nrPRACHDetect

Detect PRACH transmission

Since R2022b

Syntax

[index,offset,info] = nrPRACHDetect(carrier,prach,waveform)

[index,offset,info] = nrPRACHDetect(___,Name=Value)

Description

nrPRACHDetect detects physical random access channel (PRACH) transmission in a time-domain waveform. The function generates an internal reference waveform to correlate the input waveform with the generated reference waveform and searches for correlation output peaks that are greater than the detection threshold. The function uses the position of the strongest peak in the correlator output to determine the detected preamble index and the associated timing offset.

[index,offset,info] = nrPRACHDetect(carrier,prach,waveform) detects PRACH transmission in the time-domain waveform waveform for carrier configuration parameters carrier and PRACH configuration parameters prach. The function generates the internal reference waveform for default PRACH preamble indices from 0 to 63 and selects a default detection threshold based on the input arguments. The function returns the detected PRACH preamble index, index, timing offset, offset, and detection information, info. If waveform contains multiple PRACH instances, the function returns the preamble index and timing offset related to the PRACH instance with the strongest peak in the correlation.

[index,offset,info] = nrPRACHDetect(___,Name=Value) specifies options as name-value arguments in addition to the input arguments in the previous syntax. For example, DetectionThreshold=0.5 sets the detection threshold for the correlation.

Examples

Detect PRACH Preamble with Timing Offset

Create a carrier configuration object with six resource blocks.

carrier = nrCarrierConfig(NSizeGrid=6);

Create a PRACH configuration object. Set the cyclic shift configuration index to 1 and the preamble index within the cell to 44.

prach = nrPRACHConfig;
prach.ZeroCorrelationZone = 1;
prach.PreambleIndex = 44;

Generate a PRACH resource grid for the specified carrier and PRACH configuration.

prachGrid = nrPRACHGrid(carrier,prach);

Generate PRACH symbols and indices for the specified carrier and PRACH configuration.

prachSymbols = nrPRACH(carrier,prach);
prachIndices = nrPRACHIndices(carrier,prach);

Map the PRACH symbols to the PRACH resource grid.

prachGrid(prachIndices) = prachSymbols;

OFDM-modulate the PRACH resource grid to obtain a transmit waveform with PRACH instances.

tx = nrPRACHOFDMModulate(carrier,prach,prachGrid);

Create a received waveform by introducing a delay in the transmit waveform.

rx = [zeros(7,1); tx];

Detect PRACH instances in the received waveform. Confirm that the delay introduced in the waveform offsets the timing of the PRACH detection.

[index,offset] = nrPRACHDetect(carrier,prach,rx)

index = 
44

offset = 
7.1895

Input Arguments

carrier — Carrier configuration parameters

nrCarrierConfig object

Carrier configuration parameters for a specific OFDM numerology, specified as an nrCarrierConfig object. Only these object properties are relevant for this function.

• NSizeGrid

• SubcarrierSpacing

• CyclicPrefix

prach — PRACH configuration parameters

nrPRACHConfig object

PRACH configuration parameters, specified as an nrPRACHConfig object. Apart from the PreambleIndex property of prach, all object properties are relevant for this function.

waveform — Time-domain waveform

complex-valued matrix

Time-domain waveform, specified as a complex-valued matrix of size N-by-P.

• N is the number of time-domain samples in the waveform. If N is less than the number of samples that is needed to analyze this configuration, the function appends zeros at the end of the waveform.

• P is the number of receive antennas.

Data Types: double
Complex Number Support: Yes

Name-Value Arguments

Specify optional pairs of arguments as Name1=Value1,...,NameN=ValueN, where Name is the argument name and Value is the corresponding value. Name-value arguments must appear after other arguments, but the order of the pairs does not matter.

Example: DetectionThreshold=0.5 sets the detection threshold for the correlation.

DetectionThreshold — Detection threshold

[] (default) | real number in the range [0, 1]

Detection threshold for the correlation, specified as [] or a real number in the range [0, 1]. When you set this input to [], or if you do not specify this input, the function selects a default value based on these elements of the input arguments prach and waveform.

• PRACH format, specified by prach.Format.

• LRA value, specified by prach.LRA.

• $$N_{SYM}$$ — Number of OFDM symbols per one PRACH preamble, which is equal to prach.PRACHDuration – 2 for PRACH format C2 and prach.PRACHDuration for all other PRACH formats.

• $$P$$ — Number of receive antennas, which is the number of columns in the input waveform waveform.

This table provides the formulas that the function uses to calculate default detection thresholds for different LRA values.

LRA	Default Detection Threshold
839	$$\frac{0.02}{\sqrt{P\times N_{SYM}}}$$
139	$$\frac{0.1}{\sqrt{P\times N_{SYM}}}$$
1151	$$\frac{0.01}{\sqrt{P\times N_{SYM}}}+0.0005$$
571	$$\frac{0.02}{\sqrt{P\times N_{SYM}}}+0.001$$

Data Types: double

PreambleIndex — Set of PRACH preamble indices

[] (default) | integer-valued array

Set of PRACH preamble indices within the cell for the detection, specified as [] or an integer-valued array. The array must have at most 64 elements with integer values in the range from 0 to 63. When you set this input to [], or if you do not specify this input, the function uses default PRACH preamble indices from 0 to 63.

Data Types: double

Output Arguments

index — Detected PRACH preamble index

nonnegative integer | []

Detected PRACH preamble index, returned as one of these values.

• Nonnegative integer — The index corresponds to the strongest correlation peak across default preamble indices from 0 to 63 or the indices that you specify using the PreambleIndex name-value input argument.

• [] — No correlation peak exists above the detection threshold.

Data Types: double

offset — Timing offset of PRACH waveform in samples

real number | []

Timing offset of the PRACH waveform in samples, from the origin of the input waveform, returned as one of these values.

• Real number — The integer part of this number is the sample position of the strongest correlation peak. The fractional part of this number is the fractional delay present in the correlation peak due to the cyclic shift in the frequency domain.

• [] — No correlation peak exists above the detection threshold.

Data Types: double

info — Detection information

structure

Detection information, returned as a structure containing these fields.

Fields	Description
CorrelationPeaks	Strongest correlation peak values, where each value corresponds to default preamble indices from 0 to 63 or the indices that you specify using the PreambleIndex name-value input argument.
DetectionThreshold	Detection threshold that the function uses for the correlation.

Extended Capabilities

C/C++ Code Generation
Generate C and C++ code using MATLAB® Coder™.

Version History

Introduced in R2022b

R2023a: C/C++ code generation updates

For C/C++ code generation, the limitation to specify name-value arguments as compile-time constants has been removed.