Multi-beam satellite systems at Ka Band can provide broadband high capacity access to interactive multimedia services with a good compromise between complexity and cost. It is also well known that the traffic profile tends to be asymmetric from the user point of view, with dynamic behaviour increasing daily and higher levels of QoS being demanded.
For this reason, means to increase system efficiency in support of the demanding dynamic traffic conditions are a key aspect to increasing system competitiveness whilst keeping its quality. On the other hand, the DVB-S2 standard is recognized as providing adaptability to propagation conditions, supporting higher transmission efficiency and dedicating more resources (bandwidth and/or power) to the users able to use them.
In order to cope with this situation, the present project is intended to investigate a solution based on beam hopping techniques, consisting of the illumination of only a subset of the satellite beams through an appropriately designed beam illumination pattern.
The challenge is to satisfy as close as possible the beam traffic requests, maximizing revenues through provision of high capacity in those areas of the coverage region with high demand, and minimizing the amount of resources dedicated to low loaded regions.
As such, the focus of this activity is to fulfil the following objectives:
- Deeply investigate and assess the potential of beam hopping at system and payload levels,
- Define payload architectures suitable for beam hopping systems,
- 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 shall be assessed through detailed system simulations,
- Compare the achieved performance with the one provided under the same conditions by system configurations, where no beam hopping, but an ad-hoc bandwidth/power allocation is utilized.
Assessment of the benefits of beam hopping techniques in order to improve the use of the satellite resources in a more efficient way.
The beam hopping techniques provide the system with greater flexibility in accommodating irregular and time variant traffic requests across the coverage region. To cope with high system efficiency, operators agree in indicating flexibility as the key requirement for a satellite system targeting interactive service provision, as it allows for sustaining the inherent large uncertainty in the broadband communication market evolution.
To evaluate the improvements at system level provided by the use of beam hopping techniques, it is intended to analyse several schemes (referenced as study cases) and compare them in terms of capacity, performance and flexibility. The study cases are:
- Conventional system with regular frequency reuse and uniform power/carrier allocation,
- Flexible system with non-regular frequency reuse and flexibility in bandwidth to beam allocation,
- Beam hopping system.
By defining adequate performance comparison criteria, the gain of the beam hopping system designed will be evaluated and compared with the gain of the flexible system and the conventional one for two different scenarios, both based on DVB-S2 / DVB-RCS air interfaces as the broadband standards:
- A multistar access system over a transparent satellite with a large number of beams (around 70),
- A regenerative meshed scenario (36 beams).
An appropriate optimization methodology for the complex problem to be solved will be defined. Then such an optimization process will be simulated and results will be iteratively obtained. The optimization methodology consists basically of the following steps:
- First, a precise detailed system model will be obtained and the key parameters and interdependencies will be identified. In addition, the constraints given by the payload design will be considered in the optimization,
- Then a pre-analysis with simplified models will be carried out, performing optimization upon identified key sub-problems, for example by setting other parameters as fixed,
- Finally a global optimization shall be applied, whose output shall be delivered to the System simulator in order to start an iteration that will yield the pursued optimal solution.
Finally, the System simulation will use the optimization methodology to end up with an optimised solution as follows:
- An Optimization algorithm module that transmits a set of optimized parameters to the system simulator, which has to return a value of the performance metric corresponding to the simulated satellite system. The value of this performance metric will be used by the optimization algorithm to derive another set of optimized parameters.
- A system simulator module, that will realistically model the long term performance of a satellite system for the two envisaged scenarios and for all study cases.
The results from the optimization process will be the selection of the optimum values for the identified parameters that determine the design of the beam hopping system. The possible impact of such a system on current standards, both at physical layer and MAC layer will be evaluated.
The project is composed of three tasks:
- Task 1: It consists of the consolidation of the system scenarios. This shall include applying of a set of traffic distributions, defining a few system study cases, including both non-beam and beam hopping systems, which shall be in-depth optimized and analyzed in the following tasks. Preliminary payload architectures shall be identified and defined for each system study case, which will be used as input for the optimization and system modelling tasks.
- Task 2: The system performances for the non beam hopping study cases shall be derived. To this aim, a methodology for the complex problem of system optimization (bandwidth and power allocation, etc) shall be studied, implemented and validated in a software simulation tool.
- Task 3: The system performances for beam hopping system study cases shall be derived. A similar methodology for the complex problem of system optimization in case of beam hopping shall be studied, implemented and validated in the software simulation tool. Comparison between non beam hopping and beam hopping study cases will be carried out, assessing the gain resulting from the use of beam hopping techniques.