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Despite a rich history of successful experimentations, the on-board processing (OBP) technologies have not gained significant industry support for notable commercial deployments.
A regenerative OBP’s technology and transmission formats, having to be pre-selected at payload design, could likely lose optimality due to getting outdated, by the time it gets into in orbit operation, causing unacceptable waste of operators’ investment.
Hence, this study is to more closely review the key issues and identify architectural remedies using the emerging technologies that allow generic OBP designs which can be re-programmed in-orbit for more efficient and flexible operation.
The key objectives of the study were:
This project has been to address the constraints posed mainly by the rigid structure of the traditional regenerative OBPs. However, some other issues affecting OBP’s commercial viability, such as market needs and cost/performance ratio as compared to traditional bent-pipe carriage have also been addressed; mesh networking advantage does not adequately compensate for the large difference in throughput cost, especially that mesh traffic currently constitutes a small fraction of the total traffic.
The project has also examined some challenging technical issues presented by ground segment technology developments for use in higher frequency bands (e.g., Q/V) and multi-spot-beam future networks.
Alternative architectural design and technology solutions have been proposed including the use of SDR to remedy key constraints posed by the rigid structure of the OBPs, helping to minimize potential waste of scarce satellite resources and operators’ investment.
As regards the OBP’s commercial viability, the study further clarifies the status of market readiness, confirming mesh traffic forms a small fraction of the total traffic and that the OBP spacecraft resource requirements unfavourably skew the cost/ performance ratio of the spacecraft design. Furthermore, the study reiterates that the higher costs of mesh user terminals are likely to result in more reluctance of the users to adopt OBPs offered applications.
Considering the above issues, the study recommends a bent pipe multi-spot beam ka-band configuration as the primary mission with some transparent/regenerative capability for a secondary payload as a more viable commercial option.
While the study focus has been on the OBP technology, it has also described the key ground segment technology enablers that help to minimize end-to-end network costs. The primary focus has been in the area of link performance improvements to combat adverse effects of the higher frequency bands (e.g., Q/V) and multi-spot-beam future satellite networks, resulting in system capacity augmentation.
The lessons learnt from previous OBP experience and market assessments pointed the study mainly on broadband FSS and to the use of the OBP as a secondary payload in two specific architectures:
A. Secondary Transparent OBP:
The study used a highly flexible secondary payload that incorporates a DTPP as part of a hybrid payload. The primary payload isa conventional bent-pipe architecture, and the secondary payload is flexible (in terms of RF power and Bandwidth to beam allocation, Frequency re-use allocation, Coverage flexibility, and the capability to support a flexible user frequency plan). Coverage flexibility is provided by Forward link DBFN, Frequency Channelizer and Channel Switch with high degree of connectivity among beams.
For broadband applications, the Payload would generate a large no. of small overlapping spot beams. The key satellite resources, namely, RF power, mass and bandwidth have been allocated between the primary and secondary payload to ensure that the primary payload can provide an adequate solution for a GEO based, ka-band, multi-media satellite communication system, while still ensuring that the secondary payload is still viable.
B. Hosted Payload:
A typical architecture is shown in the figure below, where the hosted payload is connected to a steerable antenna, using its own receivers and TWTAs. As an option the hosted payload might share some of the host payload hardware (e.g., using the host receivers and TWTAs), if the design and the contractual agreement permit.
In terms of accommodation, commercial platforms should be able to offer provision on the Nadir deck to install a hosted payload steerable antenna. Such hosted payloads should incorporate a certain degree of flexibility to accomplish their functions satisfactorily. This can be provided by programmable payloads, i.e., Software Defined Radio (SDR), using the Space Telecommunication Radio System Open-architecture STRS-00001.
he project plan comprised the following tasks:
Task 1 assessed the roles, potential benefits and technology trends for both regenerative and transparent OBPs.
Task 2 provided market assessments for OBP systems over the next two decades, including requirements from commercial and institutional users.
Task 3 provided for the architectural design and technologies selection for the two identified missions, as briefly described above.
Tasks 4 and 5 were concerned with technology developments and a roadmap that will ensure sustainable synergies among network constituents for cost-effective solutions, especially when using higher frequency bands (e.g., Q/V) and multi-spot-beam configurations.
This project has already been finalized, fully achieving all its objectives, as summarized in the above items.