Introduction to Real-Time Spectrum Analysis

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1 Introduction to Real-Time Spectrum Analysis Ing. Gianfranco Miele November 23, 2010

2 Technology Trends in RF Wireless is everywhere Accelerating shift to Digital RF, fully leveraging computer technologies RF prevalent across a broad range of industries Crowded RF spectrum Increased surveillance and intelligence gathering

3 The world of RF today.. The growth is in Digital RF Consumer, commercial, military Digital devices with RF interfaces DSP replacing analog signal processing RF signals are more complex Precisely timed bursts Frequency hopping Spectral and modulation changes over time Limited Spectrum availability. Existing tools are not adequate SA and VSA have limitations, a new solution is required The time dimension can no longer be ignored Need to identify transient and random events.

4 Evolution of Signal Analysis Techniques Market Drivers SA VSA RTSA 1960s 1990s TODAY Military Communication systems Emerging solid state technology Encryption Military signal intelligence Cell phones Complex digital modulation Congested RF spectrum Pervasiveness of low cost RF in consumer electronics Growth of DSP-based, modulation-agile communication systems Measurement Challenges High frequency measurements Analog modulation Digital Demodulation Emergence of Standards Time-varying, bursted, and transient RF signals Complexity of wireless communication standards Solutions RF power vs. frequency Low noise floor High dynamic range Digital modulation analysis Flexible time-correlated multi-domain analysis Seamless capture of RF signals changing over time Frequency domain trigger

5 Why Current Solutions Aren t Adequate SA Short-Comings Limited digital modulation analysis No frequency change over time No frequency domain triggering Swept acquisition No memory Single domain views VSA Short-Comings Poor Spectrum Analyzer performance Limited dynamic range Controls and human interface unfamiliar to SA users No frequency domain trigger Misses transient events No analysis reference to time. No multi domain correlated views.

6 Time-correlated Multi-domain Analysis Time vs. Power view Frequency vs. Power view Error vector measurements Time-correlated multi-domain display Constellation view

7 Traditional Swept Architecture Input Resolution Bandpass Filter Display Time Local Oscillator Sweep

8 Real-time Architecture

9 Swept vs. Real-time Seamless Capture Swept Analyzers Real-Time Analyzers TIME FREQUENCY FREQUENCY

10 Real-time Spectrum Analysis Trigger on an RF signal based on power or frequency characteristics Capture the signal seamlessly in time, into memory Analyze the signal simultaneously in multiple domains Time Domain Frequency Domain Modulation Domain

11 Real Time Spectrum Analyzer Concepts Trigger on any event Capture the Signal seamlessly, frame by frame, into Memory Frame 1 Frame 2 Frame 3 Frame 4 Frame N Signal is stored into memory Analyze the Frequency Domain over time FFT produces frequency domain

12 Basic Operation of RTSA (1) Use TIMING menu to set acquisition length to X seconds RTSA captures X seconds of signal information in a single block Block consists of n frames, each with 1024 samples The frames are captured and stored into memory one at a time No gaps between the frames Frame 1 Frame 2 Frame 3 Frame 4 Frame n 1024 Samples per frame (fixed) Time to Acquire 1 Frame = Frame Acquisition Time Time to acquire 1 block (n frames) = acquisition length

13 Basic Operation of RTSA (2) RTSA performs FFT on each individual frame resulting in n spectra These n spectra represent a seamless history of the frequency domain characteristics Frame 1 Frame 2 Frame 3 Frame 4 Frame n Spectrum 1 Spectrum 2 Spectrum 3 Spectrum 4 Spectrum n

14 Frequency/Time Tradeoffs Wider capture bandwidth Narrower capture bandwidth Wide span Frequency domain effects Sample rate increases RBW increases Freq resolution decreases Time domain effects Time resolution increases Frame length decreases Max record length decreases Narrow Span Frequency domain effects Sample rate decreases RBW decreases Freq resolution increases Time domain effects Time resolution decreases Frame length increases Max record length increases

15 Frequency/Time Tradeoff Example Capture bandwidth = 15 MHz Capture bandwidth = 1 khz 15 MHz 1 khz Frequency domain effects Sample rate = 25.6 Msps NBW = 43.7 khz Freq resolution = 25.0 khz Frequency domain effects Sample rate = 1.6 ksps NBW = 2.67 Hz Freq resolution 1.56 Hz Time domain effects Time resolution = 39.0 nsec Frame length = 40.0 usec Max record length = 2.56 sec (for RSA3300A w/opt MB RAM) Time domain effects Time resolution = 625 usec Frame length = 640 msec Max record length = 11.4 hours (for RSA3300A w/opt MB RAM)

16 Frequency Mask Trigger Define a frequency mask which can be used to trigger on specific events in the frequency domain Reliably detect and capture elusive RF signals that a level trigger cannot see in a crowded spectral environment

17 Seamless Capture and Spectrogram The spectrogram shows how an RF signal changes over time in the frequency domain Frequency is the horizontal axis, time is the vertical axis, and power is represented by the color of the trace

18 Real Time Spectrum Analyzer Concepts Trigger on any change in the monitored spectrum Seamlessly capture and store a span of RF frequencies at once Analyze how the frequency and amplitude changes over time

19 Real Time Spectrum Analysis Capabilities Measuring Pulsed/Burst Signal Spectrogram shows frequency domain behavior over time with amplitude Spectrum view shows an instantaneous spectrum at the selected moment of time Analyzer Settings: Span 5 MHz Acquisition length 16ms Spectrum frame time 160 s

20 Real Time Spectrum Analysis Capabilities

21 New RTSA Capability: Overlapping FFTs Signal Captured in the Time Domain Acquired Signal Data Transformed into FFT Frames, No Overlap Processing 1024 Samples 1024 Samples 1024 Samples 1024 Samples 1024 Samples 1024 Samples Acquired Signal, Post-Processed with Overlap FFTs Overlap Interval Samples 1024 Samples 1024 Samples 1024 Samples 1024 Samples 1024 Samples FFT Overlap Samples 1024 Samples

22 Overlapping FFT

23 Overlapping FFT continued

24 Overlapping FFTs Zoom for the Spectrogram Top spectrogram shows no overlap, same as the WCA200A/RSA3300A Frame Resolution = 40us 768 FFT points overlap (FFT interval 256 points) Frame resolution = 10us 960 FFT points overlap (FFT interval 64 points) Frame resolution = 2.5us Frame resolution can be set to 20ns 40 or 36 MHz span A 2000x improvement over existing 40us 3.48 msec 870 usec 217 usec

25 Zooming into the Spectrogram display Without overlapping FFTs With overlapping FFTs Chirped Radar

26 Three Measurement Modes 1. S/A Mode: Real-time spectrum analysis Traditional spectrum analysis 2. DEMOD Mode: General purpose analog modulation analysis General purpose digital modulation analysis Standards based modulation analysis 3. TIME Mode: Time domain transient analysis CCDF analysis

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