Documentation

lteDLFrameOffset

Downlink frame timing estimate

Syntax

  • offset=lteDLFrameOffset(enb,waveform)
    example
  • [offset,corr]=lteDLFrameOffset(enb,waveform)
  • [offset,corr]=lteDLFrameOffset(enb,waveform,corrcfg)
  • [offset,corr]=lteDLFrameOffset(enb,waveform,'TestEVM')

Description

example

offset=lteDLFrameOffset(enb,waveform) returns the timing offset, in symbols, between the start of the input waveform and the start of the first frame. offset is measured using the reference signals defined in the LTE standard.

lteDLFrameOffset performs synchronization using the PSS and SSS for the time-domain waveform, given cell-wide settings structure, enb. It does not perform PSS/SSS cell identity search. Use lteCellSearch to perform cell identity search and provide it to lteDLFrameOffset as an input parameter in the cell-wide settings, enb.

[offset,corr]=lteDLFrameOffset(enb,waveform) also returns a complex matrix, corr, of the same dimensions as the input waveform.

[offset,corr]=lteDLFrameOffset(enb,waveform,corrcfg) provides control over which reference signals are used for timing estimation, as specified in the input structure, corrcfg.

[offset,corr]=lteDLFrameOffset(enb,waveform,'TestEVM'), provides the string 'TestEVM' to stipulate alignment of the correlation configuration with TS 36.104, Annex E [1].

Examples

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Synchronize and Demodulate Test Model Output

Synchronization and demodulation of Test Model output which has been delayed by five samples.

Initialize cell-wide parameters structure. Generate waveform for test model 1.1 with 5MHz bandwidth. A five sample delay is acheived by inserting five zeros at beginning of waveform. Compute and display the offset. Perform demodulation of the waveform accounting for the offset delay by adjusting waveform start index.

enb = lteTestModel('1.1','5MHz');
tx = [0; 0; 0; 0; 0; lteTestModelTool(enb);];

offset = lteDLFrameOffset(enb,tx)
rxGrid = lteOFDMDemodulate(enb,tx(1+offset:end));
offset =

     5

Input Arguments

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enb — Cell-wide settingsscalar structure

Cell-wide settings, specified as a structure. enb can contain these fields.

Parameter FieldRequired or OptionalValuesDescription
NDLRBRequired

Scalar integer (6,...,110). Standard bandwidth values are 6, 15, 25, 50, 75, and 100. NDLRB also accepts the standardized bandwidths in string format from the set {'1.4MHz', '3MHz', '5MHz', '10MHz', '15MHz', '20MHz'}.

Number of downlink (DL) resource blocks (RBs)

CyclicPrefixOptional

'Normal' (default), 'Extended'

Cyclic prefix length

NCellIDRequired

Integer from 0 to 503

Physical layer cell identity.

DuplexModeOptional

'FDD' (default), 'TDD'

Duplexing mode, specified as:

  • 'FDD' for Frequency Division Duplex or

  • 'TDD' for Time Division Duplex

The following parameters are only required for CellRS = 'On' or 'OmitEdgeRBs'. See corrcfg.

  CellRefPRequired

1, 2, 4

Number of cell-specific reference signal (CRS) antenna ports

The following parameters are only required when DuplexMode = 'TDD' and CellRS = 'On' or 'OmitEdgeRBs'. See corrcfg.

  TDDConfigOptional

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

Uplink or downlink configuration

  SSCOptional

0 (default), 1, 2, 3, 4, 5, 6, 7, 8, 9

Special subframe configuration (SSC)

Data Types: struct

waveform — Time-domain waveformnumeric matrix

Time-domain waveform, specified as a T-by-P numeric matrix, where T is the number of time-domain samples and P is the number of receive antennas. Use lteOFDMModulate or one of the channel model functions (lteFadingChannel, lteHSTChannel, or lteMovingChannel) to generate this matrix.

Data Types: double | single

corrcfg — Control reference signals used for timing estimationscalar structure

Control reference signals used for timing estimation, specified as a structure containing any or all of these fields.

Parameter FieldRequired or OptionalValuesDescription
PSSOptional

'On' (default), 'Off'

Primary synchronization signal (PSS) correlation mode

SSSOptional

'On' (default), 'Off'

Secondary synchronization signal (SSS) correlation mode

CellRSOptional

'Off' (default), 'OmitEdgeRBs', 'On'

Cell-specific reference signal (CRS) correlation mode

For the corrcfg fields, lteDLFrameOffset uses the reference signals, (PSS, SSS, or CellRS) as configured by initializing particular reference signal correlation mode(s) to 'On'. For CellRS, using the mode setting, 'OmitEdgeRBs', instead of 'On', removes the uppermost and lowermost resource block of reference signals from the correlation. The 'OmitEdgeRBs' method is specified for EVM testing in TS 36.104, Annex E [1]. Omitting band edge RBs removes potential transmit filtering nonlinear phase response and the resulting influence on group delay response for the overall band.

Data Types: struct

'TestEVM' — Test EVM setting'TestEVM'

Test EVM setting. As called for in TS 36.104, Annex E [1], specifying the 'TestEVM' input string, sets correlation with:

  • PSS to 'On',

  • SSS to 'Off', and

  • CellRS to 'OmitEdgeRBs'.

Data Types: char

Output Arguments

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offset — Timing offset from the start of the input waveform to the start of the first framenumeric scalar

Timing offset from the start of the input waveform to the start of the first frame, returned as a numeric scalar. It indicates the number of samples from the start of waveform, to the position in waveform where the first frame begins. offset is computed by extracting the timing of the peak of the correlation between waveform and the internally generated time-domain reference waveforms containing PSS and SSS signals. The correlation is performed separately for each antenna. lteDLFrameOffset uses the antenna with the earliest correlation peak and a correlation peak magnitude at least 50% of the maximum across the antennas to compute offset.

Data Types: double

corr — Signal used to extract timing offsetcomplex numeric matrix

Signal used to extract the timing offset, returned as a complex numeric matrix of the same size as waveform. Each column of corr is the correlation for each column (antenna) of waveform.

Data Types: double
Complex Number Support: Yes

References

[1] 3GPP TS 36.104. "Base Station (BS) radio transmission and reception." 3rd Generation Partnership Project; Technical Specification Group Radio Access Network; Evolved Universal Terrestrial Radio Access (E-UTRA). URL: http://www.3gpp.org.

Introduced in R2014a

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