READ:EVM?

Last Updated: June 19, 2009

This command makes a Error Vector Magnitude (EVM) measurement and retrieves the results.

READ:EVM?

Queries the EVM measurement results. The returned results are dependant on the setting of [SENSe:]RADIo:STANdard[:SELect]:WLAN[?].

Query Range for DSSS: Returns the following comma-separated scalar results when the modulation type is DSSS, that is [SENSe:]RADIo:STANdard[:SELect]:WLAN[?] is set to either B or GDSSs:

  1. Bit Rate: The observed bit rate for data portion of the burst: a floating number as detailed in Bit Rate and Modulation Format Values for DSSS and OFDM

  2. Burst Quality: This indicates whether or not the measurement was performed on a good (1.0) or bad (0.0) burst: a floating point of 0.0 or 1.0

  3. Chip Clock Frequency Error: The measured symbol clock frequency error of the measured burst(s): a floating point expressed in parts per million

  4. Frequency Error: a floating point in Hz

  5. Gated Power: a floating point in dBm

  6. Header Status: This is information about the PLCP header: a floating point of the following values

  7. 1: No SFD sync pattern was found in the preamble, so the header is not valid.

  8. 2: Invalid bits were found in the header, but the header was still usable.

  9. 3: The header failed the CRC check.

  10. 4: An erroneous phase shift was found between the PLCP preamble and the PLCP header.

  11. 5: A 1 Mbps barker modulated burst was found with a short preamble, which is invalid for 802.11b.

  12. 6: The status of the header is unknown.

  13. 7: Everything about the header appears correct.

  14. 8: More than one result was found during a measurement that captured more than one 11b burst.

  1. IQ Offset: a floating point in dB

  2. MAC Status: This is status information about the MAC frame constrained in the PSDU portion of the burst: a floating point of the following values

  3. 1: The status is unknown, typically because the burst is longer than the period that was measured.

  4. 2: The MAC Frame Checksum (FCS) failed.

  5. 3: The MAC Frame Checksum (FCS) passed.

  6. 4: More than one result was found during a measurement that captured more than one 11b burst.

  1. Modulation Format: The observed modulation format for the data portion of the burst. a floating point as detailed in Bit Rate and Modulation Format Values for DSSS and OFDM

  2. Peak EVM measured over the first 1000 chips of the burst: a floating point in %

  3. RMS EVM:  a floating point in %

Query Range for OFDM: Returns the following comma-separated scalar results when the modulation type is OFDM, that is [SENSe:]RADIo:STANdard[:SELect]:WLAN[?] is set to either A or GOFDm:

  1. Bit Rate: The observed bit rate for data portion of the burst: a floating number as detailed in Bit Rate and Modulation Format Values for DSSS and OFDM

  2. Burst Quality: This indicates whether or not the measurement was performed on a good (1.0) or bad (0.0) burst: a floating point of 0.0 or 1.0

  3. Frequency Error: a floating point in Hz

  4. Gated Power: a floating point in dBm

  5. IQ Gain Imbalance: a floating point in dB

  6. IQ Offset: a floating point in dB

  7. IQ Quadrature Error (sometimes referred to as quadrature skew): a floating point in degrees

  8. Modulation Format: The observed modulation format for the data portion of the burst: a floating point as detailed in Bit Rate and Modulation Format Values for DSSS and OFDM

  9. RMS EVM:  a floating point in %

  10. Symbol Clock Frequency Error: a floating point expressed in parts per million

Query Range for MIMO 802.11n: Returns the following comma-separated scalar results when the modulation type is MIMO 802.11n, that is [SENSe:]RADIo:STANdard[:SELect]:WLAN[?] is set to N. There are 3 sets of results that can be returned using READ:EVM{0:2}? If no number is specified the default is 1:

READ:EVM0?: an array of points as follows:

  1. The number of HT-LTF fields found in the observed burst: a floating point

  2. Length of the HT-DATA field found (in symbols): a floating point

  3. Modulation format of the HT-DATA field found in the analyzed burst: a floating point as detailed in Modulation Format Values for MIMO 802.11n

  4. Power of the HT-DATA field found in the analyzed burst: a floating point in dBm

  5. Indicates whether an HT-DATA field was found in the analyzed burst: a floating point of 0.0 (false) or 1.0 (true)

  6. Indicates whether an HT-LTF field was found in the analyzed burst: a floating point of 0.0 (false) or 1.0 (true)

  7. Length of the HT-SIG field found in the analyzed burst in symbols

  8. Modulation format of the HT-SIG field found in the analyzed burst

  9. Power of the HT-SIG field found in the analyzed burst: a floating point in dBm

  10. Indicates whether an HT-SIG field was found in the analyzed burst: a floating point of 0.0 (false) or 1.0 (true)

  11. Status of the HT-SIG demodulation

  12. Length of the HT-STF field found in the analyzed burst in symbols: a floating point

  13. Modulation format of the HT-STF field found in the analyzed burst: a floating point as detailed in Modulation Format Values for MIMO 802.11n  

  14. Power of the HT-STF field found in the analyzed burst: a floating point in dBm

  15. Indicates whether an HT-STF field was found in the analyzed burst: a floating point of 0.0 (false) or 1.0 (true)

  16. Length of the L-DATA field found in the analyzed burst in symbols

  17. Modulation format of the L-DATA field found in the analyzed burst

  18. Power of the L-DATA field found in the analyzed burst: a floating point in dBm

  19. Indicates whether an L-DATA field was found in the analyzed burst: a floating point of 0.0 (false) or 1.0 (true)

  20. Length of the L-LTF field found in the analyzed burst in symbols

  21. Modulation format of the L-LTF field found in the analyzed burst: a floating point as detailed in Modulation Format Values for MIMO 802.11n

  22. Power of the L-LTF field found in the analyzed burst: a floating point in dBm

  23. Indicates whether an L-LTF field was found in the analyzed burst: a floating point of 0.0 (false) or 1.0 (true)

  24. Length of the L-SIG field found in the analyzed burst in symbols

  25. Modulation format of the L-SIG field found in the analyzed burst: a floating point as detailed in Modulation Format Values for MIMO 802.11n  

  26. Power of the L-SIG field found in the analyzed burst: a floating point in dBm

  27. Indicates whether an L-SIG field was found in the analyzed burst: a floating point of 0.0 (false) or 1.0 (true)

  28. Length of the L-STF field found in the analyzed burst in symbols

  29. Modulation format of the L-STF field found in the input signal: a floating point as detailed in Modulation Format Values for MIMO 802.11n    

  30. Power of the L-STF field found in the analyzed burst: a floating point in dBm

  31. Indicates whether an L-STF field was found in the analyzed burst: a floating point of 0.0 (false) or 1.0 (true)  

  32. Number of bytes of data in the PSDU, as decoded from the HT-SIG

  33. Length of the entire burst  in symbols

    In the analyzed signal if any HT-LTF fields are found the following 3 results are returned for each HT-LTF field.

  34. Length of the HT-LTF field found in the analyzed burst in symbols

  35. Modulation format of the HT-LTF field found in the analyzed burst

  36. Power of the HT-LTF field found in the analyzed burst: a floating point in dBm

READ:EVM1? or not specified: an array of points as follows:

          Results common to all streams/channels

  1. Burst Quality: This indicates whether or not the measurement was performed on a good (1.0) or bad (0.0) burst: a floating point of 0.0 or 1.0

  2. Frequency Error: a floating point in Hz

  3. MCS of observed signal: a floating point

  4. The number of spatial streams of data found: a floating point

  5. The number of subcarriers detected in the analyzed signal: a floating point

  6. Spectral Flatness Margin: a floating point in dB. Only available for a single channel demodulation.

  7. IEEE 802.11 standard detected

  8. Symbol clock timing error: a floating point in ppm

  9. Total burst power of all measured channels: a floating point in dB

  10. Worst condition number: a floating point

    Individual channel results
     

  11. Power in burst for channel 1: a floating point in dB

  12. Data EVM measurement result for channel 1: a floating point in %

  13. IQ Gain Imbalance for channel 1: a floating point in dB

  14. IQ Offset for channel 1: a floating point in dB

  15. IQ Quadrature Error for channel 1 (sometimes referred to as quadrature skew): a floating point in degrees

  16. Peak EVM for channel 1 measured over the first 1000 chips of the burst: a floating point in %

  17. Pilot EVM measurement result for channel 1: a floating point in %

  18. RMS EVM for channel 1: a floating point in %

  19. The correlation coefficient obtained when synchronizing to the L-STF part of the OFDM pulse for channel 1

  20. Port used for channel 1: a floating point

  21. Power in burst for channel 2: a floating point in dB

  22. Data EVM measurement result for channel 2: a floating point in %

  23. IQ Gain Imbalance for channel 2: a floating point in dB

  24. IQ Offset for channel 2: a floating point in dB

  25. IQ Quadrature Error for channel 2 (sometimes referred to as quadrature skew): a floating point in degrees

  26. Peak EVM for channel 2 measured over the first 1000 chips of the burst: a floating point in %

  27. Pilot EVM measurement result for channel 2: a floating point in %

  28. RMS EVM for channel 2: a floating point in %

  29. The correlation coefficient obtained when synchronizing to the L-STF part of the OFDM pulse for channel 2

  30. Port used for channel 2: a floating point

  31. Power in burst for channel 3: a floating point in dB

  32. Data EVM measurement result for channel 3: a floating point in %

  33. IQ Gain Imbalance for channel 3: a floating point in dB

  34. IQ Offset for channel 3: a floating point in dB

  35. IQ Quadrature Error for channel 3 (sometimes referred to as quadrature skew): a floating point in degrees

  36. Peak EVM for channel 3 measured over the first 1000 chips of the burst: a floating point in %

  37. Pilot EVM measurement result for channel 3: a floating point in %

  38. RMS EVM for channel 3: a floating point in %

  39. The correlation coefficient obtained when synchronizing to the L-STF part of the OFDM pulse for channel 3

  40. Port used for channel 3: a floating point

  41. Power in burst for channel 4: a floating point in dB

  42. Data EVM measurement result for channel 4: a floating point in %

  43. IQ Gain Imbalance for channel 4: a floating point in dB

  44. IQ Offset for channel 4: a floating point in dB

  45. IQ Quadrature Error for channel 4 (sometimes referred to as quadrature skew): a floating point in degrees

  46. Peak EVM for channel 4 measured over the first 1000 chips of the burst: a floating point in %

  47. Pilot EVM measurement result for channel 4: a floating point in %

  48. RMS EVM for channel 4: a floating point in %

  49. The correlation coefficient obtained when synchronizing to the L-STF part of the OFDM pulse for channel 4

  50. Port used for channel 4: a floating point

    Individual Stream Results

  51. RMS level of the "Common Pilot Error" minus one for stream 1. This represents how much pilot tracking was needed during demodulation: a floating point

  52. Data EVM measurement result for stream 1: a floating point in %

  53. Peak EVM measurement result for stream 1: a floating point in %

  54. Pilot EVM measurement result for stream 1: a floating point in %

  55. RMS EVM measurement result for stream 1: a floating point in %

  56. RMS level of the "Common Pilot Error" minus one for stream 2. This represents how much pilot tracking was needed during demodulation: a floating point

  57. Data EVM measurement result for stream 2: a floating point in %

  58. Peak EVM measurement result for stream 2: a floating point in %

  59. Pilot EVM measurement result for stream 2: a floating point in %

  60. RMS EVM measurement result for stream 2: a floating point in %

  61. RMS level of the "Common Pilot Error" minus one for stream 3. This represents how much pilot tracking was needed during demodulation: a floating point

  62. Data EVM measurement result for stream 3: a floating point in %

  63. Peak EVM measurement result for stream 3: a floating point in %

  64. Pilot EVM measurement result for stream 3: a floating point in %

  65. RMS EVM measurement result for stream 3: a floating point in %

  66. RMS level of the "Common Pilot Error" minus one for stream 4. This represents how much pilot tracking was needed during demodulation: a floating point

  67. Data EVM measurement result for stream 4: a floating point in %

  68. Peak EVM measurement result for stream 4: a floating point in %

  69. Pilot EVM measurement result for stream 4: a floating point in %

  70. RMS EVM measurement result for stream 4: a floating point in %

    Cross Power Results
     

  71. Normalized cross power result for channel 1 from stream 2: a floating point in dB (this result is identical to the following result)

  72. Normalized cross power result for channel 1 from stream 2: a floating point in dB (this result is identical to the previous result)

  73. Normalized cross power result for channel 1 from stream 3: a floating point in dB

  74. Normalized cross power result for channel 1 from stream 4: a floating point in dB

  75. Normalized cross power result for channel 2 from stream 1: a floating point in dB (this result is identical to the following result)

  76. Normalized cross power result for channel 2 from stream 1: a floating point in dB (this result is identical to the previous result)

  77. Normalized cross power result for channel 2 from stream 3: a floating point in dB

  78. Normalized cross power result for channel 2 from stream 4: a floating point in dB

  79. Normalized cross power result for channel 3 from stream 1: a floating point in dB

  80. Normalized cross power result for channel 3 from stream 2: a floating point in dB

  81. Normalized cross power result for channel 3 from stream 4: a floating point in dB

  82. Normalized cross power result for channel 4 from stream 1: a floating point in dB

  83. Normalized cross power result for channel 4 from stream 2: a floating point in dB

  84. Normalized cross power result for channel 4 from stream 3: a floating point in dB

READ:EVM2?: Returns an array which contains the spectral flatness measurement results, one per subcarrier. These are normalized to the average value of the central subcarriers as described in the standard, such that a value of 0.0 is the average.
The numbers of results returned define the number of subcarriers. The array of subcarriers is arranged such that array element 0 represents the lowest-frequency subcarrier (eg subcarrier -28 in a 57-subcarrier signal).
 

Spectral flatness is defined in section 6.1 of the EWC HT PHY Specification document (section number taken from revision 1.25, 23-Dec-2005).

In a 20MHz channel and in corresponding 20MHz transmission in a 40MHz channel, the average energy of the constellations in each of the spectral lines – 16 to –1 and +1 to +16 shall deviate no more than ± 2 dB from their average energy. The average energy of the constellations in each of the spectral lines – 28 to –17 and +17 to +28 will deviate no more than +2/–4 dB from the average energy of spectral lines –16 to –1 and +1 to +16.

In a 40 MHz transmission the average energy of the constellations in each of the spectral lines –42 to –2 and +2 to +42 shall deviate no more than ± 2 dB from their average energy. The average energy of the constellations in each of the spectral lines –43 to –58 and +43 to +58 shall deviate no more than +2/–4 dB from the average energy of spectral lines –42 to –2 and +2 to +42. The data for this test will be based on the channel estimate step.

Bit Rate and Modulation Format Values for DSSS and OFDM

Return Value

Description

1.0

OFDM, 6 Mbps

2.0

OFDM, 9 Mbps

3.0

OFDM, 12 Mbps

4.0

OFDM, 18 Mbps

5.0

OFDM, 24 Mbps

6.0

OFDM, 36 Mbps

7.0

OFDM, 48 Mbps

8.0

OFDM, 54 Mbps

9.0

DSSS, 1 Mbps

10.0

DSSS, 2 Mbps

11.0

DSSS, 5.5 Mbps

12.0

DSSS, 11 Mbps

13.0

DSSS,  22 Mbps

14.0

DSSS,  33 Mbps

15.0

Unknown data rate

16.0

Varying data rate was seen during multi-acquisition measurement

Modulation Format Values for MIMO 802.11n

Return Value

Description

1.0

BPSK

2.0

QPSK

3.0

QAM16

4.0

QAM64

5.0

PSK8

6.0

Barker1

7.0

Barker2

8.0

CCK5.5

9.0

CCK11

10.0

PBCC5.5

11.0

PBCC11

12.0

PBCC22

13.0

PBCC33

14.0

Unknown format

15.0

Barker2 with short preamble

16.0

CCK5.5 with short preamble

17.0

CCK11 with short preamble

18.0

PBCC5.5 with short preamble

19.0

PBCC11 with short preamble

20.0

PBCC22 with short preamble

21.0

PBCC33 with short preamble

22.0

Various

23.0

QAM256

24.0

RBPSK

25.0

Auto

26.0

HT-SIG

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

Example:

READ:EVM?

Queries the EVM measurement results.