Modulation Per Allocation (Custom OFDM)
Menu Path:
This property is only valid when Resource Interface = Type2.
Modulation Per Allocation is a mapping from the resource id to the QAM Identifiers The QAM Identifiers parameter is specified in the Format tab > QAM Idenifiers text box (Custom OFDM Demod Properties dialog box). array.
For example, to determine the modulation for resource id 2, look at the QAM Identifiers array at index 2 (zero-based). Say this value is 1. Then you look at the QAM Level table at index 1 (zero-based). Say this value is 4. Then this maps to 16QAM according to the definition of the QAM Quadrature Amplitude Modulation Level values.
This property is an array of values, with one value for each allocation ID, as listed in the Resource Allocations mapping array. The values are unitless. The modulation value can be used to determine the type of modulation (BSPK/QPSK Quadrature phase shift keying/16-QAM/...etc.) for each allocation. If this array is shorter than the highest allocation ID, any values past the end are assumed to be 0.
Auto-detecting the modulation format:
Modulation value zero “unknown” is a special case that can greatly simplify Custom 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. setup. Modulation value zero “unknown” 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. Modulation zero “unknown” 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 Binary phase shift keying - A type of phase modulation using 2 distinct carrier phases to signal ones and zeros. 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
