The first objective of the project is to study, analyse and optimize beam hopping techniques in multibeam broadband satellite systems. The benefits in terms of capacity and system flexibility compared to conventional system architectures are to be assessed through detailed system simulations. The achieved performance will be compared with performance provided under the same conditions by system configurations, where no beam hopping, but an ad-hoc bandwidth/power allocation is utilised.
The second aim is to study and define payload/processor architectures suitable for beam hopping systems.
The final aim is to investigate modifications to the air interface of current standards like DVB-S2, which are necessary to support beam hopping techniques. During the course of the study various scenarios will be analysed and compared both from a technical & economical viewpoint against a set of mission scenarios.
Issues to be addressed include how well the beam hopping system can accommodate changes in traffic distribution and market developments. To investigate this, a set of capacity requirements is being established representative of potential market developments across the coverage area and for a given time period (up to 2020). These requirements will include “hot spots” to assess how well the beam hopping system can cope with large changes in traffic distribution.
Other issues include the effects of propagation losses, adjacent system interference, intra-system interferences on system capacity and impacts of performance limitations such as maximum feasible transmission rate and satellite platform constraints (mass and power). The key issue allowing the assessment of the performance of both Non-Uniform Non-Beam Hopped (Task 2) and Beam Hopped (Task 3) Systems consists of the system optimization leading to the optimum System Configuration, i.e. optimum Frequency, Polarization and Power Plans, which meet at best the target Capacity Requirements with the assigned resources (Bandwidth and Power Budget).
Such optimization approach is envisaged to be carried out on a combinatorial basis by means of a hybrid procedure generally starting with a Genetic Algorithms step which is followed by a Neighbourhood Search refinement. The optimization approach is intended to be of the constrained type in order to make the optimum System Configuration complying with the above mentioned performance and platform limitations.
When possible, parallel implementation is addressed in order to allow getting optimization results with acceptable computation time even for scenarios with high number of beams, otherwise prohibitive in terms of serial search.
The study aims at assessing and analysing the benefits of introducing on-board satellite payload flexibility with respect to more classical design of satellite payloads. The non-uniform traffic demand distribution over the coverage and the uncertainty of the evolution of the traffic demand distribution during the satellite lifetime are the main reasons to introduce on-board flexibility.
Commercial satellite operators need to ensure maximum utilization of their assets. They must achieve high fill factors throughout the lifetime of the satellite and to be able to reposition or redeploy the satellite to capture new or expanding markets if they are to reap financial reward from their investment. The operators need for enhanced utility has driven satellite manufacturers to provide enhanced flexibility. This flexibility may take the form of power, capacity (bandwidth) redistribution or changing the primary coverage region of the satellite.
During the study, the on-board payload flexibility will be investigated for a set of system scenarios and with two types of flexibility:
- Flexibility in terms of allocating non-uniform bandwidth and power to beams, It means that the satellite payload will be able to allocate more bandwidth and power in beams where the traffic demand is high. Such an approach better matches the traffic demand distribution. The flexibility may also be extended to beam size.
- Flexibility in terms of number of simultaneous illuminated beams. By implementing beam hopping techniques, it is possible to illuminate each beam a required time proportional to the traffic demand.
The reference scenario that will be considered during the study to assess the benefits of on-board flexibility is a satellite payload with uniform bandwidth and power allocation to beams.
In general, flexibility at payload level is not intended to cope with instantaneous variation of traffic demand. It follows the aggregated traffic demand variation over a longer term basis: in the order of the week/month/year. In case of beam hopping, traffic demand variation down to an hour may be supported if “statistically predictable”, i.e. if it can be configured in advance.
The study plan is divided in six tasks as described below:
In task 1, the set of preliminary system scenarios are critically reviewed and the given traffic distribution assumptions will be complemented to test the system elasticity.
In task 2, system performances will be derived for the non-beam hopping system taking into account the selected payload architectures for each system scenario derived in task 1.
In task 3, system performances for each scenario, where beam hopping techniques are utilized will be derived and available techniques for optimising the system parameters identified in Task 1 will be reviewed. The optimisation methodology implemented in Task 2 will be considered and software tools developed in task 2 will be modified to be used for the beam hopping system under consideration.
In task 4, a suitable air interface to the beam hopping system will be developed. The air interface requirements will be critically reviewed, taking into account the additional requirements identified in Task 3.
In task 5, a detailed analysis and trade-off of the payload architectures selected in Task 1 for the different system scenarios and study cases will be performed taking into account the results in terms of system performance achieved in Task 2 and 3 for the non beam hopping and beam hopping systems.
In task 6, based on the outcome of task 4 and 5, for each system scenario, the beam hopping system configuration definition and performance will be finalised. Functionalities of on-board and on-ground subsystems will be detailed.
Three draft documents have been produced. The first of these defines a set of system scenarios, which are to be used for the relative assessment of non-beam hooped and beam hopped systems. The second document describes the payload architecture to be used in support of the beam hopped missions. The third provides a concise survey of current beam hopped systems such as the Boeing “Spaceway” and the standards used by these systems.
Currently, software is being set up to support optimisation of the reference scenario against which to measure the performance of payload flexibility for both hopped and non-hopped systems.
The software tools will then be extended to enable optimisation of flexible non-hopped systems (allocating non-uniform bandwidth and power to beams as demanded by traffic requirements), and then further to enable optimisation of equivalent beam hopped systems for comparison.
In parallel, payload architectures supporting the beam hopped systems will be derived and refined taking into account the spacecraft constraints (mass & power).
Requirements of key ground stations and user terminals will be investigated together with demodulator techniques and signal processing, including techniques for making DVB-S2 compatible with beam hopping which may enhance system performance.