ADS-B Aircraft Decoder

Overview

Build a complete ADS-B receiver that decodes aircraft position and identification from 1090 MHz signals. ADS-B (Automatic Dependent Surveillance - Broadcast) uses Pulse Position Modulation (PPM) to transmit 112-bit messages containing aircraft identification, position, altitude, and velocity.

The relatively simple modulation scheme makes this an excellent stepping stone toward the more complex QPSK demodulation in the Meteor M2 capstone project. This project directly demonstrates avionics domain knowledge relevant to NZ employers like Rocket Lab, Kea Aerospace, and Dawn Aerospace.

ADS-B Protocol Overview

Frequency	1090 MHz
Modulation	Pulse Position Modulation (PPM)
Message Length	112 bits (extended squitter)
Preamble	8 μs pattern
Data Rate	1 Mbit/s
CRC	24-bit

System Architecture

1090MHz Antenna → RTL-SDR → USB → Zynq ARM → Sample Buffer → FPGA
                                                                            ↓
                                                          Preamble Detection
                                                                            ↓
                                                          PPM Demodulation
                                                                            ↓
                                                          Bit Extraction
                                                                            ↓
                                                          CRC-24 Validation
                                                                            ↓
                                                          Message FIFO → ARM
                                                                            ↓
                                                          Display/Network Output

Specifications

Input	RTL-SDR 2.4 MSPS I/Q samples
Detection Range	100+ nm with good antenna
Message Types	DF17 (Extended Squitter) minimum
Output Format	Raw hex + decoded fields
Compatibility	dump1090 network protocol

FPGA (PL) Requirements

• Preamble detection (8 μs pattern matcher)
• PPM demodulation and bit extraction
• CRC-24 validation
• Message type classification
• Decoded message FIFO

ARM (PS) Requirements

• RTL-SDR USB interface via librtlsdr
• Sample streaming to FPGA via DMA
• Message parsing (DF17 position, identification, velocity)
• Position calculation (CPR decoding)
• Output: UART, network (dump1090 compatible)

Skills Demonstrated

• Real-time Demodulation: PPM signal processing in hardware
• Protocol Implementation: Working from ICAO specifications
• CRC Algorithms: Hardware CRC-24 computation
• Complete System Integration: RF-to-display pipeline
• Zynq PS-PL Data Streaming: DMA and interrupts
• Avionics Domain Knowledge: Mode S and ADS-B

Hardware

Item	Est. Cost	Source
RTL-SDR V3 or V4	$35-50	RTL-SDR.com/Amazon
1090 MHz antenna (or DIY)	$0-30	Amazon or build from coax
SMA cables/adapters	$10	Amazon
Total	~$45-90

Resources

• The 1090 Megahertz Riddle by Junzi Sun — essential reading
• dump1090 — Reference decoder
• ADSB-Out — Protocol reference
• ICAO Doc 9871 — Official Mode S specification
• Virtual Radar Server — For visualization

Deliverables

• GitHub repo with VHDL source
• Testbench with captured ADS-B samples
• Block diagram of demodulation chain
• Screenshot of decoded aircraft on map
• Performance analysis (detection rate, range)
• Video demo showing live aircraft tracking

Prerequisites

This project requires understanding of:

• I/Q sampling and complex baseband representation
• Digital downconversion (DDC)
• Modulation schemes (ASK, FSK, PSK)
• RTL-SDR architecture and data interface

Implementation Notes

Implementation notes will be added during development.

Resource Utilization

To be measured after implementation.

Progress Log