lteFrequencyOffset

Frequency offset estimation using cyclic prefix

Syntax

foffset = lteFrequencyOffset(cfgdl,waveform)

foffset = lteFrequencyOffset(cfgul,waveform)

[foffset, corr] = lteFrequencyOffset(___)

[foffset, corr] = lteFrequencyOffset(___,toffset)

Description

foffset = lteFrequencyOffset(cfgdl,waveform) estimates the average frequency offset, foffset, of the time-domain waveform, waveform, by calculating correlation of the cyclic prefix. The parameters of waveform are given in the downlink settings structure, cfgdl. cfgdl must contain the field NDLRB to specify that a downlink signal is expected in waveform.

foffset = lteFrequencyOffset(cfgul,waveform) estimates the average frequency offset, foffset, of the time-domain waveform, waveform, by calculating correlation of the cyclic prefix. The parameters of waveform are given in the uplink settings structure, cfgul. cfgul must contain the field NULRB to specify that an uplink signal is expected in waveform.

[foffset, corr] = lteFrequencyOffset(___) also returns a complex matrix, corr, spanning one slot and containing the same number of antennas, or columns, as waveform. corr is the signal used to extract the timing of the correlation for the estimation of the frequency offset.

[foffset, corr] = lteFrequencyOffset(___,toffset) provides control over the position in the correlator output used to estimate the frequency offset. When present toffset is the timing offset in samples from the start of the correlator output to the position used for the frequency offset estimation. This input allows a timing offset to be calculated externally on a signal of longer duration than the input waveform. Which allows a short-term frequency offset estimate to be obtained while retaining the benefit of a longer-term timing estimate.

Note

If toffset is absent, the quality of the internal timing estimate is subject to the length and signal quality of the input waveform and, therefore, it may result in inaccurate frequency offset measurements.

Examples

Estimate Frequency Offset

Perform frequency offset estimation and correction on an uplink signal, to which a frequency offset has been applied.

Generate uplink RMC A3-2.

[txWaveform,rgrid,cfg] = lteRMCULTool('A3-2',[1;0;0;1],'Fdd',2);

Apply an arbitrary frequency offset of 51.2 Hz.

t = (0:length(txWaveform)-1).'/cfg.SamplingRate;
txWaveform = txWaveform .* exp(1i*2*pi*51.2*t);

Estimate and display the frequency offset.

offset = lteFrequencyOffset(cfg,txWaveform);
disp(['Frequency offset: ' num2str(offset) ' Hz'])

Frequency offset: 51.2 Hz

Correct for frequency offset.

rxWaveform = lteFrequencyCorrect(cfg,txWaveform,offset);

Perform SC-FDMA demodulation.

rxGrid = lteSCFDMADemodulate(cfg,rxWaveform);

Input Arguments

cfgdl — Downlink configuration

structure

Downlink configuration, specified as a structure having the following fields.

Parameter Field	Required or Optional	Values	Description
NDLRB	Required	Scalar integer from 6 to 110	Number of downlink resource blocks ($$N_{\text{RB}}^{\text{DL}}$$)
CyclicPrefix	Optional	'Normal' (default), 'Extended'	Cyclic prefix length
DuplexMode	Optional	'FDD' (default), 'TDD'	Duplexing mode, specified as either: 'FDD' for Frequency Division Duplex 'TDD' for Time Division Duplex
The following apply when DuplexMode is set to 'TDD'.
TDDConfig	Optional	0, 1 (default), 2, 3, 4, 5, 6	Uplink–downlink configuration
SSC	Optional	0 (default), 1, 2, 3, 4, 5, 6, 7, 8, 9	Special subframe configuration (SSC)
NSubframe	Optional	0 (default), nonnegative scalar integer	Subframe number

Data Types: struct

cfgul — Uplink configuration

structure

Uplink configuration, specified as a structure having the following fields.

Parameter Field	Required or Optional	Values	Description
NULRB	Required	Scalar integer from 6 to 110	Number of uplink resource blocks. ($$N_{\text{RB}}^{\text{UL}}$$)
CyclicPrefixUL	Optional	'Normal' (default), 'Extended'	Cyclic prefix length
DuplexMode	Optional	'FDD' (default), 'TDD'	Duplexing mode, specified as either: 'FDD' for Frequency Division Duplex 'TDD' for Time Division Duplex
The following apply when DuplexMode is set to 'TDD'.
TDDConfig	Optional	0, 1 (default), 2, 3, 4, 5, 6	Uplink–downlink configuration
SSC	Optional	0 (default), 1, 2, 3, 4, 5, 6, 7, 8, 9	Special subframe configuration (SSC)
NSubframe	Optional	0 (default), nonnegative scalar integer	Subframe number

Data Types: struct

waveform — Input time-domain waveform

numeric column vector

Input time-domain waveform, specified as a numeric column vector.

Data Types: double | single
Complex Number Support: Yes

toffset — Timing offset

scalar value

Timing offset, specified as a scalar value expressed in samples. Use toffset to control the position in the correlator output used to estimate the frequency offset. If toffset is absent, or empty, the position of the peak magnitude of the correlator output is used.

Data Types: double | single

Output Arguments

foffset — Average frequency offset estimate

scalar value

Average frequency offset estimate, returned as a scalar value expressed in Hertz. This function can only accurately estimate frequency offsets of up to ±7.5 kHz (a range of 15 kHz, the subcarrier spacing).

Data Types: double | single

corr — Correlation timing signal

numeric matrix

Correlation timing signal, returned as a numeric matrix. corr is a complex matrix that spans one slot and contains the same number of antennas, or columns, as waveform. It is the signal used to extract the timing of the correlation for the frequency offset estimation.

Data Types: double | single
Complex Number Support: Yes

Version History

Introduced in R2014a