Setting up a RFID modulation measurement

This topic provides information on connecting and successfully demodulating a signal using the RFID demodulator. A typical measurement includes the following measurement setup process (each step is discussed in the following text).

  1. Connect your signal to the VSA

  2. Configure measurement setup and input parameters

    1. Set the Center Frequency

    2. Set Frequency Span

    3. Configure the Input Range

    4. Configure Triggering

    5. Verify input signal and initial parameter settings

  3. Configure the RFID demodulator

    1. Select the RFID demodulator

    2. Open the RFID Demod Properties dialog box

    3. Click Preset to Standard...

  4. Setup measurement parameters

    1. Set forward link parameters
    2. Set return link parameters
    3. Set filter parameters
    4. Adjust clock rate (when necessary)
    5. Mirror frequency spectrum (when necessary)
  5. Configure optional measurement parameters

  6. Run the measurement

Measurement Setup Procedure

  1. Connect your Signal to the VSA

    • Single channel connection

      Connect the signal to Channel 1 on the measurement input hardware.

      Click Input > Channels and select 1 Channel. Multiple channels can be selected, but the demodulator will only use Channel 1.

    • I+jQ connection

      Connect the I and Q signals to the measurement input hardware. To configure the VSA, select Input > Channels > I + jQ.

      Notes for I+jQ input:

      • Selecting an I+jQ configuration enables DC coupling.
      • Use User Correction to correct for any offset or gain imbalance between the I and Q signals.
      • Range is set independently for the I and Q inputs, but can be coupled by selecting the Couple Paired Channels parameter.

    • Recorded signal

      Recall the recorded signal by selecting File > Recall > Recall Recording

      The center frequency and input range will be set by the recording.

    For more information about your specific measurement hardware, see the Measurement Hardware book.

  2. Configure Measurement Setup and Input Parameters

    1. Set the Center Frequency

      The VSA's center frequency must be close to the transmitted carrier frequency to achieve carrier lock. The required proximity of the center frequency to the carrier frequency varies depending on the signal type, symbol rate, and system noise. If symbol locking appears poor, to achieve better carrier locking observe the Freq Err value in the symbol table of any successfully locked measurement and add that amount to the center frequency. As a general rule, the difference between the center frequency and the carrier frequency should be within 3% of the symbol rate.

    2. Set Frequency Span

      The minimum span (information bandwidth) depends on the symbol rate. See the Span topic in the Reference for details.

    3. Configure the Input  Range

      The input range must be set correctly to obtain accurate measurements. Input ranges that are too low overload the VSA's ADC Analog-to-Digital Converter. Input ranges that are too high increase noise, which increases errors reported in error summary data, such as 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..

    4. Set up triggering (if required) 

      The default triggering mode is set to "FreeRun". However, a different type of triggering can be configured by using the parameters on the Input > Trigger tab.

    5. Verify the input signal and initial parameter settings 

      View your signal in the frequency domain (Spectrum trace) to verify the parameters you set.

  3. Configure the RFID demodulator

    1. Click MeasSetup > Measurement Type > RFID to enable the RFID demodulator.

    2. Click MeasSetup > RFID Demod Properties to display the properties and measurement parameters dialog box.

    3. Click Preset to Standard and select an RFID standard and bit rate (when applicable).

      No Standard can be selected and the measurement parameters set manually.

      However, choosing certain standards will enable functionality specific to that standard. For example, choosing ISO 18092 will add the Passive Return Link parameter to the Format tab of Demod Properties. For this reason, clicking Preset to Standard and then customizing the measurement parameters is recommended.

    Try restarting the measurement (see Step 6 below) to see whether your signal will demodulate with the default values.

  4. Setup measurement parameters

    These parameters will need to be set when the default values are not correct for your signal.

    1. Set forward link (interrogator) Format, Line Coding, and Bit Rate or Tari
    2. Set reverse link (tag) Format, Line Coding, Bit Rate and the Passive Return Link parameter
    3. Set Measurement Filter, Reference Filter, and filter Alpha / BT.
    4. Adjust the timing with the Clock Adjust parameter when necessary

    5. Set Mirror Frequency Spectrum when necessary

      RFID demodulation provides a feature that configures the demodulator to conjugate the complex time-domain waveform. This has the effect of flipping the spectrum around the VSA's center frequency.

  5. Configure optional measurement parameters

    1. Set Points / Symbol (Format tab)
    2. Specify Measurement Mode (Format tab)
    3. Specify the Direction (Format tab) of the burst

    4. Specify a different Acquision Length (Time tab)

    5. Perform a Sync Search

      Select the Sync Search parameter (Time tab) and select a Standard Pattern or specify a custom Bit Pattern

    6. Specify the index of the burst for analysis using the Burst Index parameter (Time tab)

      -or-

      Turn off Burst Search and specify Result Length, Result Offset, Sync Search Length, Sync Search Offset, and Sync Offset (Time tab) to manually select the burst to analyze

    7. Set custom thresholds for CW Lower, CW Upper, CW Settling, ASK Lower, and ASK Upper (Advanced tab)
    8. Set Normalize IQ Traces (Advanced tab)

  6. Run the Measurement

    Press the Restart ( ) button to restart the measurement.

    For help when your signal is not demodulating correctly, see the Troubleshooting topic.

Tips When Using RFID Demodulation

The following contains additional information to know when using RFID Demodulation:

ASK Reference: The VSA does not need an ideal signal to generate the reference signal. The VSA uses your signal to internally generate the ideal reference signal.

Symbol Clock: The VSA does not need an external symbol clock because the VSA internally generates the symbol clock.

Time Gating: Time gating is not available for RFID demodulation.

Averaging: Averaging is not available for demodulated trace data in digital demodulation but may be applied to numeric error data in the symbol table. For details, see Available Features.

Accuracy: To meet specifications, your signal and its modulation must be fully contained in the selected measurement span.

See Also

Troubleshooting

Using an RFID Standard Setup

Selecting the RFID Demodulator