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

2

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

3

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

4

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

5

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.

6

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.

7

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

8

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.

9

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.

10

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.

11

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

12

• 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.

13

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.

14

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

15

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