102 Chapter 14
Baseband I/Q Inputs (Option BBA) Measurement Concepts
Why Make Measurements at Baseband?
Why Make Measurements at Baseband?
Baseband I/Q measurements are a valuable means of making
qualitative analyses of the following operating characteristics:
• I/Q signal layer access for performing format-specific demodulation
measurements (for example, CDMA, GSM, W-CDMA).
• Modulation accuracy – that is,. I/Q plane metrics:
—rho
— error vector magnitude; rms, peak, or 95%
— carrier feed-through
— frequency error
— magnitude and phase errors
• Code-domain analysis (including code-specific metrics)
• CCDF of
• Single sideband (SSB) metrics for assessing output quality
• Basic analysis of I and Q signals in isolation including: DC content,
rms and peak to peak levels, CCDF of each channel
Comparisons of measurements made at baseband and RF frequencies
produced by the same device are especially revealing. Once signal
integrity is verified at baseband, impairments can be traced to specific
stages of upconversion, amplification, or filtering by RF analysis. In
addition, impairments to signal quality that are apparent at RF
frequencies may be traceable to baseband using baseband analysis.
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