DSP Basics

Block 3. DSP Basics

Purpose

Block 3 moves from signal interpretation to active IQ processing: FFT discipline, windowing, filtering, digital mixing, multirate processing and basic quality metrics.

Why this block matters

Block 2 teaches how to read a signal. Block 3 teaches how to modify, clean, shift and prepare the signal for FPGA implementation.

Core idea:

IQ input -> FFT window -> FIR filter -> digital mix -> multirate -> metrics -> FPGA-ready DSP

Main topics

Topic	Engineering meaning
FFT windows	leakage, resolution, measurement correctness
FIR/IIR filtering	frequency response, phase response, transition band, delay
Digital mixing	frequency shift through NCO/DDS and complex multiplication
Multirate DSP	decimation, interpolation, anti-aliasing, anti-imaging
Metrics	SNR, noise floor, spur level, engineering conclusion
FPGA preparation	fixed-point, latency, streaming interface, resource thinking

Labs

Lab	Topic	Main artifact	FPGA/RF connection
Lab 3.1	FFT windows and leakage	spectrum comparison	measurement discipline
Lab 3.2	FIR low-pass filtering of IQ data	response + filtered IQ	future FIR RTL block
Lab 3.3	Digital mixing and frequency shift	spectrum before/after shift	NCO + complex multiplier
Lab 3.4	Decimation with anti-aliasing filter	anti-aliasing validation	rate-change block for FPGA

Minimum lab report

Each lab should produce not just a plot, but an engineering conclusion:

1. processing goal;
2. signal parameters and Fs;
3. plot before processing;
4. plot after processing;
5. numerical metric or observation;
6. implication for FPGA/RF implementation.

Engineering result

After the block, the student can:

• select FFT windows for measurement tasks;
• design a simple FIR filter;
• explain delay and transition bandwidth;
• shift a signal in complex baseband;
• perform decimation/interpolation without destroying the spectrum;
• connect a DSP block to future fixed-point/HDL implementation;
• report DSP results reproducibly.

Connection to later blocks

Block 3 prepares DSP primitives that later become fixed-point and HDL blocks:

• FIR -> streaming FIR RTL;
• digital mixer -> NCO + complex multiplier;
• decimation -> anti-aliasing + rate-change path;
• metrics -> automated validation and reports.