The AIOTS (Advanced In Orbit Test System) ESA Project generated the need to perform measurements with traffic. To cope with this goal it is necessary to implement spread spectrum techniques. Therefore, the goal to be achieved within this project is to demonstrate the feasibility of the Spread Spectrum In- Orbit Testing concept based on the following objectives:
The most important transponder test parameters to be measured are gain/frequency response, group delay/frequency response and TWT operating point of the traffic system.
The key issue of the SS-IOT concept is the use of a spread spectrum instrument to be able to make measurements with traffic, without interfering or sacrificing the accuracy of the measurements.
Satellite in-orbit testing and periodic monitoring is a very necessary task in order to be able to predict possible malfunctioning of the transponders. The main benefit of SS-IOTS is that the communication satellite will be operational while measuring, following an identical test plan and maintaining the same accuracy level as the traditional IOT systems.
One solution to achieve the mentioned objectives is the use of a spread spectrum measurement system, which allows measuring with very low spectral density signals without interfering on the neighbouring satellite or on the transponder occupying payload.
The test signal will be a low-power spread spectrum signal that will have no measurable influence on the performance of the traffic signal. The most important feature is that the transponder performance is measured under real operational conditions and the periodic measurement enables early discovery of degradation tendencies. The spread spectrum instrument will be integrated into the AIOTS bench mentioned before, compounding the Spread Spectrum In Orbit Test System (SS-IOTS). The AIOTS has a classical IOT system architecture as shown in the following figure.
Figure 1: Classical IOT System Architecture
Four different parts can be differentiated in the SS device:
The tasks within this project are performed in four different stages:
The output of this stage is the production of the Basic Design Review documentation,
All the task of the project have been completed satisfactorily and the system developed demonstrated the accomplishment of the measurement requirements specified.
Intensive laboratory and real satellite tests in SES Astra premises were carried out during the validation phase of the project. Such campaigns demonstrated the ability to perform IOT campaigns without interrupting the service and not degrading the quality of service of the overall system, but being able to perform very accurate measurements under such traffic. This capacity represents a very attractive functionality for the satellite operators willing to minimize the effect of IOT campaigns in their satellite operations.
Moreover, the SS IOT System introduces a powerful user interface that automates most of the tasks, allows a fine tuning of the measurement and shows the results in a friendly format. The monitoring and control interface provided is based on an open TCP/IP interface that allows integrate the equipment in the customer networks and then carry out measurements remotely from any host of such network.
As a summary, the main benefits demonstrated by the system are listed below:
Finally, it can carry out measurements in Open Loop Mode. That is, when transmitter and receiver are at different locations.