Setting up a 1xEV-DO Measurement

When setting up a 1xEV-DO demodulation measurement, there are several things you need to consider. This topic tells you how to connect your signal to an 89600 VSA Analysis software and successfully demodulate digital signals. The information is provided in this order:

Connecting Your Signal to the VSA
Frequency Span
Input Range
Center Frequency
Reverse/Forward Link Direction
Chip Rates, Symbol Rates and Walsh Code Length
Result Length
Mirrored Spectrum

Connecting Your Signal to the VSA

The VSA lets you connect your carrier signal or if your measurement hardware 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 measurement hardware has two input channels, the VSA ignores the second input channel.

If your measurement hardware has a second input channel, you can also 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 lets you connect the I component of your signal to Channel 1 and 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.

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 you select a span that is too narrow, your measurement may have excessive errors or the VSA may lose carrier lock. If the span is less than the (Chip Rate ´ 1.204), 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 1xEV-DO signal):

Frequency Span ³ (1.204 ´ Chip Rate)

If you select a span that is too wide, your measurement may be affected by excessive noise and slower speed.

Using the "Preset to Default" configuration settings will select a default span that should work well.

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 data results, 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..

1xEV-DO signals can have a relatively large Peak-to-RMS voltage ratio potentially requiring a higher range setting than for other digitally modulated signals.

Center Frequency

The VSA's center frequency must be set within approximately ±500 Hz of the carrier frequency of the 1xEV-DO signal, otherwise the VSA may not be able to lock onto your signal.

The pilot PN 1) part number, or 2) packet number Offset index must mach the system PN Offset index (forward link direction only).

Reverse/Forward link direction

The VSA can demodulate both reverse link and forward link 1xEV-DO signals . Therefore you must select the input signals ReverseLink or ForwardLink direction. ForwardLink refers to the Base Station Transceiver (or Access Network) transmitted signal and ReverseLink refers to the mobile station (or Access Terminal) transmitted signal.

You can use the Preset to Standard command button to auto-configure the VSA to measure standard 1xEV-DO Forward or Reverse link signals.

Chip Rates, Symbol Rates and Walsh Code Length

To successfully demodulate 1xEV-DO signals, the VSA chip rate must match the chip rate of your 1xEV-DO signal. The Walsh Code Length determines the Symbol Rate per the following equation.

Symbol Rate = Chip Rate/Walsh Code Length

Chip Rate: 1.2288 MHz Megahertz: A unit of frequency equal to one million hertz or cycles per second.
Walsh Code Length (Symbol Rate)
(Forward Link)	(Reverse Link)
	4 (307.2 ksym/s)
	8 (153.6 ksym/s)
16 (76.8 ksym/s)	16 (76.8 ksym/s)
32 (38.4 ksym/s)
64 (19.2 ksym/s)	¾

Result Length

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

Result Length may be entered as an integral number of half slots, frames or time. If you choose to enter seconds, the VSA will automatically increment your entry as necessary to obtain an integer number of slots.

Mirrored Spectrum

The 1xEV-DO demodulation provides a feature that lets you configure 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 1xEV-DO signal is inverted, or flipped due to an IF down conversion.