Error Vector Spectrum (802.11a/g/j/p OFDM)

Menu Path: Trace > Data > Channel X > Error Vector Spectrum where X is the selected channel.

Error Vector Spectrum trace shows 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 and subcarrier Error Vector Magnitude (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.) vs. subcarrier (frequency) and Symbol (time). There is separate trace for each measurement channel and spatial stream (MIMO Multiple Input, Multiple Output: A physical layer (PHY) configuration in which both transmitter and receiver use multiple antennas. only). The Error Vector Spectrum trace allows you to easily attain information about the signal modulation quality as a function of the subcarriers.

Error Vector Spectrum trace provides the following data results: the subcarrier EVM and the RMS average subcarrier EVM. The trace analysis data includes the payload data including all Pilot and Data subcarriers for the measurement burst. Unused subcarriers are blanked and not included in the measurement analysis. There is also a plot (default White liner) of the RMS average subcarrier EVM for all subcarriers and symbols in the measurement analysis.

Marker Results	Description
carrier	specifies the marker subcarrier index.
sym	specifies the marker OFDM symbol number.
First Data Result (m%)	This is the subcarrier EVM (%) result for the marker subcarrier. Subcarrier EVM is the EVM between the measured (IQ Meas) subcarrier vector and an ideal (IQ Ref) subcarrier vector.
Second Data Result (Avg)	This is the RMS subcarrier EVM (m%) result for the marker subcarrier. RMS Subcarrier EVM is the computed RMS average of the subcarrier EVMs at a particular subcarrier for all OFDM symbols in the measurement analysis region (see RMS Error Vector Spectrum trace data).

Interpreting the Trace

The y-axis ordinal is the EVM magnitude, the x-axis ordinal is the subcarrier index, and the z-axis ordinal is the OFDM symbol. This trace format groups symbols by subcarrier index for all the symbols within the measurement burst. For example; subcarrier index -10 shows subcarrier -10 for all OFDM symbols in the measurement burst.

Trace Color coding Scheme

A multi-color coding scheme is used to make it easy to visually identify common symbols, subcarriers, and data results within various OFDM Traces. This makes cross trace data comparisons and analysis easy to accomplish. Different colors are assigned to symbols representing a common subcarrier type including: Pilot and Data subcarrier types. Some common color scheme Traces include: Error Vector Spectrum, Error Vector Time, IQ Meas, IQ Ref, and the Syms/Errs  trace data.

See Also

Available Trace Data (802.11a/g/j/p OFDM)