Tracking (Custom OFDM)
When demodulating an OFDM Orthogonal Frequency Division Multiplexing: OFDM employs multiple overlapping radio frequency carriers, each operating at a carefully chosen frequency that is Orthogonal to the others, to produce a transmission scheme that supports higher bit rates due to parallel channel operation. OFDM is an alternative tranmission scheme to DSSS and FHSS. burst, the equalizer response computed from the burst preamble is used to correct many imperfections in the OFDM signal. Because the equalizer response is not perfect, pilot tracking is used to correct for imperfections in the equalizer response and for imperfections that change over the length of the burst.
In each OFDM symbol, there are pilot subcarriers used to make the coherent detection robust against frequency offsets and phase noise. The pilot subcarriers occupy subcarriers -21, -7 , 7, and 21 and use BPSK Binary phase shift keying - A type of phase modulation using 2 distinct carrier phases to signal ones and zeros. modulation.
Pilot subcarriers transmit with a known data sequence. This information is used to determine the difference, or error, between an ideal signal and the actual received signal. Because the data is complex, the VSA calculates phase, amplitude, and timing error data. The error data can then be used to correct both pilot and data subcarrier imperfections, producing a more accurate demodulation.
| Parameter | Description |
|---|---|
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Include Data Subcarriers |
When Include Data Subcarriers is selected (true), the VSA uses both pilot and data subcarriers in phase, amplitude, and timing tracking. When deselected (false), the VSA uses only the pilot subcarrier for tracking (default is false). Some signal formats (e.g., LTE and LTE-related formats) don't include pilots for each symbol. In such cases, selecting this setting will improve EVM Error vector magnitude (EVM): A quality metric in digital communication systems. See the EVM metric in the Error Summary Table topic in each demodulator for more information on how EVM is calculated for that modulation format. by ensuring that symbols without pilot subcarriers are tracked. |
|
Track Amplitude |
When Track Amplitude is selected (true), the VSA applies pilot subcarrier amplitude error correction to the pilot and data subcarriers (default is true). |
|
Track Phase |
When Track Phase is selected (true), the VSA applies pilot subcarrier phase error correction to the pilot and data subcarriers (default is true). |
|
Track Timing |
When Track Timing is selected (true), the VSA applies pilot subcarrier timing error correction (frequency offset correction) to the pilot and data subcarriers (default is true). |
Trace Data
See Also
