Troubleshooting (W-CDMA(3GPP)/HSPA)
This topic contains information to help troubleshoot measurements when using W-CDMA Code Division Multiple Access: One of several digital wireless transmission methods in which signals are encoded using a specific pseudo-random sequence, or code, to define a communication channel. A receiver, knowing the code, can use it to decode the received signal in the presence of other signals in the channel. This is one of several "spread spectrum" techniques, which allows multiple users to share the same radio frequency spectrum by assigning each active user an unique code. CDMA offers improved spectral efficiency over analog transmission in that it allows for greater frequency reuse. Other characteristics of CDMA systems reduce dropped calls, increase battery life and offer more secure transmission. See also IS-95. (3GPP)/HSPA Demodulation. See the Setting up a W-CDMA Measurement topic for additional measurement information.
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PROBLEM |
POSSIBLE CAUSE |
SOLUTION |
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Demodulation fails to lock-on signal |
Signal not present. |
Check test setup connections |
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Carrier too far from center frequency. |
1) Adjust center frequency to ± 500 Hz of the carrier frequency 2) For downlink measurements using the SCH SYNC type, adjust the center frequency to ± 250 Hz of the carrier frequency |
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Input is over-loaded or under ranged. |
Adjust input range |
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Frequency span is too narrow. |
Increase frequency span |
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Incorrect chip rate. |
Enter correct chip rate (not symbol rate or bit rate) |
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Incorrect Scramble Code, Scramble Code Type or Scramble Code Offset. |
Make sure that the VSA settings match the input signal parameters (tab). |
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W-CDMA (3GPP) downlink SCH or CPICH Common Pilot Channel channel is missing or the signal level is to low. |
Verify that the signal includes either a SCH or CPICH channel and that the Sync Type parameter setting matches the channel type. Verify that the signal includes {TDS: this wording is strange} either a SCH and CPICH channel and that the Sync Type parameter setting matches the channel type. Adjust the signal level as necessary |
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W-CDMA (3GPP) uplink DPCCH Dedicated Physical Control Channel channel is missing or power level to low. |
Verify that the signal includes the DPCCH channel and that the power level is high enough. |
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W-CDMA signal is inverted |
Check the Mirror Frequency Spectrum setting (tab). |
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I/Q offset too large |
Reduce LO feedthrough (or DC offset for I+jQ receiver) |
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Keysight ESG firmware needs to be upgraded. (Cause only applies if this ESG is used to generate the input signal). |
Use firmware revision B.03.50 or newer to generate W-CDMA(3GPP) modulated signals.
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I/Q misaligned using I+jQ receiver |
Ensure that ch1 and ch2 trigger delays are correct |
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Noise Floor increases at channel turn on. |
The channel turned on uses a different scramble code than that set in VSA. |
Change the scramble code used to transmit the channel to match that used by the P-SS/SSCH or CPICH channels. |
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Wrong channel marked as active |
Poor SNR Signal-to-Noise Ratio (signal to noise ratio). |
Increase signal power or remove cause of noise/distortion. |
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All bits not transmitted within a physical channel. |
Transmit all bits within a physical channel, or select code-domain power for the layer associated with the physical channel of interest (single-layer code-domain power displays are accurate even if the VSA is unable to identify active channels in the composite code-domain power display). |
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Data pattern induces large disparity in power between slower channels overlaid by the channel of interest. |
Verify that your transmitter is transmitting properly. |
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Tslot and Tframe or tDPCH is incorrect (DATA? error message is displayed in the symbol table). |
Measurement Interval is less than 6 slots (fewer slots introduce a higher degree of false correlation on pilot and sync channels) |
Select 6 or more Measurement Interval slots (tab.) |
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The trace data constellation symbol 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. |
See Also
Setting up a W-CDMA(3GPP) measurement
Measurement speed and resolution considerations
