QAM Levels (Custom OFDM)
: See Preset to Standard
The parameter fill an array that specify the 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. subcarrier modulation type. The Resource Modulation file uses the QAM Identifiers parameter and QAM Quadrature Amplitude Modulation Levels parameter to specify the OFDM subcarrier modulation format. see the "Making a Custom OFDM Measurement" tutorial for more information.
| QAM Levels | Modulation | Comments |
|---|---|---|
| 0 | Unknown | Modulation auto-detection mode. |
| 1 | BPSK Binary phase shift keying - A type of phase modulation using 2 distinct carrier phases to signal ones and zeros. | |
| 2 | QPSK Quadrature phase shift keying | |
| 3 | 8 PSK Phase Shift Keying: A broad classification of modulation techniques where the information to be transmitted is contained in the phase of the carrier wave. | |
| 4 | 16 QAM | |
| 5 | 32 QAM | |
| 6 | 64 QAM | |
| 7 | 128 QAM | |
| 8 | 256 QAM | |
| 9 | 512 QAM | Does not support modulation auto-detection mode (zero "Unknown"). |
| 10 | 1024 QAM | Does not support modulation auto-detection mode (zero "Unknown"). |
| 11 | 2048 QAM | Does not support modulation auto-detection mode (zero "Unknown"). |
| 12 | 4096 QAM | Does not support modulation auto-detection mode (zero "Unknown"). |
| 13 | 8192 QAM | Does not support modulation auto-detection mode (zero "Unknown"). |
| 14 | 16384 QAM | Does not support modulation auto-detection mode (zero "Unknown"). |
| 15 | 32768 QAM | Does not support modulation auto-detection mode (zero "Unknown"). |
| 16 | 65536 QAM | Does not support modulation auto-detection mode (zero "Unknown"). |
| n/a | 8 QAM | no QAM Levels value, must use auto-detection mode (0-unknown) |
| n/a | Rotated BPSK/QPSK | no QAM Levels value, must use auto-detection mode (0-unknown) |
Auto-detecting the modulation format:
Resource Modulation value zero “unknown” is a special case that can greatly simplify Custom OFDM setup. Resource Modulation zero instructs the demodulator to detect the format automatically based on a statistical algorithm. This algorithm computes a single result (modulation format) for all subcarriers specified as zero. Resource Modulation "zero" is normally used for a group of subcarriers spread across one or more symbols that all utilize the same modulation format.
The auto-detection algorithm does not support any QAM modulation greater than 256QAM. If your signal uses these modulation formats, you must explicitly use QAM levels (9-16) shown in the table above. Auto-detection algorithm does support 8-QAM and rotated versions of BPSK and QPSK. There is no QAM level value corresponding to these formats, so if your signal uses one of these, auto-detection is the only way to demodulate these subcarriers correctly.
See Also
