The 89600 VSA software shown in this document has been replaced by the new 89600B VSA software, which enables more simultaneous views of virtually every aspect of complex wireless signals. The instructions provided herein can be used with the 89600B; however, some of the menu selections have changed. For more information, please reference the 89600B software Help: Help > Getting Started (book) > Using the 89600B VSA User Interface (book) > VSA Application Window Illustration Option B7U W-CDMA and HSPA+ Modulation Analysis 89600 Vector Signal Analysis Software Technical Overview and Self-Guided Demonstration Measure, evaluate, and troubleshoot W-CDMA and High Speed Packet Access compatible signals with the 89600 vector signal analysis (VSA) software and Option B7U. This software works with a variety of measurement hardware, including Agilent spectrum and signal analyzers, Infiniium and Infiniivision scopes, logic analyzers, ADS simulation software, the 89600S VXI based VSA systems, and more.
Table of Contents Introduction...3 W-CDMA/HSPA/HSPA+ Modulation Analysis Features... 4 Physical Layer of W-CDMA Signals... 5 Setting up the demonstration... 6 Measurement and Troubleshooting Sequence... 7 W-CDMA Downlink Analysis... 8 Spectrum and Time Domain Measurements... 9 Measuring occupied bandwidth...11 Measuring band power...12 Basic Digital Demodulation...14 Error Vector Magnitude (EVM) measurements...18 Additional CDP and CDE measurements...20 Advanced Demodulation...23 Measuring a single channel...23 W-CDMA uplink analysis...25 HSPA+ analysis...27 Summary...30 Glossary...31 Related Literature...32 2
Introduction Gain greater insight into HSPA+ signals with industry-leading HSPA+ analysis capabilities designed to help you dig deeper into your signal. The flexible 89600 VSA with Option B7U, which supports W-CDMA(3GPP) and enhanced HSPA demodulation capabilities, enables descrambling, despreading, and demodulation of W-CDMA and HSPA+ uplink and downlink signals. This solution incorporates advanced technology that does not require coherent carrier signals or symbol-clock timing signals. Additionally, the analyzer automatically identifies all active channels regardless of the symbol rate or spread-codelength. It includes a built-in root raised-cosine filter with a user-definable alpha (defines roll-off factor for chip shaping). Signal locking requires only that the carrier frequency, chip rate, uplink/downlink direction, sync type (CPICH/SCH), and scramble code be input. The demodulator uses the measured signal, called I/Q Meas Time, to generate an ideal reference signal, called I/Q Ref Time. The software uses these signals to allow you to gather more data on signal problems by providing comparison data, modulation quality data, results, and error summary data. Explore signals further with modulation analysis capabilities, including composite code domain power, composite time and channel specific analysis. Measurement results may be shown in several trace display formats as well as numeric error data formats. Flexible display scaling and marker functionality enhance these measurement capabilities. Measurement result data includes: time and frequency domain trace data, code domain power data (composite or layer specific), code domain error data (composite or layer specific), channel data results, and overall error summary results. If you have measurement hardware with two baseband channels, the 89600 VSA software provides IQ baseband measurement capability. You can also perform measurements on data from a file or the stream interface, i.e. ADS simulation or The MathWorks Simulink program. This example of versatility can be seen by the 89600 VSA s compatibility with spectrum and signal analyzers, Infiniium and Infiniivision scopes and logic analyzers. As you go through this demo guide, remember that all of the measurements and displays can be made anywhere from simulation to antenna, from baseband to RF, using the unique 89600 VSA compatibility with a wide range of front end inputs. 3 3
W-CDMA/HSPA/ HSPA+ Modulation Analysis Features These features are applicable to W-CDMA modulation analysis: Standard presets for W-CDMA (3GPP) uplink (mobile station or user equipment) W-CDMA (3GPP) downlink (mobile station) Variable, user-definable chip rate (3.84 MHz standard preset) Single code domain layer or composite code-domain power and code-domain error displays (the composite display shows all code layers simultaneously). You can normalize code-domain power to display the code-domain relative to the total signal power in the code domain. Code domain offsets table which shows time and phase offset of each active Walsh code channel Single channel time-domain displays, such as IQ measured, IQ reference, IQ magnitude/phase error, and error vector traces Composite time-domain displays, such as IQ measured time, IQ magnitude or phase error, and error vector time traces Adjustable filter alpha (default.22) Mirrored (flipped) frequency spectrums can be used to remove the effects of high-side mixing Measurement offset and interval (similar to time gating) used to select specific data slots for analysis Flexible active channel identification for code domain power (CDP) and composite results Active channel identification may be gated to analyze signals with Adaptive Modulation Coding (AMC) Predefined 3GPP Test Models 1 through 4 Variable active channel threshold Averaging for code domain trace data applied to the numeric error summary data in the symbol table Averaging for pre-demodulated spectrum, CDP, and code domain error trace data results HSPA modulation and HSPA+ modulation are extensions to the Universal Mobile Telecommunications System (UMTS) standard published by 3GPP. These additional Option B7U features are available: HSDPA and HSUPA uplink and downlink channel modulation analysis Automatic modulation scheme detection for HS-PDSCH channels using QPSK, 16QAM, or 64QAM Manual or automatic control of modulation scheme for despread HS-PDSCH channels Automatic modulation scheme detection for E-DPDCH channels using BPSK, or 4PAM Predefined Test Model 5 and Test Model 6 setup options (as defined in Section 6.1.1 of 3GPP TS.25.141 V5.7.0 (2003-06) Rel 5 technical specification). HSPA+ capabilities include 64 QAM analysis for downlink and 16QAM/ 4PAM analysis for uplink. The built-in Help text consists of over 2900 help topics. Additional information regarding any of the mentioned features above and more can be found in the Help text. 4
Physical Layer of W-CDMA Signals There are two parameters used to specify which segment of the Result Length data is used for data analysis: Measurement Interval and Measurement Offset. When these two parameters are changed, the analyzer computes the new trace data results from the current measurement data (Result Length) and does not require a new measurement cycle. Figure 1 is a representation of a typical frame structure for a W-CDMA(3GPP)/HSPA signal. Figure 1. Typical W-CDMA(3GPP)/HSPA Frame Structure. Result Length: Determines the signal capture length. This is the data used by the analyzer for demodulation and signal analysis. When you are making your own measurements, you should ensure that the result length is long enough to capture the desired data. Result Length is specified in terms of an integer number of slots or PCG s, as determined by the specific modulation type. In the case of W-CDMA(3GPP)/HSPA, they are referred to as Slots. Note: Result Length may be specified as an integer number of slots, frames or time. If you choose to specify it in seconds, the analyzer will automatically increment the time as necessary to obtain an integer number of slots. Measurement Interval: Determines the time length of the Result Length data that is used for computing and displaying the trace data results. Measurement Offset: Determines the start position of the Measurement Interval within the Result Length. Slot: One W-CDMA(3GPP) time slot is equal to 2560 chips (666.7 µs at the default chip rate). One frame is 15 slots (10 ms at the default chip rate). 5 5
Setting up the demonstration Table 1 describes the minimum hardware required to run the 89600 VSA software. Table 1. System requirements Operating System CPU Empty slots (desktop) Microsoft Windows XP Professional, Service Pack 2 600 MHz Pentium or AMD-K6 > 600 MHz (> 2 GHz recommended) 1 PCI-bus slot (Two recommended VXI hardware only) Microsoft Windows Vista Business, Enterprise, or Ultimate 1 GHz 32-bit (x86) (> 2 GHz recommended) 1 PCI-bus slot (Two recommended VXI hardware only) Empty slots (laptop) 1 CardBus Type II slot (Integrated FireWire recommended for VXI hardware only 1 ) 1 CardBus Type II slot (Integrated FireWire recommended for VXI hardware only 1 ) RAM 512 MB (1 GB recommended) 1 GB (2 GB recommended) Video RAM 4 MB (16 MB recommended) 128 MB (512 MB recommended) Hard disk 512 MB available 512 MB available Additional drives CD-ROM to load the software; license transfer requires a 3.5 inch floppy disk drive, network access, or USB memory stick CD-ROM to load the software; license transfer requires a 3.5 inch floppy disk drive, network access, or USB memory stick Interface support LAN, GPIB, USB, or FireWire 1 interface (VXI HW only) LAN, GPIB, USB, or FireWire 1 interface (VXI HW only) 1. For a list of supported IEEE-1394 (FireWire) interfaces, visit www.agilent.com/find/89600 and search the FAQ s for information on What type of IEEE-1394 interface can I use in my computer to connect to the 89600 S VXI hardware? Table 2 describes the 89600 VSA software required to use this demonstration guide. If you do not already have a copy of the software, you can download a free trial version at www.agilent.com/find/89600. Table 2. Software requirements Version Options 89600 version 9.00 or higher (89601A, 89601AN, 89601N12) (89601A, 89601AN only) -200 Basic vector signal analysis Hardware connectivity -300 (required only if using measurement hardware) -B7U or -B7N W-CDMA(3GPP)/HSPA modulation analysis or 3G modulation analysis bundle 6
Measurement and Troubleshooting Sequence When measuring and troubleshooting digitally modulated systems, it is tempting to go directly to digital modulation and the measurement tools. It is usually better to follow a measurement sequence: one that begins with basic spectrum measurements and continues with vector (combined frequency and time) measurements, before switching to basic digital modulation analysis, and, finally, to advanced and/or standard-specific analysis. This is the sequence we will use in this demo guide. This sequence of measurements is especially useful because it reduces the chance that important signal problems will be missed. 1 23 Spectrum and time domain measurements Get basics right, fi nd major problems Basic digital demodulation Signal quality numbers, constellation, basic error vector measurement Advanced digital demodulation Find specifi c problems and causes Step 1: Spectrum and time domain measurements These measurements give the basic parameters of the signal in the frequency and time domain so that correct demodulation can take place in step 2. Parameters such as center frequency, bandwidth, symbol timing, power, and spectral characteristics are investigated. Step 2: Basic digital demodulation These measurements evaluate the quality of the constellation. Along with a display of the constellation, they include static parameters such as EVM, I/Q offset, frequency error, and symbol clock error. Step 3: Advanced digital demodulation These measurements are used to investigate the causes of errors uncovered in the basic modulation parameters, particularly EVM errors. These include dynamic parameters such as error vector frequency, error vector time, and selective error analysis. The 89600 VSA software has the advantage that you can recall saved time capture recordings and analyze the signal as though you were acquiring data from hardware. In the following pages, we will recall and analyze WCDMA/ HSPA+ signals available on the 89600 VSA software demo CD. 7 7
W-CDMA Downlink Analysis Table 3. Recall the signal To begin our first measurements, let s analyze a W-CDMA downlink signal. Instructions: 89600 VSA software Preset the software Recall the recording of a W-CDMA downlink signal Toolbar menus Click File > Preset > Preset All Note: Using Preset All will cause all saved user state information to be lost. If this is a concern, save the current state before using Preset All. Click File > Save > Setup Click File > Recall > Recall Recording Navigate to the directory and load the signal: (c:\program Files\Agilent\89600 VSA\Help\Signals\3GPPDown.sdf) Start the measurement Click the restart button (toolbar, left side) Auto scale Trace A Auto scale Trace B Right click Trace A Select Y Auto Scale Right click Trace B Select Y Auto Scale Your display should look similar to Figure 2. Figure 2. Spectrum and main time display of a W-CDMA downlink signal. Trace A: This trace shows the signal s spectrum. It also displays the center frequency, span, resolution bandwidth, time length, and range of the signal. Note: Depending on when the trace was auto scaled at different points in the recording, your Y-scale values may appear to be different than the figure. However, you should still obtain the same trace data. Trace B: Displays a block of time-record samples of the signal waveform from which time, frequency, and modulation domain data is derived. 8
Spectrum and Time Domain Measurements 1 23 Spectrum and time domain measurements Get basics right, fi nd major problems Basic digital demodulation Signal quality numbers, constellation, basic error vector measurement Advanced digital demodulation Find specifi c problems and causes The first step in the troubleshooting process is to set up the signal measurement parameters. Since this signal is not burst, triggering will not be necessary. However, other parameters such as the range, scaling, center frequency, span, and bandwidth measurements are all spectral and time domain measurements that take place before demodulation. For this demonstration, the center frequency and span are already set to the appropriate values. Setting the input range is also not required for a pre-recorded signal. However, this demonstration guide will set these values as an example to illustrate how to make spectrum and time domain measurements as a reference. Table 4. RF parameters setup Instructions: 89600 VSA software Set center frequency and frequency span Set input range Toolbar menus Click MeasSetup > Frequency Enter 1GHz in the Center text box Enter 5MHz in the Span text box Click Close Click Input > Range Enter 0 dbm in the Range: text box Note: You may notice that the Range parameter can be changed to any value and will not alter the actual range value located at the top right corner of the trace. This is because the recording was made at a range of 0 dbm, and thus this value cannot be changed manually. 9
It is important to ensure your signal is spectrally clean before you begin demodulation. The following section will show you how to measure the occupied bandwidth. But first, we need to change the RBW filter and main time length so we can view the signal in more detail. Table 5. Increasing resolution and time length Instructions: 89600 VSA software Change the RBW filter and increase the frequency points for better resolution. The Auto frequency points selection chooses the best resolution for the given time capture. Auto scale Trace A and Trace B Toolbar menus Click MeasSetup > ResBW > ResBW Mode > Arbitrary (pull down menu) Check Auto for the Frequency Points parameter Click Time (tab) and set Main Time Length to 900 usec Click Close Right click in Trace A Click Y Auto Scale Right click in Trace B Click Y Auto Scale Your display should look similar to Figure 3. Figure 3. Spectrum and time display. 10
Measuring occupied bandwidth The Occupied Bandwidth (OBW) measurement, coupled with the OBW Summary table, can quickly and accurately report many useful results. Follow the steps in Table 6 to display the OBW along with the corresponding table of results. Trace B in Figure 4 displays several important measurements quickly, including the occupied bandwidth, band power, and power ratio. This signal has a nominal bandwidth of 5 MHz to allow for full viewing of the signal, while the actual bandwidth is measured at approximately 4.4 MHz. Table 6. Measuring OBW Instructions: 89600 VSA software Display OBW marker Activate OBW Summary table Pause the measurement to read the table values Toolbar menus Right click Trace A Select Show OBW Double click the Trace B title (B: Ch1 Main Time) Select Marker from the Type menu on the left-hand side of the box Select Obw Summary TrcA from the Data menu on the right-hand side of the box Click OK Click the Pause button Your display should look similar to Figure 4. Figure 4. Occupied bandwidth measurement with summary data table. 11
We will not need the OBW measurement from this point forward. Follow the steps in Table 7 to clear the OBW measurement. Table 7. Clear OBW measurement Instructions: 89600 VSA software Clear the OBW marker Toolbar menus Double click the Trace B title (B: TrcA OBW Summary Data) Select Channel 1 from the Type menu on the left-hand side of the box that appears Select Main Time from the Data menu on the right-hand side of the box Click OK Right click Trace A De-select Show OBW Measuring band power The band power marker feature measures the power of the modulated signal, or channel power, by integrating over a specified bandwidth in the frequency domain. Follow the steps in Table 8 to set up band power markers. Table 8. Setting up band power marker Instructions: 89600 VSA software Select the band power marker tool Drop the band power marker on Trace A Expand the band power marker Toolbar menus Click Markers > Tools > Band Power (Or, alternatively, you can click the band power marker button on the menu toolbar) On Trace A, move the mouse to the center frequency of the band to be measured Click to drop the marker Place the mouse pointer on the vertical band power marker and click and drag/expand the marker so it includes the entire signal Note: Adjust the center frequency of the band power marker by clicking and holding on the dashed center line and dragging it to the right frequency. Your display should look similar to Figure 5. 12
Figure 5. Band power marker display. The band power should be displayed at the bottom of the window. This is the total power inside the bandwidth of the band power marker. You can expand or shrink the width of the marker to measure the power over specific frequencies. You can control the band power marker more precisely by opening the Markers Properties window. Click Markers > Calculation to access user-settable text boxes for setting the center and width of the band power marker. We will not need the band power marker any further. To turn it off, simply rightclick anywhere in Trace A and de-select Show Band Power. This shortcut can also be used to toggle the band power marker on/off. You may also want to return the mouse curser to a pointer. Click the Pointer button in the toolbar. 13
Basic Digital Demodulation 1 23 Spectrum and time domain measurements Get basics right, fi nd major problems Basic digital demodulation Signal quality numbers, constellation, basic error vector measurement Advanced digital demodulation Find specifi c problems and causes Table 9. Demodulation setup Instructions: 89600 VSA software Select the demodulator Preset the demodulator parameters for downlink analysis Change display layout to Grid 3x2 Once you have examined your signal and verified that there are no major spectral or time problems, the next step is to demodulate it. You should always view the signal spectrum first to be sure that the signal is present, and that the center frequency, span, and input range are correct before selecting a demodulator. Follow the steps in Table 9 to setup the demodulator. Toolbar menus Click MeasSetup > Demodulator > 3G Cellular > W-CDMA(3GPP)/HSPA Click MeasSetup > Demod Properties > Format (tab) > Preset to Default > Downlink Click Close Click Display > Layout > Grid 3x2 (Or, alternatively, you can click on the drop down menu menu toolbar. Select Grid 3x2 from the available options). near the top of the Restart the measurement Click the Restart button Auto scale Traces A, B and C Pause the measurement to read the table results Right click on Trace A Select Y Auto Scale Do the same for Trace B and C. Click the Pause button Your display should look similar to Figure 6. 14
Figure 6. Six trace display of demodulated composite signal. Under different circumstances, you need to verify that the Chip Rate, Scramble Code, Scramble Type, and Sync Type parameters are set correctly. However, since we are making measurements on a pre-recorded signal, the default settings for these parameters are adequate. Trace A: Code Domain Power (CDP) trace that shows the power in each channel for the composite signal. This trace is an analysis of the distribution of signal power across the set of Code Channels normalized to the total signal power. The data is shown in a multi-color format that assigns a unique color to each code layer and related active Code Channels. This allows you to easily identify and distinguish the active Code Channels for a given code layer (Spread Code Length). Note: You can change the channel colors by clicking Display > Appearance to open the Display Appearance window. Trace C: Shows the time data results of the IQ measured signal in a vector constellation format. The trace data is computed from the first slot in the Measurement Interval after the Measurement Offset. A typical downlink W-CDMA signal contains many channels, 16 in this situation. Each channel is QPSK modulated, as seen by Trace F. This leads to a constellation that looks quite noisy. 15
Trace D: Composite error summary table shows the composite error summary data. Common error parameters, such as EVM and frequency error (Freq Err), provide quick indicators that represent the signal quality error summary information for the composite signal. Trace E: Shows the symbol table and error summary trace data for the specified Code Channel and Spread Code length. The error summary data results are shown in the upper section of the channel symbol table display. Trace F: Shows the demodulated constellation time data results for the measured input signal, sampled at the chip times, for the specified Code Channel and code layer (Spread Code Length). Specifically, it is Channel 0 on the Spread Code Length 256 (S256(0)). Due to size constraints, both Trace D and Trace E do not show all of the table results in Figure 6. Figure 7 shows all of the table results. Figure 7. Channel symbol table and composite error summary table. 16
Below is a list of table results found in the composite error summary table: Composite EVM (EVM): The error vector magnitude for the composite signal, including all spread code lengths and code channels. The table shows RMS percentage EVM, the peak (largest) percentage EVM, and the chip number with the peak percentage EVM. This parameter is computed at the chip rate. Composite magnitude error (Mag Err): The difference in amplitude between the I/Q measured signal and the I/Q reference signal for the composite signal. The display shows these magnitude error values: the RMS percentage magnitude error, the peak percentage magnitude error, and the chip number with the peak percentage magnitude error. Composite phase error (Phase Err): The difference, in phase, between the I/Q reference signal and the I/Q measured signal for composite signal, including all spread code lengths and code channels. The display shows these phase error values (in degrees): the RMS phase error, the peak phase error, and the chip number with the peak phase error. Composite IQ offset (IQ Offset): Also known as I/Q origin offset, indicates the magnitude of the carrier feed-through signal. When there is no carrier feedthrough, IQ offset is zero (infinity db). Composite frequency error (Freq Err): Shows the composite signal carrier frequency error relative to the analyzer s center frequency. This parameter is displayed in Hertz and is the amount of frequency shift, from the analyzer s center frequency, that the analyzer must perform to achieve carrier lock. Composite rho (Rho): The normalized correlation coefficient between the measured and ideal reference signals and is designated as the waveform quality factor. The maximum value of rho is 1.0, which means the measured signal and reference signal are identical. Composite slot (Slot): Identifies the time slot used for the composite measurements. The composite slot ignores the measurement offset. Composite T trigger (T trigger): Shows the amount of time, in chips, from the trigger to the start of the frame. If you select a trigger that starts the measurement at the beginning of a PCG, the T trigger value is zero chips. The T trigger value is displayed only for triggered measurements. Composite peak active CDE (Peak Active CDE): The largest active code channel code domain error (in db). This is the largest measured CDE of all active code channels in the composite signal. Composite peak CDE (Peak CDE): The largest measured code channel code domain error. This is the largest measured CDE for all code channels (active and inactive) in the base code layer (the code layer with the smallest symbol rate) in the composite signal. If averaging is on, averaging is applied to most numeric error data in the error summary data, with the following exceptions. The peak data values, such as peak EVM, peak magnitude, and peak phase error, are averaged only for the continuous peak hold averaging type. 17
Table 10. EVM and markers setup Error Vector Magnitude (EVM) measurements Two useful displays for evaluating the behavior of the composite signal are error vector time and error vector spectrum. Each trace also has its own set of markers. You can quickly set marker locations, manually re-position them, locate peak values, and couple the markers between traces to show common values. Follow the steps shown in Table 10 to setup these measurements. Instructions: 89600 VSA software Change Trace A to show error vector time Change Trace B to show error vector spectrum Change the display layout to Stacked 2 Enable markers in both traces Find the peak EVM value in both traces Toolbar menus Double click on Trace A title (A: Ch1 Composite CDP) Under the Type: column, select Channel 1 Comp Under the Data: column, select Error Vector Time Click OK Double click on Trace B title (B: Ch1 Spectrum) Under the Type: column, select Channel 1 Comp Under the Data: column, select Error Vector Spec Click OK Select Stacked 2 from the layout drop down menu on the menu toolbar Right click on Trace A and select Show Marker Do the same for Trace B Right click on Trace A and select Peak Do the same for Trace B Your display should look similar to Figure 8. 18
Figure 8. Error vector spectrum and error vector time displays. Trace A: Depending on when you paused your recording, you may have a different peak location in Trace A. This trace displays error vector time, which represents the EVM behavior over time, where chips represent time. You can view EVM time data as EVM, error vector phase, the I component, or the Q component. This feature is used to find impulsive errors such as a transient overload event or a spiking clock circuit. It is also useful for finding low frequency errors caused by close-in phase noise. Trace B: This trace shows the error vector spectrum, which is the FFT of the EVM time trace and shows the frequency content of the EVM. Trace B shows a high error signal at 1 GHz (Trace B marker value at bottom of display). This is the signal carrier frequency and represents carrier feed through. Carrier feed through is not the only signal the EVM spectrum trace will show. Any spurious signal will show up as a discrete peak in the composite error vector spectrum trace. Markers are a great tool for troubleshooting, and can be coupled between traces for even more convenient troubleshooting. You will see an example of this later in this demonstration. 19
Additional CDP and CDE measurements CDP (code domain power) and CDE (code domain error) measure the power and error of the signal by code channel. They provide more detail on the signal behavior and modulation quality than the composite EVM or rho. We will continue to use markers, to determine the color assigned to each code layer. Follow the steps shown in Table 11 to set up these measurements. Table 11. Setup of CDP and CDE. Instructions: 89600 VSA software Change Trace A to show composite CDP Change Trace B to show composite CDE Auto scale Traces A and B Toolbar menus Double click on Trace A title (A: Ch1 Composite Err Vect Time) Under the Type: column, select Channel 1 CDP Under the Data: column, select CDP Composite Click OK Double click on Trace B title (B: Ch1 Composite Err Vect Spectrum) Under the Type: column, select Channel 1 CDP Under the Data: column, select CDE Composite Click OK Right click on Trace A Select Y Auto Scale Do the same for Trace B Your display should look similar to Figure 9. Figure 9. Composite CDP and CDE measurements. 20
For W-CDMA/HSPA modulation, the CDP and CDE displays assign a unique color to each code layer and related active code-channels for a given code layer (Spread-Code-Length). If you place the marker on each color, the marker readout at the bottom of the display will show the code layer and code channel for that color. Follow the steps in Table 12. Table 12. Marker coupling setup Instructions: 89600 VSA software Change the code order in Trace B to Hadamard Couple markers. Now all information displayed will be for the same point in each trace. As you move the marker in a selected trace, it will track in all the other grids. Select the orange colored channel Toolbar menus Select Trace B by clicking anywhere in the trace Click Trace > Digital Demod Under the Code Order (drop down menu), select Hadamard Click Close Click Markers > Couple Markers Click on Trace A Drag the marker to the top of the right-most orange colored channel. Note: Depending on the size of your window, you may not be able to see this channel. Size your window appropriately until the orange channels can be seen (left side). Your display should like similar to Figure 10. 21
Figure 10. Composite signal traces with markers. Trace A: The bit-reversed generation of code channels displays related code channels adjacent to each other. The marker is on an orange colored channel and shows the following values (bottom of screen): Symbol rate: 15 ksym/s Spread code length: 256 Code number: 16 The asterisk (*) indicates the marker is positioned on an active channel Trace B: This trace shows the code channels in the Hadamard order. Note that the marker automatically points to all of the other parts of the code channel as it is spread by the Hadamard ordering, as seen by the small triangle markers. Note: if you do not see the multiple triangle markers, you may need to use your right/left arrow keys to exactly position the marker. From this point forward, we will not need markers on Trace B. Right click on Trace B and de-select Show Marker. 22
Advanced Demodulation 1 23 Spectrum and time domain measurements Get basics right, fi nd major problems Basic digital demodulation Signal quality numbers, constellation, basic error vector measurement Advanced digital demodulation Find specifi c problems and causes Measuring a single channel The instructions in Table 13 show how to use markers and the Copy Marker to Despread Chan function to quickly view a single channel in your W-CDMA/ HSPA signal. You can also go directly to the desired channel by entering its parameters in the Demod Properties menu. Table 13. Markers with despread channel feature Instructions: 89600 VSA software Toolbar menus Change the display layout to Grid 2x2 Select Grid 2x2 from the layout drop down menu on the menu toolbar Change Trace B to display the Error Vector Time trace for the selected channel Auto scale Trace B Change Trace C to display the vector diagram for the selected channel Change Trace D to display the symbol table for the selected channel Select one of the blue colored channels Select the marked channel for more detailed analysis Double click Trace B title (B: Ch 1 Composite CDE) Under the Type: column, select Channel 1 Chan Under the Data: column, select Error Vector Time Click OK Right click on Trace B and select Y Auto Scale Double click Trace C title (C: Composite Meas Time) Under the Type: column, select Channel 1 Chan Under the Data: column, select IQ Meas Time Click OK Double click on Trace D title (D: Ch1 Composite Error Summary) Under the Type: column, select Channel 1 Chan Under the Data: column, select Syms/Errs Click OK Click on Trace A and position the marker so it is selecting one of the blue colored traces which are any of the visible peaks (your color scheme maybe different) Right click on Trace A and select Copy Mkr to Despread Chan Your display should look similar to Figure 11. 23
Figure 11. Single channel measurement. Copy Marker to Despread Chan: This feature sets the despread channel parameters including: spread code length, code channel, and IQ branch. These parameters enable the following measurements: channel error vector, channel IQ measurement time, channel IQ reference time, channel mag error, channel phase error, and channel systems/error trace data. Trace B: This trace shows how the EVM changes with time (where symbols represent time) for a single code-channel within a specified code layer (Spread- Code-Length/Symbol Rate). The error vector time trace is made up of complex time-domain data. Each point in the trace has two components: I and Q. To make sense of the data, you must select an appropriate trace data format (Trace > Format > Format: drop down list). The selections in this list allow you to set what trace data format you want the trace to plot. Trace C: This shows the Channel IQ Meas trace, which is the demodulated time data, re-sampled at the chip times, for the specified code-channel and code layer (Spread-Code-Length). The data is corrected for IQ origin offset, burst amplitude droop compensation, filtering, and system gain normalization. This particular channel (as well as the others) shows a modulation scheme of QPSK, as shown by the 2x2 constellation. Trace D: This symbol table provides both error summary information and demodulated bits for the selected channel. For W-CDMA downlink signals, the symbol table also shows information about the demodulated channel, such as the number of pilot bits detected in the DPCH channel, the tdpch timing value for the DPCH channel, and the first slot used in the measurement. For additional details regarding the symbol table, see the online Help About the Channel Symbol Table (W-CDMA). For additional details about error information in the symbol table, see online Help About Channel Error Summary Data (W-CDMA). 24
W-CDMA uplink analysis The 89600 VSA software also supports uplink analysis. Pre-demodulation measurements are similar to that of downlink, so we will not repeat those measurements. However, a demodulated uplink signal has significant differences in its composite displays. Follow the steps in Table 14 to set up a W-CDMA uplink demodulation. Table 14. Uplink demodulation Instructions: 89600 VSA software Preset the software Recall the recording of a W-CDMA uplink signal Setup the demodulator Set the demodulator for uplink analysis Change the display layout to a Grid 2x2 Toolbar menus Click File > Preset > Preset All Click File > Recall > Recall Recording Navigate to the directory and load the signal: (c:\program Files\Agilent\89600 VSA\ Help\Signals\3GPPUp.sdf) Click MeasSetup > Demodulator > 3G Cellular > W-CDMA(3GPP)/HSPA Click MeasSetup > Demod Properties > Format (tab) > Preset to Default > Uplink Click Close Click on the layout drop down menu on the menu toolbar and select Grid 3x2 Restart the measurement Click the Restart button Place a marker on an uplink channel and copy the marker to despread channel Right click on Trace A Select Show Marker Click on the upper left green box Right click on Trace A Select Copy Mkr to Despread Chan Your display should look similar to Figure 12. 25
Figure 12. W-CDMA uplink demodulation. By default, Traces A, C and D show you composite displays of your signal. Composite displays show you the results of all channels and layers in your signal, and include data for both I and Q. Trace A: Notice that Trace A, Ch1 Composite CDP display, looks different than it did for the W-CDMA downlink signal. This is because uplink signals separate channels for I, data channels, and Q, control channels. The Ch1 Composite CDP display shows the I channels above the x-axis and the Q channels below the x-axis. In this situation, two channels are being transmitted on I and one channel on Q. Trace C: You may have also noticed that the constellation diagram in Trace C looks significantly different than the downlink signal. In this situation, each channel has a modulation scheme of BPSK, as seen in Trace F. Since there are only three channels being analyzed, versus the 16 in the downlink recording, the constellation will look more defined. Trace F: This trace is similar to Trace C in Figure 11, however, this particular channel has a modulation scheme of BPSK, as seen by the two constellation points. 26
HSPA+ analysis Table 15. Begin downlink HSPA+ demodulation setup The newest standard for HSPA signals is Enhanced HSPA (HSPA+). HSPA features apply to HSPA+ signals. The 89600 VSA software has a downlink HSPA+ recording that can be demodulated using the Enable HSPA Analysis feature. Table 15 sets the demodulation parameters such that it is measuring Code Channel 6 in Spread Code Length 16. This specific channel s modulation scheme is automatically detected as 64 QAM. Instructions: 89600 VSA software Preset the software Recall the recording of an HSPA downlink signal Setup the demodulator Set up the demodulation parameters Change the display layout to a Grid 3x2 Toolbar menus Click File > Preset > Preset All Click File > Recall > Recall Recording Navigate to the directory and load the signal: (c:\program Files\Agilent\89600 VSA\ Help\Signals\3GPPDownHSPA+.sdf) Click MeasSetup > Demodulator > 3G Cellular > W-CDMA(3GPP)/HSPA Click MeasSetup > Demod Properties > Format (tab) Click Preset to Default > Downlink Go to Channel/Layer (tab) Change the Spread Code Length (drop down menu) to 16 (240.0ksym/s) Change the Code Channel to 6 Click Close In the toolbar click on the layout drop down menu and select Grid 3x2 Start the measurement Click the restart button (toolbar, left side) Auto scale Traces A, B, C and F Right click on Trace A Select Y Auto Scale Do the same for Traces B, C and F Your display should look similar to Figure 13. 27
Figure 13. Demodulated downlink HSPA+ signal without HSPA analysis enabled. Notice Traces E and F show an error labeled as INACTIVE CHAN. This error states that the specified CDMA channel, S16(6), is inactive. You can also note that the constellation diagram in Trace F is consistently different than a standard 64 QAM constellation. The high EVM values listed in Traces D and E obviously indicate a problem with the demodulation. Follow the steps in Table 16 to enable HSPA analysis. Table 16. Downlink HSPA+ with HSPA analysis enabled Instructions: 89600 VSA software Set up the demodulation parameters Toolbar menus Click MeasSetup > Demod Properties Go to Format (tab) Check Enable HSPA analysis Click Close Your display should look similar to Figure 14. 28
Figure 14. Demodulated downlink HSPA+ signal with HSPA analysis enabled. You should notice significant changes in all of the demodulation traces. Before HSPA analysis was enabled, some of the channels were not being detected. EVM results in Traces D and E should be significantly better and show values < 1% rms. The constellation in Trace F is more stable with all of the constellation points falling close to the ideal constellation targets, represented as the small gray circles. 29
Summary The 89600 VSA software with Option B7U for W-CDMA/HSPA modulation analysis, along with the standard 89600 VSA features, such as the occupied bandwidth and band power measurements, provide all of the necessary tools to measure and troubleshoot W-CDMA and HSPA downlink and uplink signals as well as HSPA+ signals. With this solution, you can gain greater insight by showing as many as six traces simultaneously, with complete control over the content of those traces. Additionally, you can gather more data on signal problems with the versatile demodulator that can measure the entire composite signal, or utilize the Copy Marker to Despread Channel feature and measure specific channels, allowing you to observe and characterize any aspect of the signal. The analysis of HSPA channels lets you reach deeper into your signals and identify and track down errors. The 89600 VSA software supports a multitude of platforms, including Agilent spectrum and signal analyzers, Infiniium and Infiniivision oscilloscopes, logic analyzers, and ADS simulation software. From baseband to RF, simulation to antenna, it provides the greatest versatility for all measurements. For further detailed information on any of the features mentioned in this demonstration guide, check the built-in Help text. 30
Glossary 3GPP 3G ADS AMC BPSK CDE CDP CPICH DPCH E-DPDCH EVM HSDPA HSPA HSPA+ HS-PDSCH HSUPA I/Q OBW QAM QPSK RBW RF SCH tdpch W-CDMA Third Generation Partnership Project Third Generation Advanced Design System (Agilent EEsof design simulation software) Adaptive Modulation Coding Binary Phase Shift Keying Code Domain Error Code Domain Power Common Pilot Channel Dedicated Physical Channel Enhanced Dedicated Physical Data Channel Error Vector Magnitude High Speed Downlink Packet Access High Speed Packet Access Enhanced High Speed Packet Access High Speed Physical Downlink Shared Channel High Speed Uplink Packet Access In-phase/Quadrature Occupied Bandwidth Quadrature Amplitude Modulation Quadrature Phase Shift Keying Resolution Bandwidth Radio Frequency Synchronization Channel Timing offset value for Dedicated Physical Channel Wideband Code Domain Multiple Access 31
Related Literature 89600 Series Vector Signal Analysis Software, Technical Overview, 5989-1679EN 89600 Series Vector Signal Analysis 89601A/89601AN/89601N12 Software, Data Sheet, 5989-1786EN 89600 Vector Signal Analysis demo software, CD, 5980-1989E Hardware Measurement Platforms for the Agilent 89600 Series Vector Signal Analysis Software, Data Sheet, 5989-1753EN 89600S Series VXI-based Vector Signal Analyzers, Configuration Guide, 5968-9350E Option B7U W-CDMA/HSPA Modulation Analysis for the Agilent 89600 Series Vector Signal Analysis Software, Brochure, 5989-8080EN For more info: www.agilent.com/find/89600 www.agilent.com/find/hspa www.agilent.com/find/wcdma 32
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