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Agilent 89600 Vector Signal Analysis SoftwareOption BHD 3GPP LTEModulation Analysis
Technical Overview and Self-Guided Demonstration
2
Table of Contents Introduction ............................................................................................................................. 3
Downlink physical layer channels and signals ........................................................... 4
Uplink physical layer channels and signals ................................................................. 5
Measurement and Troubleshooting Sequence ............................................................... 6
Setting up the demonstration ......................................................................................... 7
Spectrum and Time Domain Measurements ................................................................... 8
Measuring occupied bandwidth and power ................................................................ 9
Using the spectrogram display ......................................................................................11
Basic Digital Demodulation ............................................................................................... 15
Overview of the parameters under Format tab ........................................................ 16
Overview of the parameters under Profi le tab ......................................................... 17
Overview of the parameters under LTE Allocation Editor window ..................... 18
Overview of the parameters under LTE Downlink
Control Channel Properties window ........................................................................... 19
Advanced Digital Demodulation ....................................................................................... 26
Selective channel analysis ............................................................................................ 30
EVM for data channels ................................................................................................... 30
Analyzing individual symbols ........................................................................................ 31
MIMO analysis ..................................................................................................................34
LTE uplink signal analysis .............................................................................................. 37
Summary ................................................................................................................................. 41
Glossary .................................................................................................................................. 41
Ordering Information ........................................................................................................... 42
Related Literature .................................................................................................................44
Web Resources .....................................................................................................................44
3
Third-generation UMTS, based on wideband code-division multiple access
(W-CDMA), has been deployed all over the world. To ensure that this system
remains competitive in the future, 3GPP began a project to define the long-term
evolution of UMTS cellular technology in November 2004. The specifications
related to this effort are formally known as the evolved UMTS terrestrial
radio access (E-UTRA) and evolved UMTS terrestrial radio access network
(E-UTRAN), but are more commonly referred to by the project name LTE. The
first version of LTE is documented in Release 8 of the 3GPP specifications.
3GPP’s high-level requirements for LTE include reduced cost per bit, better
service provisioning, flexible use of new and existing frequency bands, simplified
network architecture with open interfaces, and an allowance for reasonable
power consumption by terminals. These are detailed in the LTE feasibility study,
3GPP Technical Report (TR) 25.912, and in the LTE requirements document,
TR 25.913.
For more information on the LTE standard and testing concerns, see 3GPP Long
Term Evolution: System Overview, Product Development, and Test Challenges,
literature publication number 5989-8139EN.
Before beginning our demonstration, here is some useful information to help
explain the LTE downlink and uplink channels and signals.
Introduction
4
Downlink physical layer channels and signals
The DL physical channels are Physical Downlink Shared Channel (PDSCH),
Physical Downlink Control Channel (PDCCH), and Physical Broadcast Channel
(PBCH). The DL physical signals are reference signal (RS) and synchronization
signal. Table 1 below has information on the modulation format and purpose
for each of the downlink channels and signals.
Table 1. LTE downlink channels and signals
DL channels
Full nameModulation format
Purpose
PBCH Physical Broadcast Channel QPSK Carries cell-specific information
PDCCH Physical Downlink Control Channel QPSK Scheduling, ACK/NACK
PDSCH Physical Downlink Shared ChannelQPSK16QAM64QAM
Payload
PMCH Physical Multicast ChannelQPSK16QAM64QAM
Payload for Multimedia Broadcast Multicast Service (MBMS)
PCFICHPhysical Control Format Indicator Channel
QPSK
Carries information about the number of OFDM symbols (1, 2 or 3) used for transmission of PDCCHs in a sub-frame.
PHICHPhysical Hybrid ARQ Indicator Channel
BPSK with I & Q CDM
Carries the hybrid-ARQ ACK/NAK
DL signals
Full nameModulation sequence
Purpose
P-SS Primary Synchronization SignalOne of 3 Zadoff-Chu sequences
Used for cell search and identifi cation by the UE. Carries part of the cell ID (one of 3 orthogonal sequences).
S-SS Secondary Synchronization SignalTwo 31-bit M-sequences (binary)
Used for cell search and identifi cation by the UE. Carries the remainder of the cell ID (one of 168 binary sequences).
RS Reference Signal (Pilot)
Complex I+jQ pseudo random sequence (length-31 Goldsequence) derived from cell ID
Used for DL channel estimation. Exact sequence derived from cell ID, (one of 3*168=504).
5
Uplink physical layer channels and signals
Uplink (UL) physical channels are Physical Uplink Shared Channel (PUSCH),
Physical Uplink Control Channel (PUCCH) and Physical Random Access Channel
(PRACH). Two types of uplink reference signals are supported: demodulation
reference signal (DM-RS) which is associated with transmission of PUSCH
or PUCCH, and sounding reference signal (S-RS) which is not associated
with transmission of PUSCH or PUCCH. Table 2 below has information on the
modulation format and purpose for each of the uplink channels and signals.
Table 2. LTE uplink channels and signals
UL channels
Full nameModulation format
Purpose
PRACH Physical Random Access Channeluth root Zadoff-Chu
Call setup
PUCCH Physical Uplink Control Channel BPSK, QPSK Scheduling, ACK/NACK
PUSCH Physical Uplink Shared ChannelQPSK16QAM64QAM
Payload
UL signals
Full nameModulation sequence
Purpose
DM-RS Demodulation Reference Signaluth root Zadoff-Chu
Used for synchronization to the UE and UL channel estimation
S-RS Sounding Reference Signal Zadoff-ChuUsed to monitor propagation conditions with UE.
6
Measurement andTroubleshootingSequence
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.
Step 1: Spectrum and time domain measurmentsThese 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 demodulationThese 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 demodulationThese 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 LTE signals
available on the 89600 VSA software demo CD.
Spectrum and time domain measurmentsGet basics right, fi nd major problems
Basic digital demodulation
Signal quality numbers, constellation, basic error vector measurement
Advanced digital demodulationFind specifi c problems and causes
7
Setting up the demonstration
Table 3 describes the minimum hardware required to run the 89600 VSA software.
Table 4 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 3. System requirements
CharacteristicMicrosoft® Windows® XP Professional
Microsoft® Windows® Vista Business, Enterprise, or Ultimate
CPU600 MHz Pentium® or AMD-K6 > 600 MHz (> 2 GHz recommended)
1 GHz 32-bit (x86)(> 2 GHz recommended)
Empty slots (desktop)
1 PCI-bus slot (Two recommended – VXI hardware only)
1 PCI-bus slot (Two recommended – VXI hardware only)
Empty slots (laptop)
1 CardBus Type II slot (IntegratedFireWire® recommended for VXIhardware only)
1 CardBus Type II slot (IntegratedFireWire® recommended for VXIhardware only)
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
Additionaldrives
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
Interfacesupport
LAN, GPIB, USB, or FireWire1 interface (VXI HW only)
LAN, GPIB, USB, or FireWire1 interface (VXI HW only)
Table 4. Software requirements
Version 89600 version 9.00 or higher (89601A, 89601AN, 89601N12)
Options
-200
-300
-BHD
(89601A, 89601AN only)
Basic vector signal analysis
Hardware connectivity (required only if using measurement hardware)
LTE modulation analysis
1. For a list of supported IEEE-1394 (FireWire) interfaces, visit www.agilent.com/fi nd/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 89600S VXI hardware?"
Table 5. Recall the signal
Instructions: 89600 VSA software Toolbar menus
Preset the software
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
Note: The Menu/Toolbars, Display Appearance, and User Color Map may also be saved in a similar way.
Recall the recording of a 5 MHz LTE downlink signal
File > Recall > Recall Recording(c:\Program Files\Agilent\89600 VSA\Help\Signals)
Select the downlink recording Select LTE_DL_5MHz_v820.sdfClick Open
Start the measurement Click (toolbar, left side)
Auto scale Trace ARight click Trace ASelect Y Auto Scale
Auto scale Trace B Right click Trace BSelect Y Auto Scale
8
The first step in the troubleshooting process is to set up the signal measurement
parameters, such as range and scaling, and verify its spectral and time domain
behavior before demodulation takes place.
It is important to ensure your signal is clear and distinct when you make your
measurements. The following section will show how to measure the occupied
bandwidth. But first we must change the RBW filter and the main time length
so we can view a more detailed signal.
Spectrum and time domain measurmentsGet basics right, fi nd major problems
Basic digital demodulation
Signal quality numbers, constellation, basic error vector measurement
Advanced digital demodulationFind specifi c problems and causes
Table 6. Increasing resolution and time length
Instructions: 89600 VSA software Toolbar menus
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. You can change
this if you prefer.
Meas Setup > ResBW > ResBW Mode > Arbitrary
(pull down menu)
Frequency Points >Auto
Time (tab) > Main Time Length > 900 usec
Click Close
Auto scale Trace A and Trace BRight click in Trace A. Click Y Auto Scale
Right click in Trace B. Click Y Auto Scale
Figure 1. Time and spectrum display.
Note: This fi rst fi gure includes
the menu toolbar and status
bar on the top and bottom of
the window, respectively. In
the interest of displaying as
much information as possible,
the remaining fi gures will not
display them. You can toggle
them on/off by clicking Display
> Appearance > Window
9
Table 7. Measuring OBW
Instructions: 89600 VSA software Toolbar menus
Display OBW traceRight-click Trace A
Select Show OBW
Activate OBW Summary table
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
Measuring occupied bandwidth and band power
The Occupied Bandwidth (OBW) measurement, coupled with the OBW
Summary Table, can quickly and accurately report many useful results. Using
the method described in Table 7, the OBW can be displayed along with the
corresponding table of results shown. Trace B in Figure 2 displays several
important measurements quickly, including the occupied bandwidth, band
power, and power ratio. This signal has a nominal bandwidth of 7.68 MHz to
allow for full viewing of the signal, while the actual bandwidth is measured at
approximately 4.4 MHz. The power ratio is listed, but it is also a user adjustable
feature. By clicking Markers > OBW, the value in the box can be changed to
show the ratio between OBW power and total power.
Your display should look similar to Figure 2.
Figure 2. Occupied bandwidth measurement with summary data table.
Table 8. Clear OBW measurement
Instructions: 89600 VSA software Toolbar menus
Clear OBW display
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
10
The band power marker feature measures the power of the modulated signal,
or “channel power”, by integrating over a specifi ed bandwidth in the frequency
domain.
Table 9. Setting up band power marker
Instructions: 89600 VSA software Toolbar menus
Select the band power marker tool
Click Markers > Tools > Band Power
(Or, alternatively, you can click the band power marker button
on the menu toolbar)
Drop the band power marker on
Trace A
On Trace A, move the mouse to the center frequency of the band
to be measured.
Click to drop the marker.
Expand the band power marker
Place the mouse pointer on the vertical band power marker and
left click to drag/expand the marker so it includes the entire
bandwidth.
Note: You may need to adjust the center of the band power
marker so the entire bandwidth falls within the marker lines.
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 specifi c 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.
Figure 3. Band power display.
We will not need the band power marker any further. To turn it off, simply right-
click anywhere in Trace A and de-select Show Band Power. This shortcut can be
used to toggle the band power marker on/off. You will also need to return your
mouse cursor to a pointer. Click the Pointer button on the toolbar.
11
Using the spectrogram display
The spectrogram is a three-dimensional display that shows the changes in
signal spectrum over time. It is particularly useful when analyzing time-varying
signals. Features of signal transients, OFDM signal structure, and spectral
splatter can all be identifi ed with this display. Using overlap processing
improves its usefulness further. Overlap processing causes the analyzer to
adjust the amount of new data it uses for each time record, and has the effect
of causing the signal to replay in "slow motion." It is particularly useful for
locating and examining transients.
Table 10. Set up spectrogram display
Instructions: 89600 VSA software Toolbar menus
Set the time length to 100 3sec. Set
the overlap processing to 95% (You
can adjust this later to even higher
values to examine the effect of overlap
processing).
Click MeasSetup > Time
Set the Main Time Length to 100 usec
Set Max Overlap (Avg Off) to 95%
Click Close
Activate spectrum display for Trace BDouble click the Trace B title (B: Ch1 Main Time)
In the Data: column select Spectrum
Enable the spectrogram display on
Trace A
Right-click Trace A.
Select Show Spectrogram
Pause the measurement to temporarily
halt playbackClick the pause/continue button in the toolbar
Click on the color bar on the left hand side of the trace (See Figure 4 for refer-
ence). Note: If you cannot see the color bar, your window size may be too small.
Then, scroll up using your mouse scroll wheel or by pressing the up arrow key on
your keyboard. Continue to scroll up until you have a display similar to Figure 4
shown below. An exact replica is not necessary, but for many spectrum/spectro-
gram settings you should be able to see the periodic “ears” in the display, shown
as small peaks on both sides of the spectrogram. These appear at the transitions
between symbols and allow you to see the number and timing of OFDM symbol
transitions.
You may have noticed that Figure 4 has horizontal and vertical white lines. These
are markers, which can be used as another method to measure certain aspects
of the spectrogram, including the center frequency. Follow the steps in Table 11
to set up these markers.
12
Table 11. Setting up spectrogram markers
Instructions: 89600 VSA software Toolbar menus
Enable the spectrogram marker
(Make sure Trace A is active by
clicking anywhere in the trace)
Markers > Spectrogram
Check the Trace Select box, then highlight the Trace num-
ber entry box and move the spectrogram marker using the
down arrow on your keyboard. This marker initially appears as
a while horizontal line at the very bottom of the trace.
Note: Both spectrum traces are connected, so you may have
noticed that as you move the spectrogram marker up and
down along the spectrogram, the spectrum in Trace B will
reflect the correct display of the spectrum in that specific
moment in time.
Play the recording until you see two
abnormal spots of lighter color
Click the pause button in the toolbar to continue
playback on the recording. When a pair of abnormal “spots”
appear in the spectrogram, press the pause button again to
stop the playback. See the figure below for reference.
Place the spectrogram marker on the
spots
Re-position the white spectrogram marker so that it is in line
with the spots.
Enable the main trace marker Click on the diamond icon near the top of the menu
toolbar
Place marker on left spotClick on the trace where the spot is located to drop a marker
on that position
Add an offset marker Right click on the trace and select Show Offset
Move offset to marker Right click on the trace and select Move Offset to Mkr
Click and drag offset to right spotClick and drag the vertical white line over to the right until the
marker is in line with the other spot
13
The “spots” are actually spectral nulls. The middle 72 subcarriers are reserved
for P-SS, S-SS and PBCH channels and signals. In our case, P-SS and S-SS only
occupy 62 of the subcarriers, which leave these spectral nulls unoccupied on
either side of those center 62 subcarriers. Thus, since each subcarrier occupies
15 kHz, 72*15 = 1080 kHz, or approximately 1MHz. Depending on the exact
location of your markers, your offset value should be approximately this value.
Figure 4. Spectrogram display showing LTE signal structure.
Offset markers can also be used to show ∆y values. For example, you could use
this to measure the "ears", or the symbol transitions. To see the ∆y, click and
drag the horizontal white marker lines so they are aligned with the "ears." The
∆y value is shown at the bottom of the window.
In this particular situation, the center frequency was given. However, in some
cases, especially during troubleshooting, the center frequency may not be given
or clearly noticeable. The main trace marker can also be used to measure the
center frequency of the signal.
But fi rst, let us use a new set of markers. Right-click on Trace A and
un-check Show Marker. Then follow the steps in Table 12 below.
14
Table 12. Using spectrogram markers to find center frequency
Instructions: 89600 VSA software Toolbar menus
Temporarily turn off spectrogram
display
Right click anywhere on Trace A
De-select Show Spectrogram
Increase main time length to obtain a
more defined signal
MeasSetup > Time
Set the Main Time Length to 900 usec
Click Close
Adjust Y-axis settings
Double click on the upper left corner axis value on Trace A
In the Y Top pop up window, set the value to -33 dBm
Double click on the center axis value.
(It should read 15 dB/div)
In the Y /Div pop up window, set the value to 6 dB
Adjust the span
Double click on the Span value for Trace A
(lower right corner of trace)
Set the value to 5 MHz
Click OK
Restart the spectrogram
Click the Restart button
Right click anywhere in Trace A and check Show Spectrogram
Note: you should see a distinct line in the center of the spectro-
gram. If you do not, adjust the color bar as previously instructed
until it is more noticeable.
Zoom in on center
Click the Pause button to pause playback.
Click the Select Area tool on the menu toolbar
Click and drag a small square around the center line.
Select Scale X from the menu box that appears.
Click OK
Place marker on center lineUsing the same trace marker as before, place a marker on the line
that you just magnified
At the bottom of the window, the marker value should appear. The value should
read approximately 1GHz, confi rming the value of the center frequency. This line
is actually a null subcarrier that is not transmitted at the center frequency. Since
it is not being transmitted, it has a lower power level at that point, and thus is
shown in a lighter color. Your display should look similar to the fi gure below.
Figure 5. Spectrogram display showing center frequency subcarrier.
Turn off the spectrogram display and marker by right clicking on Trace A and
un-checking both Show Spectrogram and Show Marker.
15
Basic Digital Demodulation
Once you have examined your signal and verified that there are no major spectral
or time problems, the next step is to demodulate it. We'll set up a constellation
display and measure basic I/Q parameters using the LTE demodulator as shown
in Table 13. This recording has all the control channels, plus 3 different data
channels using QPSK, 16 QAM and 64 QAM modulation formats.
LTE downlink signal analysis
Spectrum and time domain measurmentsGet basics right, fi nd major problems
Basic digital demodulation
Signal quality numbers, constellation, basic error vector measurement
Advanced digital demodulationFind specifi c problems and causes
Table 13. Set up the LTE demodulator
Instructions: 89600 VSA software Toolbar menus
Change the display to show four traces
in a 2x2 grid
Display > Layout > Grid 2x2
(Or alternatively, Click on the drop down menu near the top of the
menu.
Select Grid 2x2 from the available options.)
Select the LTE demodulator MeasSetup > Demodulator > 3G Cellular > LTE
Set up the demodulator for downlink
analysis
See below for descriptions of each tab
and the parameters available
MeasSetup > Demod Properties > Format (tab)
Click Downlink from the Direction: drop down menu.
Click the Preset to Standard... box and select 5 MHz (25 RB)
from the drop down menu
Go to Profile (tab)
Click the Edit Control Params box
Make sure the PDCCH Allocation field is set to 3 for each
Subframe (Sf) Sf0 thru Sf9
Click OK.
Go to Format (tab)
Make sure Auto is selected under Cell ID
Select automatic detection of Resource
Blocks (RB)
Go to Profile (tab)
Check RB Auto Detect (Note: This setting is checked by default)
Click Close
Begin demodulationPress Restart
Your display should look similar to Figure 6
16
Figure 6. Default measurement traces for LTE demodulation.
The next section gives you information about the different parameters under the Format and Profile tabs in the MeasSetup > Demod Properties menu. You will use this information to help set up the parameters which allow the analyzer to demodulate the signal. This information is available to you in the Help text. Note that the 89600 VSA software allows you to manually set many parameters. You can also use a setup file from Agilent Signal Studio if you are using that product for signal generation. For proper demodulation, the analysis setup must
match the signal transmitted.
Overview of the parameters under Format tab
Figure 7. LTE demodulation Format tab.
Direction: Drop-down list to select LTE direction, either Downlink or Uplink.
Bandwidth: Drop-down list to select LTE bandwidth, ranges between
1.4 MHz to 20 MHz.
Preset to Standard: This button presets all demodulation parameters to default
values, and also presets the demodulator to the specified bandwidth.
Sync Type: Selects the type of Synchronization; Physical Synchronization Signal
(P-SS) or Reference Signal (RS).
17
CP Length: Selects the cyclic prefix used in the transmitted signal. There are two
choices, "Normal" and "Extended." The software can auto-detect which to use,
or let the user specify manually.
Cell ID: Cell ID determines the physical layer cell identity. There are 504 possible
physical layer cell identities. A specific value may be entered, or it may be
automatically determined by selecting “Auto.”
RS-PRS: Selects the Pseudo Random Sequence (PRS) used for the Reference Signal
(RS). The software can auto-detect which to use or it can use a custom setting.
Number of Tx Antenna: Dictates the number of transmit antennas the demodulator
should search for.
TX Antenna: There can be up to four different antenna ports on a downlink
transmitter. The RS sequence for the different antenna ports can be demodulated
to make an analysis on each antenna port.
Antenna Detection Threshold: User-settable dB value such that signals from the
different antenna ports must be above to be detected by the demodulator.
Tx Diversity/MIMO: Transmit Diversity/Multiple-Input Multiple-Output. This
controls additional features including Control Channel Precoding and Shared
Channel Precoding.
Control Chan Precoding: Drop down menu to turn Transmit Diversity (Tx Diversity)
on or off in the control channel.
Shared Chan Precoding: Drop down menu to turn Transmit Diversity (Tx Diversity)
on or off in the shared channel.
Overview of the parameters under Profile tab
Figure 8. LTE demodulation Profile tab.
RB Auto Detect: Enables auto detection of shared channel (user) allocations. The
demodulator groups allocations by modulation type. Note: This setting is checked
by default.
Composite Include: Determine which channels and signals are displayed on traces
and included in EVM and Power composite results.
Edit User Mapping: Click to open LTE Allocation Editor window, shown in Figure 9.
Edit Control Parameters: Click to open LTE Downlink Control Channel Properties,
shown in Figure 10.
18
Overview of the parameters under LTE Allocation Editor window
Figure 9. LTE Allocation Editor window
RB Auto-Detect: Automatically detect the Resource Block (RB) and slot allocation
for each burst based on modulation format used for each downlink shared channel
(PDSCH).
Include: Select or De-Select accompanying modulation format.
Name: Specifies name of modulation format used for the data channel.
PDSCH: Physical Downlink Shared Channel.
RB Start/End: Specifies the RB allocation (in frequency domain) for a particular
data channel.
Slot Start/ End: Specifies time slot allocation (in time domain) for a particular data
channel.
Mod Type: Specifies the modulation format used for the data channel (QPSK, 16
QAM, 64 QAM).
Power Boost (dB): The power of the subcarriers relative to the 0 dB level
determined by the RS power level.
RB mapping for PDSCH: When the resource blocks are not auto-detected, you can
manually add allocations and set specific RB Start/End and Slot Start/End values
for them. These will appear in the RB mapping grid, from which you can click and
drag to reposition or resize allocations.
19
Overview of the parameters under LTE Downlink Control Channel Properties window
Figure 10. LTE Control Channel Properties window.
P-SS: Primary-Synchronization Signal.
S-SS: Secondary-Synchronization Signal.
PBCH: Physical Broadcast Channel.
PCFICH: Physical Control Format Indicator Channel.
RS: Reference Signal.
PDCCH: Physical Downlink Control Channel.
Power Boost: The power of the subcarriers relative to the 0 dB level determined by
the RS power level.
Allocations (Symbols per subframe): Determines the amount of symbols
designated for each subframe.
Subframe: Subframe number; 0-9.
# Symbols: Specifies the number of symbols under each respective subframe.
Const: When selected, the number of symbols specified under Subframe 0 is cou-
pled to the other Subframes. De-select to manually enter individual values.
PHICH: Physical Hybrid ARQ Indicator Channel.
Despread IQ Orthog Seq Index: When selected, the traces display PHICH constel-
lation points after dispreading. This arbitrarily remaps the demodulated values
of individual PHICH sequences on the I and Q value of the subcarriers containing
those sequences. When cleared, PHICH constellation points are displayed as
received, which is the summation of all PHICHs within the same PHICH group.
Allocation (Ng): Determines the number of PHICH groups per subframe;
1/6, 1/2, 1, or 2.
Duration: Tells the demodulator how many symbols per subframe are used by
PHICH; Normal or Extended.
20
Table 14. Display frame summary information
Instructions: 89600 VSA software Toolbar menus
Change Trace C to show the frame
summary
Double click the Trace C trace title (C: Ch1 OFDM Err
Vect Spectrum)
In the Data: column select Frame Summary
Click OK
Auto scale Trace BRight click on Trace B
Select Y Auto Scale
When you turn on digital modulation analysis, you automatically receive the
default measurements in the default locations. But they are easy to change to
display any available trace data in any trace location. As we begin our measure-
ments, let's change one of the traces to show the Frame Summary data next to
the constellation so that you can easily interpret the colors.
But first we need to increase the number of slots in the Measurement Interval.
Click MeasSetup > Demod Properties > Time (Tab). Set the Result Length to 20.
You should have a display similar to the one in Figure 11 below. Let's look at
some of the traces:
Figure 11. LTE constellation and frame summary information.
Trace A: Composite constellation diagram color-coded by the channel type
as shown in Trace C. The RS (pilot) uses Pseudo Random Sequence (PRS) for
modulation, shown in the constellation diagram in cyan (light blue). The P-SS is
transmitted as a Zadoff-Chu sequence and thus appears as irregularly spaced
points on a circle (pink color).
Trace B: Spectrum trace showing pre-demod measurements including center
frequency, span, resolution bandwidth (RBW) and time length. There is no change
to this trace even though we are making demodulation measurements.
21
Trace C: Summary of all active channels including EVM for each channel, their
relative power modulation format and allocated RB for each channel. The color
of the channel mirrors the color-coding used in other displays, such as the
constellation diagram. Below is a list of the channels and their descriptions.
P-SS: Primary-Synchronization Signal.
S-SS: Secondary-Synchronization Signal.
PBCH: Physical Broadcast Channel.
PCFICH: Physical Control Format Indicator Channel.
PHICH: Physical Hybrid ARQ Indicator Channel.
PDCCH: Physical Downlink Control Channel.
RS: Reference Signal.
PDSCH_QPSK: Physical Downlink Shared Channel: QPSK modulation format.
PDSCH_16QAM: Physical Downlink Shared Channel: 16 QAM modulation format.
PDSCH_64QAM: Physical Downlink Shared Channel: 64 QAM modulation format.
Non-alloc: All non-allocated channels.
Trace D: Summary table listing many EVM measurements. Consult the Help text
for a full listing of all possible error summary results.
One of the greatest strengths of the 89600 VSA is its error analysis. Here we'll
look at the wide range of built-in error traces available to you.
22
Your display should be similar to what is shown in Figure 12.
Figure 12. LTE error traces.
Table 15. View the multiple EVM traces supported
Instructions: 89600 VSA software Toolbar menus
Change the display to show six traces Select Grid 3x2 from the layout drop down menu
Change Trace B to show EVM per
Resource Block (RB)
Double click the Trace B title (B: Ch1 Spectrum)
In the Data: column select RB Error Mag Spectrum
Click OK
Change Trace C to show EVM per
subcarrier
Double click the Trace C title (C: Ch1 Frame Summary)
In the Data: column select Error Vector Spectrum
Click OK
Change Trace D to show the frame
summary
Double click the Trace D title (D: Ch1 Error Summary)
In the Data: column select Frame Summary
Click OK
Change Trace E to show EVM per
time slot
Double click the Trace E title (E: Ch1 OFDM Err Vect Time)
In the Data: column select RB Error Mag Time
Click OK
Change Trace F to show EVM per
symbol
Double click the Trace F title (F: Ch1 Frame Summary)
In the Data: column select Error Vector Time
Click OK
Auto scale all traces (except Trace D) Right click on each trace and click Y Auto Scale
23
Here is information describing the traces you just changed. In some descriptions
you will see "z-axis" mentioned. Access to these z-axis values is possible by
placing a marker on the trace and using the up/down arrow keys to walk through
the points available and see the measurement values.
Trace B: OFDM RB Error Magnitude Spectrum — Shows the EVM of each RB with
respect to frequency, and displays EVM for every slot during that RB. The x-axis
is RB, y-axis is EVM, and z-axis is slot. This example uses a 5 MHz LTE profile
which has 25 RBs as shown on the x-axis. This is a useful display to see the
range of EVM performance per user allocation and is unique to Agilent.
Trace C: OFDM Error Vector Spectrum — Shows the EVM for each subcarrier
and displays the difference between the measured symbols and the reference
symbols for each subcarrier. The x-axis is subcarrier, the y-axis is EVM and the
z-axis is symbol. For a 5 MHz LTE signal, there are 300 subcarriers (25 RB x
12 subcarrier/RB).
Trace E: OFDM RB Error Magnitude Time — Shows the EVM of each RB with
respect to time during the measurement interval and displays EVM for each RB
during that slot. The x-axis is slot, y-axis is EVM, and z-axis is RB. The default
capture interval for the LTE application is 1 frame (20 slots). This trace shows
EVM across the 20 slots as shown on the x-axis.
Trace F: OFDM Error Vector Time — Shows the EVM for each symbol and displays
the difference between the measured symbols and the reference symbols for
each symbol in the measurement interval. The x-axis is symbol, the y-axis is EVM
and the z-axis is subcarrier. The default capture interval for the LTE application
is 20 slots. For signals using a normal cyclic prefix, there are 7 symbols/slot.
This means that for 20 slots there are 140 symbols, as shown here on the x-axis.
This trace clearly shows the different control channels. For example, you can
clearly see the PDCCH channels (shown in a yellow color) occupying the first
3 symbols in each sub-frame.
You may have noticed that the edges of the Error Vector Spectrum traces are high-
er than normal. By default, the software matches the standard’s method of EVM
calculation. It measures the EVM at two points, takes the maximum between the
two and uses that as the EVM at that point. Then, while calibrating the equalizer,
it takes the average over 19 RS (pilots). This will lead to a high EVM if the signal
was transmitted using a bad filter. For our purposes, this high EVM problem can be
resolved by adjusting the appropriate settings under the Advanced tab. Follow the
steps in Table 16 below to do so.
24
Your display should look similar to Figure 13 shown below.
Figure 13. Six display window of various EVM traces.
For our purposes, we will follow the standard. To return to the original settings,
follow the steps below in Table 17.
Table 16. Reduce the EVM by adjusting the EVM averaging window
Instructions: 89600 VSA software Toolbar menus
Turn off Moving Average FilterClick MeasSetup > Demod Properties > Advanced (tab)
and de-select Moving Avg Filter
Choose EVM Window CenterSelect EVM Window Center under the Symbol Timing
Adjust options
Table 17. Return to original setting
Instructions: 89600 VSA software Toolbar menus
Turn on Moving Average FilterClick MeasSetup > Demod Properties > Advanced (tab)
and select Moving Avg Filter
Choose Max of EVM Window
Start / End
Select Max of EVM Window Start / End under the Symbol
Timing Adjust options
Click Close
25
The LTE application also has the ability to measure power in each RB and each
slot. Let's view both EVM and power in each RB and Slot.
When finished, your display should look similar to the one shown in Figure 14.
Figure 14. Power per RB and Slot.
Trace B now shows EVM in each RB, while Trace C shows the Power in each
RB. Similarly, Trace E shows EVM in each time slot, while Trace F shows the
power in each time slot.
Table 18. Power per RB and Slot
Instructions: 89600 VSA software Toolbar menus
Change Trace C to show Power
per RB
Double click the Trace C title (C: Ch1 OFDM Err Vect
Spectrum)
In the Data: column select RB Power Spectrum
Click OK
Change the y-axis scale of Trace C
to dB
Double click Lin Mag on y-axis of Trace C
In the Format drop down menu, select Log Mag (dB)
Click OK
Change Trace F to show power
per Slot
Double click the Trace F title (F: Ch1 OFDM Err Vect Time)
In the Data: column select RB Power Time
Click OK
Change the y-axis scale of Trace F
to dB
Double click Lin Mag on y-axis of Trace F
In the Format drop down menu, select Log Mag (dB)
Click OK
26
Advanced Digital Demodulation
Advanced demodulation techniques allow you to focus in on signal errors, or set
up the analyzer so that more detailed troubleshooting is possible.
To begin with, we'll focus in on slot zero in the OFDM Error Vector Time display
to more carefully analyze our signal and its errors.
Your display for Trace F should look similar to the one shown in Figure 15.
Spectrum and time domain measurmentsGet basics right, fi nd major problems
Basic digital demodulation
Signal quality numbers, constellation, basic error vector measurement
Advanced digital demodulationFind specifi c problems and causes
Table 19. Selective slot analysis
Instructions: 89600 VSA software Toolbar menus
Change Trace C to show EVM per
subcarrier
Double click the Trace C title (C: Ch1 OFDM RB Power Spectrum)
In the Data: column select Error Vector Spectrum
Click OK
Change Trace F to show EVM per
symbol
Double click the Trace F title (F: Ch1 OFDM RB Power Time)
In the Data: column select Error Vector Time
Click OK
Zoom on slot #0 (i.e. 1st 7 symbols) of
the EVM per symbol trace - Trace F
Markers > Tools > Select area or use the select area box
from the tool bar
Click and hold to drag a box around the first time slot on Trace F,
less than 10% of the first x-axis grid.
Select Scale X & Y
Click OK
The x-axis should now display symbols 0 to 6. If not, go to
Trace > X Scale > and set Left Reference to 0 Sym and
Right Reference to 6 Sym
Click Close
Auto scale Trace F Right click on Trace F and click Y Auto Scale
Return mouse cursor to pointer Click on the Pointer button in the toolbar
27
Figure 15. OFDM EVM for slot 0 only. Colors shown correspond to channel type.
Looking at slot 0 we can see a lot of information. Remember that there are
7 symbols in a slot. The channel type is color-coded, and matches the color
coding used in the Frame Summary trace.
Symbol 0: RS (cyan color) is transmitted on every 6th subcarrier, while PDCCH
channels (yellow), PCFICH channels (purple), and PHICH channels (light red) are
transmitted on the rest of the subcarriers.
Symbols 1 & 2: More PDCCH channels (yellow).
Symbol 3: All of the subcarriers are used to transmit user data (PDSCHs), as
shown by red (QPSK), orange (16 QAM) and dark green (64 QAM).
Symbol 4: RS (cyan color) is transmitted on every 6th subcarrier. The rest of
the subcarriers are used to transmit user data (PDSCHs) as shown by the
other colors.
Symbol 5: S-SS (blue color) is transmitted on the center 72 subcarriers (only
62 out of the reserved 72 subcarriers are used; the remaining 10 subcarriers are
not used). The rest of the subcarriers are used to transmit user data (PDSCHs),
as shown by the different colors.
Symbol 6: P-SS (pink) is transmitted on the center 72 subcarriers (only 62 out
of the reserved 72 subcarriers are used; the remaining 10 subcarriers are not
used). The rest of the subcarriers are used to transmit user data (PDSCHs), as
shown by the different colors.
Note: Some of the channel colors may not be as noticeable as the others. You
can confirm that certain channels are being transmitted by using the marker tool
and observing the marker information that appears at the bottom of the window.
Also, you may have noticed that PBCH (light green) is not seen in any of the
above symbols. This is because slot 0 does not transmit PBCH. If you change
your scale x-axis to show slot 1 (symbols 7 to 13), you will see the first occur-
rence of PBCH. To do so, right click under Trace F on the x-axis annotation area,
and select X-Scale. Set Left Reference to 7 and Right Reference to 13.
To go back to the full scale, go to Edit > Undo Scale, or Trace > X Scale > Full
Scale.
28
Another useful capability is marker coupling. This allows you to view error sources
from different measurements. For instance, if you see an error and place a marker
on it, you can track that same point in the signal in different error displays.
In the example below, we are going to create an "error" by asking the analyzer to
make a measurement that does not match the actual signal. You will adjust the
P-SS power boost level value, which is used to normalize those channels.
Your display should be similar to the one shown in Figure 16.
Notice that the markers all report data from the same point in time, but in
different error domains. Notice that the marker also gives you information on
channel type. In this situation, since we set the Power Boost level for P-SS
channel to be slightly higher than the rest, it stands out as a higher EVM. Notice
the color-coding throughout the different displays, showing the P-SS (pink) has
been selected and coupled throughout the displays. This method of marker
coupling provides a very convenient troubleshooting method.
Table 20. Marker coupling
Instructions: 89600 VSA software Toolbar menus
Turn off the RMS trace (white line
across Traces B, C, E and F)
Click on Trace B. Under Trace > Digital Demod > uncheck Show 2D Avg LineClick CloseDo the same on Traces C, E and F
Auto scale all traces (except Trace D) Right click on each trace and click Y Auto Scale
Change the amplitude of the P-SS
channel to show a different value
MeasSetup > Demod Properties > Profile (tab)
Click the Edit Control Params… box to open the LTE
Downlink Control Channel Properties window
Set the Power Boost value for P-SS to 0.8 dB
Click OK
Before closing the Demod Properties window, note that, as
a convenience, the power boosting levels for all channels are
shown, including the new value for the P-SS which you just
adjusted.
Click Close to close the Demod Properties window
Couple markers between displays
Right click on Trace A and select Show Marker. Do this for all
traces (except Trace D).
Once the marker is placed in all traces (except Trace D), couple
the markers by going to Markers > Couple Markers
Place marker on P-SS channel
Now click on Trace C so the marker is on one of the P-SS
carriers (Pink).
The markers in all the other displays will show the same point in
time but provide different error views.
29
Figure 16. Markers coupled across traces.
Table 21. Turn off coupled markers and change P-SS Power Boost level back to normal
Instructions: 89600 VSA software Toolbar menus
Turn off the markers in each display
Right click on each trace and uncheck Show Marker .
Note: Coupling Markers will automatically place a marker on
Trace D. Since the Frame Summary trace does not support a
right click, go to Markers and un-check Show Marker, this will
clear the empty marker status line at the bottom of the window.
Change the value of Power Boost for
P-SS back to original value
MeasSetup > Demod Properties > Profile (tab)
Click the Edit Control Params button to open the LTE
Downlink Control Channel Properties window
Set the Power Boost value for P-SS to 0.65 dB
Click OK
Click Close
30
Selective channel analysis
This recording signal has 3 downlink shared channels (PDSCHs) using QPSK,
16 QAM and 64 QAM modulation formats. The QPSK channel occupies the
fi rst 9 RBs (subcarrier –150 thru subcarrier –43); the 16 QAM user occupies the
center 8 RBs (subcarrier –42 thru subcarrier 54 excluding DC); and the 64 QAM
user occupies the last 8 RBs (subcarrier 55 thru subcarrier 150). Remember that
each RB has 12 subcarriers, so in each 5 RBs there are 60 subcarriers.
We can clearly see these allocations by making measurements only on the data
channels.
EVM for data channels
The analysis software allows users to make EVM measurement on selected
channels only. Let's set up the analyzer to measure EVM for the data channels,
but not for control channels and signals:
Your display should be similar to the one shown in Figure 17.
Figure 17. EVM analysis of data channels only.
Table 22. Selecting specific channels for analysis
Instructions: 89600 VSA software Toolbar menus
Turn off control channels and signals
from the analysis
MeasSetup > Demod Properties > Profile (tab)
Un-check P-SS, S-SS, PBCH, PCFICH, PHICH,
PDCCH, and RS
Click Close
31
Now all the traces and EVM results include only data channels with no control
channels or signals included. You can clearly see the allocation for each user in
terms of RB, slot, subcarrier and symbol. The color coding makes it very easy to
distinguish the different users.
Notice all of the channels are still registered and recognized, seen under the
Frame Summary table, even though we have de-selected the control and reference
channels. This convenient feature allows for specific channel analysis without
forgetting the presence of the other channels.
Let's turn the control channel analysis back on.
Analyzing individual symbols
For in-depth troubleshooting, the analysis software allows users to selectively
measure specific symbols, slots, sub-frames or a frame within the signal. Before
we make measurements on a symbol-by-symbol basis, let's quickly review the
Time tab under MeasSetup > Demod Properties which contains parameters
describing the signal time length, alignment, and measurement region.
For more information on each of these parameters, see the 89600 Help Text.
Figure 18. Demodulation Time tab used to adjust analysis region.
measurementoffset
measurementinterval
result length
analysisstart
boundary
0 ms = trigger
DL: frame start0 ms = UL: beginning of first slot
Time
Raw Main Time
Search Time
Figure 19. LTE analysis regions.
Table 23. Turn the control channel analysis back on
Instructions: 89600 VSA software Toolbar menus
Turn the analysis of control channels
and signals back to ON
MeasSetup > Demod Properties > Profile (tab)
Select P-SS, S-SS, PBCH, PCFICH, PHICH, PDCCH, and RS
Click Close
32
The analysis software allows you to modify the following parameters:
Result Length: Determines the signal capture length. This is the data used by
the analyzer for demodulation and signal analysis.
Analysis Start Boundary: This specifies the boundary at which the Result
Length must start. For DL signals, you can choose to begin at the frame,
half-frame, subframe or slot boundary. For UL signals, only the slot boundary
start position is available. This is because there are no sync channels for the
UL signal, so it is difficult to automatically determine frame and sub-frame
boundaries.
Measurement Interval: Determines the time length of 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.
The ability to examine specific symbols individually allows you to make all of
the available measurements on just this symbol. In other words, you can gate
the measurement window to examine only symbol N. The following example
will set up the analyzer to look at only the 7th symbol of slot 0, and perform
EVM measurements on this symbol.
Your display for symbol #0 analysis should look similar to the one shown
in Figure 20. All measurements shown are now made for symbol #0 only,
which contains the reference signal (cyan color), PDCCH (yellow color), and
PCFICH (purple color), all of which use QPSK modulation. It also contains PHICH
(bright red color) which uses BPSK modulation.
Table 24. Measuring EVM on specific symbols
Instructions: 89600 VSA software Toolbar menus
Change the measurement interval and
measurement offset to measure symbol
#0 i.e. Reference Signal and PDCCH
Meas Setup > Demod Properties > Time (tab)
Change Measurement Interval to 0 Slots. This will automati-
cally set the measurement interval to 1 symbol-time. Therefore
analysis will be made on 1st symbol (i.e. symbol #0).
Click Close
See Figure 19 below
Change the measurement interval and
measurement offset to measure the
7th symbol (i.e. symbol # 6) which
contains the PSCH and PDSCH
Meas Setup > Demod Properties > Time (tab)
Change Measurement Offset to 6 symbol-times. This will
move the "measurement window" to measure the 7th symbol (i.e.
symbol #6), which is P-SS plus user data.
Click Close
Change Trace B to show Spectrum
Double click Trace B title (B: Ch1 OFDM RB Error Mag
Spectrum)
In the Data: column select Spectrum
Click OK
Auto Scale Trace B Right click Trace B and select Y Auto Scale
Change Trace E to show CCDF
Double click the Trace E title (E: Ch1 OFDM RB Error Mag Time) In the Data: column select CCDFClick OK
Restart the measurementClick the Restart button.
See Figure 20 below
33
Figure 20. Single symbol measurement showing EVM for Symbol #0.
Figure 21 below shows an analysis of Symbol #6, the last symbol in the 1st
time slot.
Figure 21. Single symbol measurement showing EVM and CCDF analysis for Symbol #6.
34
Here, all measurements are made for symbol #6 which contains the P-SS and all
of the user data channels (PDSCH’s). The P-SS uses a Zadoff-Chu sequence, as
shown by the circle (pink) on the constellation display. The PDSCH channels use
QPSK, 16QAM, and 64 QAM modulation formats. Notice the spectrum display
in Trace B. It shows the spectrum of only the P-SS channel (which occupy the
center 72 subcarriers) and the PDCCH channels (which occupy the 1st 9 RB’s or
108 subcarriers).
The Complementary Cumulative Density Function (CCDF) shows what percentage
of signals are a given amount (in dB) above the RMS average of the signal in
the Measurement Interval.
Trace E shows a gated CCDF measurement; i.e. it is the CCDF of symbol #6 which
contains the P-SS and PDSCH only. While we are only looking at the CCDF of
symbol #6 in this example, we could just as easily make a CCDF measurement
across a time slot or subframe. That would allow us to characterize distortion
across an LTE frame. Some of the LTE timeslots and subframes contain more
channels and signals compared to others. For example, subframe 1 of an LTE
frame contains all of the control channels and signals as well as payload data,
whereas subframe 2 is mostly payload data. Making CCDF measurements
on a symbol, slot or subframe basis allow us to see which symbols, slots or
subframes introduce the most distortion.
For more information on CCDF measurements, see the 89600 VSA Help text.
MIMO analysisThe 89600 LTE analysis software also has the capability to analyze transmit
diversity encoded MIMO signals. Table 25 explains how to recall the proper
recording and setup file for MIMO analysis.
Table 25. Recall a single antenna MIMO signal
Instructions: 89600 VSA software Toolbar menus
Preset the software
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
Recall the recoding of a 5 MHz LTE
downlink MIMO signal
File >Recall > Recall Recording
(c:\Program Files\Agilent\89600 VSA\Help\Signals)
Select the MIMO downlink recordingSelect LTE_DL_5MHz_4Ant_Port0_v820.sdf
Click Open
Recall the appropriate setup fileFile > Recall > Recall Setup
(c:\Program Files\Agilent\89600 VSA\Help\Signals)
Select the MIMO downlink setup fileSelect LTE_DL_5MHz_4Ant_Port0_v820.set
Click Open
Restart the recording Click the Restart button.
35
Your display should look similar to Figure 22 below.
Figure 22. LTE downlink MIMO signal.
Trace B shows the Equalizer Channel Frequency Response as decoded by the
Matrix Decoder for each transmitter port. This measures the equalizer frequency
response for the analyzed signal. In this case, there is only one port that is trans-
mitting data, thus showing the single line in the trace.
Trace C displays information about the antenna port transmissions detected
by the demodulator. The first column lists the various measurement results for
each antenna port. One of the antenna ports is always selected as the refer-
ence antenna port. In this case, since we only have one antenna port transmit-
ting data, it is considered to be the reference antenna port. This is why RSPwr,
RSTiming, RSPhase, RSSymClk and RSFreq are set to zero. RSEVM and RSCTE
are the two metrics that cannot be zero because they are error values specific to
each antenna port. In a signal with multiple antenna ports, these metrics would
report information relative to the reference antenna port. Below is a list and
description of the table results found in the MIMO Info table.
RSPwr (dB): Average (RMS) RS Signal Power
RSEVM (%rms or dB): Average (RMS) RS EVM. Units are determined by the
Report EVM in dB parameter
RSCTE (%rms): Average (RMS) RS Common Tracking Error
RSTiming (seconds): RS timing error
RSPhase (degrees): Average (RMS) RS phase error
RSSymClk (ppm): Average RS symbol clock error
RSFreq (Hz): RS frequency shift error
36
Follow the steps on the table below to recall a signal that utilizes multiple
antennas.
Your display should look similar to Figure 23 below.
Figure 23. LTE downlink MIMO signal with multiple ports.
This recording is of a signal that utilizes four antenna ports. Due to window size
constraints, Figure 23 does not show metrics for the fourth antenna port. But
as we discussed earlier, the values for each antenna port, except RSEVM and
RSCTE, are relative to the reference antenna port. In this case, it is Port 0.
Now that you have made a variety of downlink measurements, let's examine LTE
uplink signals as well.
Table 26. Recall a multi-antenna MIMO signal
Instructions: 89600 VSA software Toolbar menus
Preset the software
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
Recall the recoding of a 5 MHz LTE
downlink MIMO signal
File >Recall > Recall Recording
(c:\Program Files\Agilent\89600 VSA\Help\Signals)
Select the MIMO downlink recordingSelect LTE_DL_5MHz_4Ant_v820.sdf
Click Open
Recall the appropriate setup fileFile > Recall > Recall Setup
(c:\Program Files\Agilent\89600 VSA\Help\Signals)
Select the MIMO downlink setup fileSelect LTE_DL_5MHz_4Ant_ v820.set
Click Open
Restart the recording Click the Restart button.
37
When you are fi nished, your display should look similar to the one shown in
Figure 24.
LTE uplink signal analysis
The 89600 LTE analysis software provides both uplink and downlink LTE signal
analysis in a single option. Thus, the uplink analysis has similar features and
capabilities as downlink analysis. Because of that, we'll focus next on what
is unique to uplink measurements.
The most significant differences include:
1) Uplink RB auto-detection behavior
2) User must choose to display either PUSCH or PUCCH
Let's quickly examine an uplink signal and the measurements and displays to
help understand these differences.
Table 27. Uplink signal analysis
Instructions: 89600 VSA software Toolbar menus
Preset the software
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
Note: The Menu/Toolbars, Display Appearance, and
User Color Map may also be saved in a similar way.
Go to the default signal directoryFile > Recall > Recall Recording
(c:\Program Files\Agilent\89600 VSA\Help\Signals)
Select a 5 MHz LTE uplink recording Select LTE_UL_Multi_5MHz_v820.sdf
Click Open
Recall the appropriate setup file
File > Recall > Recall Setup
(c:\Program Files\Agilent\89600 VSA\Help\Signals)
Select LTE_UL_5Mhz_v820.set
Click Open
Change display layout to Grid 3x2 Select Grid 3x2 option from the layout drop down menu
Change Trace D to show Frame
Summary
Double click Trace D title (D: Ch1 Error Summary)
In the Data: column select Frame Summary
Click OK
Change Trace F to show Error
Summary
Double click Trace F title (F: Ch1 Frame Summary)
In the Data: column select Error Summary
Click OK
Start the measurement Click (toolbar, left side)
Auto scale Traces A, B, C and E Right click on each trace and click Y Auto Scale
38
Figure 24. Uplink signal analysis, showing the combined time domain and
frequency domain composite "constellation."
Trace A: For uplink signals, the demodulation RS (pilot) is in the frequency
domain but the uplink data channel (PUSCH) is in the time domain due to
SC-FDMA scheme used for uplink data channels. The I/Q Meas trace therefore
overlays the time domain and frequency domain display to show both data
channel as well as the DM-RS (pilot) constellation diagram. The DM-RS (pilot)
uses a Zadoff-Chu sequence and is shown by the circle (cyan color). The PUSCH
channels in this example use QPSK and 16 QAM modulation, as shown by the 2x2
and 4x4 constellations, respectively.
Trace B: Trace B shows a combination of PUSCH and PUCCH channels that are
transmitted. For this recording, the signal is defined to have two users: User 1
and User 2. User 1 allocates all 20 slots for RB 5-9 for PUSCH with a modulation
type of QPSK. User 2 allocates all 20 slots for RB 15-19 for PUSCH with a
modulation type of 16QAM. These are the broad, center two spectral peaks. The
narrow, outer spectral peaks are transmitting PUCCH for RB 0 and RB 24. Both
users’ allocations are equally dispersed on both RB 0 and RB 24. Note: Under the
Profile (tab), you will only see User 1 shown. This is because the Auto detection
function has combined the two users and distinguished them by their modulation
type.
Trace E: Note that this trace clearly shows the DM-RS (pilot), cyan color,
occupying symbol #3 of each timeslot.
39
Trace F: You may notice that the Trace F Error Summary table in the figure is
missing some of the table elements. This is due to a smaller window size used in
this demo guide, and can be fully seen by expanding the window size. Figure 25
below shows the Error Summary table with full content. For explanations of all
table results, please refer to the Help text.
Figure 25. Error Summary table
Note: Uplink RB Auto-detect works best when a unique sync slot is identified.
This is due to the fact that there are no sync signals for UL, and this unique sync
slot allows the analysis software to acquire absolute radio frame slot number
alignment, which in turn supports measurement of any individual slot and symbol
within the UL radio frame.
As mentioned earlier, one of the most significant differences between uplink
and downlink signal analysis is for uplink measurements, the control (PUCCH)
and shared (PUSCH) channel cannot be analyzed simultaneously. Let’s explore
this difference by switching between the control (PUCCH) and shared (PUSCH)
channels.
Table 28. Single channel uplink signal analysis
Instructions: 89600 VSA software Toolbar menus
Go to the Profile tab under demodula-
tion propertiesMeasSetup > Demod Properties> Profile (tab)
Expand information under User 1 Click the plus box adjacent to User_01 to expand list of channels
Select PUCCH for analysis
Click the PUCCH box
Click the PUCCH DMRS box
Note how the PUSCH select boxes are automatically unchecked
Click Close
Auto scale Traces B, C, and E
Right Click Trace B and select Y Auto Scale
Do the same for Traces C and E
See Figure 26 below
40
Figure 26. Uplink signal analysis showing PUCCH transmitted.
Trace C: As predicted earlier, since PUCCH has been selected for analysis,
Trace C now shows EVM results for RB 0 and RB 24. You can see that this
trace correlates to Trace B by noticing the coupled markers between the two.
You can switch between PUCCH and PUSCH by selecting the appropriate check
boxes next to the channel names.
41
Summary
Glossary
The 89600 VSA software with Option BHD for LTE modulation analysis provides
the tools necessary to measure and troubleshoot 3GPP LTE uplink and downlink
signals. Comprehensive error measurements allow you to look at error versus
subcarrier, symbol, resource block or slot. Sophisticated analysis is also possible
when focusing on individual channels, symbols, or time. The addition of new
MIMO analysis capabilities continues to enhance the existing advanced digital
demodulation techniques. The 89600 VSA software is supported through a
multitude of platforms, including oscilloscopes, spectrum analyzers, etc. From
baseband to RF, simulation to antenna, it provides the greatest versatility for all
measurements in all possible domains. No matter how simple or complex the
measurement, 89600 VSA software meets all your trouble-shooting needs.
3GPP 3rd Generation Partnership Project
3G 3rd Generation
AMC Adaptive Modulation and Coding
ACK Acknowledgement
CAZAC Constant Amplitude Zero Auto Correlation
CCDF Complementary Cumulative Distribution Function
CP Cyclic Prefix
DL Downlink (base station to subscriber transmission)
DM RS Demodulation Reference Signal
DFTS-OFDM Discrete Fourier Transform Spread - Orthogonal
Frequency Division Multiplexing
EVM Error Vector Magnitude
FDD Frequency Division Duplex
HSDPA High Speed Downlink Packet Access
HSPA High Speed Packet Access
LTE Long Term Evolution
MBMS Multimedia Broadcast Multicast Service
MIMO Multiple Input Multiple Output
NACK Negative Acknowledgement
OFDM Orthogonal Frequency Division Multiplexing
OFDMA Orthogonal Frequency Division Multiple Access
OS Orthogonal Sequence
PAPR Peak-to-Average Power Ratio
P-BCH Physical Broadcast Channel
PCFICH Physical Control Format Indicator Channel
PDCCH Physical Downlink Control Channel
PDSCH Physical Downlink Shared Channel
PHICH Physical Hybrid ARQ Indicator Channel
PMCH Physical Multicast Channel
PRACH Physical Random Access Channel
PRS Pseudo Random Sequence
P-SS Primary - Synchronization Signal
PUCCH Physical Uplink Control Channel
PUSCH Physical Uplink Shared Channel
QAM Quadrature Amplitude Modulation
QPSK Quadrature Phase Shift Keying
RB Resource Block
RS Reference Signal (pilot)
SC-FDMA Single Carrier - Frequency Division Multiple Access
S-SS Secondary - Synchronization Signal
TDD Time Division Duplex
TrCH Transport Channel
TTI Transmission Time Interval
UL Uplink (Subscriber to base station transmission)
W-CDMA Wideband - Code Division Multiple Access
42
89601A Vector signal analysis software
Note: For initial purchases including Option 200, a discount
item, D12, will be applied to provide a discount corresponding
to 1 year of software update service.
Options Option 200 required
89601A-200 Basic vector signal analysis software
89601A-012 12 months bundled software update subscription service
(qualifi es for 12 month discount)
89601A-024 24 months bundled software update subscription service
(qualifi es for 12 month discount)
89601A-300 Hardware connectivity
89601A-AYA Flexible modulation analysis
89601A-B7N 3G modulation analysis bundle
89601A-B7T cdma2000/1xEV-DV modulation analysis
89601A-B7U W-CDMA/HSPA modulation analysis
89601A-B7W 1xEV-DO modulation analysis
89601A-B7X TD-SCDMA modulation analysis
89601A-B7R WLAN modulation analysis
89601A-B7S IEEE 802.16-2004 OFDM modulation analysis
89601A-B7Y IEEE 802.16 OFDMA modulation analysis
89601A-B7Z IEEE 802.11n modulation analysis
89601A-BHA TETRA modulation analysis and test
89601A-BHB MB-OFDM ultra-wideband modulation analysis
89601A-BHC RFID modulation analysis
89601A-BHD LTE modulation analysis
89601A-105 Dynamic link to EEsof/ADS
89601A-106 Dynamic link to The MathWorks Simulink Model-Based Design
Ordering Information
43
89601AN Vector signal analysis software (fl oating license for 1 server)
Note: For initial purchases including Option 200, a discount
item, D12, will be applied to provide a discount corresponding
to 1 year of software update service.
Options Note: multiple quantities of one option may be ordered per
each server. Option 200 required. Every user must have
Option 200, so the maximum quantity of any option may not
exceed the quantity of Option 200. For multiple servers, order
additional 89601AN.
89601AN-012 12 months bundled software update subscription service
(qualifi es for 12 month discount)
89601AN-024 24 months bundled software update subscription service
(qualifi es for 12 month discount)
89601AN-200 Basic vector signal analysis software
89601AN-300 Hardware connectivity
89601AN-AYA Flexible modulation analysis
89601AN-B7N 3G modulation analysis bundle
89601AN-B7T cdma2000/1xEV-DV modulation analysis
89601AN-B7U W-CDMA/HSPA modulation analysis
89601AN-B7W 1xEV-DO modulation analysis
89601AN-B7X TD-SCDMA modulation analysis
89601AN-B7R WLAN modulation analysis
89601AN-B7S IEEE 802.16-2004 OFDM modulation analysis
89601AN-B7Y IEEE 802.16 OFDMA modulation analysis
89601AN-B7Z IEEE 802.11n MIMO modulation analysis
89601AN-BHA TEDS modulation analysis and test
89601AN-BHB MB-OFDM ultra-wideband modulation analysis
89601AN-BHC RFID modulation analysis
89601AN-BHD LTE modulation analysis
89601AN-105 Dynamic link to EEsof/ADS
89601AN-106 Dynamic link to The MathWorks Simulink Model-Based Design
Ordering information (continued)
44
Related Literature
Web Resourses
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
Understanding the Intricacies of LTE, LTE poster, 5989-7646EN
Move Forward to What's Possible in LTE,
Agilent's LTE Solutions Guide, 5989-7817EN
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
3GPP Long Term Evolution: System Overview, Product Development, and Test
Challenges, 5989-8139EN
For additional information, visit:
www.agilent.com/find/89600
www.agilent.com/find/LTE
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Printed in USA, September 15, 2008
5989-7698EN