Transmitter Spectral Mask Test (DSSS/OFDM)

Introduction

The Transmitter Spectral Mask measurement includes the in-band and out-of-band spurious emissions. This test specifies that the transmitted signal does not exceed the IEEE 802.11 a, b, g specified spectral mask. The reference level power is taken as the Power Spectral Density (PSD) in the signal.

Spectral mask margin is the worst difference between the spectral mask and the measured PSD. A positive value indicates the minimum margin by which the PSD passed this test. A negative value indicates the worst-case amount by which the PSD failed this test. This test ensures that multiple WLAN devices do not unduly interfere with each other. The spectrum test can be a good indicator of deteriorating performance.

Optimum Use of N4010A Input Range Settings

To obtain best accuracy, it is important to ensure that:

  1. The N4010A input range is adjusted so that the DUT signal is close to the maximum input level without causing overload.

  2. The N4010A input range should be above -20dBm, ideally above 0dBm. External fixture losses should be kept as low as possible.

When the N4011A hardware is connected to the N4010A RF In/Out port, signal levels higher then -5dBm are recommended.

Enhanced Dynamic Range

Factors such as device variability and high fixture losses can lead to marginal pass/fail conditions at the lowest level of the mask. An enhanced dynamic range setting is available for the 802.11b DSSS spectral mask measurement. This can only be used with the 66 MHz span. This setting provides an enhancement of 5 dB but is also slower than the non-enhanced measurement. This is controlled by the IncreasedDynamicRange Property. The default is off.

Programmatically setting up the N4010

Ensure the N4010 WLAN Test DLL (COM or .NET version) has been set up as shown in Step 1 - Reference the Dynamic Link Library (DLL) and Step 2 - Create the Instrument Object to reference and create a connection with the N4010 instrument via the VISA resource address. The following procedure can be followed as part of a test script along with the other tests after the N4010 connection has been made, and prior to disconnection via the Dispose() method.

The N4010 measurement setup properties below can be common to all measurements in one test sequence when the WLAN device transmit parameters are constant. These setup conditions must be reset when the WLAN device parameters change.

Spectral mask Test Procedure Summary

The following steps summarize the procedure required to configure the WLAN DUT and the N4010, make the EVM Measurement, and recover the results:

    1. N4010: Setup Frequency, for example, Channel 1 at 2.412GHz, by setting the Frequency property

    2. N4010: Setup Power Range, for example, 5dBm, by setting the PowerRange property

    3. N4010: Setup Max Packet Length, for example, 970e-6, by setting the MaxPacketLength property

    4. N4010: Setup Trigger Style, for example, MagLevel, by setting the TriggerStyle property

    5. N4010: Setup Trigger Level, for example, 0.3V, by setting the TriggerLevel property

    6. N4010: Setup Trigger Delay, for example, -2e-6, by setting the TriggerDelay property

    7. N4010: Setup Trigger Holdoff, for example, 60e-6, by setting the TriggerHoldoff property

    8. WLAN DUT: Setup frequency band, for example, 802.11b

    9. WLAN DUT: Setup channel, for example, channel 1 at 2.412GHz (that is, N4010 = WLAN DUT Frequency)

    10. WLAN DUT: Setup transmit power

    11. WLAN DUT: Setup modulation type, for example, 11Mbps, CCK

    12. WLAN DUT: Start transmitting packets

    13. N4010: Initiate the Spectral Mask Measurement

    14. N4010: Retrieve the Spectral Mask Margin Measurement Result

Enhanced Dynamic Range setting:

    1. N4010: Setup span, 66 MHz

    2. N4010: Setup Enhanced, on

Spectral Mask Test Procedure Programming Detail

Using the same steps as the above summary procedure, this procedure shows the required N4010 WLAN DLL commands.

  1. N4010: Setup Frequency, for example, Channel 1 at 2.412GHz, by setting the Frequency property

    Inst.Frequency = 2.412e9;

    // Sets the N4010 Tx / Rx Frequency

  2. N4010: Setup Power Range, for example, 5dBm, by setting the PowerRange property

    Inst.PowerRange = 5.0;

    // Sets the N4010 maximum expected power range to optimize dynamic range

  3. N4010: Setup Max Packet Length, for example, 970e-6, by setting the MaxPacketLength property

    Inst.MaxPacketLength = 970e-6;

    // Sets the N4010 acquisition length for 802.11b DSSS measurements


    Or


    Inst.MaxSymbolsUsed = 16;

    // Sets the N4010 acquisition length for 802.11a/g OFDM measurements

  4. N4010: Setup Trigger Style, for example, MagLevel, by setting the TriggerStyle property

    Inst.TriggerStyle = Agilent.N4010.WLanTest.Enums.TriggerStyle.MagLevel;

    // Sets the N4010 trigger style

  5. N4010: Setup Trigger Level, for example, 0.3V, by setting the TriggerLevel property

    Inst.TriggerLevel = 0.03;

    // Sets the N4010 trigger level

  6. N4010: Setup Trigger Delay, for example, -2e-6, by setting the TriggerDelay property

    Inst.TriggerDelay = -2e-6;

    // Sets the N4010 trigger delay

  7. N4010: Setup Trigger Holdoff, for example, 60e-6, by setting the TriggerHoldoff property

    Inst.TriggerHoldoff = 60e-6;

    // Sets the N4010 trigger holdoff

  8. WLAN DUT: Setup frequency band, for example, 802.11b

    // DUT Specific command to set frequency band

  9. WLAN DUT: Setup channel, for example, channel 1 at 2.412GHz (that is, N4010 = WLAN DUT Frequency)

    // DUT Specific command to set transmit frequency

  10. WLAN DUT: Setup transmit power

    // DUT Specific command to set transmit power

  11. WLAN DUT: Setup modulation type, for example, 11Mbps, CCK

    // DUT Specific command to set modulation type

  12. WLAN DUT: Start transmitting packets

    // DUT Specific command that turns transmitted power on ready for measurement

  13. N4010: Initiate the Spectral Mask Measurement

    Inst.IEEE80211b_SpectralMask_Initiate();

    // Initiates the N4010 DSSS 802.11b Spectral Mask Measurement


    Or


    Inst.IEEE80211a_SpectralMask_Initiate();

    // Initiates the N4010 OFDM 802.11a or 802.11g Spectral Mask Measurement

  14. N4010: Retrieve the Spectral Mask Margin Measurement Result

    Result = Inst.IEEE80211b_SpectralMask_Margin

    // Returns the N4010 DSSS 802.11b Spectral Mask Margin Result


    Or


    Result = Inst.IEEE80211a_SpectralMask_Margin.

    // Returns the N4010 OFDM 802.11a or 802.11g Spectral Mask Margin Result
    // A positive value indicates the minimum margin by which the PSD passed this test.
    // A negative value indicates the worst-case amount by which the PSD failed this test.

 

Enhanced Dynamic Range setting:

  1. N4010: Set the span to 66 MHz

    Inst.IEEE80211b_SpectralMask_Span = 66000000.0;

    // Sets the span to 66 MHz

  2. N4010: Set the gain enhancement on

    Inst.IEEE80211b_SpectralMask_IncreasedDynamicRange = true;

    // Sets the 5 dB gain enhancement on