Basic Mode and Multi-Carrier Waveforms

In this example, you will use the N7615C software to create a waveform that contains 3 "basic" carriers for WiBro. You might use this type of setup for designing and manufacturing power amplifiers and repeaters.

1. From the Welcome dialog, select Mx1 (Single Antenna Simulated Hardware).

   1. Click Instrument in the navigation tree on the left. Set the instrument's frequency to 2.345 GHz and leave the amplitude at the default value of –10 dBm.

   2. Click Waveform Setup in the navigation tree on the left.

      The table at the top shows the default setup with a single carrier. The type of carrier depends on whether the software is set up to connect to an instrument that has a license for basic or advanced capability. The buttons above the table allow you to access the predefined configurations, add a basic or advanced mode carrier, delete a carrier, or copy a carrier.  

2. Click the button to see the predefined configurations that are available, then click cancel to return to the Waveform Setup. If the table shows an advanced carrier, click the button to delete it and then click to add a basic OFDMA carrier.

3. Change Downlink Ratio to 63.952%. This is the default for WiBro.

4. Click on Carrier 1 in the table or in the navigation tree on the left to access more signal parameters. Reference Specification is available on this window. Change the Bandwidth value to 8.75 MHz. The value of n will update to 8/7.

5. Click Downlink in the tree view to view the available parameters.

6. Click on Zone #1, PUSC and note the simple setup window for the zone. The frame graph is displayed at the bottom of the window. In a basic carrier, you cannot configure bursts so there is no zone-level view. Change Modulation Format to 64QAM and Number of Symbols to 26.  

7. The MAC PDU table at the bottom of the window allows you to configure the MAC PDU. Click Data Type and see the Data Source Selection window to choose the Data Type. You can choose S(QPSK), S(16QAM), S(64QAM), PN 9, PN 15 or User Defined Bits to input any desired data. For this example, leave the Data Type at the default choice of PN9. You have completed the carrier configuration.  

8. Click Waveform Setup and then click the button twice to add 2 carriers with the same configuration.

9. Click Carrier 2 and change the Frequency Offset to -9 MHz.  

10. Click Carrier 3 and change the Frequency Offset to 9 MHz.

    This completes the basic setup of the 3FA signal.

11. Click Waveform Setup and then click the button in the toolbar. You will see the CCDF graph for the waveform (all 3 carriers). Note that the default view is now the Burst CCDF, although Waveform CCDF is still available. The CCDF for each individual carrier can be viewed by clicking on that carrier in the navigation tree. Click here for more information. 

    Notice that the CCDF shows a high peak-to-average ratio that is much higher than that for each individual carrier. This comes from signals adding in phase due to all 3 carriers being identical, and usually you will want a lower peak-to-average ratio. Try changing the following parameters and then generating the waveforms again to view the change in the CCDF for the overall waveform. Be sure to click Waveform Setup to view the correct CCDF.   

    1. Click on each carrier and try changing the Initial Phase. (Example: Try setting Carrier 1 to -10 degrees and Carrier 3 to 180 degrees)  

    2. Click on the zone node for each carrier and change the Data Bit Offset values.

12. Click Waveform Setup, select the Waveform tab near the bottom of the window, and use the drop down arrow to view the power, I/Q, and spectrum plots for the waveform.

13. Click the Power Envelope tab.

    The yellow line shows the relative power for the waveform, and you can see the relative amplitude levels for different symbols by moving the mouse over a portion of the downlink burst. The dark red portion shows the symbols that are used as the power reference for the instrument. By default, the software turns marker 4 on during these symbols (see marker settings on Waveform Setup page), and marker 4 is used to control the ALC hold function in the instrument (as shown in Instrument setup page, under 6. Dual ARB Marker Utilities). These are the symbols where the instrument's ALC will be active, so the power level of these symbols will be equal to the instrument's amplitude setting.

    You can choose to change the power reference by clicking on a different set of symbols. When you do this, the new symbols will be shown in dark red. When you move the mouse over that section, it will be shown as amplitude = 0 dB and the levels elsewhere in the waveform will be relative to that value. The new amplitude offset value will be displayed in the Waveform Setup parameter table above the graph, as ALC Reference Offset under 3. Marker and Other Settings. The power level of these selected symbols will now be equal to the instrument's amplitude setting.

14. Click the button in the toolbar to download the waveform to the instrument. On the spectrum analyzer, use the band power markers to measure the power level in each carrier. What do you observe about the power levels? 

15. The relative power level for each carrier can be adjusted by clicking on the Carrier node and changing the power setting. This allows you to compensate for any flatness imperfections in the instrument.

16. If desired, set up the 89601A software to demodulate the signal and measure the EVM.

    Some important notes:

    • You can import *.xml setup files from the N7615A into the N7615C by changing the file type selection when you open a settings file. However, the *.scp setup files cannot be used with N7615A version 1.2.2.0 or earlier.  

    • The VSA can only demodulate a single carrier. Therefore, the demodulation analysis data that you see is only for the carrier at the center frequency.