The project aims at designing, developing and testing a Proof-of-Concept (PoC) Test-Bed of an On-Ground Beam-Forming (OGBF) and Multi User Detection (MUD) system to demonstrate the feasibility of such technology for space telecommunication application.
The activity will demonstrate the obtainable improvements in performance with the introduction of OGBF/MUD with respect to a conventional on-board beamforming satellite system (that will be defined and used as benchmarking system).
The main aim of the proposed activity is to assess and show the obtainable performance improvements that can be achieved utilizing the On-Ground Beam-Forming (OGBF) technique in conjunction with Multi User Detection (MUD) in comparison with the traditional on-board beam forming.
The work results will allow conclusions to be drawn on the viability to adopt these techniques in the context of space telecommunications. Such a goal will be achieved through a study Phase (Phase 1) and an implementation Phase (Phase 2).
During Phase 1, an overall OGBF-MUD architecture will initially be defined. Its performance will be comparatively assessed in two steps, namely the OGBF alone and then the full OGBF-MUD system. The activity will conclude with issuing the specifications of a proof-of-concept real-time Test-Bed sufficiently representative of a full-fledged OGBF-MUD system, which will be designed, developed and tested along Phase 2. Such a Test Bed, implemented using both COTS hardware and ad-hoc programmed FPGAs will demonstrate the usefulness and suitability of the chosen architecture for future satellite systems.
The following aspects will need to be traded-off and detailed:
- Efficient ground/space partitioning and payload architecture definition,
- Beamforming impairments analysis (mismatches, different frequency conversions, propagation channel, different Doppler per channel, etc.),
- On-ground calibration techniques, comprising the analysis of the following aspects:
- Reference calibration signal and/or beacons,
- Estimation/calibration algorithms,
- Sensitivity of the algorithms’ performances to SNIR, traffic, scintillation, etc.
- On-ground signal processing algorithms, including:
- Spatial filtering (e.g. adaptive array processing, nulling, etc.),
- Multi-User Detection (e.g. co-channel interference cancellation techniques, etc.).
The current strong interest in ground beamforming was dictated by the development of very large antenna reflectors to be used in L and S-band mobile satellites. These large antennas are a must when targeting communication with hand-held devices.
As only a single large reflector can be accommodated on-board, antenna beam-forming techniques are required for good antenna performances. On-Board Digital Beam-Forming (DBF) can be a solution in that case, as it was, for example, in some of the current and past mobile satellite systems (e.g. Thuraya and Inmarsat 4).
With the increase in the reflector size, an increase in the required number of feeds for covering a given geographical region is also experienced. The on-board complexity for DBF would correspondingly increase. However, the advantages of OGBF go beyond the possible reduction in on-board complexity. OGBF has additional advantages with respect to on-board DBF as it allows more advanced signal processing (including Multi-User Detection) to be done at the GW with significant potential benefits.
Also, ground beam-forming is of further significant help with Hybrid Systems, i.e. systems which exploits a terrestrial network infrastructure for filling the gap of the satellite coverage (particularly in urban areas).
The reference payload architectures for the Forward Link (FL) and the Reverse Link (RL) are shown in the figures below.
It is assumed that 3 GWs are present in the system, each one controlling 5 MHz on all the feeds. Although, a fully analog payload implementation is feasible, a DSP-based payload is considered advantageous, at least in a multi-GW scenario, as it reduces the amount of analog HW requirements.
The on-board DBF blocks are absent if OGBF operates on feed signals (feed-level OGBF). The complexity of the on-board DSP is smaller in the presence of OGBF as, in addition to the absence for on-board DBF, there is no requirement for high resolution on-board filtering to implement per channel beam-forming. With OGBF, in fact, per-channel beamforming can be done on-ground.
Also no variable bandwidth filtering is required for the on-board DSP in case of OGBF. This requirement is important instead for a system with on-board DBF to retain a high degree of flexibility. The FL Digital Processor is mainly composed by a set of wideband Digital Demultiplexers, each one receiving an FDM signals transmitted by a single GW, and a set of Digital Multiplexers, one per feed and per polarization, each one assembling a 15 MHz band from three 5 MHz segments coming from the feeder links.
In total, six wideband digital demultiplexers (each one demultiplexing at least 51 channels of 5 MHz) and 102 (51 per polarization) digital multiplexers, assembling three 5 MHz channels into a 15 MHz signal, are required in the FL processor. For the RL payload, the DSP processor is quite specular to that of the FL with the wideband DEMUX substituted with a wideband MUX and the per-feed MUX substituted by per-feed DEMUX.
Baseline FL payload high-level architecture
Baseline RL payload high-level architecture
The project is expected to last 24 months and is divided in the following two contractual phases:
- Phase 1 - Full-scale System Definition and Test-Bed Architectural Design
- Phase 2 - Test-Bed Detailed Design, Integration and Testing
The activity breakdown is as follows:
- Phase 1
- WP 10 - Space/Ground Architecture and Requirements Definition,
- WP 20 - Test-Bed Preliminary Design.
- Phase 2
- WP 30 - Test-Bed Detailed Design,
- WP 40 - Test-Bed Implementation,
- WP 50- Validation/Test Campaign,
- WP 60 - Design Consolidation, Technology Roadmap and Recommendations.
Phase 1 has been successfully closed, and phase 2 has started.