nrPRACHOFDMInfo

Get PRACH OFDM information

Since R2020b

Syntax

info = nrPRACHOFDMInfo(carrier,prach)

info = nrPRACHOFDMInfo(carrier,prach,'Windowing',samples)

Description

info = nrPRACHOFDMInfo(carrier,prach) provides dimensional information relevant to physical random access channel (PRACH) orthogonal frequency-division multiplexing (OFDM) modulation for carrier configuration parameters carrier and PRACH configuration parameters prach.

info = nrPRACHOFDMInfo(carrier,prach,'Windowing',samples) specifies the number of time-domain samples over which the function applies raised cosine windowing and overlapping of OFDM symbols.

Examples

Get PRACH OFDM Information

Specify carrier configuration parameters.

carrier = nrCarrierConfig;

Configure PRACH for format A1.

prach = nrPRACHConfig('ConfigurationIndex',106,'SubcarrierSpacing',15);

Generate and display the PRACH OFDM information.

info = nrPRACHOFDMInfo(carrier,prach)

info = struct with fields:
                   Nfft: 1024
             SampleRate: 15360000
    CyclicPrefixLengths: [152 0 144 0 144 0 152 0 144 0 144 0 0 0]
           GuardLengths: [0 0 0 0 0 0 0 0 0 0 0 0 0 144]
          SymbolLengths: [1176 1024 1168 1024 1168 1024 1176 1024 1168 1024 1168 1024 1024 1168]
           OffsetLength: 0
              Windowing: 72

Get PRACH OFDM Information for Custom Windowing

Set carrier configuration parameters, specifying a subcarrier spacing of 60 kHz.

carrier = nrCarrierConfig('SubcarrierSpacing',60);

Configure and generate PRACH symbols.

prach = nrPRACHConfig;

Generate and display the PRACH OFDM information, specifying the number of samples over which the OFDM modulator applies windowing and overlapping of OFDM symbols.

samples = 95;
info = nrPRACHOFDMInfo(carrier,prach,'Windowing',samples)

info = struct with fields:
                   Nfft: 49152
             SampleRate: 61440000
    CyclicPrefixLengths: 6336
           GuardLengths: 5952
          SymbolLengths: 61440
           OffsetLength: 0
              Windowing: 95

Generate PRACH OFDM Information for Multiple PRACH Slots

Generate PRACH OFDM information for multiple PRACH slots. The example shows that the actual PRACH slot duration deviates from the nominal duration to ensure that the slot spans the entire active PRACH preambles.

Specify carrier configuration parameters.

carrier = nrCarrierConfig;

Configure PRACH for format 1.

prach = nrPRACHConfig;
prach.DuplexMode = 'FDD';
configurationIndex = 47; % Format 1
prach.ConfigurationIndex = configurationIndex;

Obtain the nominal PRACH slot duration.

totSubframes = prach.SubframesPerPRACHSlot

totSubframes = 
3

Obtain the starting subframes for the active PRACH preambles from the PRACH configuration tables.

configTable = prach.Tables.ConfigurationsFR1PairedSUL;
subframeNumber = configTable.SubframeNumber{configurationIndex+1,:}

subframeNumber = 1×2

     1     6

Display the PRACH OFDM information for PRACH slot number 0. The first nominal PRACH slot period, lasting totSubframes number of subframes, spans subframes 0, 1, and 2. However, according to TS 38.211 Table 6.3.3.2-2, the first active PRACH preamble starts in subframe 1 and ends in subframe 3. To ensure that the PRACH slot spans the whole active preamble, the PRACH slot must contain one additional subframe. Therefore, the value of OffsetLength is equal to one subframe.

prach.NPRACHSlot = 0; % Default value
ofdmInfo = nrPRACHOFDMInfo(carrier,prach);
disp(ofdmInfo);

                   Nfft: 12288
             SampleRate: 15360000
    CyclicPrefixLengths: [10512 0]
           GuardLengths: [0 10992]
          SymbolLengths: [22800 23280]
           OffsetLength: 15360
              Windowing: 430

Display the PRACH OFDM information for PRACH slot number 1. The lengths of the symbol, cyclic prefix, and guard are empty. Therefore, the corresponding waveform lasts zero subframes. In this case, the PRACH slots are balanced with the nominal PRACH slot period. The value of OffsetLength is zero.

prach.NPRACHSlot = 1;
ofdmInfo = nrPRACHOFDMInfo(carrier,prach);
disp(ofdmInfo);

                   Nfft: 12288
             SampleRate: 15360000
    CyclicPrefixLengths: [1×0 double]
           GuardLengths: [1×0 double]
          SymbolLengths: [1×0 double]
           OffsetLength: 0
              Windowing: 430

Display the PRACH OFDM information for PRACH slot number 2. The first subframe of the PRACH slot is subframe 4 and spans subframes 4, 5, and 6, without the additional subframes. However, according to TS 38.211, the first active PRACH preamble starts in subframe 6 and occupies subframes 6, 7, and 8. To ensure that the PRACH slot spans the whole active preamble, the PRACH slot must contain two additional subframes. Therefore, the value of OffsetLength is equal to two subframes.

prach.NPRACHSlot = 2;
ofdmInfo = nrPRACHOFDMInfo(carrier,prach);
disp(ofdmInfo);

                   Nfft: 12288
             SampleRate: 15360000
    CyclicPrefixLengths: [10512 0]
           GuardLengths: [0 10992]
          SymbolLengths: [22800 23280]
           OffsetLength: 30720
              Windowing: 430

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. The function uses only these properties of this input.

• FrequencyRange

• DuplexMode

• ConfigurationIndex

• SubcarrierSpacing

• LRA

• NPRACHSlot

samples — Number of time-domain samples for OFDM symbol windowing and overlapping

nonnegative integer (default depends other input values) | []

Number of time-domain samples over which the function applies raised cosine windowing and overlapping of OFDM symbols, specified as a nonnegative integer or [].

If you do not specify this input, or if you specify it as [], the function sets this input to the maximum value E that does not impact error vector magnitude (EVM) tests, as specified in TS 38.101-1 Annex F.5.5 and TS 38.101-2 Annex F.5.5. E is equal to value of floor((N_CP − W) × info.Nfft ⁄ N_{FFT, nominal}), where N_CP, W, and N_{FFT, nominal} are the values in the table columns labeled "Cyclic prefix length", "EVM window length", and "FFT size", respectively.

Data Types: double

Output Arguments

info — OFDM information

structure

OFDM information, returned as a structure containing these fields.

Fields	Values	Description
Nfft	Positive integer	Number of FFT points
SampleRate	Positive integer	Waveform sample rate
CyclicPrefixLengths	1-by-N vector of nonnegative integers, where N is the number of OFDM symbols in a PRACH slot	Cyclic prefix lengths of each OFDM symbol, in samples
GuardLengths	1-by-N vector of positive integers, where N is the number of OFDM symbols in a PRACH slot	Guard lengths of OFDM symbols, in samples
SymbolLengths	1-by-N vector of nonnegative integers, where N is the number of OFDM symbols in a PRACH slot	OFDM symbol lengths, in samples
OffsetLength	Nonnegative integer	Length, in samples, of the initial time offset between the start of the configured PRACH slot period to the start of the cyclic prefix
Windowing	Nonnegative integer	Number of time-domain samples over which the function applies raised cosine windowing and overlapping of OFDM symbols

For long formats, for which the LRA property of the prach input is 839, the first slot of a PRACH preamble can occur part of the way through the nominal PRACH slot period. In this case, the function increases the value of the OffsetLength field, which ensures that the OFDM waveform spans the entire active PRACH preamble. To balance these slots with the nominal PRACH slot period, some inactive PRACH slots have OFDM waveforms that are shorter than the nominal PRACH slot period. The function conveys this by returning the CyclicPrefixLengths and GuardLengths fields as [], corresponding to no OFDM symbols, and setting the OffsetLength field equal to the number of empty subframes required.

Data Types: struct

References

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

[2] 3GPP TS 38.101-1. “NR; User Equipment (UE) radio transmission and reception; Part 1: Range 1 Standalone.” 3rd Generation Partnership Project; Technical Specification Group Radio Access Network.

[3] 3GPP TS 38.101-2. “NR; User Equipment (UE) radio transmission and reception; Part 2: Range 2 Standalone.” 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 samples input argument must be compile-time constant. Include {coder.Constant('Windowing'),coder.Constant(samples)} in the -args value of the codegen function. For more information, see the coder.Constant (MATLAB Coder) class.

Version History

Introduced in R2020b