Introduction—GNSS Basics

All Global Navigation Satellite Systems (GNSS) work by measuring the transmission-time delay from a satellite to a GNSS receiver.

With a clear view of the sky and an unobstructed path to multiple satellites, a modern GNSS receiver is able to calculate its position rapidly and accurately.

But atmospheric effects can alter the speed of the signals to an indeterminate degree, and signals can be obscured by buildings, or reflected off surfaces such as the sea—all of which will compromise receiver performance: Extending acquisition time or reducing sensitivity and accuracy.

Thorough evaluation of receiver performance is crucial in the R&D of any GNSS-enabled technology, and requires that the impact of these various sources of impairment is taken into account.

A valuable technique for performing such testing is the Recording of real-world RF signals and their subsequent Playback in the lab.

In summary:

• Complete evaluation of receiver performance requires real-world signals
• Real-world conditions are not repeatable making comparable trials difficult
• Record and Playback Systems (RPS) provide real-world, repeatable test conditions  

Why Record and Playback

One of the fundamental challenges in GNSS receiver evaluation is that live RF signals and conditions are always changing. Satellites move constantly, and different antenna positions are subject to different environmental impairments.

Although modelling such effects as part of a complete, controlled, simulated GNSS environment is the preferable option for the vast majority of receiver performance testing applications, testing with real-world signals remains a vital step in GNSS receiver R&D.

Since is it impossible to exactly repeat a trial against a live sky—and since field tests are both costly and time-consuming—the benefits of recording a sample of RF for repeated playback in the lab are clear.

Being by its nature representative of the real world, the record and playback approach perfectly complements GNSS simulation as a source of GNSS signals for comprehensive receiver testing.

In summary, recording live RF signals for playback in the lab:

• Eliminates the time and cost of repeatedly testing in the field
• Eliminates the uncertainly of live sky testing by making real-world signals repeatable

GSS6400

Spirent’s GSS6400 Record Replay System is a complete, standalone system, designed for gathering data in the field and replaying it with optimal fidelity and performance back in the lab.

Built on over 25 years’ leading the world in GNSS testing, other key advantages of the Spirent GSS6400 include:

• New Feature: Synchronised playback—start playback on a pulse, enabling easy integration of the GSS6400 with other test systems and applications
• New Feature: Synchronous/asynchronous record and playback of two channels of serial digital data alongside the digitized GPS L1 , GLONASS L1, Galileo L1 and even QZSS signals, supporting the designing and testing of integrated GNSS devices
• New Feature: Spirent’s regularly updated Live Sky data sets give you access to RF environments recorded at major locations worldwide, without ever leaving the R&D lab
• Automated test scripts, remote control and fast network access
• OCXO playback included at no extra cost

Further Innovations

Spirent is committed to the continuing development of its GNSS testing systems. Other recent enhancements to the GSS6400 include:

• Increased bandwidth option for Galileo support
• Optional inbuilt solid state drive for rugged operation
• Optional external battery pack for longer battery life
• Event marker
• CAN Bus Interface kit
• RS232 Interface kit

The GSS6400

• Is simple to operate
• Provides repeatable test environments
• Represents real world conditions
• Makes collaboration easy with scenarios portable between units

On-Demand Webinars 

GSS6400 Help Sheets

GSS6400 "How To" Help Sheet #1
This help sheet explains the use of the Built-in Attenuator in the GSS6400 Record Playback Systems

GSS6400 "How To" Help Sheet #3
This help sheet explains the Repeatability Test using the GSS6400 RPS (Static GPS Signals)

GSS6400 "How To" Help Sheet #4
This help sheet explains how to Extract a Section of Data from a Recorded File in the GSS6400 Record Playback Systems.

GSS6400 "How To" Help Sheet #6
This help sheet explains the use of FTP to Transfer Files Between GSS6400 and External Devices