OFDM Standards Measurements

Last Updated: June 19, 2009

The OFDM Standards Measurements tab groups together the following tests for 802.11 a/g (OFDM) DUT transmitters.

Test Set Requirements: N8300A Wireless Networking Test Set Version A.02 and above.

Center Frequency Leakage Test

Center Frequency Leakage is the portion of the transmitter energy that leaks through the transmitter components. This unwanted energy appears in the modulated signal at the signal center frequency. This test specifies center frequency leakage relative to total transmitted power. Energy at the centre frequency of the carrier can cause problems with receiver structures that use zero frequency intermediate signals. 802.11a specifically avoids using the centre carrier for transmission.

IEEE Std 802.11a-1999 16 September 1999 Paragraph 17.3.6.1 Transmitter Center Frequency Leakage

SCPI Commands: [SENSe:]CFLeakage, FETCh:CFLeakage?, READ:CFLeakage?

Test Procedure Summary

The following steps summarize the procedure required to configure the WLAN DUT and the N8300, make the CFL Measurement, and recover the results:

    1. N8300: Setup Frequency, for example Channel 1 at 2.412GHz.

    2. N8300: Setup Power Range, for example 5dBm.

    3. N8300: Setup Max Symbols Used, for example 16.

    4. N8300: Setup Frames Used, for example 10.

    5. N8300: Setup Trigger Style, for example Maglevel.

    6. N8300: Setup Trigger Level, for example 0.3V.

    7. N8300: Setup Trigger Delay, for example -2e-6.

    8. N8300: Setup Trigger Holdoff, for example 60e-6.

    9. WLAN DUT: Setup frequency band, for example 802.11a/g

    10. WLAN DUT: Setup channel, for example, channel 1 at 2.412GHz (that is, N8300 = WLAN DUT Frequency)

    11. WLAN DUT: Setup transmit power

    12. WLAN DUT: Setup modulation type, for example 54 Mbps

    13. DUT: Start transmitting packets

    14. N8300: Press Init to make the measurement.

Frequency Error

The Frequency Error is part of the EVM measurement and displayed here in as a parts-per-million (ppm) result.

 

SCPI Commands: CALCulate:EVM, [SENSe:]EVM, FETCh:EVM?, READ:EVM?

Test Procedure Summary

The following steps summarize the procedure required to configure the WLAN DUT and the N8300, make the EVM Measurement, and recover the results:

    1. N8300: Setup Frequency, for example Channel 1 at 2.412GHz.

    2. N8300: Setup Power Range, for example 5dBm.

    3. N8300: Setup Max Packet Length, for example 970e-6.

    4. N8300: Setup Frames Used, for example 10.

    5. N8300: Setup Trigger Style, for example MagLevel.

    6. N8300: Setup Trigger Level, for example 0.3V.

    7. N8300: Setup Trigger Delay, for example -2e-6.

    8. N8300: Setup Trigger Holdoff, for example 60e-6.

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

    10. WLAN DUT: Setup channel, for example, channel 1 at 2.412GHz (that is, N8300 = WLAN DUT Frequency).

    11. WLAN DUT: Setup transmit power.

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

    13. WLAN DUT: Start transmitting packets.

    14. N8300: Press Init to make the measurement.

EVM (Error Vector Magnitude)

Error Vector Magnitude (EVM), the transmitter modulation accuracy test, is calculated by comparing the actual measured signal with an ideal reference signal to determine the error vector. The EVM value is the root mean square (RMS) value of the error vector over time at the instants of the symbol (or chip) clock transitions. Every chip has its own error vector; EVM is the RMS average of all errors in a packet of 1000 chips.

IEEE Std 802.11b-1999 16 September 1999 Paragraph 18.4.7.8 Transmit modulation accuracy
IEEE Std 802.11a-1999 16 September 1999 Paragraph 17.3.9.7 Transmit modulation accuracy test
 

 

 

 

SCPI Commands: CALCulate:EVM, [SENSe:]EVM, FETCh:EVM?, READ:EVM?

Test Procedure Summary

The following steps summarize the procedure required to configure the WLAN DUT and the N8300A, make the EVM Measurement, and recover the results:

Spectral Flatness

Spectral flatness is a measurement of the power variations in the carriers of an OFDM (IEEE 802.11A/G) signal. It is measured during the 8ms channel estimation phase of the burst, with all 52 carriers active but after the start of a normal burst. This test specifies a mask for the magnitude response of the transmitter channel.

Spectral flatness must be within 2 dB for 16 sub carriers and within +2/-4 dB for all sub carriers, the 0 dB level is established over 16 sub carriers.

IEEE Std 802.11a-1999 16 September 1999 Paragraph 17.3.9.6.2 Spectral Flatness

SCPI Commands: [SENSe:]SFLatness, FETCh:SFLatness?, READ:SFLatness?

Test Procedure Summary

The following steps summarize the procedure required to configure the WLAN DUT and the N8300, make the EVM Measurement, and recover the results:

    1. N8300: Setup Frequency, for example Channel 1 at 2.412GHz.

    2. N8300: Setup Power Range, for example 5dBm.

    3. N8300: Setup Max Symbols Used, for example 16.

    4. N8300: Setup Frames Used, for example 10.

    5. N8300: Setup Trigger Style, for example, Maglevel.

    6. N8300: Setup Trigger Level, for example 0.3V.

    7. N8300: Setup Trigger Delay, for example -2e-6.

    8. N8300: Setup Trigger Holdoff, for example 60e-6.

    9. WLAN DUT: Setup frequency band, for example 802.11a/g

    10. WLAN DUT: Setup channel, for example, channel 1 at 2.412GHz (that is, N8300 = WLAN DUT Frequency)

    11. WLAN DUT: Setup transmit power

    12. WLAN DUT: Setup modulation type, for example 54 Mbps

    13. WLAN DUT: Start transmitting packets

    14. N8300: Press Init to make the measurement.