Sub-GHz RF Image Transmission System for Search & Rescue Drone

Led communications subsystem design for a senior design drone project, achieving 3+ km operational range with custom packet protocol and 1 Mbps sustained data rates.

Key Highlights

•3+ km operational range validated in line-of-sight field tests
•1 Mbps sustained data rate for image transmission
•Custom packet protocol with CRC/ARQ for reliability achieving 99.2% packet delivery rate
•Successfully integrated with YOLOv5 object detection pipeline

Embedded SystemsRF CommunicationSenior DesignWireless

Tech Stack

CPythonTI CC1312R SimpleLinkUARTJPEG CompressionLuckfox Pico Ultra2-FSK Modulation

System Architecture & Implementation

The communications subsystem served as the critical link between the autonomous drone and ground station, enabling real-time transmission of both object detection alerts and compressed video streams. The system architecture consisted of three primary components: 1. Embedded Transmitter (Drone-Side): • TI CC1312R SimpleLink wireless MCU configured for 868 MHz Sub-GHz operation • Custom C firmware implementing packet framing, CRC calculation, and UART buffering • Integration with Luckfox Pico Ultra for JPEG compression and frame capture • Real-time prioritization: alert packets transmitted with higher priority than image data 2. Custom RF Protocol: • Packet structure: Header (16 bytes) + Payload (variable) + CRC16 • Support for both alert messages (low-latency, <50ms) and image chunks (throughput-optimized) • Basic ARQ implementation with selective retransmission for corrupted packets • Achieved 99.2% packet delivery rate in field conditions 3. Ground Station Software (Python): • Real-time packet reception and reassembly • JPEG decompression and image display pipeline • Logging and diagnostics for performance analysis

Real time Image transfer and UI example from Purdue SPARK Demo

Technical Challenges & Solutions

Challenge 1: Balancing Latency vs. Throughput Object detection alerts required low-latency transmission (<100ms), while image data needed high throughput (1 Mbps). Solved by implementing a dual-queue system with priority scheduling in the firmware. Challenge 2: Packet Loss in Long-Range Scenarios Initial testing at 2+ km showed 15-20% packet loss due to signal fading. Implemented forward error correction and adaptive retry logic, reducing effective loss to <1%. Challenge 3: Power Constraints CC1312R power consumption at 10 dBm output threatened flight time. Optimized transmission duty cycle and implemented dynamic power scaling based on RSSI feedback from ground station.

Radio latency measurements

UART logs showing transfer connection

Testing & Validation

Conducted comprehensive field testing across multiple environments: • Open Field Tests: Validated 3.2 km maximum range with line-of-sight • Urban Environment: Achieved 1.1 km range with building obstructions • Interference Testing: Verified operation in 2.4 GHz WiFi saturated areas • Reliability Metrics: 99.2% packet delivery, <80ms average latency for alerts

Field testing demonstrating 3+ km operational range. X marks the ground station location while the circles are the drone-side locations.

Key Takeaways & Future Work

This project demonstrated the viability of Sub-GHz communication for drone telemetry applications, particularly in scenarios requiring long range and obstacle penetration. Future enhancements could include adaptive modulation schemes (2-FSK to 4-FSK based on link quality) and integration of mesh networking for multi-drone coordination. The system was successfully demonstrated at the senior design showcase, receiving positive feedback from industry judges for its practical approach to solving real-world search-and-rescue communication challenges.

Overview

Design and implement a robust, long-range wireless communication system capable of transmitting real-time compressed images and alert data from an autonomous search-and-rescue drone with onboard object detection to a ground station over distances exceeding 3 km. Led the communications subsystem design and implementation for a senior design drone project. Architected a custom packet transmission protocol optimized for Sub-GHz operation (868 MHz, 2-FSK modulation) achieving 1 Mbps sustained data rates. Developed embedded C firmware for the TI CC1312R radio module with UART interfacing to the flight controller. Implemented Python-based ground station software for JPEG decompression, packet reassembly, and real-time image display. Designed custom framing with CRC error detection and basic ARQ for reliability.

Impact & Results

▸3+ km operational range validated in line-of-sight field tests
▸1 Mbps sustained data rate for image transmission
▸Custom packet protocol with CRC/ARQ for reliability achieving 99.2% packet delivery rate
▸Successfully integrated with YOLOv5 object detection pipeline
▸Achieved <80ms average latency for alert messages with dual-queue priority scheduling
▸Demonstrated at senior design showcase with positive industry feedback for real-world search-and-rescue applications

Project Links

GitHub Repository View Report