

PRBs occupied by PRACH preamble, returned as a nonnegative integer column vector. (starts at n_PRB, zero-based).

• If no PRACH is present, the info.PRBSet field is empty.

• If PRACH is present, the info.PRBSet field contains six consecutive Physical Resource Block (PRB) indices, indicating the frequency-domain location of the PRACH.

Note

The PRACH uses a different SC-FDMA 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

Length of zero correlation zone plus 1, specified as a positive integer (NCS). NCS corresponds to the complete extent of autocorrelation lags (0 and NCS–1 non-zero) that exhibit perfect correlation properties (1 at 0 lag, 0 at non-zero lags). NCS is expressed directly, as in the standard, related to the fundamental Zadoff-Chu 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

Cyclic shift or shifts of Zadoff-Chu 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

Physical root Zadoff-Chu 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 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

Sampling rate of the PRACH modulator, returned as a numeric scalar. The function computes the sampling rate using the following equation: SamplingRate = 30720000  / 2048 ×Nfft where Nfft is a function of the Number of Resource Blocks given by ue.NULRB.

NRB

Nfft

6

128

15

256

25

512

50

1024

75

2048

100

2048

In general, Nfft 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/Nfft) of no more than 85%.

Data Types: double

Base timing offset, in microseconds. This field is used for the detection test in TS 36.104 [1]. (duration of NCS/2)

Data Types: double

Data Types: struct

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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 0-3, 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 5.7.1-2 for FDD and Table 5.7.1-4 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 5.7.1-2 for FDD or Table 5.7.1-4 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 5.7.1-4. 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 5.7.1-4.

Note

In accordance with this logic,

• if chs.ConfigIdx is absent, ue.NSubframe and ue.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 by ltePRACH consists of all zeros.

References

[1] 3GPP TS 36.104. “Evolved Universal Terrestrial Radio Access (E-UTRA); 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 (E-UTRA); 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 (E-UTRA); Physical layer; Measurements.” 3rd Generation Partnership Project; Technical Specification Group Radio Access Network. URL: https://www.3gpp.org.