nrPRACH

Generate PRACH symbols

Since R2020a

Syntax

[sym,info] = nrPRACH(carrier,prach)

[sym,info] = nrPRACH(carrier,prach,'OutputDataType',datatype)

Description

[sym,info] = nrPRACH(carrier,prach) returns the physical random access channel (PRACH) symbols, as defined in TS 38.211 Section 6.3.3 [1]. The input carrier specifies carrier configuration parameters for a specific OFDM numerology. The input prach specifies PRACH configuration parameters. The function also returns the structure info, which contains carrier-dependent information about the PRACH.

[sym,info] = nrPRACH(carrier,prach,'OutputDataType',datatype) specifies the data type of the PRACH symbols.

Examples

Generate and Map PRACH Symbols to Grid

Configure the PRACH and the carrier with default properties.

carrier = nrCarrierConfig;
prach = nrPRACHConfig;

Generate PRACH symbols and indices using the specified carrier and PRACH configuration parameters.

prachSym = nrPRACH(carrier,prach);
prachInd = nrPRACHIndices(carrier,prach);

Generate a PRACH resource grid of all zeros.

prachGrid = nrPRACHGrid(carrier,prach);

Map the PRACH symbols to the PRACH resource grid by using the indices.

prachGrid(prachInd) = prachSym;

Analyze PRACH Root Sequence Indices

Analyze physical root Zadoff-Chu sequence indices by generating 64 orthogonal PRACH preambles for two different PRACH configurations.

Root Sequence Indices with Single Value

Configure the PRACH and the carrier with default properties.

carrier = nrCarrierConfig;
prach1 = nrPRACHConfig;

Set the PRACH logical root sequence index to 0. For this value, the physical root sequence index is 129, as defined in TS 38.211 Table 6.3.3.1-3.

prach1.SequenceIndex = 0;

Set the PRACH cyclic shift configuration index to 1. For this value, each PRACH preamble has a different cyclic shift value, based on ${\mathit{N}}_{\mathrm{CS}}$ from TS 38.211 Table 6.3.3.1-5.

prach1.ZeroCorrelationZone = 1;

Generate 64 PRACH preambles to store the physical root sequence indices and cyclic shift values.

rootSequence1 = NaN(1,64);
cyclicShift1 = NaN(1,64);
for preambleIndex = 0:63
    prach1.PreambleIndex = preambleIndex;
    [~,info] = nrPRACH(carrier,prach1);
    rootSequence1(preambleIndex+1) = info.RootSequence;
    cyclicShift1(preambleIndex+1) = info.CyclicShift;
end

Verify that in each preamble, the physical root sequence index is 129, which is the expected value from configuring the logical root sequence index to 0.

disp(rootSequence1)

   129   129   129   129   129   129   129   129   129   129   129   129   129   129   129   129   129   129   129   129   129   129   129   129   129   129   129   129   129   129   129   129   129   129   129   129   129   129   129   129   129   129   129   129   129   129   129   129   129   129   129   129   129   129   129   129   129   129   129   129   129   129   129   129

Verify that each preamble has a different cyclic shift value.

disp(cyclicShift1)

     0    13    26    39    52    65    78    91   104   117   130   143   156   169   182   195   208   221   234   247   260   273   286   299   312   325   338   351   364   377   390   403   416   429   442   455   468   481   494   507   520   533   546   559   572   585   598   611   624   637   650   663   676   689   702   715   728   741   754   767   780   793   806   819

Root Sequence Indices with Different Values

Configure another PRACH with default properties.

prach2 = nrPRACHConfig;

Set the PRACH logical root sequence index to 0. For this value, the physical root sequence index is 129, as defined in TS 38.211 Table 6.3.3.1-3.

prach2.SequenceIndex = 0;

Set the PRACH cyclic shift configuration index to 0. For this value, each PRACH preamble has the same cyclic shift value, equal to 0, based on TS 38.211 Table 6.3.3.1-5.

prach2.ZeroCorrelationZone = 0;

Generate 64 PRACH preambles to store the physical root sequence indices and cyclic shift values.

rootSequence2 = NaN(1,64);
cyclicShift2 = NaN(1,64);
for preambleIndex = 0:63
    prach2.PreambleIndex = preambleIndex;
    [~,info] = nrPRACH(carrier,prach2);
    rootSequence2(preambleIndex+1) = info.RootSequence;
    cyclicShift2(preambleIndex+1) = info.CyclicShift;
end

Check the physical root sequence indices and cyclic shift values. Even though the logical root sequence index, prach.SequenceIndex, is 0, not every physical root sequence index value is the expected value of 129. Because the cyclic shift value is zero in each preamble, the function nrPRACH obtains the physical root sequence indices by taking consecutive logical index values. The returned physical root sequence indices correspond to logical indices 0 to 63 from TS 38.211 Table 6.3.3.1-3.

disp(rootSequence2)

   129   710   140   699   120   719   210   629   168   671    84   755   105   734    93   746    70   769    60   779     2   837     1   838    56   783   112   727   148   691    80   759    42   797    40   799    35   804    73   766   146   693    31   808    28   811    30   809    27   812    29   810    24   815    48   791    68   771    74   765   178   661   136   703

disp(cyclicShift2)

     0     0     0     0     0     0     0     0     0     0     0     0     0     0     0     0     0     0     0     0     0     0     0     0     0     0     0     0     0     0     0     0     0     0     0     0     0     0     0     0     0     0     0     0     0     0     0     0     0     0     0     0     0     0     0     0     0     0     0     0     0     0     0     0

Input Arguments

carrier — Carrier configuration parameters

nrCarrierConfig object

Carrier configuration parameters for a specific OFDM numerology, specified as an nrCarrierConfig object.

prach — PRACH configuration parameters

nrPRACHConfig object

PRACH configuration parameters, specified as an nrPRACHConfig object. The function uses only these properties of this input.

• FrequencyRange

• DuplexMode

• ConfigurationIndex

• SubcarrierSpacing

• LRA

• SequenceIndex

• PreambleIndex

• RestrictedSet

• ZeroCorrelationZone

• ActivePRACHSlot

• NPRACHSlot

datatype — Data type of output symbols

'double' (default) | 'single'

Data type of the output symbols, specified as 'double' or 'single'.

Data Types: char | string

Output Arguments

sym — PRACH symbols

complex column vector | []

PRACH symbols, returned as a complex column vector or an empty array. The number of symbols depends on the PRACH configuration prach. The function returns an empty array when the PRACH preamble is not active in the current slot.

Data Types: single | double

info — Carrier-dependent PRACH information

structure

Carrier-dependent PRACH information, returned as a structure containing these fields:

Fields	Description
RootSequence	Index or indices of physical root Zadoff-Chu sequence
CyclicShift	Cyclic shift or shifts of Zadoff-Chu sequence
CyclicOffset	Cyclic shift or shifts corresponding to a Doppler shift of 1/TSEQ, where TSEQ is the length of the PRACH sequence (applies to restricted set only)
NumCyclicShifts	Number of cyclic shifts corresponding to a single PRACH preamble sequence

Note

Logical root sequence index prach.SequenceIndex determines the returned physical root Zadoff-Chu sequence index RootSequence, based on TS 38.211 Table 6.3.3.1-3 and Table 6.3.3.1-4. However, if the preamble index within the cell, specified by prach.PreambleIndex, results in insufficient amount of cyclic shifts available at index prach.SequenceIndex, the function nrPRACH obtains the physical root sequence index by taking consecutive logical root sequence indices, following the process described in TS 38.211 Section 6.3.3.1. In this case, the value of RootSequence differs from the expected index, specified by prach.SequenceIndex. For an example, see Analyze PRACH Root Sequence Indices.

References

[1] 3GPP TS 38.211. “NR; Physical channels and modulation.” 3rd Generation Partnership Project; Technical Specification Group Radio Access Network.

Extended Capabilities

C/C++ Code Generation

Generate C and C++ code using MATLAB® Coder™.

Usage notes and limitations:

The datatype input argument must be compile-time constant. For example, when specifying 'single' as the output data type, include {coder.Constant('OutputDataType'),coder.Constant('single')} in the -args value of the codegen function. For more information, see the coder.Constant (MATLAB Coder) class.

Version History

Introduced in R2020a