cdma base station meas
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Rolland Zhang
Business Development Engineer
21 August, 2001
CDMA Base Station Measurements
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Module Objectives
At the end of this module you will be able to:
Understand why maintenance testing is important
Be familiar with key CDMA transmitter measurements
Be able to relate the measurements to solving networkproblems
Be familiar with Agilent Technologies CDMA Base StationTest Solution
Understand the differences in IS-95 and IS-2000 BaseStation measurements
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Why Do Maintenance Test?
System performance is a big competitive issue
Periodic maintenance helps prevent shutdown
Equipment problems may only show up as reducedcapacity
Monitoring for interference finds problems unrelated tonetwork equipment
Systems will be stressed as loading increases
Defective components may be hidden by CDMAs softhandoff, power control, and error correction
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Generic CDMA Base Station Elements
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Base Station Parametric Measurements
Total Power (Average Power & Channel Power)
Waveform Quality (Rho)
Carrier Feedthrough
Frequency Tolerance (Frequency Error)
Pilot Time Tolerance (Time Offset)
Code Domain Power
Power and Noise
Complex Power
Fast Power
Code Domain Fast Power
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Transmitter Test Setup
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Why is Forward Link Power Management
Important?
Powermanagement is critical to maximizing the systemscapacity
Network operators sometimes attempt to set power higherto extend coverage to reduce infrastructure cost; resultcan be pilot pollution problems
Initial settings for the sites must be accurate to matchsettings specified by the RF engineering department
More power is not necessarily better but can lead tointerference and dropped calls
Too little power for the site may result in dead spotsbetween sites.
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Why is Accurate TX Power Measurements
Important?
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Other Factors in Power Management
Cable losses
Antenna gain
Antenna downtilt
Environmental effects
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Making Power Measurements
Calibration
Average power measurement using the AgilentTechnologies E6380A versus a conventional power meter
What the Average Power measures
Active cell site versus configured cell site
Specifications
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Non-Linearity in the Frequency Domain
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What is Rho?
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Why is Rho Important?
Key measure of modulation quality
Analogous to FM accuracy/distortion (AMPS) and EVM(TDMA systems)
Rho performance affects site/sector coverage area and capacityin the site/sector
Rho failures can indicate problems in:
Compression in linear amplifiers
Magnitude and phase errors in the IQ modulator
Phase non-linearity (group delay)Spurious signals in thetransmission path
Carrier feedthrough
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What is a Pilot?
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Time Offset
Measure of Short Code sequence timing versus SystemTime
Checks the start of PN offset as compared to the evensecond clock signal
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What is Pilot Time Tolerance?
Time offsets outside of specifications can affect handoffsbetween cells - the island effect
Time offset is one of the parameters that will lead to errors inposition location with the introduction of E911 and networkoperator services
Potential causes for failures of pilot time tolerance:
GPS receiver and timing distribution failures
Cells with a propagation delay greater than the PN Offsettime period
The timing delay adjustment (used to compensate for timedelays through the sites cabling) may be off
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Frequency Tolerance
This measurement cannot be made with any frequencycounter
Frequency tolerance (Frequency Error) specifications:
0.05 ppm PCS (99 Hz @ 1980 MHz) 0.05 ppm Cellular (40 Hz @ 850 MHz)
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Why is Frequency Error Important?
GPS drift or out-of-lock condition can create the island cell effect
Frequency drift can lead to site timing errors which will lead toerrors in position location with the introduction of E911 andnetwork operator services
Failures point to problems in GPS receiver and timingdistribution (to perform this test requires
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Code Domain Power
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Code Domain Power
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Non-Linearity in Walsh Code Channels
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Code Domain Power and Noise
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Code Domain Measurement Results
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Carrier Feedthrough
Carrier feedthrough (origin offset)
Should be < -25 dBc
Carrier feedthrough in I/Q Domain and Frequency Domain
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CW Interference in the Code Domain
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Noise in the Code Domain
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AWGN in the Code Domain
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Code Domain Timing and Phase
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Error Vector Magnitude
EVM = RMS magnitude value of the error vector (inpercentage)
Magnitude Error
Phase Error
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IQ Plots
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Return Loss Test
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Summary
Why we test
Why Power is a Critical Base Station Parameter
What Tests are Performed on a Base Station
What the Test Results mean
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Titl f P t ti A il t R t i t d Page 36
Double click on a formatted chart
(samples on next two pages). The
Chart Menu Barwill becomeactive. From the menu bar, selectChart >Chart Type (Alt+C+T) to
open the dialog box shown.
1. Select the Custom Types tab.
2. Choose User-defined.
3. Click Add. Another window openswith fields to enter a name and
description.
4. Click Set as default chart.
(Repeat steps 1-4 for each chart.)
1
2
3
4
Format Charts Quickly and Consistently by
Setting User-defined Preferences for Each
Chart Type.These preferences are application specific and will always beavailable once you set the preferences on your computer.