How to Test Sensitivity of Long Range DSSS PHY on E4432B

Overview

Silicon Labs has provided a Long Range DSSS PHY to help customers to achieve the crucial design element of maximum effective range. The Long Range feature is described in UG460.

The Long Range DSSS PHY is derived from the highly optimized IEEE802.15.4 Zigbee PHY. Currently the detailed parameters of this PHY is not public and users can't customize it. To help customers test the sensitivity of their final Long Range products, we implement a tool to generate the ARB waveforms.

This article introduces the approach of testing the sensitivity of Silicon Labs Long Range PHY on Agilent E4432B, including the tool of generating the ARB waveform, the steps of setting the E4432B and how to do the PER test.

If you are using any other Signal Generator, or have further questions about this approach, please feel free to contact us through Silicon Labs support portal, thanks.

Hardware Required

• Signal Generator E4432B
• IEEE 488.2 GPIB to USB cable (One of the following).
  • Agilent 82357B USB/GPIB Interface
  • NI GPIB-USB-HS
• PC
• DUT

Software Required

• IEEE 488.2 GPIB Driver (Install the driver according to your GPIB card provider).
  • Agilent 82357B USB/GPIB Driver
  • NI GPIB-USB-HS Driver
• Silabs_LR_WaveformGenerator.exe (Please make sure the GPIB driver is installed before running this tool).

Connection

Notes:

• Please use the GPIB driver to verify the GPIB connection. Assuming you are using the NI GPIB-USB-HS card, you can start the program NI Max to verify it.
  
  
  
• The serial port connection is used to run CLI commands on the DUT.

How It Works

Generate Waveform

1. Start the tool Silabs_LR_WaveformGenerator.exe.

2. Fill the payload which you want test. The header and CRC of the frame will be automatically updated. The long range PHY uses IEEE802.15.4 frame format, like below:

   
   
   

   Notes:

   • The byte order in the GUI of the tool is the same with the byte order of the packet over the air.
   • The LongRange PHY uses IEEE802.15.4 frame format. The maximum frame size is 127 bytes. As the CRC field takes 2 bytes, users can input maximum 125 bytes as the payload.

3. Fill the waveform file name. This is the waveform file name stored on the signal generator. The filename is non-case-sensitive.

4. Press the button “Generate” to generate the IQ data.

   
   
   

5. Click the button Scan to scan the connected E4432B, then click the Download button to download the generated waveform to the instrument. It takes about 30~40 seconds to complete. The waveform file will be stored on E4432B as a non-volatile file.

Settings of E4432B

1. On the signal generator keypad, press the Mode button and then select Arb Waveform Generator | Dual Arb.

2. Choose Select Waveform. If the ARB waveform list is empty, choose Waveform Segments.

3. Select Load, then use the wheel to navigate to the waveform file LR_9K6, then select Load Segment From NVARB Memory.

4. Press Return, navigate to the waveform file, then choose Select Waveform.

5. Press Return.

6. Select Arb Setup, and under Arb Sample Clock, input the sample clock with the keypad and then Enter. Press the Return button. Here is how to calculate the sample clock. In the IQ waveform, each bit is represented by 16 points. The sample clock should be:

   sample clock = data rate * spread factor * 16 / 2

   For example, for Long Range PHY DSSS 9.6kbps, the spread factor is 8, then the sample clock should be set to:

   sample clock = 9.6 * 8 * 16 / 2 = 614.4 KHz

   Here:

   • The number 9.6 is the data rate. The supported data rate includes:
     • 1.2
     • 2.4
     • 4.8
     • 9.6
     • 19.2
     • 80
   • The number 16 in the equation means the IQ points for each bit. It's fixed in the tool.
   • As we will split the data into I and Q, then we will divide the result with 2.

   Below is a the sample clock for the LongRange PHYs with different data rate.

   Data Rate	Sample Clock
   1.2 kbps	76.8 kHz
   2.4 kbps	153.6 kHz
   4.8 kbps	307.2 kHz
   9.2 kbps	614.4 kHz
   19.2 kbps	1228.8 kHz

7. Set the following:

   • Arb Reference -> Int
   • Recon Filter -> 8 MHz
   • Marker Pol -> Neg
   • Mkr2 to RF Blank -> On

8. Press Return button.

9. Select Trigger -> Single.

10. Select Trigger Set-up and set the following:

    • Trigger Source -> Ext
    • Ext Pol -> Neg
    • Ext Delay -> Off

11. Verify that the displayed menu in the middle of the screen shows the following before continuing:

    • Sample Clock 614.4 KHZ
    • Reconstruction 8 MHz
    • Ref Freq 10 MHz (Int)
    • Trig Type Single
    • Trig Source Ext
    • Polarity Neg
    • Retrigger Off
    • Delay Off

12. Turn Arb to On.

Test

Please refer to section 4.2.3 of AN972 to learn the testing steps.

The general steps are:

1. Flash a RAILTEST program to the DUT.
2. On the console of the DUT, run the following command to stop the receiving state.

   rx 0
   

3. On the console of the DUT, run the following command to start PER test.

   perrx 1000 10000
   

   The first argument 1000 means to test 1000 packets.
   The second argument 10000 means to delay 10000 us between each packets.
   By running this command, the DUT will generate a pulse on the GPIO to trigger the Signal Generator to transmit a packet every 10000 us, total 1000 packets.
4. Use command perstatus or status to check the status.
5. Adjust the transmitting power of the E4432B and then repeat step 3/4 until the PER reaches the tolerance.

Test Report

We have made a test based on the board EFR32FG14 2400/490 MHz 19 dBm Radio Board with TCXO (SLWRB4261A). The test is done in a shielded room. The test result is like below.

Test Result of Long Range DSSS 1.2 kbps PHY

SG Tx Power	SG Tx Count	DUT Rx Count
-129.0	1000	1000
-130.0	1000	934
-129.2	1000	985
-129.2	5000	4972
-129.3	5000	4957
-129.4	5000	4955

Conclusion: With PER tolerance set to 1%, the sensitivity is -129.4 dbm. The result is in accord with the measured data in table 3-1 of UG460 (Pay attention that the DUT uses a TCXO which makes the result a little better).

Test Result of Long Range DSSS 9.6 kbps PHY

SG Tx Power	SG Tx Count	DUT Rx Count
-130.0	1000	0
-120.0	1000	997
-125.0	1000	32
-122.5	1000	781
-121.3	1000	977
-120.7	1000	986
-120.4	1000	997
-120.5	1000	991
-120.6	1000	989
-120.5	5000	4970

Conclusion: With PER tolerance set to 1%, the sensitivity is -120.5 dbm. The result is in accord with the measured data in table 3-1 of UG460 (Pay attention that the DUT uses a TCXO which makes the result a little better).

FAQ

How to configure the trigger pin in RAILTEST?

On Simplicity Studio V5, open the .slcp file of the RAILTEST project, open the configuration of the component RAILtest Application, Core, you can select a GPIO as the trigger.

References

• KBA:Understanding DSSS Encoding and Decoding on EFR32 Devices
• KBA:How to Download 802.15.4 Arbitrary Waveform Files to Agilent Signal Generator E4432B
• KBA:How to Manually Set-up the Arb Waveform Generator for functional test
• Generation_of_IEEE_802154_Signals
• E44xxB ESG Signal Generators SCPI Command Reference