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StatusCompleted
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Status date2008-12-19
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Activity Code1B.003
The study aims to identify, analyse, simulate, optimise and demonstrate resource management (RM) schemes for adaptive fade mitigation techniques with the necessary corresponding algorithms, functionalities, protocols, signalling information and formats for future broadband, DVB-based satellite systems leading to a higher efficiency with respect to current systems.
The study will propose solutions and recommend RRM schemes for modifications of the current DVB-S2/RCS air interface standards allowing an evolutionary development of the current standards. Also cost of terminals and gateway will be considered in the evaluation of different RRM schemes to support the competition of satellite systems with low cost mass market products of the competing terrestrial networks.
Appropriate RM techniques will include CAC and scheduling algorithms, MAC protocols and signalling resource allocation algorithms. In order to optimise the resource management for FMT under realistic conditions, the considerations will take into account physical layer impairments, such as channel estimation errors, synchronisation performance and interference.
The study will investigate the performance of the RM solutions through detailed simulations. A sophisticated simulator will be developed that allows in-depth modelling of the satellite system, and will implement the pre-selected RRM architecture, algorithms and protocols. End-to-end service simulation will derive system performance measures for efficiency and quality.
A sophisticated simulation tool for radio resource management (RRM) in DVB-S2/RCS systems using fade mitigation techniques will be developed to assess the performance of possible RRM algorithms and protocols.
Profound research on potential RRM schemes will be performed and advanced algorithms and protocols will be developed and assessed.
Efficient radio resource management is key for the service cost of satellite systems. The competition with terrestrial networks forces satellite services to come down in cost. Fade mitigation techniques offer enormous potential on spectrum saving or on the increase in bit rate. This study will enable
- Operators to manage the flexibility of FMT systems
- Manufacturers to build versatile gateways and terminals that can exploit the FMT techniques; it will provide a versatile tool for research and development of RRM for DVB-S2/RCS
Simulator for DVB-RCS adaptive fade mitigation techniques:
A simulator was developed to investigate DVB-S2/RCS systems in detail. The simulator is based on OMNET++ libraries. This library features:
- Discrete Event Simulation Environment
- Modular Architecture / Simulation Kernel
- Command line (CmdEnv) or GUI (TkEnv)
- Windows® and Unix-Like Systems Compatible
The simulator architecture implements a full DVB-RCS system architecture including gateway, satellite and terminal nodes. Pre-processing of traffic and rain scenarios allow faster and repeatable simulations. Using Matlab post-processing routines, a variety of measurements can be analysed:
- ModCod Distribution
- Time Series of all bit and packet rates
- Message Losses, Delay and Jitter
- Resource Requests (CRA, RBDC, VBDC / AVBDC)
- Load Estimation of schedulers
The following figure gives an impression of the simulator GUI:
A functional architecture of radio resource management (RRM) in DVB-S2/RCS systems supporting ACM and other FM techniques is depicted in the figure below.
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Basically, two entities are performing the RRM: the gateway and the terminals. The gateway may perform: i) layer 1 functions such as power control channel estimation, and frequency allocation, and mode selection, ii) layer 2 functions such as MAC fragmentation, encapsulation, scheduling and congestion control, and finally iii) layer 3 functions such as call admission control. The terminal may have similar functions. |
click for larger image |
In the case of the regenerative scenarios, there is a similar central entity "Network control center" (NCC) for the central control of RM. In addition, functionalities of the RM can also be performed in the satellite depending on the level of processing that the satellite is able to do. Such satellite function may include: scheduling of downlink traffic, and channel estimation/power control.
Basically, one should distinct between data plane and signalling plane. Application data are forwarded over the DVB-S2/RCS data transport network with appropriate interworking functions at layer 3 (routing, NAT, etc.). Layer 2 adopts the data for the physical layer transmission between gateway and terminal, or between terminal and gateway, respectively. In the signalling plane interaction at each layer can take place between the data and signalling plane, e.g., for monitoring of buffers in the data plane and requesting new resources via the signalling plane.
Adaptive return link structures have been proposed for future versions of the RCS return link with use of ACM. The structures could have fixed information per slot however at different symbol rate and varying burst length. Thus, the slot durations will vary in a frame organisation. The organisation and assignment of the frame structure may vary from frame to frame. One central point of the RRM management is the continuous management of the frame structure and the adoption to changing physical layer constraints by assigning new slots and physical layer modes to terminals. A superframe structure with consecutive frames can be assumed furthermore.
The study has five tasks:
- Reference system scenarios consolidation and review of state-of-the-art resource management (RM) techniques
- Development of radio resource management (RRM) techniques for efficient support of adaptive FMT
- RRM simulator development
- RRM optimization and detailed system performance assessment.
- Simulator training and support.
In detail the following sub-tasks are included:
- A review of state-of-the-art RM techniques in terrestrial systems,
- Consolidation of the two reference scenarios
- Definition of functional, operational and performance requirements for RRM techniques in the two reference scenarios, i.e., DVB-S2/RCS with adaptive FMT in use
- Definition of a functional architecture for RRM with specified interactions between functions and layers, and including the mapping between functions and system entities.
- Development and assessment of RRM techniques for DVB-S2/RCS systems employing FMT
- Complexity and cost analysis as well as impact on current standards
- Definition of requirements and high-level architecture for the RRM simulator to identify the required areas of simulation and scenarios for RRM.
For the simulator development the following work plan is envisaged:
- Specification of the simulator architecture displaying all components and their inter-relation
- Detailed design of all simulator components,
- Development of a detailed test and validation methodology
- Implementation and integration of the simulator in code
- Final test and validation of the whole simulator, including all single modules and interfaces, and assessment of overall simulator capability and performance.
The simulator serves for extensive system simulations towards
- A joint performance optimization of the integrated RRM techniques together with the adaptive FMT
- Comparison of the different RRM strategies in terms of performance, complexity, signalling overhead and impact on the DVB-S2/RCS standards
- Detailed assessment of end-to-end performance for the reference systems.
Project Results
The project investigated DVB-S2/RCS with adaptive fading mitigation techniques using the simulator tool. The simulation confirmed impressive improvements of adaptives systems in throughput and efficiency compared with non-adaptive systems. However, it could be also shown that the system improvements depend on many factors that need to be optimized in a joint way. Such factors are radio resource segmentation, scheduling behavior, encapsulation protocol, and the resource allocation scheme.
The following key findings have been found:
- The DVB-S2 forward link with ACM increases the throughput by 40 - 50% compared to CCM system,
- Generic Stream Encapsulation (GSE) should be used in the forward link, it outperforms MPE/ULE by ~20%,
- Improved pool schedules should used to pack IP packets to BBFrames. Such schedules contribute with up top 30% to the efficiency of a DVB-S2 system,
- In the return link, DVB-RCS can benefit from ACM and improve the system efficiency by doubling the link capacity,
- Bursts with a fixed number of symbols (fixed burst length, FBL) should be used in the return link. However such burst require an encapsulation protocol that can cope with variable number of information bits in the burst. An efficient protocol for encapsulation in the return link is again GSE,
- The combination of GSE with FBL bursts can improve the return link capacity by ~100% compared to conventional DVB-RCS.