CDMA Base Station Meas

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Rolland Zhang

Business Development Engineer

21 August, 2001

CDMA Base Station Measurements


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Title of Presentation

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Agilent Restricted Page 2

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

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4. Click Set as default chart.

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Format Charts Quickly and Consistently by

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CDMA Base Station Meas