Troubleshooting Advanced Design System (ADS)

Known problems using ADS cdma2000 Library, (version 1.5.1), with the 89600 VSA cdma2000 Demodulation (Opt B7T).

1) For both Forward and Reverse links, the baseband RF Radio Frequency: A generic term for radio-based technologies, operating between the Low Frequency range (30k Hz) and the Extra High Frequency range (300 GHz). frequency spectrums are the complex conjugate of actual cdma2000 signals.

Un-flip the displayed frequency spectrum to produce the correct display. Select the Mirror Frequency Spectrum check box (Click MeasSetup > Demod Properties > Format tab).

To fix this in the simulation, invert the final Q signal or invert the LO phase in the up conversion modulator.

2) The initial phase decimator (D2) in the ADS Reverse link modulator, (the CDMA2K_RevHPSK component), is incorrect which leads to a completely different I channel spreading sequence.

Select the modulator, pushing down to its schematic, and changing the Phase property from 0 to 1. Unfortunately, this library component cannot be saved, so it must be modified each time ADS is entered.

3) In the CDMA2K_RevHPSK component, the phase of the length 2 Walsh cover sequence generator (C4) is inverted.

This could be a none issue: Because all channels are only I and Q channels, this results in either complex conjugation of the final output (I Channels) or both inversion and complex conjugation (Q Channels), so leaving this in place effectively fixes problem (1) above.

This can be corrected by inserting a Gain block in series with the output of the Walsh generator (C4) with the Gain property set to -1.

4) The 89600 VSA can only demodulate Reverse link signals with a long code mask of 0.

Because binary 0 maps to +1.0 Float, a Const component with Level set to 1.0 should be substituted for the long code generator in Reverse link simulations.

5) The Example Forward link simulations do not include the phase equalization filter described in 3.1.3.1.14.2 of cdma2000 specification. This results in excessive 89600 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. measurement results.

Enable external IF Calibration using a calibration file that applies the necessary phase correction data.

Procedure:

1) Copy this calibration file "%PROGRAMFILES%\Keysight\89600 Software <ReleaseVersion>\89600 VSA Software\Cal\CDMA2kPhaseDist.cal" to a convenient place, such as your project file data directory;

2) Load and apply the cal data: Click Input > User Correction > IF Filter check box, and locate the cal file.

Note: If an IQ measurement is being performed, apply the calibration file to both channels.