IQ Ref (LTE)
In downlink mode, shows the reference IQ values of the subcarriers from the output of the FFT Fast Fourier Transform: A mathematical operation performed on a time-domain signal to yield the individual spectral components that constitute the signal. See Spectrum. (frequency domain).
When analyzing channels transmitted on C-RS Cell-specific RS antenna ports with transmit diversity or spatial multiplexing, this trace shows the channel data values after precoding has been removed. When precoding is removed, the subcarrier notation does not apply to channel data values since the values do not have a one-to-one correspondence with on-air subcarriers. See the MIMO Decoding topic for more information.
For downlink signals, PDSCH Physical Downlink Shared Channel IQ data used in calculating this trace comes from the layer chosen when selecting this trace. Other LTE Long Term Evolution channels/signals are included in Layer traces for convenience. For more details, see the Layer Traces and Resource Element Distribution topic.
For uplink signals, the IQ data comes directly from 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. symbol FFT, except for PUSCH Physical Uplink Shared Channel. PUSCH subcarriers are despread before being used in calculations.
In uplink mode, when PUSCH is included in analysis, shows PUSCH IQ values after despreading (IFFT Inverse Fast Fourier Transform), overlaid on the the other channels/signals' reference IQ values, which come directly from the output of the symbol FFT. To view PUSCH points in the frequency domain instead, use the IQ Freq Ref trace. See the SC-FDMA Symbol Points section in for more information.
Only the points of channels/signals selected in Composite Include are shown on this trace. The color of a point indicates which channel/signal the point belongs to. The colors of the channel/signals are shown in the Frame Summary trace.
The data in this trace comes from the interval specified by Measurement Interval and Measurement Offset.
See the IQ Meas topic for more information.
See Also
