Spectrum & Power Measurements Using the E6474A The E6474A Agilent drive-test system provides a...
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Transcript of Spectrum & Power Measurements Using the E6474A The E6474A Agilent drive-test system provides a...
IntroductionWith the rapid development of wireless technologies, it has become increasingly important
to maintain a high-performance and fully optimized network. Quality and reliability of
service have grown exponentially in importance over the years and now greatly infl uence
the customer’s choice of a service provider.
The E6474A Agilent drive-test system provides a low-cost, lightweight, customizable and
easy-to-use platform solution for spectrum monitoring and interference detection. The
system can perform the basic functions of a spectrum analyzer, but also has recording
capabilities that allow data to be collected and then post-processed.
With this spectrum measurement and analysis tool, the entire network can be examined, in
both downlink and uplink, increasing the chance of discovering spurious transmissions. In
addition, the W1314A family of receivers is designed with a signifi cantly low noise fi gure
for easier noise fl oor characterization.
Networks of all technologies - LTE, WiMAX, UMTS, EVDO, HSPA+ cdma2000, GSM and
GPRS - can benefi t from spectrum monitoring for network optimization, troubleshooting,
infrastructure installation and even manufacturing.
This application note describes how the spectrum measurements contribute throughout the
“network lifecycle.” Each stage in the cycle -- band clearing, site evaluation, optimization
and quality of service -- can benefi t greatly by using the Agilent drive-test system.
Figure 1. E6474A Agilent Drive-Test System
Spectrum & Power Measurements Using the E6474A Wireless Network Optimization PlatformApplication NoteBy Richard Komar
ContentsIntroduction ...........................................1
Band Clearing ........................................2
Using the spectrum analyzer for band
clearing .......................................2
Site Evaluation .......................................7
CW Power Measurements ................7
Channel Power Measurement...........8
Interference Control ............................11
Internal interference ........................11
Downlink interference .....................11
Uplink interference ..........................11
Base station interference.................11
External interference .......................11
Spectograph ........................................12
Appendix: Optimization Features,
Capabilities and Specifi cations ............12
Events (Alarms)................................12
Event confi guration ..........................13
Basic event confi guration ................13
User Events ......................................13
Markers ..........................................15
Spectrum Noise Floor & Sensitivity
Specifi cations ............................16
Lee’s Criteria - Equation 1 ...............16
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Band ClearingPrior to cellsite turn-up, a given area must be deemed “interferer free.” The intended
coverage area should be driven, searching for spurious or illegal transmissions or
interference. With excellent sensitivity, the spectrum analyzer enables the user to view and
record interferers.
Band clearing is used for the following applications:
• To eliminate interference prior to network turn-up
• To add new channels to the existing network
• To clear spectrum to provide space for new bands or additional channels
• To determine possible interferers
Using the spectrum analyzer for band clearing
1. Open two spectrum analyzer views, one for uplink frequencies, one for downlink
frequencies and horizontally tile them as shown in Figure 2. For more details on how
to confi gure your hardware and how to use the E6474A software, refer to the User’s
Guide (E6474-90090) and the online help.
Figure 2. Uplink and Downlink Spectrum Views
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2. Open a properties panel for each spectrum analyzer view (Figures 3 and 4). Set the
band and channelization for both views.
Figure 3. Uplink Spectrum Analyzer View Properties
Figure 4. Downlink Spectrum Analyzer View Properties
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3. Open a properties panel for each spectrum analyzer measurement (Figures 5 and 6)
and set the center frequency and span. Set the IF bandwidth to 200 KHz to lower the
spectrum noise fl oor.
Figure 5. Uplink Spectrum Analyzer Properties
Figure 6. Downlink Spectrum Analyzer Properties
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4. Select Event Wizard from the Confi guration pull-down menu, highlight the receiver
device and highlight the Spectrum Clearing event. Press Next.
5. Since you had created two spectrum analyzer views, one for uplink and one for
downlink, you will see a Resolve Additional Information screen which shows the two
spectrum analyzer views. Highlight the Downlink spectrum analyzer and press Resolve
button repeatedly until you see the Next option button activate. Press Next.
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6. Click on Edit Event Conditions to view or change the desired threshold at which to
trigger the event (in this example, the threshold was changed to -65 dbm).
7. In the Event Action view, select Add if you want to add a sound and/or message action
in addition to the existent marker action. Highlight each action to customize it. Press
Next.
8. Select View > System Panels > Active Events List and check Project. If you expand
Project, you will see the Spectrum Clearing event and its actions. Right click on any
item to change its properties.
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9. Start either Live Mode or Logging Mode to capture band clearing data (Figure 7).
Figure 7. Band Clearing using a Spectrum Analyzer View and an Event
10. Select View > System Panels > Event Output View to see a description of the event
when it is triggered (See Figure 8). Notice all events are listed by frequency where the
signal exceeded -65 dbm.
Figure 8. Event Output View for Band Clearing
11. Repeat Steps 5 through 10 above for the uplink band.
As an alternative to setting up an event, if not logging data, the Max Hold function can
be used to monitor the network without having to constantly observe the screen. It will
show the maximum values over all measurements since the option was selected. The Max
Hold selection is in the Averaging pull-down menu in the spectrum analyzer measurement
properties panel (Figure 9).
Figure 9. The Max Hold Selection
Site EvaluationBefore a new cell site is installed, site evaluation tests are run and data is analyzed. These
tests are done in the following manner:
• Setting up a test transmitter at the candidate site
• Driving the intended coverage area and recording the transmitted signal strength
• Plotting the collected data on a map corresponding to the drive route
• Tuning the predictive model using the drive test data
Many candidate sites may be tested before choosing a cell location. However, instead of
testing each location individually, the CW power analyzer can measure multiple CW signals
simultaneously. Site evaluation can then be determined by a single drive of the proposed
coverage area, reducing the time spent in the fi eld.
CW Power Measurements
Continuous Wave (CW) power is defi ned as the peak power of a transmitted signal in a
user-defi ned resolution bandwidth. CW testing is the most important task executed for site
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evaluation. When collecting data using the CW power analyzer, the “At Least” averaging
technique is used to give confi dent results. In order to have 90 percent confi dence in the
predictive model, the data used to tune that model needs to meet Lee’s Criteria. Lee’s
Criteria states that during data collection, at least 50 measurements must be taken every
40 wavelengths of distance in meters. (Distance = 40λ = 40(c/f) = 14.1 m at 850 MHz,
6.3 m at 1900 MHz, and 5.7 m at 2.1 GHz.). See “Lee’s Criteria - Equation 1” on page 16
and Table 1 in the Appendix for additional values.
The “At Least” averaging feature is found on the Averaging pull-down menu of the CW
power analyzer measurement properties panel (Figure 10) and is an essential key to
collecting accurate data.
Figure 10. Averaging set to At Least
In addition, when measuring multiple CW signals simultaneously, as described above, the
test frequencies should be contained within 1 MHz to maintain Lee’s Criteria. For example,
870, 870.2, 870.4, 870.6, and 870.8 MHz would be suffi cient test transmissions.
Channel Power Measurement
Channel power is the total integrated power in a user-defi ned channel width. A modulated
transmitter can be used in conjunction with channel power measurements to further
characterize a site.
Using the CW power analyzer for site evaluation testing
1. Set up a signal source that will transmit a CW signal at the desired power level.
2. Open a receiver bar chart common view (Figure 11) to use as a CW Power Analyzer
view
Figure 11. CW Power Analyzer View
3. Open a properties panel for the CW power analyzer view (Figure 12). Set the band,
channelization, and chart title.
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Figure 12. CW Power Analyzer View Properties
4. Open a properties panel for the CW power analyzer measurement (Figure 13) and
set the preselector, channelization band, channelization, CW Power List – Yes, User
List, Averaging ( At Least), Averages (50) and Measurement by Distance (for your
frequency band per Equation 1 and Table 1 in the Appendix).
Figure 13. CW Power Analyzer Properties
5. Select Event Wizard from the Confi guration pull-down menu, highlight the receiver
device and highlight the CW Low Power event. Press Next.
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6. Click on Edit Event Conditions to view or change the desired threshold at which to
trigger the event (in this example, the threshold was changed to -90 dbm).
7. In the Event Action view, select Add if you want to add a sound and/or message action
in addition to the existent marker action. Highlight each action to customize it. Press
Next and Finish.
8. Select View > System Panels > Active Events List and check Project. If you expand
Project, you will see the CW Low Power event and its actions. Right click on the event
if you want to change its properties.
9. Turn on your transmitter and turn on Live or Logging Mode, start driving and collect
CW power data for your site evaluation (Figure 14).
Figure 14. Site Evaluation using a CW Power Analyzer View & an Event
10. Select View > System Panels > Event Output View to see a description of the event
when it is triggered (See Figure 15).
Figure 15. CW Low Power Event
11. You can also set up your own custom events by referring to the Appendix for event
confi guration.
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Interference Control
Internal interference
Internally generated interference, or interference that occurs as a result of one’s own
network, is a major cause of performance problems. Internal interference can occur in
both the uplink and downlink frequency bands either at the base station or in the intended
coverage area.
Downlink interference
Internal interference in the downlink can be from a variety of causes such as:
• Adjacent channel interference (GSM)
• Co-channel interference (GSM)
• Pilot pollution (CDMA)
• Scrambling code pollution (UMTS)
• Transmitted base station noise
• Faulty power amplifi er stages
Internally generated interference from this list will cause poor network performance.
To insure quality service, the E6474A Agilent drive-test system is used to monitor pilot
pollution, scrambling code pollution, adjacent channel interference and co-channel
interference.
Uplink interference
The E6474A Agilent drive-test system can make measurements in the uplink frequency
band. Internal uplink interference can be adjacent or can be co-channel interference from
frequencies in reuse. Uplink interference can be very diffi cult to detect in the case of GSM,
because of the time-burst transmissions. Also, carrier-to-interference (C/I) measurements
will be different at different periods due to power control (when the mobile powers up or
down depending on its proximity to the base station).
The spectrum analyzer measurement can easily be connected to the receive antenna of
the base station to make uplink interference measurements. This will display the uplink
spectrum as seen by the cell’s antenna. This data can be viewed, recorded, and analyzed
either at the site or at a later time. The measurement procedure is similar to that of band
clearing. So, for this application, simply connect the base station receive antenna to the
receiver input and follow the steps in “Using the spectrum analyzer for band clearing” on
page 2, opening only one spectrum analyzer measurement view for the uplink frequencies.
Base station interference
The E6474A Agilent drive-test system can be used to monitor interference at the base
station. It is often necessary to troubleshoot this area when switch events have been
triggered. The receiver can be used to investigate any internal station interferers. Possible
interferers include RF leakage within or between cabinets, antenna base plates, cables,
or connectors. External interferers can be detected by connecting the base station receive
antenna directly to the receiver. The RF environment in the immediate vicinity and selected
radius of the base station can then be examined on the spectrum analyzer. The spectrum
analyzer can help detect both manufacturing fl aws and quality control issues.
External interference
External interference can occur in either the uplink or downlink frequency bands.
Examples include:
• Paging transmitters
• Competitor networks (adjacent bands)
• Illegal transmissions
• Spurs and harmonics from other transmitters
• Radar
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• Industrial appliances
• Special mobile radios (SMR)
• Cordless telephones
Interference caused by external sources, such as 900-MHz cordless phones, can be
continuous or time-bursted. For time-bursted interferers, long-term monitoring may be
required. In the example of the cordless phone, an event for a signal occurring above a
particular threshold (for a given duration of time) would need to be set. This is because the
cordless phone generates interference when it turns on and remains continuous for the
duration of the cordless phone call.
SpectographThe spectrograph view provides a shaded mapping of a spectrum type value. This is useful
if you want to see if you have any period interferers in your received RF signal.
Description of properties
Chart Title Enter the text you wish displayed above the chart.
Auto Scale? Enable this option to have the chart automatically scale the X
and Y axis.
Min Enter the minimum value to be used for the Y axis.
Max Enter the maximum value to be used for the Y axis.
Base Color Select the base color to be used for coloring the lines displayed
on the chart.
Rainbow Enable this option to change the color range to be spread
across the color spectrum.
Chart Type Select either Spectrogram or Fast Line type charts. The
spectrogram type chart displays a view over time looking
‘down’ onto a spectrum type data item. Using this type of
display it is possible, for example, to easily see repeating
interferers - these will appear as dashed marks going up the
display.
The Fast Line type display changes the chart to display data in
the same way as the line chart view.
Color Setup Select this dialog to open the color and binning dialog box. This
dialog box is used for adding binning regions for the displayed
data. Enter the upper and lower ranges and then select the
autofi ll button to automatically insert equally spaced values and
colors.
Threshold 1 This positions a horizontal line on the Fast Line type chart.
Threshold 2 This positions a horizontal line on the Fast Line type chart.
Remove Action Select this property to open a dialog box that lists the events
associated with this view.
To remove an event from the view:
1. Select this property to open the events overview dialog box.
2. Select the event you wish to remove. In project mode, select
the event listed under the project option. In fi le mode, select
the event listed under fi le option.
3. Select the Remove button.
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If an interfering signal is intermittent, the Spectrograph view can be used to visualize the
spectrum signal over a scrolling time window. The “width” of the color bar shows the
extent of the interfering frequency and the color shows the amplitude.
Appendix: Optimization Features, Capabilities and Specifi cations
Events (Alarms)
Event confi guration
One of the major benefi ts of the drive-test system is its ability to record data. A number
of complex events can be set to mark trouble spots or areas that require attention. These
events can be made up of single or multiple conditions. Events can be confi gured to
respond with a sound, notifi cation or a particular action when the measurement result
meets a user-specifi ed criteria. Events notify the user that the drive-test system has
encountered specifi c conditions, such as a power level greater than or less than a specifi ed
value. Any given measurement can carry more than one event. The user can also specify a
minimum duration of time before an event is triggered or re-triggered.
Basic event confi guration
Refer to the online help for a full animated demonstration of how to create an event and
how to add custom events to your views and logged data.
User Events
When driving a network, actions may occur that have not been pre-set as events. User
events can be inserted to mark these points during data collection. In other words, if data
is being recorded and an area of interference is encountered, that segment of the data can
be marked and played back later for in-depth analysis.
The User Event tab is within the Options dialog box. To open it, click Tool > Options on the
menu bar, then click the User Event tab. It allows you to confi gure the User Event feature.
User Events are events that are dynamically added during logging using a pre-defi ned
function key. You can also defi ne the marker and text used for the user event.
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There are two types of user events:
• User Event with text entry on pop-up box - When you select the assigned
function key (F2 default) a dialog box appears and you can enter any text to go with the
marked event. When you close the text box, even though you may have moved further
on from the marker point, the text information is automatically saved with the position
of the marker.
A marker is added to the views in your project that support event display. The user
event marker is added at the point you selected the F2 key even though the data
display had moved on after you had entered your text. An event is added to the Event
Output View automatically as well.
• User Event with pre-defi ned text message - When you select the assigned
function key (F12 default) a marker is added to your open views and the event is
displayed in the event output view. However no dialog box opens and you do not have
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to enter any text. Instead the event uses the text you defi ne in the options dialog box
(see above) and this text is used for all of these types of events. This is useful if you
have a known event or situation you want to mark during data logging, but do not want
to keep entering the same text.
During playback the text pop-up box message is displayed on the screen and remains open
until you close it.
To quickly edit a user event double-click on the event listed in the Active Events Lists
system panel.
During playback, you can cycle through the user events that occurred while logging the
data. This allows you to skip directly to each marked or evented segment rather than
reviewing the complete recorded section.
Markers
Markers can be used on spectrum traces to display the numeric value of the trace at a
particular X coordinate. The following commands are features of the spectrum analyzer
view:
The marker controls at the top of the spectrum analyzer view are used for adding, deleting
and control the markers that you can place on a signal trace.
The following summarizes what each marker control does: of marker controls
Add a marker Select this icon to add a marker to the chart
Delete a marker Select this icon to delete the highlighted marker.
Delta Select this icon to display the difference between the last two
added markers. The delta is displayed under the last selected
marker.
To Max Select this icon to move the highlighted marker to the
maximum peak value on the display.
To Min Select this icon to move the highlighted marker to the minimum
value on the display.
Center on Marker Select this icon to move the displayed line to the center based
on the center marker.
Left Peak Select this icon to move the marker to the far left peak of the
display
Right Peak Select this icon to move the marker to the far right peak of the
display.
Auto Peak Select the drop-down arrow next to this marker to enable the
marker conditions. There are Auto peak off, Full trace, +/- 1
point, +/- 2 points, +/- 3 points.
Spectrum Noise Floor & Sensitivity Specifi cations
Agilent W1314A Series Receivers:
Accuracy ±1.5 dB typical (0° to 55°C)
±1.0 typical (20° to 30°C)
Internally generated spurious noise: -120 dBm
Spectrum Analyzer (30 KHz RBW) Updates / Second
Span (4 MHz, IFBW 5 MHz) 25
Span (10 MHz, IFBW 5 MHz) 14
Span (25 MHz, IFBW 5 MHz) 6
Span (50 MHz, IFBW 5 MHz) 3
For complete receiver technical specifi cations, refer to the Agilent W1314A Multi-band
Wireless Measurement Receiver Data Sheet, 5989-7970EN.
Lee’s Criteria - Equation 1
At least 50 measurements within 40 wavelengths:
Distance = 40 wavelengths = 40(c/f)
c = speed of light (300,000,000 m/s), f = transmit frequency
Table 1. Values for distance measurement interval to satisfy Lee’s Criteria
Frequency Distance 850 MHz 14.1 m
900 MHz 13.3 m
960 MHz 12.5 m
1800 MHz 6.7 m
1900 MHz 6.3 m
2.0 GHz 6.0 m
2.1 GHz 5.7 m
This information is subject to change without notice© Agilent Technologies, Inc. 2010, Printed in UK, February 8, 2010
5990-5239EN