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Downlink frame timing estimate



offset=lteDLFrameOffset(enb,waveform) returns the timing offset, in samples, 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. Note that this function does not perform PSS/SSS cell identity search. The cell identity must be provided in enb. The function lteCellSearch can be used to perform cell identity search.

[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 input 'TestEVM' to stipulate alignment of the correlation configuration with TS 36.104, Annex E [1].


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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 achieved by inserting five zeros at the beginning of the 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)
offset = 5
rxGrid = lteOFDMDemodulate(enb,tx(1+offset:end));

Input Arguments

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

Parameter FieldRequired or OptionalValuesDescription

Scalar integer from 6 to 110

Number of downlink resource blocks (NRBDL)


'Normal' (default), 'Extended'

Cyclic prefix length


Integer from 0 to 503

Physical layer cell identity


'FDD' (default), 'TDD'

Duplexing mode, specified as either:

  • 'FDD' for Frequency Division Duplex

  • 'TDD' for Time Division Duplex

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


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.


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

Uplink–downlink configuration


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

Special subframe configuration (SSC)

Data Types: struct

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. waveform should be at least one subframe long and contain the PSS and SSS signals. Use lteOFDMModulate or one of the channel model functions (lteFadingChannel, lteHSTChannel, or lteMovingChannel) to generate this matrix.

Data Types: double | single

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

Parameter FieldRequired or OptionalValuesDescription

'On' (default), 'Off'

Primary synchronization signal (PSS) correlation mode


'On' (default), 'Off'

Secondary synchronization signal (SSS) correlation mode


'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

Test EVM setting, specified as 'TestEVM'. As defined in TS 36.104 [1], Annex E, sets correlation with:

  • PSS to 'On',

  • SSS to 'Off', and

  • CellRS to 'OmitEdgeRBs'.

Data Types: char | string

Output Arguments

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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

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


[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).

Version History

Introduced in R2014a