Error Vector Time (802.16 OFDM Demodulation)

Menu Path: Trace > Data > Channel > Error Vector Time

Error Vector Time trace data shows the signal RCE (EVM) vs. Time and frequency. Error Vector Time provides the individual symbol EVMs for each subcarrier at each symbol for all symbol-times within the burst. The symbols in the burst are on the x-axis. For each symbol, the EVMs for all 200 subcarriers (subcarrier 0 is not used) are shown. The trace data includes data results for the pilot and data subcarriers. This trace data allows you to easily attain information about the signal modulation quality as a function of the symbol-times.

Symbol 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. is the magnitude of the error vector between the measured symbol vectors (IQ Meas) and ideal symbol vectors (IQ Ref). RMS Error Vector Time trace data is the average of the symbol EVMs of all the subcarriers at each symbol-time. This plot of the RMS average EVM at each symbol (includes all 200 subcarriers at that symbol) is displayed as a white line on the Error Vector Time trace data.

Interpreting the trace data

The y-axis annotates the EVM magnitude and the x-axis annotates 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 number (which range from 0 to the last symbol-time within the burst). The z-axis annotates the OFDM subcarrier number (which includes all 200 subcarriers, subcarrier 0 is not used). Each x-axis symbol-time on the trace data shows the individual symbol EVMs for all subcarriers at that particular symbol-time. Placing a marker on a symbol provides the symbol number, the subcarrier number, the symbol EVM and the RMS average of symbol EVMs at that particular symbol-time.

The Error Vector Time trace data uses a multi-color trace data that assigns a unique color to the pilot subcarriers, the data subcarriers and the RMS Error Vector Spectrum trace data. There are also separate colors assigned for the different data modulation types: BPSK Binary phase shift keying - A type of phase modulation using 2 distinct carrier phases to signal ones and zeros. (magenta), QPSK Quadrature phase shift keying (red), 16QAM (blue), and 64QAM (green). The colors are user definable, see Display Preferences.

This Error Vector Time trace data shows a demodulated OFDM IEEE Institute of Electrical and Electronics Engineers. A US-based membership organisation that includes engineers, scientists, and students in electronics and related fields. The IEEE developed the 802 series wired and wireless LAN standards. Visit the IEEE at http://www.ieee.org 802.16a/d signal with a result length of 15 symbol-times (0 through 14).

Trace data display symbols:

• Red squares: Identifies the data subcarrier EVMs.

• White squares: Identifies the pilot subcarrier EVMs.

• Green vertical lines: Identifies common OFDM symbol-times.

• White line: Plot of the RMS average symbol EVM at each symbol-time. This is the same trace data as the OFDM RMS Error Vector Time trace data.

• White diamond: Identifies the marker position.

Trace A Marker trace data:

• Symbol-time number:  3

• Subcarrier number:  -11 (subcarrier 0 is not used)

• Symbol EVM:   2.7396 % (for subcarrier -11, symbol 3)

• RMS average symbol EVM: 2.575 % Avg (for all subcarriers at symbol 3)

See Also

RMS Error Vector Spectrum (802.16 OFDM)

RMS Error Vector Time (802.16 OFDM)

Available Trace Data (802.16 OFDM)