Fsh Wcdma Demod v1 1

8/13/2019 Fsh Wcdma Demod v1 1

1/25

WCDMA Demodulation with the R&S FSH

Paul Denisowski, Application Engineer


2/25

WCDMA Demodulation with the R&S FSH4/8Version 1.1 by Paul Denisowski

WCDMA Demodulation with the FSH4/8

Option FSH-K44 3GPP WCDMABTS/Node B Pilot Channel and EVM

Measurement Application enables the

demodulation and analysis of 3GPP

WCDMA BTS signals using the FSH4/8

handheld spectrum analyzer This option is enabled using a license key

code : no additional hardware or separate

software/firmware is required on the FSH.


3/25


Easy operation

Only two operating steps :

Select the 3GPP WCDMA mode

Set the center frequency


4/25


Setting the center frequency

FSH frequencies can be set either as frequencies

(e.g. 1953.2 MHz) or as channels (e.g. 9766)

Channels are defined in channel tables

FSH has predefined channel tables for all wireless

standards (GSM, WCDMA, LTE, WCDMA,

CDMA2K, TD-SCDMA, etc.) and bands.


5/25


WCDMA channel tables

Custom tables can also be defined using the free FSH4View utility


6/25


Result Display

There are six modes available foranalyzing WCDMA downlink

signals :

Spectrum Overview

Code Domain Power

Code Domain Channel Table

Scrambling Codes

Isotropic Antenna

Result Summary

The Code Domain Power / ChannelTable and Isotropic Antenna

measurements require the FSH-

K44E option.


7/25


Spectrum Overview

Shows the measured

WCDMA signalspectrum.

Similar to spectrumanalyzer mode. Allowsthe user to do basicspectrum measurementswithout switching back toSpectrum mode.

Channel bandwidth limitsare shown by verticallines.

Markers can be set tomeasure frequencies andlevels. If more detailed spectral analysis is needed,

simply switch to the FSH Spectrum mode


8/25


Scrambling Codes

The primary and secondary scrambling

codes are needed to demodulate a WCDMAsignal.

Scrambling code can be entered manually or

can be automatically determined by the FSH.


9/25


Scrambling Code

For each BTS,

primary and

secondary

scrambling

code and

CPICH power

are displayed inboth table form

and as a bar

chart

8 BTS signals

can bedisplayed at the

same time


10/25


CPICH

The Common Pilot Channel (CPICH) is ageneral reference channel for power andquality.

CPICH is the most important channel forradio network planning. CPICH coveragedetermines the overall coverage of aWCDMA cell. It is also used by UEs for

cell channel quality estimation, cellselection, and handover.

More CPICH power means bettercoverage but increases pilot pollution inthe network.

No other code channels should beoperated with a higher power level thanCPICH.


11/25


Result Summary


12/25


General information

Frequency, band, transducer

Analyzer settings (ref level, ref offset,

attenuation, preamp, sweep type, etc.)

Primary and secondary scrambling code


13/25


Global results

Synchronization state (OK or NOT FOUND)

Impairment measurements : carrier

frequency error, I-Q offset, gain

imbalance and composite EVM

Total downlink power in dBm

Number of active channels and

scrambling code

Code domain error measurements


14/25


Carrier Frequency Error / IQ Offset

Carrier frequency error is the deviation of

the received frequency from the idealfrequency.

If the carrier frequency error exceeds a

certain amount, synchronization may not

be possible. Carrier frequency error can

be displayed in either Hz or ppm. IQ (origin) offset is also called carrier

leakage, carrier feedthrough, or

relative carrier leakage power (RCLP).

IQ offset can be caused by local oscillator

(carrier) leakage or a baseband DC offsetand generates interference in the central

part of the signal.


15/25


Gain Imbalance

The I and Q channel should be precisely 90 degrees apart.

A gain imbalance causes these channels to have differentamplitudes.

Gain imbalance can result in asymmetric constellations.

Expressed in dB, with the sign indicating the direction of imbalance

Positive imbalance Negative imbalance


16/25


Peak CDE / Average RCDE

Both Peak CDE and Average RCDE aremeasurements of modulation quality.

CDE (code domain error) is the ratio of theobserved power in an unoccupied codechannel to the power in an occupied codechannel (e.g. CPICH).

Peak CDEis the maximum error for all

codes (i.e. the code channel subject to thegreatest interference). It is used todiscover and limit inter-code cross-talk.

Average RCDEis the ratio of the meanpower of the error projection onto thatcode to the mean power of the active code

in the composite reference waveform.Only applicable to 64QAM modulatedcodes.


17/25


Channel results

Primary and secondary sync channel power

CPICH information P-CCPCH information

These four channels : P-SCH, S-SCH, CPICH, and P-CCPCH are

all critical components in the UE cell search procedure


18/25


Steps in WCDMA cell search

P-SCH(primary synchronizationchannel) is used to acquire slotsynchronization.

S-SCH(secondary synchronizationchannel) is used to acquire framesynchronization and identify the codegroup.

CPICH(common pilot channel) isexamined to find the primaryscrambling code.

P-CCPCH(primary common controlphysical channel) is detected andBCH (broadcast channel), whichcontains the system information in theform of MIB and SIBs, can now beread.


19/25


Ec/Io and EVM

Ec/Io is the strength of the

serving pilot relative to theinterference from its own celland all other cells on the samefrequency.

Error Vector Magnitude (EVM)is a measure of how much a

signal deviates from the ideamodulation scheme.

High EVM indicates distortionswhich limits the ability of thereceiver to demodulate the

signal properly. Often causedby poor RF conditions(interference).


20/25


Code Domain Power


21/25


Code Domain Channel Table

No code channel should have

power higher than CPICH

Symbol rates (data rates) are

based on spreading factor (SF),

e.g. SF 256 = 15 kbps.

Pilot bits can be used for

channel estimation


22/25


Signal Settings

By default, the FSH does measurementson base stations with one antenna.

For base stations with two antennas, you

have to specify which antenna the FSH

should synchronize to.


23/25


Power Settings

Absolute Code Power shows the codepowers for CPICH, P-CCPCH, P-SCH and

S-SCH independently.

Code Power Relative to CPICHshows

the channel powers relative to CPICH (N

dB)

Here powers are shown relative (Rel) to CPICH power (-94.96 dBm)


24/25


GPS / Position Information

If an appropriate GPS receiver (HA-

Z240) is attached to the FSH, it can also

display position information with all

demodulation measurements.


25/25


Questions / discussion

Fsh Wcdma Demod v1 1

Documents

Transcript of Fsh Wcdma Demod v1 1