IQ Meas (802.16 OFDM)

When 802.16 OFDM Demodulation is enabled, IQ Meas is the measured IQ symbol values of the subcarriers. There is one complex value for each subcarrier for each symbol-time in the burst.

There may be multiple modulation formats present, in which case the constellation will be an overlay of all formats present. The FCH symbol and all pilots are BPSK Binary phase shift keying - A type of phase modulation using 2 distinct carrier phases to signal ones and zeros., the data modulation is one of BPSK, QPSK Quadrature phase shift keying, 16QAM, or 64QAM and there can be more than one data modulation format. The constellation trace data shows both data and pilot subcarriers. The pilots and data values are shown with different colors.

Pilot BPSK (White)

Burst BPSK (Magenta)

Burst QPSK (Red)

Burst 16QAM (Blue)

Burst 64QAM (Green)

The colors shown on 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. IQ Meas data trace are the same as those on the OFDM Syms/Errs data trace. The individual format colors can be changed in the Color tab of the Display Preferences dialog box (Utilities > Display Preferences > Color). The Pilot can be selected by trace ( A–F). The individual formats are listed Mod Type 1 – 12. To change a color, select Pilot or Mod Type X (where X is a number 1-12) in the Element scroll text box. Press the Color button and select a color to associate with the Pilot or Mod Type. See Color Tab for more information.

The IQ Meas image shows all four possible digital modulation formats. As the 802.16 OFDM pulse stream is progressively demodulated, the composite constellation diagram will show only the formats demodulated. See Subframe Info

The IQ Meas trace skips the initial burst preamble. If an additional preamble is embedded within the data, it is skipped over and not shown.

As the data bursts are demodulated, the formats found in them will be displayed.

This is similar to IQ Meas Time (Digital Demod). The difference is that there are 200 values at each symbol-time, rather than just a single value.