PAGE CONTENTS
Objectives
The technical objectives were to:
- Define the air-interface requirements for broadband access to a MEO satellite network in 2 selected reference scenarios: Scenario 1 with a dual-antenna user terminal located at the beam centre, and Scenario 2 with a single-antenna user terminal receiving signals from the sidelobes of different beams.
- Develop relevant transmission and reception schemes for these two scenarios, namely a seamless (i.e., without packet loss) handover technique (when two MEO satellites are in view, one rising and one setting) and diversity combining (when only one MEO satellite is in view). To this purpose, physical and higher layer handover techniques were considered, as well as various flavours of Maximum Ratio Combining, Equal Gain Combining, and Selection Combining
- Demonstrate achievable space link performance using an endto-end test-bed implemented in hardware including the transmit/receive techniques for the first selected scenario. To this purpose, a demod was prototyped.
Challenges
The first challenges were in the investigation of the trade-off between performance and complexity of the different combining techniques and layer 2 handover. The design and prototyping of the seamless (i.e., without packet loss) handover and the chosen combining technique provided challenges from the hardware implementation point of view. Additionally, the performance evaluation of sidelobe communications in Scenario 2 provided theoretical and practical challenges.
System Architecture
Scenario 1 – A user terminal is served by the MEO satellite network. The receiver employs two antennas and two receive chains, and signal combining is carried out at the baseband digital domain. The use of two receive chains is to ensure a make-before-break handover between two satellites (the setting and the rising one) in the visibility of the user terminal. Combining is active only when one satellite is visible, and the two receive chains receive two replicas of the same transmitted signal. The combining architecture includes the nature of combining per-se and its position.
Scenario 2 – A user terminal is served by the MEO satellite network but without steering a satellite beam directly to it. Its geographical location is in between multiple spot beams coming from the same or different satellites. As none of the satellite beams is pointing to the user terminal directly, useful power is received only through the sidelobes, which renders each individual received signal very weak. The planned architecture sustains low rate communications with terminals outside the normal coverage of a satellite beam by transmitting and receiving data on multiple beams (from the same or different satellites) in a region, and dynamically adjusting the proportion of data sent on a particular beam via ACM-type feedback.
Plan
Preparatory Phase: The initial phase of the activity dealt with consolidation of the scenarios, determining the scope of the prototype activity and deriving the requirements, configuring the air-interfaces, devising novel transmission and reception techniques, listing the performance metrics and preparation of a simulation plan.
Software Development Phase: A software simulator for assessing the performance of devised techniques using DVB-S2X air-interface was implemented in Matlab. The milestone was Preliminary Design Review.
Prototype Development: A significant effort of the project dealt with the design, development, and validation of the prototype to demonstrate the cost, functionality, and the performance of the selected techniq
Current Status
The project is completed and the prototype was produced. Scenario 1 was selected to assess the performance of seamless handover and combining. Before the prototype design, a software simulation campaign was run to choose the most appropriate combining technique. The prototype was designed accordingly, and it underwent an extensive test campaign aiming at the assessment of both handover and combining. The prototype successfully passed all the tests and its features could be included in the next generation of modems by Newtec. Scenario 2 led to high-level capacity and outage investigations of sidelobe communications, performed by means of software simulations.
