Troubleshooting (802.16 OFDM)
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 89600 VSA Version Differences and Measurement TIPS for additional measurement information.
802.16 OFDM Troubleshooting Table
PROBLEM |
POSSIBLE CAUSE |
SOLUTION |
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Signal not present. |
Check connections |
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Carrier too far from center frequency. |
Adjust . The VSA center frequency must be within 2 * Subcarrier Spacing to lock properly. |
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Input is over-loaded or under ranged. |
Adjust RCE Relative Constellation Error is the RMS level of the Error Vector Magnitude, averaged over all subcarriers and all detected OFDM symbols. (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. . Typically, the best |
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Frequency span is too narrow. |
Increase frequency . A frequency span of at least 1.2 * the nominal BW is required for 802.16 OFDM signals. |
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OFDM signal has inverted frequency spectrum |
Check the setting ( tab). |
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802.16 signal has incorrect FCH symbol at start of burst |
Check the Data Sub-carrier Modulation selection ( tab).
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Wrong modulation format |
Select correct modulation format |
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Search length too short. |
Increase or adjust triggering to ensure that the leading and trailing edges of a pulse are fully within the . |
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Signal is not pulsed. |
802.16-OFDM TDD Time Division Duplex: A duplexing technique dividing a radio channel in time to allow downlink operation during part of the frame period and uplink operation in the remainder of the frame period. mode is assumed by default. If the signal is not pulsed, turn off . |
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Search length not optimized |
Try the following method to determine when performing a :SL = (2*MaxOn) + MaxOff Where: SL is search length in seconds. MaxOn is the maximum on time of a pulse in seconds. MaxOff is the maximum off time between pulses in seconds. |
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I/Q misaligned using I+jQ receiver. |
The trace will shows as a "V" shape. Click tab, select the check box and adjust the delays for each input channel. |
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89611 with ESA H70 hardware need adjusting. |
Adjust the Tuner Maximum Mixer Level for the ESA. |
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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 check box). |
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Signal is transmitting incorrect pilot bits. |
If the signal is transmitting incorrect pilot bits, the CPE level will be high, both in the Syms/Errs summary and on the trace. Turning off and possibly may help ( tab). |
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Signal has longer than usual transition region between symbols |
Change to be more negative ( tab). |
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Noise or interference from adjacent signals. |
Reduce the to eliminate excess noise and interfering signals. |
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OFDM signal has inverted frequency spectrum |
Try inverting the frequency spectrum ( tab). It is possible for the VSA to appear to synchronize to a signal with inverted frequency content. |
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Signal amplitude varies during the burst. |
Turn on ( tab). |
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802.16 signal has incorrect length portion of SIGNAL symbol at start of burst |
Override the auto detection of ( tab). |
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Center frequency not close enough to signal carrier frequency |
Adjust . |
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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. |
See Also