RTLinux-Based Radar Signal Acquisition and Processing System Design

RTLinux-Based Radar Signal Acquisition and Processing System Design

Modern radar systems demand high-throughput data acquisition and deterministic real-time processing. As signal complexity and data volume increase, system performance is increasingly constrained by operating system latency, hardware bandwidth, and software architecture.

This article presents a redesigned radar signal acquisition and processing system based on RTLinux, focusing on real-time task control, system architecture, and performance validation.

🚧 Limitations of Legacy Radar Systems

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The original system exhibited several structural and performance bottlenecks:

• ISA bus architecture with limited throughput
• Slow signal acquisition and processing speed
• Multi-display output with poor visualization efficiency
• Frame loss under high-speed display conditions
• System instability under Windows 98

Real-Time Constraints

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Windows 98 lacks deterministic behavior:

• Unpredictable interrupt response latency
• Non-deterministic task scheduling
• Limited system customization

These limitations make it unsuitable for modern radar signal processing requirements.

⚙️ RTLinux Architecture and Advantages

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RTLinux enhances Linux with a lightweight real-time kernel, enabling deterministic task execution while retaining the full Linux ecosystem.

Core Characteristics

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• Hard real-time interrupt handling
• Kernel-space execution for real-time tasks
• User-space execution for non-real-time tasks
• Preemptive scheduling with strict priority control

RTLinux inserts a real-time layer between hardware interrupts and the Linux kernel, ensuring that time-critical tasks are always serviced first.

Performance Characteristics

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• Interrupt response time: microsecond-level latency
• Deterministic scheduling
• Scalable with hardware performance

These properties make RTLinux suitable for high-speed signal acquisition systems.

🖥️ System Architecture and Hardware Design

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The upgraded radar system integrates modern hardware components:

• High-performance PC platform
• PCI-based high-speed data acquisition board
• Signal transfer board
• Integrated display subsystem

Hardware Improvements

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• Migration from ISA to PCI bus (hundreds of MB/s throughput)
• High-speed A/D and D/A conversion
• On-board preprocessing and buffering

These upgrades significantly improve data acquisition bandwidth and processing efficiency.

🧩 Signal Acquisition and Processing Workflow

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The system processes radar signals in a multi-stage pipeline:

1. Signal sampling via acquisition board
2. Amplitude quantization and feature extraction
3. Integration with azimuth and carrier frequency data
4. Preprocessing to compute parameters:
   • Carrier frequency
   • Pulse width
   • Pulse repetition interval
   • Time of arrival
5. Buffering and transfer to processing modules
6. Analysis, visualization, and storage

This pipeline ensures continuous, high-throughput signal processing.

🔄 RTLinux Task Model and Control Framework

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The system divides tasks into real-time and non-real-time domains.

🧠 Real-Time Tasks (Kernel Space)

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• Data acquisition
• Signal control
• Hardware interaction

Functional Structure

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Each real-time module includes:

• init_module() — resource allocation and task initialization
• cleanup_module() — resource release and task termination
• Real-time task function — core processing loop

Responsibilities

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• Interrupt handling
• Data acquisition from hardware
• Immediate response to control signals

🖥️ Non-Real-Time Tasks (User Space)

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• Data analysis and decoding
• Signal visualization
• System control and configuration

Linux user space provides:

• Strong computation capabilities
• Graphical display support
• File and database integration

🔗 Inter-Process Communication Design

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Communication between system components is implemented using FIFO and shared memory mechanisms.

FIFO Channels

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• FIFO1: data transfer from real-time to user space
• FIFO2: internal control buffering
• FIFO3: control commands from user space to real-time modules

Communication Flow

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1. Acquisition board triggers interrupt
2. Real-time module reads data
3. Data is transmitted via FIFO1
4. User-space process performs analysis and visualization
5. Control commands sent back via FIFO3

This design ensures deterministic data flow and low-latency control.

📊 Integrated Display System

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The upgraded system replaces multi-display output with a unified visualization interface.

Display Features

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• Simultaneous visualization of:

  • Azimuth
  • Carrier frequency
  • Pulse repetition frequency
  • Pulse width

• Improved clarity and persistence

• Faster operator interpretation

This significantly enhances usability and operational efficiency.

🧪 Real-Time Performance Evaluation

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System performance was validated using interrupt response time measurements.

Test Environment

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• CPU: Pentium 4 (1.7 GHz)
• Memory: 256 MB
• Storage: 40 GB HDD
• Interrupt source: parallel port (10 μs interval)

Results

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• Single-task mode: 4–7 μs latency
• Multi-task mode: 7–9 μs latency

Analysis

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• Stable microsecond-level response
• Minimal degradation under multi-task load
• Meets real-time requirements for radar processing

🔍 Conclusion

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The RTLinux-based redesign significantly improves the performance and reliability of the radar signal acquisition and processing system.

Key outcomes:

• Deterministic real-time control with microsecond latency
• Increased data throughput via PCI-based acquisition
• Modular architecture with clear task separation
• Improved visualization and operator efficiency
• Enhanced system stability compared to legacy platforms

RTLinux provides a practical and scalable solution for modern radar systems, combining real-time determinism with the flexibility of Linux. This approach enables efficient upgrades of legacy systems while meeting the growing demands of high-speed signal processing.