Troubleshooting MB-OFDM Measurements

This topic contains information to help troubleshoot measurements when using 802.16 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. Demodulation. Also review Setting up an 802.16 OFDM Demodulation Measurement for additional measurement information.

802.16 OFDM Troubleshooting Table

PROBLEM	POSSIBLE CAUSE	SOLUTION
Demodulation fails to lock on signal or SYNC NOT FOUND error message	Signal not present.	Check connections
	Carrier too far from center frequency.	Adjust center frequency. The analyzer center frequency must be within 200 kHz kiloHertz: A radio frequency measurement (one kilohertz = one thousand cycles per second). to lock properly.
	Input is over-loaded or under ranged.	Adjust input range. Typically, the best (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 achieved when the range is as small as possible while avoiding overloads.
	Frequency span is too narrow.	Increase frequency span. A frequency span of at least 1.6 GHz Gigahertz: A frequency measurement which equals one billion hertz. for TFC Transport Format Combination 1-4 signals and 550 MHz Megahertz: A unit of frequency equal to one million hertz or cycles per second. for TFC 5-7 MB-FDM signals.
	MB-OFDM signal has inverted frequency spectrum	Check the Mirror Frequency Spectrum setting (MeasSetup > Demod Properties > Advanced tab). Note that Synchronization, header demodulation, and demodulation at Data Rates <= 80 Mb/s work independently of the Mirror Frequency Spectrum setting.
	Time Frequecy Code incorrect	Set to correct TFC.
	Incorrect Preamble Type setting	Specify the correct Preamble Type, or set Preamble Type to Auto.
	Search length too short.	Increase search length, or adjust triggering to ensure that one complete packet is fully within the search length. Optionally, reduce Result length so that a smaller packet size is expected.
	Search length too short.	Increase search length, or adjust triggering to ensure that the leading and trailing edges of a pulse are fully within the search length.
Poor constellation display, demodulation results.	The Data Rate is incorrect.	Set the correct Data Rate.
EVM larger than expected	I/Q misaligned using I+jQ receiver.	The "Error Vector Spectrum" trace will shows as a "V" shape. Click Utilities > Calibration > External Amplitude tab, select the Calibration Constants check box and adjust the delays for each input channel.
	89611 with ESA H70 hardware need adjusting.	The "Error Vector Spectrum" trace will shows as a "V" shape. Click Utilities > Calibration > External Amplitude tab, select the Calibration Constants check box and adjust the delays for each input channel.
	89611 with ESA H70 hardware need adjusting.	Adjust the Tuner Maximum Mixer Level for the ESA.
	I/Q gain imbalance using I+jQ receiver.	1) Check that impedance is identical for both input channels. 2) Adjust the gains for each input channel (Click Utilities > Calibration > External Amplitude tab > Calibration Constants check box).
	Noise or interference from adjacent signals.	Reduce the span to eliminate excess noise and interfering signals.
EVM good, but Sync Correlation coefficient not good	Time Frequecy Code incorrect	Set to correct TFC.
The trace data constellationsymbol location shape, such as dots, is not properly displayed.	The display driver is not functioning correctly.	Contact your PC manufacturer to see if a newer version of the display driver is available. If not, try decreasing the hardware acceleration. See the Windows documentation for instructions.