Server-side GNSS Aquisition and Positioning
Within a software defined radio implementation of a GNSS receiver, the signal aquisition, measurement determination and positioning is carried out in software. It is therefore not necessary to carry out this "processing" on the same device that captures the signals transmitted from the satellites and received at the antenna.

RETROFIX is a server-based service that operates with raw data files captured by NSL's Primo Front End and can be tested at www.retrofix.org. Depending on your application, this demonstrates a number of benefits over conventional GNSS.

Example RETROFIX Implementation
  • low power requirements of the capture device or IC
  • rapid capture at the desired instant in time
  • extremely small footprint for integration into third party devices
  • positioning only when required (on demand)
  • aquisition, positioning and integrity using the latest algorithms
  • multi-constellation solution (GPS + Glonass)
There are 3 devices to consider when implementing a RETROFIX solution; capture, control, and compute.
  1. The capture device comprises an GNSS antenna, the RF FE along with some logic device controlling the capture of the signal and its storage or transmission.
  2. The control device interfaces with the logic on the capture device passing the trigger for captureand with the RETROFIX server sending to it the captured signal.
  3. The RETROFIX server receives the captured signal, computes and returns a position solution along with all associated quality metrics.

How much data is required?

Digitised GNSS RF signal is typically captured at a rate of 750kB per second. It is possible to compute a position with just 2ms of signal (1500 bytes), but this would only be successful in good signal reception, open sky, environments. On the other hand, 1s of data will guarantee a position in virtually any environment but the data storage/transmission prohibits practical use.

NSL recommend a sensitivity to filesize compromise of 200ms (150 kB) permitting positioning in indoor environments.

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