Setting up a W-CDMA(3GPP) Measurement

When setting up a W-CDMA Code Division Multiple Access: One of several digital wireless transmission methods in which signals are encoded using a specific pseudo-random sequence, or code, to define a communication channel. A receiver, knowing the code, can use it to decode the received signal in the presence of other signals in the channel. This is one of several "spread spectrum" techniques, which allows multiple users to share the same radio frequency spectrum by assigning each active user an unique code. CDMA offers improved spectral efficiency over analog transmission in that it allows for greater frequency reuse. Other characteristics of CDMA systems reduce dropped calls, increase battery life and offer more secure transmission. See also IS-95.(3GPP) demodulation measurement, there are several things to consider. This topic provides information to connect your signal to the 89600 VSA software and successfully demodulate W-CDMA(3GPP) signals. Additional information for setting up an HSPA measurement is in the HSPA+ MIMO Overview topic. A typical measurement includes the following measurement setup process (each step is discussed in the following text):

Connecting Your Signal to the VSA
Configure the Center Frequency and Span
Configure the Input Range
Configure Triggering (if required)
Verify input signal capture and initial parameter settings
Configure the Demodulator
1. Select the W-CDMA(3GPP)/HSPA demodulator
  
  (for HSPA signals see Setting up an HSPA measurement topic.
2. Set the Scramble Code
3. Set the Uplink/Downlink Direction
4. Set the Chip Rates, Symbol Rates, and Spread Code Length
5. Set the Result Length
6. Set the Filtering
7. Set the Mirrored Spectrum
8. Select a Test Model
Run the measurement

Also, see Setting up an HSPA measurement.

W-CDMA(3GPP) Measurement Setup Information

Connecting Your Signal to the VSA

The VSA connects your carrier signal or, if your VSA has two input channels, the raw I (In-phase) and Q (Quadrature-phase) signals.

For all receiver configurations except I + jQ, connect your signal to Channel 1. In this case, the VSA assumes that your signal contains both the I and Q components (the carrier signal). If your VSA has two input channels, the VSA ignores the second input channel.

If your VSA has a second input channel, connect the raw I (In-phase) and Q (Quadrature- phase) signals. To do this, select Input > Channels > I + jQ. With this configuration, the VSA removes the quadrature mixer from the demodulator's signal flow, which connects the I component of your signal to Channel 1; the Q component to Channel 2.
Notes for I+jQ input:
- Selecting an I+jQ configuration enables DC coupling.
- Use User Correction to correct for any offset or gain imbalance between the I and Q signals.
- Range is set independently for the I and Q inputs, but can be coupled by selecting the Couple Paired Channels parameter.
Configuring the Center Frequency and Span
1. Setting the Center Frequency
  
  The VSA's center frequency must be set within approximately ±500 Hz of the carrier frequency of the W-CDMA (3GPP) signal, otherwise the VSA may not be able to lock onto your signal.
  
  For W-CDMA downlink with the "SCH" sync type, the center frequency may need to be within ±300 Hz of the carrier frequency.
2. Setting the Frequency Span
  
  When selecting a frequency span, select the narrowest span that includes all of your signal components (select a span that is slightly larger than the bandwidth of your signal). If a span that is too narrow is selected, your measurement may have excessive errors or the VSA may lose carrier lock. If the span is less than the chip rate * (1+filter alpha), the VSA shows "DATA?" to indicate that the results may not be accurate.
  
  For best results, the frequency span should be set according to the following formula (filter alpha is the filter characteristic of the Nyquist filter used to demodulate the W-CDMA signal):
  
  Frequency Span ³ (1 + Filter alpha) ´ Chip Rate
  
  If a span that is too wide is selected, your measurement may be affected by excessive noise and slower speed.
  
  Using the Preset to Standard configuration settings will select a default span that should work well.
Configuring the Input Range:

The input range must be set correctly to obtain accurate measurements. Input ranges that are too low overload the VSA's ADC Analog-to-Digital Converter. Input ranges that are too high increase noise, which increases errors reported in error summary data, such as EVM Error vector magnitude (EVM): A quality metric in digital communication systems. See the EVM metric in the Error Summary Table topic in each demodulator for more information on how EVM is calculated for that modulation format..
Set up triggering (if required)

The default triggering mode is set to "FreeRun". However, if a different trigger mode is desired, now is the time to configure the triggering.
Verify the input signal and initial parameter settings

View your signal in the frequency domain to verify the parameter settings you set in steps 1-3.

Configuring the demodulator for W-CDMA(3GPP) measurements

The demodulator parameters can be configured manually or the Preset to Standard parameter can be used. Preset to Standard will automatically set up the demodulator parameters to one of the provided standard defaults (see Using a Standard Setup topic).

Set the demodulator to W-CDMA/HSPA.

This will enable the W-CDMA(3GPP) demodulator properties and measurement parameters. For HSPA measurements, select Enable HSPA Analysis (see Making HSPA Measurements).
Setting the Scramble Code

Specify the scramble code to match the W-CDMA measured signal.
Setting the Uplink/Downlink channel Direction

The VSA can demodulate both uplink and downlink W-CDMA signals. Therefore select the desired uplink or downlink direction. Downlink refers to the Base Station (or base station transceiver) to mobile station (MS mobile station: A station in the mobile service intended to be used while in motion or during halts at unspecified points. A mobile station (MS) is always a subscriber station (SS) unless specifically excepted otherwise in the standard.) channel. Uplink refers to the mobile station (or User Equipment) to Base Station channel.

Setting the Chip Rate, Symbol Rate and Spread Code Length

To successfully demodulate W-CDMA signals, the VSA Chip Rate must match the chip rate of your W-CDMA signal. The Spread Code Length determines the Symbol Rate per the following equation.

Symbol Rate = Chip Rate/Spread Code Length

	CHIP RATE: 3.84 MHz Megahertz: A unit of frequency equal to one million hertz or cycles per second.
	Spread Code Length (Symbol Rate)
	(Downlink)	(Uplink)
	-	2 (1920 ksym/s)
	4 (960 ksym/s)	4 (960 ksym/s)
	8 (480 ksym/s)	8 (480 ksym/s)
	16 (240 ksym/s)	16 (240 ksym/s)
	32 (120 ksym/s)	32 (120 ksym/s)
	64 (60 ksym/s)	64 (60 ksym/s)
	128 (30 ksym/s)	128 (30 ksym/s)
	256 (15 ksym/s)	256 (15 ksym/s)
	512 (7.5 ksym/s)	-

Setting the Result Length

Result Length determines the signal capture length in terms of the number of slots (or equivalent slot time). Make sure that the result length is long enough to capture all the desired data.

Result Length may be entered as an integer number of slots, frames or time. If seconds are entered, the VSA will automatically increment your entry as necessary to obtain an integer number of slots.
Set the Filtering

For W-CDMA(3GPP) demod, the measurement filter is a root raised cosine (RRC) filter with user definable alpha capability (default alpha value = 0.22). This differs from the filtering capabilities available with either Digital Demod or Video demodulation. With those two demod types there is the option of selecting a measurement and reference filter (see About Filters).
Setting the Mirrored Spectrum

Wideband CDMA demodulation provides a feature that configures the VSA's demodulator to conjugate the complex time-domain waveform. This has the effect of flipping the spectrum around the VSA's center frequency. This feature is useful when the W-CDMA signal is inverted, or flipped due to an IF down conversion.
Select a Test Model

3GPP provides specific Test Models for conducting certain tests. By specifying a Test Model, automatic channel identification is bypassed, and measurements assume a reference signal corresponding to the selected Test Model. (See Test Model).

Run the Measurement

HSPA+MIMO Measurements

Refer to HSPA+ MIMO Overview for more information about about making an HSPA+MIMO Multiple Input, Multiple Output: A physical layer (PHY) configuration in which both transmitter and receiver use multiple antennas. Measurement.