Title:  Modem prototype for MEO broadband access
Funding source: ESA - European Space Agency
Partners: Newtec, SES, O3b
Principal investigator: Dr. Bhavani Shankar
Researchers:  Dr. Nicolò Mazzali, Dr. Ahmad Gharanjik

Satellites with their wide coverage can enable “anytime/anywhere access”, at affordable costs, thereby staking claim in future 5G networks. In particular, the satellite component, through its inherent structure to support perceived multimedia traffic growth, ubiquitous coverage, enabling machine to machine communications and critical telecommunication set-up, as well as aiding the backhauling and trunking aspects, can augment the 5G service capability.  Traditionally GEO satellites (geostationary satellites) have been considered for providing requisite services due to wider coverage and simpler network management and user terminal processing. The use of non-geostationary satellite for very high speed data services has been taking momentum in the past years. In particular, the launch of the first O3b MEO constellation satellites is a recent example of a new mission concept, taking advantage of a lower latency and a higher radiated power to cover under-served geographical areas compared to existing broadband coverage in GEO.

While service provisioning by MEO satellites benefits from higher throughputs and lower latencies, the nature of the mobile infrastructure brings in novel aspects in architecture, network management, and ground segment. Multiple satellites/beams in conjunction with multiple receivers provide new scenarios characteristic to MEO constellations.  These, in turn, offer new opportunities that demand a fresh look at the design of ground system components and air interface protocols. The objectives of the new design would be enhanced transmission capability with guaranteed availability, especially since some of the networks operate in the Ka-band.

In this activity, the consortium investigated an exhaustive and comprehensive approach towards devising and prototyping an enhanced cost-effective MODEM for MEO Broadband access. Scenarios and key operational aspects of MEO satellites were first consolidated towards defining the air interface, including the physical layer.  The elements of the air-interface relevant to the characteristic features of MEO systems including Doppler and handover between multiple satellites, such as synchronization and support for a wide range of signal-to-noise-ratios, were investigated. Mechanisms to enhance the signal reception during the steady phase as well as during handover were devised, their performance analysed. These include various flavours of Maximum Ratio Combining, Equal Gain Combining, LLR Combining as well as handover at physical layer and higher layers. The implementation ease, system impact, and scalability (e.g., to multiple terminals) of the techniques were traded with the performance leading to a short-listing of techniques and subsequent prototyping of the same.

The initial phase of the activity dealt with key preparations to be undertaken; these include consolidation of the scenarios (developing on those provided in the Statement of Work), 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. Subsequently, a software simulator for assessing the performance of devised techniques using DVB-S2X air-interface was implemented in Matlab. A significant effort of the project deals with the design, development and validation of the prototype to demonstrate the cost, functionality, and the performance of the selected techniques. We built upon the simulation result expectations in gain improvements and the consideration of the defined practical use cases of interest and verified systematically the results through an extensive testing campaign. New in the cost-effective prototype with respect to the state-of-the art were intra-modem combining of multiple received streams and a scalable (to multiple terminals in a shared forward link) and seamless handover mechanism agnostic of the physical layer and with a minimal system impact (e.g. off-the-shelf modems without new air interfaces to achieve seamless handovers; and a minimal impact on the ACM mechanism). At the completion of the project, the hardware, software, and firmware, together with user manual, are delivered to ESA, which permits further demonstrations and testing of specific use cases outside the scope of this activity.

The project also presents avenues or potential spin-offs for exploiting the output of the activity including the extensions to multiple terminals, return channels, LEO satellites as well as a satellite demonstration.

Objectives

The technical objectives were to

1. Define air interface requirements for MEO satellite networks for 2 selected reference scenarios
2. Develop relevant transmission and reception schemes for these 2 scenarios
3. Demonstrate achievable space link performance using an end-to-end test-bed implemented in firmware including the transmit/receive techniques for the first selected scenario.

Conclusions

In this activity a modem prototype for MEO satellites has been investigated. After the scenario consolidation, two distinct scenarios were identified. In Scenario 1 the terminal user is in the centre of the beam and has two antennas, while in Scenario 2 it is located close to a beam edge and has only one antenna. Scenario 2 has led to high-level capacity and outage investigations of sidelobe communications, performed by means of software simulations. On the other hand, Scenario 1 was selected to assess the performance of seamless handover and diversity combining. Before the prototype design, a software simulation campaign was run to choose the most appropriate combining algorithm and position. The prototype was designed accordingly, and it underwent an extensive test campaign aiming at the assessment of both handover and combining. The prototype has successfully passed all the tests and its features could be possibly included in the next generation of modems by Newtec, both stand-alone and dialog.  

Project Partners: SnT, University of Luxembourg, Luxembourg, Newtec, Belgium, SES, O3b, Luxembourg

Funding Source:  European Space Agency (ARTES 5.1)

Project Duration: 03/2016  to 11/2017

Project Team:

Project Manager: Dr. Bhavani Shankar 

Research Team:  Dr. Nicolò Mazzali, Dr. Ahmad Gharanjik

 Contact: 

Dr. Bhavani Shankar 

Research Scientist

Interdisciplinary Centre for Security, Reliability and Trust (SnT)

29, avenue J.F.Kennedy

L-1855, Luxembourg