IQsignal

User Guide

Litepoint CorporationLPT802-11-L00

Rev. 1.2.6

December 7th, 2006

Rev. 1.2.6 2

Revision History

TrademarksCopyright 2004-2006 Litepoint Corporation All rights reserved. No part of this manual may be reproduced or transmitted in any form or

by any means without the written permission of Litepoint Corp.

IQview is a registered tradermark of LitePoint Corp. IQflex, IQsignal and IQwave are trademarks of Litepoint Corp.

Microsoft Windows is a registered trademarks of Microsoft Corporation in the United States and/or other countries.

All trademarks or registered trademarks are owned by their respective owners.

The information furnished by Litepoint Corp. is believed to be accurate and reliable. However, no responsibility is assumed by Litepoint for its use. Litepoint reserves the right to change specifications and documentation at any time without notice.

AttentionLitePoint Corporation reserves the right to make changes in specifications and other

information contained in this document without prior notice!

Litepoint Corporation makes no warranty of any kind with regards to this material, including but not limited to, the implied warranties of merchantability and fitness for a particular purpose. Litepoint shall not be liable for errors contained herein or for material or consequential damages in connection with the furnishing, performance, or use of this material.

LitePoint Corporation575 Maude Court

Sunnyvale, CA 94085-2803United States of America

Telephone: 1 408 456 5000Facsimile: 1 408 456 0106

E-mail: support@litepoint.comwww.litepoint.com/support

Release date Revision Change DescriptionDecember 12, 2006 GUI version1.4.0.p Updated to reflect 1.2.6 release software.

Table of Contents

Revision History........................................................................................... 2Trademarks.................................................................................................. 2Attention....................................................................................................... 2

Using the IQsignal Application........................................9Vector Signal Analyzer ....................................................................................... 9Main Menu ....................................................................................................... 13

File Menu ................................................................................................... 14Setup Menu ............................................................................................... 15Parameters ................................................................................................ 15Setting the Parameters .............................................................................. 15Loading Calibration Files IQview ............................................................... 19Tools Menu ................................................................................................ 19Help ........................................................................................................... 20

Analyzing Graph Options ................................................................................. 21Amplitude................................................................................................... 24Spectrogram .............................................................................................. 26Power Spectrum Density ........................................................................... 27Power Measurement Results Window....................................................... 29EVM and Power Measurement Result Window......................................... 32Spectrum Mask .......................................................................................... 34CCDF......................................................................................................... 34Symbol Constellation ................................................................................. 35Spectral Flatness ....................................................................................... 37Local Oscillator Leakage ........................................................................... 37Phase noise (PSD) .................................................................................... 39Phase Error (Time) .................................................................................... 41Power On Ramp ........................................................................................ 42Power Down Ramp.................................................................................... 42I&Q Signals................................................................................................ 44Short Training Symbols.............................................................................. 45Frequency Error......................................................................................... 45Error Vector Magnitude Versus Carrier...................................................... 47Error Vector Magnitude (EVM) Versus Time.............................................. 47Eye Diagram Graph ................................................................................... 50Amplitude vs. Time Graph (OFDM) ........................................................... 51

Using the Zooming Tool ................................................................................... 51Rev. 1.2.6 3

Using the Slider Method to Zoom .............................................................. 51

Using the Left-Click and Drag Method to Zoom......................................... 52VSA Panel Tool ................................................................................................ 55

Slider Operation......................................................................................... 55Tracking Operation .................................................................................... 57Fast DC Update Button.............................................................................. 58Reset Compensation Button...................................................................... 58Optimize EVM Operation ........................................................................... 58

Vector Signal Generator................................................................................... 59Main Menu ....................................................................................................... 70

File Menu ................................................................................................... 70Tools .......................................................................................................... 70Help ........................................................................................................... 71

VSG Panel Tool................................................................................................ 71Rev. 1.2.6 4

List of Figures

Figure 1. EVM Measurement Application Main Window ........................................................... 10Figure 2. Example of User Defined MHz input option (2410MHz selected) ............................. 13Figure 3. File Menu ................................................................................................................... 14Figure 4. Setup Menu ............................................................................................................... 15Figure 5. Parameters Window .................................................................................................. 16Figure 6. Parameters Window Indicating Connection Not Established .................................... 20Figure 7. Load Calibration Files IQview Menu Item .................................................................. 20Figure 8. Tools Menu ................................................................................................................ 21Figure 9. Help windows showing software version along with other information. ..................... 21Figure 10. Drop-down Menus for Selecting Analysis on Captured Signal .................................. 22Figure 11. Analyze Mode Graph Options (Top Left, Left and Right Drop-Down Menus) ............ 22Figure 12. Amplitude Display Mode for 802.11a/g OFDM signal ................................................ 24Figure 13. Same display as in Figure 12, but enabling Display Packet Information. Observe the

purple marker. ............................................................................................................ 25Figure 14. Illustration of purple markers indicating the 802.11b packet being analyzed. ............ 26Figure 15. Illustration of a bad packet, where data stops before the expected end of packet

(Symbol Timing Tracking is set to off). ....................................................................... 27Figure 16. Zooming of the packet in Figure 15, allows the analysis of the good part of a

incorrectly formatted data packet. .............................................................................. 28Figure 17. Spectrum Plot with WDCT blocker ............................................................................ 28Figure 21. Example of PDS graph measuring a CW signal with 1MHz offset ............................ 29Figure 18. Traditional Spectrum Analyzer View .......................................................................... 29Figure 19. PSD Graph for 802.11a/g signal (upper left), Turbo mode signal (upper right), ASTM

DSRC (lower left), and quarter rate signal (lower right) ............................................. 30Figure 20. PSD Graph for 802.11b Signal .................................................................................. 31Figure 21. Example of PDS graph measuring a CW signal with 1MHz offset ............................ 31Figure 22. Power Measurement Results Window ....................................................................... 32Figure 23. EVM & Power Measurements Result Window 802.11b (left) and 802.11a/g (right) .. 33Figure 24. By right clicking on the I/Q Match window the unit of the amplitude imbalance can be

selected ..................................................................................................................... 34Figure 25. Spectrum Mask Graph for 802.11b Signal ................................................................. 35Figure 26. Spectrum Mask Graph OFDM 802.11a/g Signal ....................................................... 35Figure 27. CCDF Graph for OFDM 802.11a/g Signal (Left) and DSSS 802.11b signal (Right) .. 36Figure 28. CCDF Compressed OFDM Signal Graph (Left) and compressed DSSS Signal Graph

(Right) ........................................................................................................................ 36Figure 29. Symbol Constellation Graph for 802.11b Signals. 1Mbps (left), 2Mbps, 5.5Mbps, and Revision 1.2.6 5

11Mbps CCK (right) - the latter all have the same constellation ................................ 37

Figure 30. Symbol Constellation Graphs OFDM 802.11a/g Signals. 6/9Mbps (BPSK) - upper left, 12/18Mbps (QPSK) - upper right, 24/36Mbps (QAM-16) - lower left, 48/54Mbps (QAM-64) - lower right. ......................................................................................................... 38

Figure 31. Spectral Flatness Graph for OFDM 802.11a/g Signal ............................................... 39Figure 32. LO (DC) Leakage Graph for OFDM 802.11a/g Signal ............................................... 39Figure 33. LO (CD) Leakage Graph for correct test signal (Left) and normal 802.11b DSSS signal

(Right) ........................................................................................................................ 40Figure 34. Spectral plot of the required 802.11b test signal to measure LO (DC) leakage ......... 40Figure 36. Phase Noise Time Graph (CCK) ............................................................................... 41Figure 35. Phase Noise (PSD) Graph ........................................................................................ 41Figure 37. Phase Noise Time Graph for OFDM 802.1a/g Signal ................................................ 42Figure 38. Power On Ramp Graph for 802.11b (11Mbps) .......................................................... 43Figure 39. Power Down Ramp Graph for CCK ........................................................................... 43Figure 40. I&Q Signals for 802.11b ............................................................................................. 44Figure 41. I&Q Signals for OFDM 802.11a/g .............................................................................. 44Figure 42. STS Pretzel from 801.11a/g Signal ........................................................................... 45Figure 43. Frequency error for baseband signal with very small frequency error for 802.11b .... 46Figure 44. Coarse Frequency Error for Short and Long Training Sequence (OFDM 802.11a/g

Signal) .......................................................................................................................46Figure 45. Illustration of frequency pulling during Short Training Sequence. ............................. 47Figure 46. EVM Versus Carrier for OFDM 802.11a/g Signal ...................................................... 48Figure 47. EVM Versus Symbol for OFDM 802.11a/g Signal ..................................................... 48Figure 49. EVM vs. Symbol plot with same captured signal as in Figure 47 but with fewer sub-

carriers selected ........................................................................................................ 49Figure 48. Pop-up window to define the sub-carriers to be analyzed ......................................... 49Figure 51. Eye Graph for 802.11b Signal ................................................................................... 50Figure 50. EVM Versus Time for 802.11b Signal (CCK) ............................................................. 50Figure 52. Amplitude vs. time graph for OFDM modulated signal. ............................................. 51Figure 53. Zoom Slider ............................................................................................................... 52Figure 54. Amplitude Graph Showing Time Interval Capture in 500 Microseconds ................... 53Figure 55. Zoom Time Slider Repositioned to the Right ............................................................. 53Figure 56. Left-Click and Drag Method ....................................................................................... 54Figure 57. Illustration of zooming on one of the two lower windows. Left before zoom, Right

resulting zoom ........................................................................................................... 54Figure 58. Starting the VSA panel .............................................................................................. 55Figure 59. VSA panel after startup .............................................................................................. 56Figure 60. Slider portion of VSA Panel. ...................................................................................... 56Figure 61. Portion of VSA panel used to control tracking ........................................................... 58Figure 62. Optimize EVM portion of VSA Panel ......................................................................... 59Revision 1.2.6 6

Figure 63. Optimize EVM window after executing Optimize EVM .............................................. 60Figure 64. VSA Panel after performing Optimize EVM and Transfer values to Sliders. ............. 61

Figure 65. Vector Signal Generator Main Window ...................................................................... 62Figure 66. Illustration of user defined frequency input for VSG panel ........................................ 62Figure 67. Red Bomb Indicator on VSG. Also observe the two added common mode control slide

bars after enabling the Set CMV ............................................................................... 64Figure 68. Vector Signal Generator File Menu ........................................................................... 70Figure 69. Vector Signal Generator Tool menu ........................................................................... 70Figure 70. About IQview Window ............................................................................................... 71Figure 71. The VSGpanel Pop-up Window ................................................................................. 72Figure 72. Relationship between IQ mismatch in dB and IQ mismatch in %. ............................. 73Figure 73. Red Bomb Indicator of Impaired Transmit IQ Signal ................................................. 75Figure 74. Red Bomb Indicator of Impaired Transmit VSG Signal ............................................. 76Revision 1.2.6 7

Rev. 1.2.6 8

List of Tables

Table 1. EVM Measurement Application Window Description.............................................. 10Table 2. File Menu................................................................................................................ 14Table 3. Parameters Window ............................................................................................... 16Table 4. Tools Menu .............................................................................................................21Table 5. Analyze Mode Graph Options (Top Left Menu) ...................................................... 23Table 6. Analyze Mode Graph Options (Left Menu) ............................................................. 23Table 7. Summary of units for compensation ....................................................................... 57Table 8. Vector Signal Generator Functions......................................................................... 63Table 9. Overview of supplied wave forms to use with IQ signal.......................................... 65Table 10. File Menu description.............................................................................................. 70

Vector Signal AnalyzerUsing the IQsignal Application

IQsignal is an Error Vector Magnitude (EVM) Measurement Application specifically designed for analyzing the complex signals generated in 802.11 a/b/g radio frequency (RF) communica-tions. Additionally, the application is capable of verifying compliance with the applicable 802.11a/b/g specification.

This application includes two separate tools:

Vector Signal Analyzer Vector Signal Generator

Before being able to use either of these tools, a connection to IQview must be established. A detailed description of this exist in the IQview User Guide[4].

Vector Signal Analyzer

The Vector Signal Analyzer captures RF or Baseband data being output by the transmitter por-tion of the 802.11 Device Under Test (DUT) into the tester's input ports, and performs several different analyses of this captured data to verify the performance of the DUT. When the IQsig-nal EVM Measurement Application is launched, the Vector Signal Analyzer starts as the default tool. If the tester's input ports are receiving a signal, the acquisition and analysis of that signal begins immediately as soon as the Start or Auto Range button is pressed. Note, it is recom-mended to press the Auto Range button once, to ensure optimal dynamic range of the received signal.

Figure 1 illustrates the EVM Measurement Applications main window after performing a data capture and analyzing the captured data.Rev. 1.2.6 9

Vector Signal AnalyzerTable 1 lists and defines the parameters that can be set at the main EVM Measurement Appli-cation window.

Figure 1. EVM Measurement Application Main Window

Feature DescriptionStart Button/Stop Button Initiates either single mode or continuous mode data capture and analysis. If

Single is selected, pressing Start will perform a single capture. If Cont is selected and the Start button is pressed, continuous capture is initiated, and the button display will change the text to Stop. Pressing Stop during continuous mode operation will to stop the measurement process.

Auto Range Performs an automatic gain setting to optimize the dynamic range of the received signal. It is recommended to use Auto Range before starting the first capture. Rev. 1.2.6 10

Table 1. EVM Measurement Application Window Description.

Vector Signal AnalyzerCont/Single Enables Single mode or Continuous mode data capture and analysis operation. The Cont radio button enables continuous mode data capture and analysis, and the Single radio button enable a single capture after pressing start

IQ Swap Allows an interchange between the I and Q channel data. This swapping capability is useful when the data source itself has its I and Q channels swapped.

Analyze A/G Selects 802.11a or g (OFDM) type for analysis.

Analyze B Selects 802.11b (DSSS) type for analysis.

RF Channel Allows selection of a WLAN input channel from this pull-down list when the input mode is RF. (For further details, see "Parameters" presented later in this chapter). Two sets of predefined channels exist - one set for 802.11 and one set for ASTM channel frequencies - The desired channel set can be selected by right-clicking on the RF Channel select box. By selecting User Defined, MHz, the user can enter the desired frequency, in case the frequency does not exist in the pull-down list. Depending on the hardware version, steps of 1 MHz or 500 kHz may be applied to the tester. Hardware versions earlier than 1.4 do not support 500 kHz steps and will use a 1MHz step, though the GUI will allow entry in 500 kHz steps.When User Defined, MHz is selected, a window next to the RF Channel select will appear, and the desired frequency can be entered. This is illustrated in Figure 2. When the input mode is baseband, this setting has no effect. Available RF Channel selections for the 802.11 b/g standards are in the 2.4 GHz range and 4.9-6.0 GHz. range; for the 802.11a standard, the range is 4.9-6.0 GHz.

Max Sig. Level Can be manually specified by either typing the desired level into the window or by clicking the up and down arrows next to the input box. The specified level should be greater than or equal to the peak level of the signal. After Auto Range has been pressed, the signal level selected by the Auto Range algorithm is displayed. Note, when including an external attenuator loss (External Attn) the Max Sig. Level is referred to the input of IQview, and not to the DUT.

External Attn Can be used to specify losses external to the IQview. The results displayed in the program are compensated with the specified loss. E.g. when specifying a 2dB cable loss, the measured power is increased by 2dB before being displayed in the program.

Trigger Settings In RF mode, three different options can be selected here: Free run, external trigger input, and signal trigger input. In base band only mode, only the free run and external trigger are available. Below the trigger mode drop-down menu, there is the trigger level, which can be manually specified by either typing the desired level into the window or by clicking the up and down arrows next to the input box. This setting specifies the trigger level relative to Max Sig. Level. The trigger marker (red circle at the extreme left of the Amplitude vs Time graph) indicates the current trigger level.

Feature DescriptionRev. 1.2.6 11

Table 1. EVM Measurement Application Window Description.

Vector Signal AnalyzerRF input When selected, the signal must be supplied to the RF input port. If not selected, the signal must be supplied to the base band inputs.

Measurement Window Displays measurement results in this window. If the current choice is PSD, Spectrum Mask or CCDF, and I/Q signals or STS pretzel are selected, then the Power Measurement Results window appears. Both current and average power measurements results are displayed. If the current choice is Symbol Const (Symbol Constellation), Spectral Flatness, or LO (DC) Leakage, and other analysis where EVM is calculated, three EVM Measurement results (pilot, data and all) appear along with the measured power when analyzing OFDM signal. When analyzing DSSS (802.11b) signals, only two EVM results are presented: average and peak. Both current and average EVM measurements are displayed. Two additional windows below the measurement window appear when EVM results are presented. These windows contain information about mismatch and frequency error and phase noise. For further details, see "Power Measurement Results Window" and "EVM and Power Measurement Result Window" in this chapter.

Select and Drag Function Zooms in on captured data to specify a portion of the capture to be analyzed data and to show it in the top graph, with the time (horizontal) axis stretched out for the zoomed portion. Moving the Zoom Slider to the left causes the graphical display to zoom out; moving the Zoom Slider to the right causes the graphical display to zoom in. When zooming in on data, the visible part of the data in the top graph represents the portion of the data that has been zoomed in on. Only the data shown in the top graph is analyzed. The Time Slider may be used to move the visible window of the zoomed selection back and forth along the time axis. Alternatively, one can select the desired portion of the signal by defining a window by left-clicking and dragging the mouse cursor over the desired area. For further details concerning the Time Slider, see "Using the Zooming Tool" presented later in this chapter.

Power Time Graph This window displays a graphical representation of the measured data. The blue trace represents the peak amplitude value, while the red trace represents the amplitude as a moving average over 40 samples.

Display Packet Information If Display Packet Information is checked, a window inside the top measurement window will display a summary of the packet being analyzed. Note, the data is only displayed when an EVM analysis is performed, e.g. the three Measurement windows are displayed.

Feature Description

Table 1. EVM Measurement Application Window Description.Rev. 1.2.6 12

Main MenuMain Menu

The Main menu consists of the following menu items:

File Setup Tools Help

Figure 2. Example of User Defined MHz input option (2410MHz selected)Rev. 1.2.6 13

Figure 3 illustrates the File Menu.

Main MenuFile Menu

Table 2 lists and defines the File Menu items.

Figure 3. File Menu

Menu Items DescriptionOpen Signal File Opens previously captured and saved data from a signal file for analysis. The

filename for a signal file has the file extension .SIG. Wave files with extension .MOD can also be opened.

Save Signal File Saves captured data to a signal file with extension .SIG for later analysis. .SIG files can be used only by the IQview EVM Measurement application. Two submenus exist for this save option.

Complete Signal: Saves the complete capture independent of what is shown in the top graph

Zoomed Signal: Saves only the portion of the signal that is currently shown in the top graph

Save Generator File Saves captured data for use as an input file (modulator file) to the Vector Signal Generator applications signal window. The file has the file extension .MOD.

Save PSDU data Saves the captured data of the packet to a text file. Two save options exists:

Packet Info PSDU: Saves the data of the complete packet. Saving this includes information about the decoded packet along with the PSDU data.

PSDU: Saves the data of the PSDU (data) portion of the packet only Print Page Print the current view to the selected printer. The standard Windows print dialogue is

displayed when selected

Load Setup Loads a previously saved setup

Save Setup Saves the current setup to a file. Table 2. File MenuRev. 1.2.6 14

Main MenuSetup Menu

The Setup menu contains two major submenus:

Parameters Load Calibration Files IQview

Figure 4 illustrates the Setup menu.

Parameters

You can set user-defined parameters at the Parameters window. Figure 5 illustrates the Param-eters window.

Table 3 lists and defines these parameter options.

Load Default Setup Loads the default settings for the application.

Exit Exits the program.

Figure 4. Setup Menu

Figure 5. Parameters Window

Parameters DescriptionTester IP Address The IP address of the tester being used must be entered into this window,

prior to starting a test. The standard IP address format should be used, for example, 192.168.100.254.CAUTION: Verify that the subnet mask in Microsoft Windows is set accordingly.

Sample Interval Selects the duration of time for a sample capture. For instance, if the 500 us setting is selected, then a sample is captured and analyzed for a 500 usec interval in time.

Menu Items Description

Table 2. File Menu (Continued)Rev. 1.2.6 15

Table 3. Parameters Window

Main MenuEVM Averaging Choices are: 1, 10, 20, 40, 60, 80, 100The number of most recent measurement that are used to calculate the average EVM number displayed in the measurement results window (average column).

Trigger Timeout (sec) Choices are: 0.5, 1.5, 5, 15, 30, 45, 60 secondsSets the time that IQsignal waits to try to acquire (trigger on) a signal, before it times out, and returns the control back to the user. In normal operation a low value is suggested unless the user is trying to capture signal being transmitted in a communication link between two cards.

OFDM Optimization Parameters

Phase Tracking/Corr (applies to OFDM only)

Choices are: Off, Sym-by-Sym Corr., Moving Avg. 10 Sym. Selecting the Moving Average over 10 Symbols is recommended. The Symbol-by-Symbol Connection will mask phase noise in the transmitter. This can be used as a diagnostic tool. If the EVM improves significantly when switching from Moving Average to Symbol-to-Symbol, the transmitter is likely to have excessive phase noise.The Phase Tracking Off mode can be used when the carriers and references of the transmitter and receiver are phase locked or when low frequency carrier phase noise is suspected to be present. The Moving Average over 10 Symbols may mask low frequency phase noise.

Channel Estimate (applies to OFDM only)

Choices are: 2nd Order Polyfit, Raw, Long Symbol, and Raw, Full Packet. In the Raw, Long Symbols mode, the channel is estimated by averaging the 2 long symbols in the long training Sequence. No other averaging is performed. In the 2nd Order Polyfit mode, the channel response is approximated by the best 2nd order polynomial over the frequency band occupied by the long OFDM symbols. This mode should only be selected if the channel is essentially flat over the frequency band occupied by the OFDM signal. This mode should not be used when there is a substantial roll-off over the frequency band due to transmit filtering.In the Raw, Full Packet, the complete packet is used for the channel estimate.

Symbol Timing Tracking (applies to OFDM only)

Choices are: Off/On.It is recommended to set this to On.

Frequency Sync. (applies to OFDM only)

Choices are: Short Training Symbols, Long Training Symbols, Full Data Packet. Before the OFDM symbols are demodulated with an FFT, the received signal has to be corrected for the carrier frequency error. This error is either estimated on the basis of the Short or Long training symbols or over the full packet. The recommended setting is Short Training Symbols, except when the received signal shows frequency dynamics during the start of the packet. In this case, either the Long Training Symbols or the Full Data Packet method should be used.

Parameters DescriptionRev. 1.2.6 16

Table 3. Parameters Window (Continued)

Main MenuAmplitude Tracking(applies to OFDM only)

Choices are Off/On.Enables and disables the Amplitude tracking.

OFDM Modulation Type Four choices exist:

802.11a/g 802.11 Turbo Mode ASTM DSRC Quarter rate802.11a/g should be selected to analyze normal 802.11 OFDM signals.

802.11 Turbo Mode should be selected to analyze Atheros Turbo Mode signals. The signal resembles a standard OFDM signal with 52 sub-carriers, but everything is spaced at twice that of the normal 802.11 signal, resulting in a signal with approximately 40MHz bandwidth. Additionally the number of symbols in the short training sequence is doubled resulting in the same duration of the short training sequence as in 802.11 OFDM modulated signals. ASTM DSRC or half rate should be used to analyze half rate OFDM modulated signals. This signal also resembles a standard OFDM signal with 52 sub-carriers, but everything spaced at half that of the normal 802.11 signal, resulting in a signal with approximately 10MHz bandwidth.Quarter rate should be used to analyze quarter-rate OFDM signals. The signal resembles a standard OFDM signal with 52 sub-carriers, but everything is spaced at a quarter of that of the normal 802.11 signal, resulting in a signal with approximately 5MHz bandwidth.

Examples of the produced spectrums are shown later in this document.

OFDM EVM Method The 802.11a/g standard specifies the EVM calculation method. This method expects a channel response that does not vary substantially. If the channel response shows notches, the standard EVM method yields unreliable results.

The 'Multipath' method has been added to provide reliable results for these cases. In this mode the EVM is calculated by comparing the received signal with the transmitted signal modified by the estimated channel response.

In the standard mode the EVM is calculated by comparing the received signal, modified by the inverse of the estimated channel response, with the transmitted signal.

In both cases, the transmitted signal is estimated by feeding the received signal, modified by the inverse of the channel response, through a multi-level slicer

Parameters DescriptionRev. 1.2.6 17

Table 3. Parameters Window (Continued)

Main MenuIf one wants to analyze a captured signal using different compensation algorithms, one can open the parameter window and select different compensation methods. Pressing the Zoom button on the left side of the screen will cause the signal displayed in the signal window to be

DSSS Optimization Parameters

Equalizer taps (applies to DSSS only)

Choices are: Off, 5, 7, or 9 Taps.The recommended setting is Off. The larger the number of taps, the more the equalizer can correct for Inter Symbol Interference (ISI) present in the transmitter.If the EVM improves substantially when changing from 5 to 9 Taps, the transmitter is likely to have too much ISI.When the performance of a transmitter and receiver pair with matching filters is to be assessed, the 5 Tap setting should be used.When using the EVM Calculation, 11b Std. Tx mod acc (see below), the Equalizer Taps should be set to Off.

Remove DC (applies to DSSS only)

Choices are: Off or On.The recommended setting is Off. The On setting should only be used if the DC Offsets are known to be substantial relative to the desired signal level. This can be the case if the RF signal level is extremely low, or if there is a DC-offset present when using the baseband inputs.

EVM calculation (applies to DSSS only)

Choices are: 11b Std., Tx mode acc or rms error vector.The 11b Standard Transmit Modulation Accuracy method applies the algorithm defined in IEEE 802.11b-1999 Standard Section 18.4.7.8 to the sampled data after carrier and symbol timing recovery.The rms error vector method applies the standard rms error vector algorithm.1

Instrument RX IF Normally, measurements are taken with RX IF set at 0 MHz. This menu item allows setting IF to the following options: 0 MHz, 5 MHz, 10 MHz and 11 MHz; or the user may type in a value for user defined. This can be useful if one wants to analyze e.g. EVM at an intermediate frequency in the system, that is not directly supported by the IQview. In this case, one can use an external mixer to down-convert the signal to one of the selectable IF frequencies, and then connect the output of the external mixer to one of the baseband input ports. It is not suggested to use 0 MHz in this case, as DC offset created by the down-conversion will distort the measurements.

1. rms evm = with s_in_norm(k) = and s_dec(k) = selects closest

to s_in_norm(k). s_in(k) is the sampled data, once per chip, after carrier and symbol timing recovery.

Parameters Description

Table 3. Parameters Window (Continued)

s_in_norm(k) s_dec(k)( )2 s_in(k)s_in 2

------------------- 1 j( )2

-------------------Rev. 1.2.6 18

re-analyzed using the new selected parameters, where after all results will be updated.

Main MenuSetting the Parameters

1. In the Setup menu, select the Parameters menu.The Parameters window displays, as shown in Figure 5.

2. Enter the required IP address, for example, 192.168.100.254.3. For the pull-down menu options, continue selecting the remaining user-defined options.4. Click OK.

When an acceptable IP address is entered and the remaining options have been set, the system displays the following message IQview connection established!.

NOTE: If you entered an unacceptable IP address, the following error message displays, IQview not found: Check IP Add/LAN., as shown in Figure 6.

Figure 6. Parameters Window Indicating Connection Not EstablishedRev. 1.2.6 19

Main MenuLoading Calibration Files IQview

The Load Calibration Files IQview menu item allows the user to load the needed calibration files from the IQview Tester to the PC running IQsignal. Figure 7 illustrates the Load Calibration Files IQview menu item.

To load the calibration files, simply select the Load Calibration Files IQview menu item and the files begin to immediately load. The system message, Loading Calibration data from IQview displays immediately on the top of the main screen.

Tools Menu

Figure 8 illustrates the Tools menu. For details on how to use the Vector Modulator, see "Vec-tor Signal Generator" at the end of this chapter. The VSG panel opens a separate tool that operates in continuous mode

Table 4 lists and describes the Tools menu items.

Figure 7. Load Calibration Files IQview Menu Item

Figure 8. Tools Menu

Menu Items DescriptionVector Signal Generator Starts the Vector Signal Generator tool. For further details, see the section,

"Vector Signal Generator" presented later in this chapter.

VSA Panel Launches the VSA Panel tool - see section "VSA Panel Tool"

Save Plots Brings up the current analysis plots, and offers to save the plots to a file. Rev. 1.2.6 20

Presently this only works when analyzing OFDM signalsTable 4. Tools Menu

Selecting Analysis ModeHelp

Help brings up a window where the version of the software is displayed along with other infor-mation. This is shown in Figure 9.

Figure 9. Help windows showing software version along with other information.

Selecting Analysis Mode

The two options are 802.11 abg or Bluetooth.

Note: This users guide describes the usage for the 802.11 abg mode. The IQsignal for Blue-tooth users guide describes the usage for Bluetooth Mode.Rev. 1.2.6 21

Analyzing Graph OptionsAnalyzing Graph Options

The Analyze Graph Options consists of three drop down menus that are located at the bottom, far-right side of the main window:

Left Top Left Right

These three windows pull-down menus will allow you to deploy 18 different graphs based on your captured data samples. Figure 10 shows the possible selection of drop-down menus to select different analyses to be performed on the captured signal, and Figure 11 illustrates the left and right Analyze Mode Graph Options menus.

To select an analysis graph from the drop-down menus, simply select a menu item. The Top Left drop down menu controls the plot shown in the main analysis window, the Left drop down menu controls the graph that displays in the lower, far-left side of the main window. The Right drop-down menu controls the graph between the far left graphs and the drop-down menus.

Table 5 lists and describes the Analyze Mode Graph Options for the Top Left Menu.

Table 6 lists and describes the Analyze Mode Graph Options for the Left Menu.

Amplitude

The amplitude option is the normal mode of operation, where the receive power vs. time is pre-sented. Figure 12 shows a typical 802.11a/g captured signal when using amplitude mode. The blue graph represents the instantaneous power, and the red graph represents the average power over a symbol duration.

Enabling the Display Packet Information, a window with relevant information about the packet is shown on top of the plot in the lower right-hand corner, as shown in Figure 13. The Display

Figure 10. Drop-down Menus for Selecting Analysis on Captured SignalRev. 1.2.6 22

Analyzing Graph OptionsFigure 11. Analyze Mode Graph Options (Top Left, Left and Right Drop-Down Menus)

Options DescriptionAmplitude Shows the captured signals amplitude over time. The plot shows both instantaneous

power and the peak power averaged over a symbol time

Spectrogram Presents a 3D plot of the power at a given frequency over time. The display is a top view of a spectrum analyzer over time, where the color coding represents the signal strength at the given frequency. Red represents the strongest signal and green represents the weakest signal.

Table 5. Analyze Mode Graph Options (Top Left Menu)Rev. 1.2.6 23

Analyzing Graph OptionsOptions DescriptionPSD Plots the power density versus the frequency spectrum for the analyzed signal, over the

range of +/- 20 MHz from the center frequency. It is possible to zoom on the plot, if higher detail is desired - see section "Using the Zooming Tool"

Spectrum Mask Plots the spectrum of the analyzed signal along with the limits specified by IEEE 802.11, over the range of +/-33 MHz from the center frequency, thus providing a quick visual check that the spectrum conforms to the 802.11 specification. This analysis will attempt to determine the signal type from analyzing the packet information at the beginning of the packet, so it is advisable to use packeted transmission. However, if one uses continuous transmission with no gaps, one will have to select the signal type above the main signal window to display the appropriate spectral mask. If both analysis types are selected, IQsignal will default to 802.11b mode.

CCDF Plots the peak to average power distribution, an alternative measure for crest factor. The horizontal axis is for the power level above the average power level, and the vertical axis plots the probability of that power level occurring. The CCDF is only measured over a single packet, so the gap does not contribute to the measurement. The packet used for the analysis is marked with purple markers. If the capture contains more than 1 packet, one can zoom on the other packet in the capture, and press the Zoom button, where after the CCDF is calculated for the packed displayed in the main analysis window. This graph reveals any compression of the signal that may exist.

Symbol Constellation Shows the quality of the demodulated data in the complex plane for each symbol in the analyzed frame. For OFDM data the data carrier are colored red; the pilot tones are colored green. For 802.11b symbols of the preamble are colored green, and the data symbols are colored red.

Spectral Flatness Shows the spectral flatness of the sub-carrier spectrum as compared with the limits imposed by the 802.11 specification. This is only available for a and g signals.

LO (DC) Leakage Shows the energy level of the carriers relative to that of the center carrier and therefore reveals the amount of LO Leakage. Observe, that a special signal is required if one wants to analyze LO leakage of an 802.11b signal. This is discussed in greater detail in "Local Oscillator Leakage".

Phase Noise (PSD) Analyzes phase versus frequency. Graphs the estimated PSD plot of the synthesizer measured during the burst.

Phase Error (Time) Analyzes phase error versus time. Graphs the estimated phase error (noise) of the synthesizer vs. time during the burst.

Power On Ramp Used for 802.11b mode. Analyzes the on-ramp time for an 802.11b signal. For accurate results an un-modulated CW signal should be used. The analysis can also be performed on an OFDFM signal, but there is no related IEEE spec.

Power Down Ramp Used for 802.11b mode. Analyzes the down-ramp time for an 802.11b signal. For accurate results an un-modulated CW signal should be used. The analysis can also be performed on an OFDFM signal, but there is no related IEEE spec.

Table 6. Analyze Mode Graph Options (Left Menu)Rev. 1.2.6 24

Analyzing Graph OptionsPacket Information will only display the packet information if one of the following analysis are selected in the Left Selection Window:

CCDF Symbol Const Spectral Flatness LO (DC) Leakage Phase Noise (PSD) Phase Error (Time) Power On Ramp Power Down Ramp

or selecting one of the following from the Right Selection Window:

Freq. Error EVM vs. Carrier (OFDM) EVM vs. Symbol 802.11.b Eye Diagram Ampl vs. Time (OFDM).

Otherwise No Data Available will be displayed, as no demodulation of the captured data has been performed.

Figure 12. Amplitude Display Mode for 802.11a/g OFDM signalRev. 1.2.6 25

Analyzing Graph OptionsWhen measuring signals, purple markers placed above the signal indicate which packet is selected for the analysis. This is illustrated in Figure 14, for the analysis of an 802.11b signal. Note, if no demodulation is performed, the markers will not appear.

The packet markers can be used to help identify bad packets. If a bad packet is detected - e.g. it is too short, the marker will illustrate the expected duration of the packet - thus in this case extend beyond the end of the packet. This is illustrated in Figure 15.

Figure 13. Same display as in Figure 12, but enabling Display Packet Information. Observe the purple marker.

Figure 14. Illustration of purple markers indicating the 802.11b packet being analyzed.Rev. 1.2.6 26

Analyzing Graph OptionsAs a result of the packet ending too early, very bad EVM results are presented. This gets even worse if compensation algorithms that work on the full packet are enabled. By zooming on the desired packet, so the packet end extends the zoomed area (see "Using the Zooming Tool"), the data is now analyzed correctly, and produces the results based on the zoomed area only. Note, the CRC error is still observed (as one cannot test CRC without a complete packet), but the real performance is now revealed. Remember, to include the beginning of the packet, oth-erwise the packet cannot be demodulated. Zooming on the above bad packet, reveals a nice signal, as illustrated in Figure 16.

Spectrogram

Figure 15. Illustration of a bad packet, where data stops before the expected end of packet (Symbol Timing Tracking is set to off).Rev. 1.2.6 27

The spectrogram mode is useful for capturing live signals with an antenna. In many cases there can be a disturbing signal, that will be difficult to analyze with a normal spectrum plot.

Analyzing Graph OptionsWith the spectrogram the spectrum can be shown over time. The X axis represents time and the Y axis represents frequency. The color coding represents the strength on the signal, with red being the maximum strength, and green being minimum strength. Figure 17 shows the spectrogram plot of a captured signal. The figure shows an 802.11b signal starting at 150 sec and a wireless phone WDCT starting at 410 sec at a carrier of +7 MHz to the WLAN signal. The equivalent spectrum plot is shown in Figure 18. The WDCT signal in this case may block the WLAN receiver.

Power Spectrum Density

Figure 19 illustrates the Power Spectrum Density (PSD) graph for an 802.11a/g signal which is located in the Left Graph window. The figure also shows the power spectral density for other

Figure 16. Zooming of the packet in Figure 15, allows the analysis of the good part of a incorrectly formatted data packet.Rev. 1.2.6 28

OFDM signals that can be analyzed using IQsignal.

Analyzing Graph OptionsFigure 20 illustrates the Power Spectrum Density (PSD) graph for an 802.11b signal.

When the PSD graph is selected from the menu, the Power Measurement Results window also displays in the upper right corner of the main window, as shown in Figure 22. For details con-cerning the Power Measurement Results window, see the following section.

It should be noted that the power spectral density plot can be used to display the power spec-tral density of signals other than 802.11 signals. One can easily display the power spectral den-sity of e.g. a CW signal. Naturally one will have to operate the system in free-run mode. An example of the power spectral density of a CW signal is shown in Figure 21.

Figure 17. Spectrum Plot with WDCT blocker

Figure 18. Traditional Spectrum Analyzer ViewRev. 1.2.6 29

Analyzing Graph OptionsPower Measurement Results Window

The Power Measurement Results window, as shown in Figure 22, lists the power measure-ments and averages in dBm for the following:

Peak Power - measured peak power of the capture Av Power (all) - averaged power of the full capture Av Power (no gap) - averaged power of the packet in the capture (the gap between pack-

ets are removed from the power calculation.

Figure 19. PSD Graph for 802.11a/g signal (upper left), Turbo mode signal (upper right), ASTM DSRC (lower left), and quarter rate signal (lower right)Rev. 1.2.6 30

Max. Avg. - The peak value of the amplitude, calculated as a moving average over 40 samples.

Analyzing Graph OptionsThe first column shows the measurement of the current packet, and the second column shows the average of the last X packets, where X is the number chosen in the parameter setup (EVM/Power Averaging) and also displayed next to the Avg. heading. By pressing the button right above the Average column, the average value will be reset.

The Power Measurements window (Figure 22) displays when any of the following menu items

Figure 20. PSD Graph for 802.11b Signal

Figure 21. Example of PSD graph measuring a CW signal with 1MHz offset Rev. 1.2.6 31

are selected simultaneously from the Left (PSD, Spectrum Mask, CCDF (for DSSS signals)) and Right (IQ Signals, STS Pretzel) drop-down menus.

Analyzing Graph OptionsWhen measuring signals with gaps (packets), the purple markers indicate the selected packet for analysis as discussed above. The data reported represents the data of the selected packet. If the capture contains more than one packet, one can zoom the other packet, and press the zoom button, where after the first packet in the zoomed area will be selected (see"Using the Zooming Tool").

EVM and Power Measurement Result Window

Selecting one of the following menu items from the Left Selection Window:

CCDF (for OFDM signals) Symbol Const Spectral Flatness LO (DC) Leakage Phase Noise (PSD) Phase Error (Time) Power On Ramp Power Down Ramp

or selecting one of the following from the Right Selection Window:

Freq. Error EVM vs. Carrier (OFDM) EVM vs. Symbol 802.11.b Eye Diagram

Figure 22. Power Measurement Results WindowRev. 1.2.6 32

Ampl vs. Time (OFDM)

Analyzing Graph Optionswill cause the Power Measurement Result Window to change to the EVM and Power Measure-ment Window shown in Figure 23.

The EVM & Power frame displays the current EVM in the PSDU as well as the average from the last X packets. The power measurement over the whole frame is also displayed - again cur-rent and averaged over the last X packets. The power measurement results are the same as in Figure 3-11. For 802.11b signals, the average and the peak EVM are shown. Note that the Tools/Parameter window allows selection of two different EVM algorithms. When the classic EVM algorithm is used, the EVM is calculated over the full PSDU, or all samples present after the preamble if the sampled data does not extend over the full frame. If the IEEE 802.11b stan-dard method is selected, the EVM is calculated over the last 1000 samples (11 MHz sampling), or the complete PSDU if fewer samples are present. The peak EVM is taken either over the full PSDU or over the 1000 samples for the first and the second method respectively.

For 802.11a/g signals, the average EVM is shown for the data and pilot carriers separately, as

Figure 23. EVM & Power Measurements Result Window 802.11b (left) and 802.11a/g (right)Rev. 1.2.6 33

well as averaged over all carriers.

Analyzing Graph OptionsThe I/Q Match frame shows the results for the I/Q Amplitude and Phase imbalances in % and degrees respectively. The numbers in dB provide an approximation of the best achievable EVM if the Amplitude error (or Phase error) would be the only impairment present - thus its contribu-tion to the overall EVM.

When measuring 802.11b signals and the signal has been acquired, the LO Leakage is dis-played as shown above. This LO leakage is relative to the total signal power. This result is cal-culated from the I/Q constellation of a standard 11b signal. The 802.11 standard prescribes a LO leakage measurement with the scrambler disabled, a 1/0 data pattern, and QPSK modula-tion. The requirement is expressed as the difference between the sinc envelope of the discrete frequency components and the power measured at the carrier frequency. This difference should be at least 15 dB. The envelope is about 10 dB down relative to the total signal power. So the standard requirement of -15 dB translates to a LO leakage requirement not to exceed 25 dBc.

Note: - it is possible to change the unit of the amplitude mismatch between % and dB by right clicking on the I/Q Match text box. This is illustrated inFigure 24.

The Frequency frame shows the results for the carrier frequency error, the symbol clock fre-quency error, and the rms phase noise.

Spectrum Mask

When the Spectrum Mask graph is selected, the Power Measurement Results window displays at the upper right corner of the main window, as shown in Figure 22. As indicated in the figure the measurement bandwidth is 100kHz as specified by the IEEE specification. If the captured data does not include the preamble of the packet (e.g. when measuring a continuously trans-mitted signal), the desired mask can be selected/displayed by selecting either Analyze A/G (for OFDM) or Analyze B (for DSSS).

Figure 24. By right clicking on the I/Q Match window the unit of the amplitude imbalance can be selectedRev. 1.2.6 34

Figure 25 illustrates the Spectrum Mask graph for 802.11b signal.

Analyzing Graph OptionsAs the other supported OFDM modulations do not have a well defined spectral masks, only the spectrum will be shown for these modulations when choosing the spectral mask plot option. The plotted bandwidth stays +/-40MHz for all analysis.

Figure 26 illustrates the Spectrum Mask graph for OFDM 802.11a/g signal.

Figure 25. Spectrum Mask Graph for 802.11b Signal

Figure 26. Spectrum Mask Graph OFDM 802.11a/g SignalRev. 1.2.6 35

Analyzing Graph OptionsCCDF

Figure 27 displays the CCDF (Complementary Cumulative Distribution Function) graph for OFDM 802.11a/g signal. The blue curve represents the measured signal, and the purple curve represents the ideal curve for an OFDM signal. Compare Figure 27 with Figure 28. It is clear that the OFDM signal is significantly affected by the compression, where as it is less obvious for the DSSS signal. When the CCDF graph is selected, the EVM Measurement Results win-dow displays at the upper right corner of the main window, as shown in Figure 23.

Figure 28 shows an example of a CCDF compressed signal. Observe the faster roll-off.

Symbol Constellation

The Symbol Constellation graph, which displays in the Left Graph window, shows the quality of the demodulated data in the complex plane for each symbol in the analyzed frame. Figure 29 shows the Symbol Constellation graphs for the four possible modulation types for an 802.11b signal. The green dots represent the demodulated data of the preamble (BPSK) and the red dots represent the demodulated data of the PSDU (Physical layer Service Data Unit) for a QPSK signal. For DSSS modulation the demodulated data points coincide with two of the four data points, as illustrated in the figure.

Figure 30 illustrates a Symbol Constellation graph for an OFDM 802.11a/g signal. The red dots/symbols represent demodulated data; the green dots/symbols represent the demodulated data of the pilot tones.

Figure 27. CCDF Graph for OFDM 802.11a/g Signal (Left) and DSSS 802.11b signal (Right)Rev. 1.2.6 36

Analyzing Graph OptionsSpectral Flatness

The Spectral Flatness displays in the Left Graph window and shows an estimate based on the long training sequence of the spectral flatness of the sub-carrier spectrum as compared with the limits imposed by the 802.11 specification. When the Spectral Flatness graph is selected, the Measurements windows also displays in the upper-right corner of the main window, as

Figure 28. CCDF Compressed OFDM Signal Graph (Left) and compressed DSSS Signal Graph (Right)

Figure 29. Symbol Constellation Graph for 802.11b Signals. 1Mbps (left), 2Mbps, 5.5Mbps, and 11Mbps CCK (right) - the latter all have the same constellationRev. 1.2.6 37

shown in Figure 22. Figure 31 illustrates the Spectral Flatness graph for OFDM 802.11a/g sig-nal.

Analyzing Graph OptionsSelecting the Spectral Flatness and the LO leakage plot windows results in EVM results being displaying in the Result Window.

The spectral flatness does not make sense in the contents of 802.11b DSSS signals, so no data is displayed.

Figure 30. Symbol Constellation Graphs OFDM 802.11a/g Signals. 6/9Mbps (BPSK) - upper left, 12/18Mbps (QPSK) - upper right, 24/36Mbps (QAM-16) - lower left, 48/54Mbps (QAM-64) - lower right. Rev. 1.2.6 38

Analyzing Graph OptionsLocal Oscillator Leakage

The LO (DC) Leakage result is measured during the long training symbol. It shows the energy level of the carriers relative to that of the center carrier, and thus reveals the amount of LO Leakage. When the LO Leakage graph is selected, the Power Measurements Window also dis-plays in the upper right corner of the main window, as shown in Figure 22.

Figure 32 illustrates the LO (DC) Leakage graph for OFDM 802.11a/g signal. The red plus sign (+) represents the IEEE specified 2dB limit.

Measuring LO leakage on an 802.11b DSSS signal requires a special test signal that is pro-vided by the DUT. According to the IEEE specification [1] a 0101 modulated signal with the scrambler turned off must be transmitted.

Figure 33 shows the LO leakage measurement window for the special test signal as well as a normal 802.11b DSSS signal when measuring LO leakage.

Figure 34 shows the full spectral plot of the test signal analyzed in Figure 33

Phase noise (PSD)

Figure 35 illustrates the Phase Noise (PSD) graph.

Figure 31. Spectral Flatness Graph for OFDM 802.11a/g SignalRev. 1.2.6 39

Analyzing Graph OptionsFigure 32. LO (DC) Leakage Graph for OFDM 802.11a/g Signal

Figure 33. LO (CD) Leakage Graph for correct test signal (Left)1 and normal 802.11b DSSS signal (Right)

1. The test information presented in the left figure is caused by the scrambler being disabled, as the preamble does not contain correct packet information.Rev. 1.2.6 40

Analyzing Graph OptionsPhase Error (Time)

Figure 36 illustrates the Phase Error (Time) graph for a CCK modulated 802.11b signal. The abrupt change in the graph illustrated the transition from BPSK modulation to QPSK modula-tion.

Figure 34. Spectral plot of the required 802.11b test signal to measure LO (DC) leakage

Figure 35. Phase Noise (PSD) GraphRev. 1.2.6 41

Figure 37 illustrates the Phase Error (Time) graph for OFDM 802.11a/g signal.

Analyzing Graph OptionsPower On Ramp

Figure 38 illustrates the Power On Ramp graph for 802.11b (CCK) modulated signal. The plot shows an averaged version of the power (Black) as well as a peak hold measured over a 1s rolling window (Green). The measured Power-On time (the time it takes the power to go from 10% to 90%) is presented, along with information of the time difference between the time

Figure 36. Phase Noise Time Graph (CCK)

Figure 37. Phase Noise Time Graph for OFDM 802.1a/g SignalRev. 1.2.6 42

where the packet reaches 90% of power, and the actual start of the packet.

Analyzing Graph OptionsPower Down Ramp

Figure 39 illustrates the Power Down Ramp graph for 802.11b (CCK) modulated signal. The plot shows an averaged version of the power (Black) as well as a peak hold measured over a 1s rolling window (Green). The measured Power-Down time is presented (the time it takes the power to go from 90% to 10%), along with information of the time difference between the time where the packet goes below 90% for more than 1s and the actual end of the packet1. The nature of the CCK signal may cause erroneous power down results. Using an un-modu-lated CW signal provides the most reliable measurement results.

I&Q Signals

The I&Q Signals shows the I and Q signals voltages plotted against time. When the I&Q Sig-nals graph is selected, the Measurements window also displays in the upper right corner of the main window, as shown in Figure 22. Figure 40 illustrates the I&Q Signals graph for 802.11b.

Figure 41 illustrates the I&Q Signals graph for OFDM 802.11a/g signal.

Figure 38. Power On Ramp Graph for 802.11b (11Mbps)Rev. 1.2.6 43

1. Note, the shift in the peak power curve is caused by the measuring of the peak power over 1s, so it will produce a shift by 1s in the down ramp.

Analyzing Graph OptionsShort Training Symbols

The Short Training Symbols (STS) pretzel, which displays in the right graph window, is an x-y

Figure 39. Power Down Ramp Graph for CCK

Figure 40. I&Q Signals for 802.11b Rev. 1.2.6 44

plot of the I signal (along the x, or real, axis) versus the Q signal (along the y, or imaginary, axis) during the short preamble. The term 'pretzel' refers to the pretzel-like shape of the plot.

Analyzing Graph OptionsThe effects of phase and frequency errors, compression and filtering, and I/Q mismatch may (after some practice) be discerned from the shape of this plot.

Figure 42 illustrates an STS Pretzel measured from an OFDM 802.11a/g signal. The STS Pret-zel is not available for the 802.11b signal.

Frequency Error

The Frequency Error graph displays the frequency error of the captured data. For DSSS sig-

Figure 41. I&Q Signals for OFDM 802.11a/g

Figure 42. STS Pretzel from 801.11a/g SignalRev. 1.2.6 45

nals (802.11b) the frequency error throughout the packet is displayed, and for OFDM (802.11a/g), only the frequency error through the short and long training symbols are displayed. Figure

Analyzing Graph Options43 illustrates the Frequency Error plot for 11b for a signal with an artificially, linearly changing frequency starting at around 350 usec. The blue line represents the instantaneous frequency measured every symbol. The red line is the frequency averaged over 11 symbols..

Figure 44 illustrates a typical frequency response during the short training sequence of an OFDM signal. The blue graph illustrates the frequency error during the short training sequence, and the black graph illustrates the frequency error of the second symbol in the long training sequence. The green dots shown represent a linear extrapolation between the two. Note, for OFDM, the frequency error reported in the freq window (Figure 23) is measured over the full packet, and does not necessarily correlate with the average frequency error displayed in the graph1.

Figure 45 illustrates frequency pulling of the VCO by the turn on of the power amplifier during the short training sequence of an OFDM signal. In this case the frequency settling is completed before the end of the long training symbol. Given this, one should expect significant improve-ment in the EVM measurement, if one selects the Frequency Sync to use the long Training symbol rather than the short training symbol.

Error Vector Magnitude Versus Carrier

The Error Vector Magnitude (EVM) versus the Carrier plot graph shows the EVM for each sub-carrier averaged over all symbols within the data frame. When the EVM versus Carrier graph is

Figure 43. Frequency Error plot for 11b for a signal with an artificially, linearly changing frequency starting at around 350 usecRev. 1.2.6 46

1. If the frequency is settled, it should correlate, but if there is still frequency settling, it is likely a difference may exist.

Analyzing Graph Optionsselected, the Measurements window also displays the overall EVM results in the upper right corner of the main window, as shown in Figure 23.

Figure 46 illustrates the EVM Versus Carrier graph for OFDM 802.11a/g signal. The plots green points represent the rms average EVM of the four pilot carriers, and the red points repre-sent rms EVM of the 48 data carriers. The blue dotted lines represent the peak (worst) EVM

Figure 44. Coarse Frequency Error for Short and Long Training Sequence (OFDM 802.11a/g Signal)

Figure 45. Illustration of frequency pulling during Short Training Sequence.Rev. 1.2.6 47

value measured for the given carrier during the analyzed packet. EVM Versus Carrier is used only for 802.11a/g signal.

Analyzing Graph OptionsError Vector Magnitude (EVM) Versus Time

The EVM versus the Symbol plot shows the EVM for each symbol averaged over all sub-carri-ers within frame data. Figure 47 illustrates a graph for the EVM Versus Symbol Number for OFDM 802.11a/g signal. The red points represent the rms EVM for the given symbol. Again the blue dotted lines represent the peak EVM of all the sub carriers for the given symbol.

Figure 46. EVM Versus Carrier for OFDM 802.11a/g SignalRev. 1.2.6 48

Figure 47. EVM Versus Symbol for OFDM 802.11a/g Signal

Analyzing Graph OptionsObserve a button called Select Carriers above the right window appears when EVM vs. Sym-bol is selected. Pressing this button enables the user to select one or more specific sub-carri-ers to be analyzed and plotted. Pressing the button creates an input windows shown in Figure 48.

From the window it should be clear how to select the desired sub-carriers. If a single carrier is to be analyzed, simply type the number of the sub carrier (-26 to 26). If a range of sub-carriers are desired, type start sub-carrier:stop sub-carrier - e.g.4:8. If more complex selections are desired, the selection can be included in square brackets []. E.g. if sub-carriers -26,-1, 1 and 26 and 26 are to be selected, one can e.g type [-26 -1:1 26]. After the desired sub-carriers are selected, press the zoom button in the left side of the main window, where after the plot will be updated with the data analyzed based on only the selected carriers. Figure 49 shows the anal-ysis result when selecting the carriers of the last example. Observe the text in the Select Sub-Carriers button becomes red when only a subset of the sub-carriers are selected. The pop-up text box in Figure 48 shows the currently selected carriers. Note, if only one sub-carrier is selected, only the red points appear as the plot will show the instantaneous value.

Figure 50 illustrates the EVM Versus Time for 802.11b signal with the 11b EVM calculation set to rms error vector. The instantaneous EVM per symbol is plotted - the blue lines. The red line in the graph shows the EVM averaged over 11 symbols (chips). The horizontal axis is time since start of packet. The plot shows the EVM over the full packet, except for the first approxi-mately 10 usec. When the 11b EVM calculation is set to 11b Std. Tx mod acc, the EVM over the last 1000 chips of the PSDU are shown.

Eye Diagram Graph

The Eye graph analyzes the error vector magnitude. The Eye graph is available only for the 802.11b signal. Figure 51 illustrates the Eye Graph for 802.11b signal.

Figure 48. Pop-up window to define the sub-carriers to be analyzedRev. 1.2.6 49

Analyzing Graph OptionsAmplitude vs. Time Graph (OFDM)

The Amplitude vs. Time Graph presents the difference in symbol power at a given symbol in the packet vs. the power of the symbols of the long training sequence (LTS). This can be used

Figure 49. EVM vs. Symbol plot with same captured signal as in Figure 47 but with fewer sub-carriers selected

Figure 50. EVM Versus Time for 802.11b Signal (CCK)Rev. 1.2.6 50

to detect power variation during the packet, as well as providing an estimate of how accurate the channel estimate is. The Amplitude vs. time can only analyze OFDM signals.

Analyzing Graph OptionsFigure 51. Eye Graph for 802.11b Signal

Figure 52. Amplitude vs. time graph for OFDM modulated signal.Rev. 1.2.6 51

Using the Zooming ToolUsing the Zooming Tool

The IQView EVM application has a zooming tool that allows you to zoom in on the main data graph in order to stretch the plot out along the time (horizontal) axis. There are two methods for using the zoom tool:

Slider Method Left-clicking and Dragging Method

Note: In future releases of the software, the slider method may no longer be supported.

Using the Slider Method to Zoom

The Slider Method for zooming, uses two slider bars. The one below the main power window (Time Window), and the one in the lower right side below the text windows (ZOOM). The slide bar below the main window is used to move the selected time window (ZOOM) over the cap-ture.

The Zoom Slider (Zoom) selects the time window being analyzed. As you move the Time Win-dow control bar, all three graphs (top and bottom) on the main window change in unison. The Zoom Slider allows you to view from far right to far left, the maximum size of the captured anal-ysis displayed in the top graph. Figure 53 illustrates the zoom slide with the mouse pointing to the control bar of the slider.

The top graph (shown in Figure 54) illustrates a capture set up for 500 microsecond intervals. See "Parameters" in this chapter for changing the time intervals for analyzing captures.

This functionality allows the user to zoom to a specific point in time, and magnify it. If continu-ous capturing is used, the zoomed area will be maintained, allowing the user to inspect a spe-cific point in time over multiple packets - e.g. the transition from pre-amble to data contents in an 802.11b signal1.

Figure 53. Zoom SliderRev. 1.2.6 52

1. This assumes the signal trigger is enabled, so the event will happen at the same point in time relative to the cap-ture start.

Using the Zooming ToolTo focus on a specific section of the top graph, simply slide the Time Slider (as shown in Figure 55) to the desired portion of graph that you want to view. Notice that the slider bar now is positioned further to the right and as a result, the top graph focuses on a specific portion of the graph. Compare Figure 54 to Figure 55 to see the difference in the top graph after repositioning the Time Slider from left to right.

Figure 54. Amplitude Graph Showing Time Interval Capture in 500 MicrosecondsRev. 1.2.6 53

Figure 55. Zoom Time Slider Repositioned to the Right

Using the Zooming ToolUsing the Left-Click and Drag Method to Zoom

To use the left-click and drag method to zoom in on a particular section of the top graph, simply left click your mouse. As you begin a drag movement, a thin-lined rectangle (frame) appears. Discontinue dragging and release the mouse when you have selected the exact area of the graph that you want to focus on. Figure 56 illustrates the Left-Click and Drag Method for zoom-ing.

Note: The bottom graphs do not change when performing this type of zoom.The Left-Click and Drag method also works on the two graphs below the as illustrated in

Figure 57.

To zoom out from the current view, press the right mouse key (or Shift-right click). Repeat

Figure 56. Left-Click and Drag Method

Figure 57. Illustration of zooming on one of the two lower windows. Left before zoom, Right resulting zoomRev. 1.2.6 54

pressing the right mouse key until the full view is reestablished.

VSA Panel ToolWhen one has selected the desired portion of a power signal window, the data can be analyzed using only the data displayed in window by pressing the Zoom button in the left side of the screen. The zoom button enables a reevaluation of the signal displayed in the power signal window.

Note: Zooming using the Left-click and Drag method, does not allow the zoomed position to be maintained when running in continuous mode, as in the Zoom Slider mode.

VSA Panel Tool

The VSA Panel is a tool to help further analyze a DUTs receivers RF performance. This is done by connecting the IQ of the RF chip to the baseband inputs of IQview1. The VSA panel enables the user to compensate baseband impairments of the received signal, allowing the user to determine the best possible performance of the a DUT in terms of RF performance. The compensation is introduced to a captured baseband signal, before it is analyzed by the signal processing of IQsignal. This emulates the performance of a baseband modem capable of removing baseband impairments as part of its receiver implementation. The tool works on both saved signals as well as real time captured signals, and works on signals captured on both the RF and base band port of IQview. Again, the tool is designed to compensate impairments of the DUT receiver, so it is suggested only to use it for baseband signal captures. Using it to compensate captured RF signals may provide unreliable results (e.g. if a frequency offset is present).

The VSA Panel is started by selecting it in the tools menu of IQsignal Vector Signal Analyzer application. This is shown in Figure 58.

The VSA panel starts as an application in a separate window, and will initially appear as shown in Figure 59.

The VSA Panel only has one menu - the file menu, where the only option is to exit the program.

Figure 58. Starting the VSA panelRev. 1.2.6 55

1. Note, IQviews baseband inputs are 50 Ohm, so in most cases a driver between the RF chip and the baseband input will be required.

VSA Panel ToolThe VSA panel offers three main modes of operation: The slider operation, the tracking opera-tions and the automatic Optimize EVM operation.

Slider Operation

The sliders are controlled by the part of the VSA Panel windows shown in Figure 60.

The sliders are used to manually introduce compensation on the signal. By introducing com-pensation, one can compensate existing impairments in the captured signal. As can be seen 5 possible compensation can be introduced:

Amplitude mismatch Phase mismatch Group delay DC offset on the I signal and on the Q signal

Detailed explanation of the 5 different compensations is presented in "VSG Panel Tool" later in

Figure 59. VSA panel after startupRev. 1.2.6 56

this manual

VSA Panel ToolBefore introducing a compensation, the given compensation must be enabled. That is done by clicking the check box below the desired compensation. If the compensation is not enabled, even if a non zero value is introduced on using the slider, it will be ignored. Data can be intro-duced by either sliding the slider using the mouse, or by entering the desired value directly in the text box below the slider. The units of the five possible compensation settings are pre-sented in Table 7.

When operating on a captured signal (not running in continuous mode), one will have to press the Zoom button on the IQsignal main window, for the changes in the VSA Panel to be reflected in the shown results.

Figure 60. Slider portion of VSA Panel.

Compensation UnitAmplitude Imbalance %

Phase Imbalance Degrees

Group delay ns

I and Q DC offset V

Table 7. Summary of units for compensation Rev. 1.2.6 57

VSA Panel ToolTracking Operation

Tracking Operation is used when performing continuous captures. The portion of the VSA panel related to tracking is shown in Figure 61.

By setting tracking to on, the slider will be updated so it will track the input signal to compen-sate the impairments in the received signal. The time constant controls how fast signal changes can be tracked. The time constant is shown relative to signal timing in IQsignal, and is not a real time number.

Note, the current version of the VSA Panel does not support tracking of the group delay. A fixed value can be added, but it is currently not possible to vary the group delay when using continu-ous capture. Naturally, it can still be manually changed while performing continuous capture.

Furthermore, some requirements exist for the tracking to be functional. The tracking mecha-nism assumes that on average the transmitted signals I and Q are not correlated and that the average power in the transmitted I and Q signal is the same, for example the input of an ideal 11a/g signal with varying, random data. Note, the preamble used in DSSS system as well as the lowest rate (1Mbps) in 802.11b do not meet the criterion of the I and Q signals not being correlated, since BPSK modulation has 100% correlation between I and Q signals. Given this, the tracking will not work on 1Mbps 802.11b signals, and may not work well on other 802.11b signals where the capture contains predominantly the preamble.

Besides enabling tracking, two additional buttons are included:

Fast DC Update Button

Fast DC update measures the DC value on the I and on the Q signal, and adjusts the DC offset sliders to compensate the measured value. Note, one should only use this option when analyz-ing OFDM signals, as DSSS signals carry DC information, so a wrong value may be calcu-lated1. Furthermore, IQview may contribute slightly to the DC offset when measuring signals with very low DC contents. This can in most cases be ignored.

Figure 61. Portion of VSA panel used to control trackingRev. 1.2.6 58

1. For long DSSS captures, the result is likely to be correct, as the DC information will be averaged out.

VSA Panel ToolReset Compensation Button

The Reset Compensation button reset all values of the sliders to 0.

Optimize EVM Operation

The last part of the VSA panel shown in Figure 62, calculates the receivers amplitude and phase imbalance compensation which optimizes the captured signals EVM.

Optimize EVM consists of a report window and two buttons. Pressing the optimize EVM button, will perform an automatic optimization of EVM on the current capture in IQsignal. Given this, it not advisable to run continuous capture when performing the EVM optimization, as the capture that is being optimized may not be the same as the one shown in IQsignal after the capture. Furthermore, it is required that the start of the packet is present in the capture, as it is the case for all EVM analysis in IQsignal.

Figure 63 shows the Optimize EVM portion of the VSA Panel after Optimize EVM has been executed. Note, the derived phase and amplitude values will only correspond to the value shown in IQsignal when measuring on baseband input signals.

As can be seen the best possible EVM is presented as well as the compensation values needed to achieve this EVM value. By pressing the Transfer Values to sliders, the found values

Figure 62. Optimize EVM portion of VSA PanelRev. 1.2.6 59

are transferred to the sliders. This is shown in Figure 64.

Vector Signal GeneratorVector Signal Generator

The Vector Signal Generator is a separate program that generates complex signals that are output by the tester's RF or Baseband output ports to verify the performance of the receiver portion of the 802.11 Device Under Test (DUT).

To run the Vector Signal Generator application, select Vector Modulator, located in the Tools menu. Figure 65 illustrates the Vector Signal Generators main window. The blue graph shows the instantaneous power of the signal, and the red signal shows the power averaged over one symbol. Table 8 lists and defines the Vector Signal Generator functions.

Figure 67 illustrates the red bomb which indicates that the vector signal generator is not working optimally, or impairments have been introduced by the VSG Panel IQ impairment tool (See"VSG Panel Tool")

Table 9 describes the supplied waveform files, as well as additional files included with the IQsignal application. The signal waveforms available in the drop-down Signal box, are named wave1-wave8.mod. If one wants to replace the default waves with one of the other supplied wave forms, one can simply copy the desired wave form to a file called the same a the one to be replaced, overwriting the existing file.

Figure 63. Optimize EVM window after executing Optimize EVMRev. 1.2.6 60

Vector Signal GeneratorFigure 64. VSA Panel after performing Optimize EVM and Transfer values to Sliders.Rev. 1.2.6 61

Vector Signal GeneratorFigure 65. Vector Signal Generator Main WindowRev. 1.2.6 62

Figure 66. Illustration of user defined frequency input for VSG panel

Vector Signal GeneratorFunctions DescriptionRF ON/RF OFF Starts and stops the Vector Signal Generator. A green LED will display next to

the RF ON/RF OFF button (see Figure 67) when an output signal is provided.

TX Mode TX Mode selects whether the VSG produces a continuous signal, or transmits the signal stored in the VSG a predetermined number of times. To enable the predetermined number of packets, select Packets selector, and enter the number of packets desired. Input range is 1 to 65334. Note, if two packets exist in the selected wave form, twice the entered number of packets will be transmitted.

RF Output (Checkbox) Selects the output mode of the RF and Baseband ports. When checked, the vector signal is output on the RF port and monitored on the Baseband ports. If not checked, the vector signal is output on the Baseband ports. When the VSG is enabled, a green LED will display next to the RF ON/ RF OFF button along with text indicating of the output is RF or baseband only.

RF Channel Selects an RF output channel. Available selections are:

2412 MHz to 2484 MHz in increments of 5 MHz. 4900MHz to 5805 MHz in increments of 20 MHz. (some selection not

included) User defined frequency, by selecting User Defined, MHz - 1MHz resolution

(see Figure 66)

IQ Swap (Checkbox) When checked, the I signal and the Q signal are interchanged on the RF or Baseband output ports. Otherwise, they are not interchanged.

Signal (Pull-Down List) Selects the type of signal to use. See Table 9 for more detail.

Signal Level Shows the RMS signal level of the current output signal. Use the slider to set the desired level, type in the desired level in the input box, or enable the VSGpanel to set the desired level from this application (see later).

Signal Level Slider Sets the output signal level, by clicking on the directional arrows, or by dragging the level indicator.

NOTE: If the output level is set beyond the optimal performance range of the IQview vector signal generator, a red bomb signal will appear in the upper right hand of the application window. This is shown in Figure 67. By dragging the mouse over the bomb signal, additional information is provided (See Figure 67). Note, using the impairment panel to introduce impairments to the signal will also produce the red bomb.

Common Mode Voltageset CMV

When set CMV is enabled, two additional slide bars appear - one to control the base band I-output and one to control the base band Q-output. These can be used to set the common mode output voltage of the baseband outputs.

Gap Power Off (Checkbox) When checked, enables RF Power off during gap period.

Information Displays textual information about the signal being generated.

Graphical Representation Provides a graphical representation of the output signalRev. 1.2.6 63

Table 8. Vector Signal Generator Functions

Vector Signal GeneratorFigure 67. Red Bomb Indicator on VSG. Also observe the two added common mode control slide bars after enabling the Set CMVRev. 1.2.6 64

Vector Signal GeneratorAlong with the wave file is also a detailed description of the corresponding data contents of the packet.

Wave file name Description PSD plot of wavewave1.mod, wave54rc_1000.mod

54Mbps, TX_length:1000, Raised Cosine window, 10 samples @ 80MHz Psdu_Wave54rc_1000.txt: the corresponding PSDU binary information of wave54rc_1000.mod

Wave2.mod, wave36rc_1000.mod

36Mbps, TX_length:1000, Raised Cosine window, 10 samples @ 80MHz Psdu_wave36rc_1000.txt: the corresponding PSDU binary information of wave36rc_1000.mod

Wave3.mod, wave18rc_1000.mod

18Mbps, TX_length:1000, Raised Cosine window, 10 samples @ 80MHz Psdu_wave18rc_1000.txt: the corresponding PSDU binary information of wave18rc_1000.mod

Table 9. Overview of supplied wave forms to use with IQ signalRev. 1.2.6 65

Vector Signal GeneratorWave4.mod, wave9rc_100.mod

9Mbps, TX_length:100, Raised Cosine window 10 samples @ 80MHz Psdu_wave9rc-100.txt: the corresponding PSDU binary information of wave9rc_1000.mod

wave9rc_1000.mod 9Mbps, TX_length:1000, Raised Cosine window 10 samples @ 80MHz Psdu_wave9rc_10000.txt: the corresponding PSDU binary information of wave9rc_1000.mod

Wave5.mod, wave1rc_100.mod

1Mbps, TX_length:100, long preamble, Raised Cosine filter, 6 symbols long, Roll off: 1.0Psdu_wave5rc_100.txt: the corresponding PSDU binary information of wave1rc_100.mod

wave1gr_100.mod 1Mbps, TX_length:100, long preamble, Gaussian & Rect filter, length 6, Roll off: 0.5Psdu_wave1gr_100.txt: the corresponding PSDU binary information of wave1gr_100.mod

wave1gr_1000.mod 1Mbps, TX_length:1000, long preamble, Gaussian & Rect filter, length 6, Roll off: 0.5Psdu_wave1gr_1000.txt: the corresponding PSDU binary information of wave1gr_1000.mod

Wave file name Description PSD plot of wave

Table 9. Overview of supplied wave forms to use with IQ signalRev. 1.2.6 66

Vector Signal GeneratorWave6.mod, wave2rc_100.mod

2 Mbps, TX_length:100, long preamble, Raised Cosine filter, 6 symbols long, Roll off: 1.0Psdu_wave2rc_100.txt: the corresponding PSDU binary information of wave2rc_100.mod

wave2gr_100.mod 2Mbps, TX_length:100, long preamble, Gaussian & Rect filter, length 6, Roll off: 0.5Psdu_wave2gr_100.txt: the corresponding PSDU binary information of wave2gr_100.mod

wave2gr_1000.mod 2Mbps, TX_length:1000, long preamble, Gaussian & Rect filter, length 6, Roll off: 0.5Psdu_wave2gr_1000.txt: the corresponding PSDU binary information of wave2gr_1000.mod

Wave7.mod, wave5p5rc_100.mod

5.5 Mbps, TX_length:100, long preamble, Raised Cosine filter, 6 symbols long, Roll Off: 1.0Psdu_wave5p5rc_100.txt: the corresponding PSDU binary information of wave5p5rc_100.mod

Wave file name Description PSD plot of wave

Table 9. Overview of supplied wave forms to use with IQ signalRev. 1.2.6 67

Vector Signal G