The GNSS-SRP FOUR supports a scalable master–slave architecture, enabling the creation of large, fully phase-coherent multi-channel systems by interconnecting multiple units.

A single GNSS-SRP FOUR can operate as a master unit, distributing both reference clock and timing synchronization signals to up to three slave units, resulting in a system with up to:

  • 16 fully coherent RX channels
  • 16 fully coherent TX channels
Multi-unit GNSS-SRP FOUR coherent expansion diagram

Synchronization Architecture

As illustrated in the system diagram, synchronization between units is achieved through:

  • Reference clock distribution (REF OUT → REF IN)
    The master unit distributes a common frequency reference to all slave units, ensuring all RF front-ends share the same time and frequency base.

  • PPS signal distribution (PPS OUT → PPS IN)
    A shared pulse-per-second (PPS) signal provides deterministic time alignment across all devices.

  • Deterministic FPGA-based alignment
    An integrated calibration and alignment procedure implemented in the FPGA firmware compensates for:

    • Cable delays,
    • Front-end phase offsets,
    • Channel-to-channel mismatches.

    This guarantees repeatable phase coherence across all channels, even in distributed configurations.

Data and Control Topology

Each GNSS-SRP FOUR unit operates as an independent SDR node, connected to the host system via high-speed interfaces (e.g., 10 GbE over SFP). This enables:

  • Parallel data acquisition from all units,
  • Distributed processing architectures,
  • Scalable bandwidth depending on system requirements.

The modular approach allows flexible system design, from compact 4-channel setups to large-scale coherent antenna arrays.

Applications

This multi-unit capability enables advanced system configurations such as:

  • Antenna arrays with up to 16 antennas,
  • High-resolution direction-of-arrival (DoA) estimation,
  • Adaptive beamforming,
  • Coherent multi-transmitter RF testbeds.

Key Advantages

  • Linear scalability without external synchronization hardware,
  • Single-master timing reference for the entire system,
  • Deterministic and repeatable phase alignment,
  • Seamless integration with existing GNSS-SRP FOUR software and firmware ecosystem.

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